An ACI ProvisionalStandard ACI 562-16 Reported byACI Committee562 Commentary Concrete Structures and Rehabilitation ofExisting Assessment, Repair, and Code Requirements for First Printing ISBN: 978-0-87031-000-0
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures and Commentary
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American Concrete Institute 38800 Country Club Drive Farmington Hills, MI 48331 Phone: +1.248.848.3700 Fax: +1.248.848.3701 www.concrete.org CODE REQUIREMENTS FOR ASSESSMENT, REPAIR, AND
REHABILITATION OF EXISTING CONCRETE STRUCTURES
(ACI 562-16) AND COMMENTARY
An ACI Standard
Reported by ACI Committee 562
Keith E. Kesner Kevin Conroy Chair Secretary
James Peter Barlow Robert F. Joyce Antonio Nanni F. Michael Bartlett Lawrence F. Kahn Jay H. Paul Randal M. Beard Paul L. Kelley Eugenio M. Santiago Eric L. Edelson Carl J. Larosche Constadino Sirakis Garth J. Fallis John S. Lund Gene R. Stevens Paul Gaudette Marjorie M. Lynch Fred R. Goodwin Tracy D. Marcotte
Consulting Members Peter Emmons Randall W. Poston
Subcommittee Members
Jared Brewe Gaur Johnson J. Gustavo Tumialan Kip Gatto Patrick D. Martin David W. Whitmore Anton Gueorguiev
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
SYNOPSIS
ACI 562-16 – “Code Requirements for Assessment, Repair and Rehabilitation of Existing Concrete
Structures” was developed to provide design professionals involved in the assessment of existing concrete structures a code for the assessment of the damage and deterioration, and the design of appropriate repair and rehabilitation strategies. The code provides minimum requirements for assessment, repair, and rehabilitation of existing structural concrete buildings, members, systems and where applicable, nonbuilding structures. ACI 562-16 was specifically developed to work with the International Existing
Building code (IEBC) or to be adopted as a stand-alone code.
Keywords: assessment; bond; damage; licensed design professional; durability; existing structure; evaluation; FRP; interface bond; maintenance; rehabilitation; reliability; repair; strengthening; unsafe.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CONTENTS Chapter 1—General requirements 1.1 General 1.2 Criteria for the assessment and design of repair and rehabilitation of existing concrete structures 1.3 Applicability of this code 1.4 Administration 1.5 Responsibilities of the licensed design professional 1.6 Construction documents 1.7 Preliminary evaluation Chapter 2—Notation and Definitions 2.1 Notation 2.2 Definitions Chapter 3—Referenced standards Chapter 4—Criteria when using this code with International Existing Building code (IEBC) 4.1 General 4.2 Compliance method 4.3 Unsafe structural conditions 4.4 Substantial structural damage 4.5 Conditions of deterioration, faulty construction or damage less than substantial structural damage 4.6 Conditions of deterioration, faulty construction, or damage less than substantial structural damage without strengthening 4.7 Additions 4.8 Alterations 4.9 Changes of occupancy Chapter 5—Loads, factored load combinations, and strength-reduction factors 5.1 General 5.2 Load factors and load combinations 5.3 Strength reduction factors for rehabilitation design 3 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
5.4 Strength reduction factors for assessment 5.5 Additional load combinations for structures rehabilitated with external reinforcing systems Chapter 6—Assessment, evaluation, and analysis 6.1 Structural assessment 6.2 Investigation and structural evaluation 6.3 Material properties 6.4 Test methods to quantify material and member properties 6.5 Structural analysis of existing structures 6.6 Structural serviceability 6.7 Structural analysis for repair design 6.8 Strength evaluation by load testing 6.9 Recommendations Chapter 7—Design of structural repairs 7.1 General 7.2 Strength and serviceability 7.3 Behavior of repaired systems 7.4 Interface bond 7.5 Materials 7.6 Design and detailing considerations 7.7 Repair using supplemental post-tensioning 7.8 Repair using fiber-reinforced polymer (FRP) composites 7.9 Performance under fire and elevated temperatures Chapter 8—Durability 8.1 General 8.2 Cover 8.3 Cracks 8.4 Corrosion and deterioration of reinforcement and metallic embedments 8.5 Surface treatments and coatings Chapter 9—Construction 4 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
9.1 General 9.2 Stability and temporary shoring requirements 9.3 Temporary conditions 9.4 Environmental issues Chapter 10—Quality assurance 10.1 General 10.2 Inspection 10.3 Testing of repair materials 10.4 Construction observations Chapter 11—Commentary references Appendix A—Criteria when using this code as a stand-alone code A.1 General A.2 Design-basis code criteria A.3 Unsafe structural conditions A.4 Substantial structural damage A.5 Conditions of deterioration, faulty construction or damage less than substantial structural damage A.6 Conditions of deterioration, faulty construction, or damage less than substantial structural damage without strengthening A.7 Additions A.8 Alterations A.9 Changes of occupancy
PREFACE
This code provides minimum requirements for assessment, repair, and rehabilitation of existing structural concrete buildings, members, systems and where applicable, nonbuilding structures. This code can supplement the International Existing Building Code (IEBC 2015), supplement the code governing existing structures of a local jurisdictional authority, or act as a stand-alone code
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) in a locality that has not adopted an existing-building code. When this code is used as a stand- alone code, Appendix A is used in place of Chapter 4. This code provides requirements for assessment, design and construction, or implementation of repairs and rehabilitation, including quality assurance requirements, for structural concrete in service. This code has no legal status unless it is adopted by the jurisdictional authority. Where the code has not been adopted, it provides minimum requirements for assessment, and design and construction of repair and rehabilitation of existing structural concrete. ACI 318 provides minimum requirements for the materials, design, and detailing of structural concrete buildings and, where applicable, nonbuilding structures prior to issuance of a letter of occupancy or prior to the legally defined declaration of an existing structure and for new construction within existing structures where noted herein. Key changes from ACI 562-13 to ACI 562-16 include: revisions to definitions used in the code to bring this document into conformance with IEBC 2015 and other standards for existing structures; adding specific criteria requirements for assessment and design of repair and rehabilitation for varying levels of damage, deterioration, or faulty construction in Chapter 4 when using this code with IEBC and in Appendix A when using this code as a stand-alone code; and re- organization and revision of Chapter 1 to address the amendments of Chapters 2 and 4. Technical changes are summarized at the end of this document.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 1—GENERAL stand-alone code in a jurisdiction without a code REQUIREMENTS governing existing structures.
1.1—General 1.1.3 The intent of this code is to safeguard the 1.1.1 ACI 562, “Code Requirements for public by providing minimum structural Assessment, Repair, and Rehabilitation of requirements for existing structural concrete Existing Concrete Structures,” is hereafter members, systems, and buildings. referred to as “this code.” 1.1.3C The intent of this code is to address the 1.1.2 Scope—This code shall apply to safety of existing structures through assessment assessment, repair, and rehabilitation of existing requirements that demonstrate an approximation concrete structures as a code supplementing the of the structural reliability using demand- International Existing Building Code (IEBC), as capacity ratio limits of Chapter 4 or Appendix A part of a locally adopted code governing existing and, if necessary as determined by the buildings or structures, or as a stand-alone code assessment, increase the structural capacity by for existing concrete structures. repair or rehabilitation. 1.1.2C Scope—This code defines assessment, Unless prohibited by the jurisdictional design, construction and durability requirements authority, if an existing structure is shown to be for repair and rehabilitation of existing concrete unsafe in accordance with 4.3 or A.3, the structures. Throughout this code, the term structure should be rehabilitated using 4.3 or A.3. “structure” means an existing building, member, Using the demand-capacity ratio limits of 4.5.1 system, and, where applicable, nonbuilding or A.5.1, repair of the existing structural concrete structures where the construction is concrete or to its pre-deteriorated state is permitted based on mixed construction with concrete and other material properties specified in the original materials. construction (per Chapter 6), and substantiated Chapter 4 provides assessment, repair, and engineering principles of the original design. rehabilitation criteria if this code is used as a Where requirements of the original building code supplement to the IEBC for concrete members are appreciably changed in the current building and systems. code, the licensed design professional may Appendix A provides assessment, repair, and consider using 4.5.2 or A.5.2. rehabilitation criteria when this code is used as a Beyond the restoration assessment requirements of 4.5.1 and 4.5.3 or A.5.1 and A.5.3, the structural reliability principles of 4.5.2 7 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) or A.5.2 are permitted. These alternative building code is to be replaced by the current requirements provide acceptable safety if the building code to provide structurally adequate current building code demand exceeds the resistance and reliability. original building code demand or if the regulations of the original building code provide 1.2—Criteria for the Assessment and Design an unacceptable level of structural reliability. of Repair and Rehabilitation of Existing Concrete Structures 1.1.4 All references in this code to the licensed 1.2.1 The “existing-building code” refers to the design professional shall be understood to mean code adopted by a jurisdiction that regulates persons who possess the knowledge, judgment existing buildings or structures. and skills to interpret and properly use this code 1.2.1C The code governing existing buildings and are licensed in the jurisdiction where this in the United States is commonly the IEBC code is being used. The licensed design developed by the International Code Council professional is responsible for and in charge of (ICC). The IEBC provides regulations for the assessment or rehabilitation design, or both. evaluations of damage and the limit for damage 1.1.4C The licensed design professional should to be repaired using the original building code. If exercise sound engineering knowledge, this limit is exceeded or if the licensed design experience, and judgment when interpreting and professional judges the structural safety to be applying this code. unacceptable based on rational engineering 1.1.5 The requirements of this code are principles, rehabilitation is necessary in provided using strength design provisions for accordance with the requirements of the current demands and capacities, unless otherwise noted. building code. 1.1.5C When this code permits the original 1.2.2 The “current building code” refers to the building code regulations to be used and that general building code adopted by a jurisdiction code uses allowable stress design: those that presently regulates new building design and provisions should be substituted for strength construction. design as noted in 4.5.3 or A.5.3; the licensed 1.2.2C The current building code establishes design professional is not required to use, but the design and construction regulations for new should consider using strength design provisions construction. Strength design regulations of the of this code as a check in the assessment of current building code include: existing structures originally designed with allowable stress methods; and the licensed design professional may judge when the original 8 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
a) required strengths computed using question at the time the existing structure was combinations of factored loads (strength permitted for construction. design demands) 1.2.3C This definition of “original building b) design strengths (capacities) based on code” is consistent with the building code in testing of materials, members, and systems effect at the time of original permitted c) analytical methods used to calculate construction per the IEBC. In assessing existing member and system capacity structures, the licensed design professional may d) strength reduction factors, which have need to consider changes in the codes enforced been established to be consistent with by the local jurisdictional authority for the reliability indices used with the strength structure from the time of the original design design demands through the time of the completion of The current building code provides acceptable construction. safety based on consistent statistical probabilities Reference to design requirements of the for new construction. The resulting demand- original building code should include: demands capacity ratios of the current building code determined using either nominal loads, load provide the limits that need not be exceeded if factors, and load combinations of the original designing new construction or assessing and building code or using allowable design loads designing repairs and rehabilitation of existing and load combinations of the original building structures. code; capacities determined using either strength The general building code in the United States is design and reinforcement detailing provisions, usually based on the International Building Code and strength-reduction factors of the original (IBC) published by the ICC. Prior to 2015, building code or using allowable stress design Chapter 34 of the IBC included provisions for provisions of the original building code; and existing buildings. For the design and construction materials. Requirements for construction of new concrete structures, the IBC concrete design and construction include and most other older general building codes often previous versions of ACI 318, concrete codes reference ACI 318, Building Code Requirements predating ACI 318, or concrete provisions within for Structural Concrete and Commentary, with the original building code. A structural exceptions and additions. assessment using allowable stress design 1.2.3 The “original building code” refers to the provisions of the original building code should be general building code applied by the coupled with an evaluation using current jurisdictional authority to the structure in standards to increase the understanding of 9 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) structural behavior and to judge if more Chapter 4 applies if a jurisdiction has adopted the consistent and safe remedial recommendations International Existing Building Code (IEBC) as are necessary using the current building code. the existing building code. Appendix A applies if 1.2.4 Design-Basis Code Criteria a jurisdiction has not adopted the IEBC or if a 1.2.4.1 The types of design-basis code criteria jurisdiction has adopted this code. used in this code are assessment criteria and 1.2.4.2C Classifying the rehabilitation design-basis criteria. The design-basis code category using criteria and requirements of criteria of this code shall be used to assess and Chapter 4 or Appendix A defines the design-basis design rehabilitations of existing members, criteria, which is used to design the repair or systems, and structures. rehabilitation work. 1.2.4.1C If a jurisdiction has adopted the IEBC, 1.2.4.3 Assessment criteria shall be used to then the design-basis code criteria are based on classify the rehabilitation work and to establish the IEBC with supplemental requirements of this the design-basis criteria. code for unsafe structural conditions, damage 1.2.4.4 Design-basis criteria shall be used to less than substantial structural damage, establish the applicable building code for repair deterioration of concrete and reinforcement, and rehabilitation design. faulty construction, serviceability issues, and 1.2.4.5 ACI 318-14 shall be the design basis durability for existing concrete. For substantial code for new members and for connection of new structural damage, additions, alterations, and members to existing structures. changes in occupancy, the IEBC establishes limits to which an assessment and design of 1.3—Applicability of this code repair and rehabilitation can occur in 1.3.1 This code is applicable when performing accordance with the original building code. an assessment, repair or rehabilitation design and Above these limits, an assessment and design of remedial construction of existing concrete the repair and rehabilitation is in accordance structures including buildings and nonbuilding with the current building code. Current and structures where the existing structure’s original building code provisions are construction is concrete or a mix of concrete and supplemented by this code to address existing other materials. concrete members, systems, and buildings. 1.3.1C Existing concrete structures may 1.2.4.2 Assessment and design-basis criteria require an assessment, repair or rehabilitation and the requirements for applying these criteria are provided in Chapter 4 and Appendix A. 10 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) design for considerations beyond the minimum not in conflict with the code governing existing requirements of this code. building. For the portions of concrete piling in Nonbuilding concrete structures can include, air or water, or in soil not capable of providing but are not limited to arches, tanks, reservoirs, adequate lateral restraint throughout the piling bins and silos, blast- and impact-resistant to prevent buckling, the provisions of this code structures, and chimneys. govern. 1.3.2 Considerations beyond the minimum 1.3.4 Soil-supported slabs requirements of this code, such as those for 1.3.4.1 This code shall apply to the assessment progressive collapse resistance, redundancy, or and repair or rehabilitation of soil-supported integrity provisions are permitted. The licensed structural slabs that transmit vertical loads or design professional is permitted to require lateral forces from the structure to the soil. assessment, design, construction, and quality 1.3.5 Composite members assurance activities that exceed the minimum 1.3.5.1 This code shall apply to the assessment requirements of this code. Regulations of the and repair or rehabilitation of the concrete current building code need not be exceeded when portions of composite members. assessing, designing repair and rehabilitation 1.3.6 Precast and prestressed concrete work or installing remedial work of existing 1.3.6.1 This code shall apply to the assessment structures. and repair or rehabilitation of structural precast 1.3.3 Foundations and prestressed concrete members, systems, and 1.3.3.1 This code shall apply to the assessment connections, and cladding transmitting lateral and repair or rehabilitation of existing structural loads to diaphragms or bracing members. concrete foundation members. 1.3.7 Nonstructural concrete 1.3.3.1C Foundation members and systems 1.3.7.1 This code is not intended for repair of should include those constructed using plain or nonstructural concrete or for aesthetic reinforced concrete including but not limited to improvements, except if failure of such repairs spread footings, mat foundations, concrete piles, would result in an unsafe condition. drilled piers, grade beams, pile and pier caps, 1.3.7.1C Where nonstructural concrete and caissons embedded in the ground. The design requires repair, that repair is not required to and installation of new pilings fully embedded in comply with or satisfy the requirements of this the ground are regulated by the current building code. The licensed design professional designing code. For repair of existing foundation members repairs to nonstructural concrete should consider and systems, the provisions of this code apply if the consequence of repair failure to determine if 11 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) there are provisions of this code that are weak-column frames; and anchorage of walls to applicable. flexible diaphragms. Significant improvements to 1.3.8 Seismic resistance the seismic resistance of a building can be made 1.3.8.1 Evaluation of seismic resistance and using repair techniques that provide less than rehabilitation design shall be in accordance with those detailing and reinforcement methods the code governing existing buildings if one has required for new construction. As an example, been adopted or this code if a code governing providing additional reinforcement to confine existing buildings has not been adopted. If using concrete in flexural hinging regions will increase this code for evaluation of seismic resistance and the energy dissipation and seismic performance rehabilitation design, ASCE/SEI 41 shall apply. even though the amount of confinement 1.3.8.1C Provisions of ASCE/SEI 41 are reinforcement may not satisfy the confinement supplemented by ACI 369R, which provides requirements for new structures (Kahn 1980; guidance on seismic repair and rehabilitation Priestley et al. 1996; Harris and Stevens 1991). measures. Visual Screening for Potential Seismic Hazards 1.3.8.2 If rehabilitation for seismic resistance is (FEMA P-154, 3rd Edition), Mitigation of not required by the code governing existing Nonductile Concrete Buildings (ATC-78 buildings or this code, voluntary retrofit for Project), Seismic Performance Assessment of seismic resistance shall be permitted. IEBC Buildings (ATC-58), and Quantification of Section 403.9 shall apply if the IEBC is used with Building Seismic Performance Factors (FEMA this code for voluntary retrofit of seismic P-695 Report) Identification and Mitigation of resistance. When this code is used without a code Nonductile Concrete Buildings (ATC 78-1) governing existing buildings, the licensed design address seismic assessment and resistance in professional shall use the current building code existing concrete structures. supplemented by ASCE/SEI 41 and ASCE/SEI 7 Components of the seismic-force-resisting to design seismic retrofits. New seismic retrofits system that require strength and ductility should shall not create structural irregularities. be identified. Force-controlled (nonductile) 1.3.8.2C Conditions for evaluation of seismic action is acceptable for some classifications of resistance and design of retrofits are provided in components of the seismic-force-resisting system ACI 369R, Chapter 3 and Appendix A2 of IEBC (ASCE/SEI 41). The strength requirement of this and ASCE/SEI 41. Critical conditions requiring code, Section 7.1 is applicable to these force- engineering review are: irregular building controlled components. ASCE/SEI 41 and ACI configurations; non-ductile or strong-beam- 369R provide information on rehabilitation for 12 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) seismic resistance. Seismic-resisting components investigate the submitted data, require additional requiring energy-dissipating capability should data, and formulate rules governing design-basis maintain the ability to dissipate energy after code criteria, design and construction of such repair. Design and detailing requirements for systems to comply with the intent of this code. seismic resistance of cast-in-place or precast These rules shall be of the same force and effect concrete structures are addressed in ACI 318 and as the provisions of this code if approved and 369R. disseminated by the jurisdictional authority. 1.4.2C New methods of design, new materials, 1.4—Administration and new uses of materials for repair and 1.4.1 This code shall govern in matters rehabilitation usually undergo a period of pertaining to the assessment and repair or development before being specifically covered in rehabilitation of existing concrete structures and, a code. Hence, good systems or components where applicable, nonbuilding structures where might be excluded from use by implication if the construction is concrete or mixed construction means are not available to obtain acceptance. with concrete and other materials, except For systems considered under this section, wherever this code is in conflict with the specific tests, load factors, strength-reduction regulations of the jurisdiction authority or code factors, deflection limits, and other pertinent governing existing buildings. Wherever this code requirements should be set by the local is in conflict with requirements in other jurisdictional authority and should be consistent referenced standards, this code shall govern. with the intent of this code. Provisions of this 1.4.2 Approval of special systems of design or section do not apply to model analysis used to construction—Sponsors of any repair or supplement calculations or to strength evaluation rehabilitation design or remedial construction of existing structures. system, which does not conform to this code but which has been shown to be adequate by 1.5—Responsibilities of the Licensed Design Professional successful use, analysis, or testing, shall have the right to present the data on which their design or 1.5.1 The licensed design professional for the construction is based to the jurisdictional project is responsible for 1) assessing; 2) authority or to a board of examiners appointed by designing, detailing, and specifying the work the jurisdictional authority for review and proposed and material requirements; 3) approval. This board shall have authority to establishing requirements to maintain load paths for the work proposed; and 4) preparing 13 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) construction documents of the work proposed and To protect the public safety, an observed unsafe specifying a quality assurance program. structural condition should be reported to the Construction documents shall provide sufficient contractor, owner or jurisdictional authority to detail and clarity to indicate the location, nature mitigate the condition. Remedies may include and extent of the work proposed and show in temporary shoring or construction as part of the detail that they will conform to the requirements remedial work. of this code and the requirements of the local 1.5.3 Basis of design report jurisdictional authority. 1.5.3.1 The licensed design professional for the 1.5.1C During the assessment part of the project shall prepare a basis of design report. investigation, the licensed design professional The basis of design report shall include: should request that the owner provide all a) a description of the building, including age available information regarding the condition of of construction, structural systems, the building, plans, previous engineering reports, identified original building code, and past disclose the presence of any known hazardous and current uses materials in the work area, and any other b) documentation of unsafe structural pertinent information to the parties involved in conditions in the work area of the structure the work. This information may require that determined in the assessment remedial measures be taken before or during the c) documentation of substantial structural construction process and should be considered in damage in the work area the scope of work. d) members and systems of the work area 1.5.2 Unsafe structural conditions—The requiring increase in capacity beyond the licensed design professional for the project shall demand of the original building code report observations of exposed structural defects e) modifications such as additions, in the existing construction within the work area alterations, or changes in occupancy representing obvious unsafe structural conditions f) conditions and details of the proposed requiring immediate attention to the appropriate rehabilitation work authorities. g) past history of concrete repairs and 1.5.2C During repair construction, unsafe rehabilitations structural conditions may be uncovered and h) assessment criteria and findings made evident. Unsafe structural conditions of i) design-basis code criteria and basis of uncovered circumstances of the existing rehabilitation design construction may be observed in the work area. j) material selection parameters 14 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
k) shoring needs A maintenance protocol should be provided in l) quality assurance and quality control the basis of design report, or in as-built or close- (QA/QC) requirements out documents. Maintenance of the repair can be m) types and frequency of future inspection incorporated in the instruction manuals from the n) types and frequency of future maintenance licensed design professional, contractor, or 1.5.3.1C The basis of design report provides a product manufacturers. Documents and records summary of the assessment of the existing of observations, inspections and tests should be structure, and a summary of or reference to the provided to the owner as necessary for future construction documents used for rehabilitations. work. Information on some structures may be unavailable or unnecessary if strengthening is 1.6—Construction documents not required and should be so noted in the basis 1.6.1 The construction documents for of design report. The licensed design professional rehabilitation work proposed shall provide should check with the jurisdictional authority to sufficient detail and clarity to convey the determine filing requirements of the basis of location, nature and extent of the work and the design report. necessary information to perform the work in A maintenance protocol that addresses project- conformance with the requirements of this code specific conditions provides the most effective and the local jurisdictional authority. method to ensure durability and should be Specifications shall require that materials used established as part of the repair or rehabilitation for repair and rehabilitation construction satisfy design that includes inspections and period of this code and governing regulatory requirements time between inspections, after completion of the at the time the work is implemented. repair installation. Maintenance and frequent 1.6.1C As necessary, the construction preventative approaches that occur early in the documents should indicate: service life of the structure generally result in (a) Name and date of issue of the building code improved service life with less interruption and a and supplements to which the assessment, lower life-cycle cost (Tuutti 1980; ACI 365.1R). repairs, or rehabilitation conforms Recommendations should be provided to the (b) Design-basis code criteria used for owner on inspection and maintenance to be conditions addressed by the documents undertaken during the remaining design service (c) Design assumptions and construction life of the repair material or the repaired part of requirements including specified the structure. 15 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
properties of existing and remedial If computer-based analyses and designs, such as materials used for the project and the finite element are used, they should include input, strength requirements at stated ages or and computer-generated output. stages of the construction 1.6.3 The licensed design professional shall (d) Details, locations and notes indicating the provide the owner with copies of basis of design size, configuration, reinforcement, report, assessment reports, project documents, anchors, repair materials, preparation field reports, and other project documents requirements, and other pertinent produced by the licensed design professional in information to implement the repairs, addition to documenting the location of the strengthening, or rehabilitation of the completed repairs to the extent of the licensed structure design professional’s contractual obligations. (e) Magnitude and location of prestressing The licensed design professional shall notify the forces owner if this information is filed with the (f) Anchor details for prestressing jurisdictional authority. reinforcement 1.6.3C Documentation of the project and (g) Development length of reinforcement and repairs that have been carried out, including length of lap splices structural observations, inspection reports by (h) Type and location of mechanical or welded others, test results, and recommendations on splices of reinforcement inspection and maintenance to be undertaken (i) Shoring or bracing criteria necessary during the remaining design service life of the before, during, and at completion of the repaired part of the concrete structure, should be assessment, repair, or rehabilitation provided to the owner. The extent and type of projects quality assurance records should include those (j) Quality assurance program including required in the construction documents. It is good specific inspections and testing practice for the owner to keep documentation of requirements repairs, inspections, testing, monitoring, and 1.6.2 Calculations pertinent to design shall be investigations for future reference. filed with the construction documents if required by the jurisdictional authority. Model analysis 1.7—Preliminary evaluation shall be permitted to supplement calculations. 1.7.1 Preliminary evaluation of an existing 1.6.2C Analyses and designs should include structure shall include investigation and review of calculations, evaluation and design assumptions. the structure, plans, construction data, reports, 16 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) local jurisdictional codes, and other available b) review of plans and observation of current documents of the existing structure. Existing in- structural conditions indicate damage or place conditions shall be visually or otherwise deterioration of the structure below the investigated to verify existing geometry and level requiring evaluation by 4.4 and 4.5 or structural conditions. A.4 and A.5 1.7.1C The goal of the preliminary evaluation c) modifications for additions, alterations, is to examine available information about the and changes in occupancy are not planned. structure within the work area, and to make an Repairs are permitted that address durability initial determination of its adequacy to withstand and serviceability of 4.6 or A.6 without analyzing in-place environmental conditions and design members and systems and checking the demand- loads. The results of the preliminary evaluation capacity ratio limits of 4.3 through 4.5 or A.3 should be used to make decisions regarding the through A.5 if the structure is determined to be current in-place condition, need for additional structurally acceptable. Structural performance information, work items necessary as part of the should be considered acceptable if past and assessment, possible rehabilitation design and present performance has been satisfactory and construction work to consider, and if there is a observations do not indicate structural distress need for temporary shoring for safety of the beyond levels expected. existing structure. The preliminary evaluation The extent of damage or deterioration should results should be updated as additional data be limited and the licensed design professional regarding the examined structure become should not have a concern about the capacity of available. the structure if repairs are completed using the The licensed design professional may provisions of 4.6 with verifying the demand to determine that 4.6 or A.6 applies in a preliminary capacity limits of 4.4 and 4.5 or A.4 and A.5. assessment based on engineering judgment and 1.7.2 The preliminary evaluation shall without analysis if all of the following are determine if unsafe structural conditions are confirmed: present, substantial structural damage has a) historical performance of the structure and occurred, damage less than substantial structural visual observation of the structural damage has occurred, faulty construction is condition of members and systems indicate present, or deterioration is present and shall acceptable behavior precluding evaluation report these conditions in accordance with 1.5.2 by 4.3 or A.3 and 1.5.3.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
1.7.2C Unsafe structural conditions may 1.7.4C Strength calculations should be based require the owner install shoring, limit access, or on in-place conditions and should include an take other measures to mitigate these conditions. assessment of the loss of strength due to Substantial structural damage refers to damage deterioration mechanisms. Guidelines for in a structure that has resulted in a significant assessing in-place conditions include ACI decrease in either the gravity or lateral load 201.2R, ACI 214.4R, ACI 228.1R, ACI 228.2R, resistance of a structure. The IEBC provides a ACI 364.1R, ACI 437.1R, FEMA P-58, FEMA P- definition for substantial structural damage when 154, FEMA 306, FEMA 307, ASCE/SEI 11, this code is used to supplement the IEBC. If this ASCE/SEI 41, ATC 20-89, ATC 45-04, and ATC- code stands-alone, A.4 defines substantial 78 as well as The Concrete Society Technical structural damage. The preliminary evaluation is Report 68 (2008). When material test results are generally the first portion of the work necessary initially unavailable, historical properties based to determine the rehabilitation category. Chapter on typical values used at the time of construction 6 provides details for a complete assessment. can be used in preliminary evaluation. If 1.7.3 For the purpose of performing a available, material properties from construction preliminary evaluation, it is permitted to assume documents can also be used in a preliminary the criteria of the original or current building code evaluation. or assessment criteria of Chapter 4 or Appendix The assessment of existing structures should A. initially focus on critical gravity-load-resisting 1.7.3C The assumed preliminary evaluation members such as columns, walls and members criteria should be substantiated or modified in that are expected to have limited ductility, accordance with the assessment details of followed by an assessment of the lateral-load- Chapter 6. resisting system. 1.7.4 The in-place strength of the existing Assessing fire damage and other deterioration structure shall be determined considering in- mechanisms that result in a change in material place geometric dimensions and material properties (such as compressive strength or properties including effects of material modulus of elasticity) should include an deterioration and other deficiencies. If material evaluation of the effect of the damage on the properties are not immediately available, a material properties and the impact of the damage preliminary evaluation shall be completed using on the performance of the existing structure. material properties as described in Chapter 6. Examples of deterioration mechanisms that result in possible changes in material properties 18 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) include corrosion of steel reinforcement, thermal damage, concrete reactions such as alkali- aggregate, and freezing and thawing. Deficiencies to be documented include cracking, spalls, member deflection, cross- section dimensions different than specified on the original construction drawings, and construction tolerances exceeding those permitted under the original building code.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 2—NOTATION AND Ra = service load capacity of structural DEFINITIONS member, system, or connection including effects of damage, deterioration of This chapter defines notation and terminology concrete and reinforcement, and faulty used in this code. construction determined using allowable stresses according to the original 2.1—Notation building code. c = depth of neutral axis, in. Rn = nominal capacity of structural member, D = dead load acting on the structure system, or connection excluding the dt = distance from extreme compression fiber effects of damage, deterioration of to centroid of extreme tension concrete and reinforcement, and faulty reinforcement, in. construction
f Rcn = current in-place nominal capacity of c = average core strength modified to structural member, system, or connection account for the diameter and moisture including the effects of damage, condition of the core, psi deterioration of concrete and fc = specified concrete compressive strength, reinforcement, and faulty construction psi Rex = nominal resistance of the structure during fceq = equivalent specified concrete strength an extraordinary (i.e., low-probability) used for evaluation, psi event computed using the probable fy = specified yield strength of steel material properties reinforcement, psi S = snow load acting on the structure
f y = average yield strength value for steel Tg = glass transition temperature, F reinforcement, psi U = demand using nominal loads and fyeq = equivalent yield strength of steel factored load combinations for strength reinforcement used for evaluation, psi design provisions (LRFD) kc = coefficient of variation modification Uc = demand using nominal loads of the factor for concrete testing sample sizes current building code and factored load ks = coefficient of variation modification combinations of ASCE/SEI 7 for factor for steel testing sample sizes strength design provisions (LRFD) L = live load acting on the structure n = number of sample tests 20 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
ACI provides a comprehensive list of Uo = demand using nominal loads and definitions through an online resource, “ACI factored load combinations of the Concrete Terminology,” original building code for strength design http://terminology.concrete.org. Definitions provisions (LRFD) provided here complement that resource. U * o = demand using nominal loads of the 2.2C Additional repair-related definitions are original building code and factored load provided by “ICRI Concrete Repair combinations of ASCE/SEI 7 for Terminology,” strength design provisions (LRFD) http://www.icri.org/GENERAL/repairterminolog
Us = demand using service loads of the y.aspx. original building code and load assessment—refer to structural assessment combinations of the original building assessment criteria—codes, standards, loads, code demands, capacities, strength reduction factors, V = coefficient of variation (a dimensionless materials, material properties, connections, quantity equal to the sample standard details, and protections used in the evaluation deviation divided by the mean) bond—1. adhesion of applied materials to determined from testing of concrete or reinforcement or other surfaces against which steel samples from structures they are placed, including friction due to
Vni = nominal interface shear stress shrinkage and longitudinal shear in the concrete
Vu = interface shear and repair materials engaged by the bar
t = net tensile strain in the extreme tension deformations. 2. adhesion or cohesion between reinforcement at nominal strength layers of a repair area or between a repair material
y = yield strain of steel reinforcement and a substrate produced by adhesive or cohesive = strength reduction factor properties of the repair material or other supplemental materials throughout the service ex = strength reduction factor used to check strength of the structure without external life of the repair. reinforcement after an extraordinary bond-critical application—strengthening or event repair system that relies on load transfer from the substrate to the system material achieved through 2.2—Definitions shear transfer at the interface, where bond rather than mechanical attachment is used as the primary load transfer mechanism. 21 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
capacity—the strength, stiffness, ductility, construction documents—written and graphic energy dissipation and durability, of a material, documents and specifications prepared or member or system as determined by analysis or assembled that describe the location, design, testing. materials, and physical characteristics of the Commentary: this definition has been expanded elements of a project necessary for obtaining a from ACI Concrete Terminology for this code. building permit and for construction of the compatible—the ability of two or more project. materials to be placed in contact or in sufficiently damage—changes in the capacity of an existing close proximity to interact with no significant structure resulting from events, such as loads and detrimental results. displacements. composite construction—a type of Commentary: deterioration from aging and construction using members produced by faulty construction should not be considered as combining different materials (for example, damage. concrete and structural steel); members produced dangerous—any concrete building, structure, or by combining cast-in-place and precast concrete, portion thereof that meets any of the conditions or cast-in-place concrete elements constructed in described below shall be deemed dangerous: separate placements but so interconnected that 1. The building or structure has collapsed, has the combined components act together as a single partially collapsed, has moved off its foundation, member and respond to loads as a unit. or lacks the necessary support of the ground. connector steel—steel elements, such as 2. There exists a significant risk of collapse, reinforcing bars, shapes, or plates, embedded in detachment or dislodgement of any portion, concrete or connected to embedded elements to member, appurtenance, or ornamentation of the facilitate concrete member connectivity. The concrete building or structure under nominal purpose of connector steel is to transfer load, loads. restrain movement, and provide stability. 3. Unsafe structural condition has been contact-critical application—strengthening determined in the building or structure. or repair system that relies on load transfer from Commentary: this definition has been modified the substrate to the system material achieved from the IEBC. Potentially dangerous conditions through bearing perpendicular to the interface. of an existing member or system include the Commentary—an example of a contact critical following: unsafe structural conditions, application is the addition of a confinement instability, falling hazards, or noncompliance jacket around a column. with fire resistance ratings. 22 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
demand—the force, deformation, energy equivalent cover—a system to supplement input, and chemical or physical attack imposed on insufficient concrete cover to improve durability a material, member, or system which is to be or fire protection to that equivalent to the resisted. minimum cover specified in the design basis demand-capacity ratio—ratio of nominal code. demand to capacity. Evaluation—refer to structural evaluation design basis code—legally adopted code existing structure—structure for which a legal requirements under which the assessments, certificate of occupancy has been issued. For repairs, and rehabilitations are designed and structures that are not covered by a certificate of constructed. occupancy, existing structures are those that are design-basis criteria—codes, standards, complete and permitted for use or otherwise loads, displacement limits, material properties, legally defined as an existing structure or connections, details, and protections used in the building. design of mandated or voluntary work. factored load—product of the nominal load design service life (of a building, component, and load factor. or material)—the period of time after faulty construction—deficient construction installation or repair during which the resulting from errors or omissions in design or performance satisfies the specified requirements improper construction causing displacement of if routinely maintained but without being supporting portions of the structure or resulting in subjected to an overload or extreme event. deficient materials, geometry, size or location of durability—ability of a material or structure to concrete members, reinforcement or connections. resist weathering action, chemical attack, glass transition temperature—midpoint in abrasion, and other conditions of service and transition over which a polymer resin changes maintain serviceability over a specified time or from a glassy state to a viscoelastic state as service life. measured pursuant to ASTM D4065. Tg – 27F is effective area of concrete—cross-sectional the glass transition temperature minus 27F. area of a concrete member that resists axial, in-place condition—current condition of an shear, or flexural stresses. existing structure, system, member, connection effective area of reinforcement—cross- including component sizes and geometry, sectional area of reinforcement assumed to resist material properties, faulty construction, axial, shear, or flexural stresses. deterioration, and damage from an event.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Interface reinforcement—existing or along a load path of a structural system to the supplemental reinforcement that is properly ground. anchored on both sides of an interface; post- owner—corporation, association, partnership, installed reinforcement such as adhesive anchors individual, or public body or authority with or mechanical anchors, or other mechanical whom the contractor enters into an agreement and connections providing a method of force transfer for whom the work is provided. The owner is the across an interface. party in legal possession of the structure. interface shear stress—shear stress resulting rehabilitation—repairing or modifying an from transfer of forces at bonded interfaces existing structure to a desired useful condition. between repair material and existing substrate Commentary: this definition is adapted from used to achieve composite behavior. ACI Concrete Terminology – “the process of jurisdictional authority—person or entity that repairing or modifying a structure to a desired has legal control over the applicable building useful condition.” The definition is specific for code and permitting procedures for a structure. concrete rehabilitation and is inclusive of the Commentary: An example of a jurisdictional IEBC definition – “Any work, as described by the authority is the local building official. categories of work defined herein, undertaken in licensed design professional—(1) an engineer an existing building.” Herein, concrete or architect who is licensed to practice structural rehabilitations include: repair to restore original design as defined by the statutory requirements of capacity; strengthening to increase the capacity the professional licensing laws of a state or to the current building code requirements; jurisdiction; (2) the engineer or architect, licensed seismic retrofits per ASCE/SEI 41; and as described, who is responsible for the structural modifications addressing additions, alterations, design of a particular project (also historically and change of occupancy. engineer of record). repair—the reconstruction or renewal of Commentary: this definition is adopted from concrete parts of an existing structure for the ACI Concrete Terminology. purpose of its maintenance or to correct nominal load—magnitude of load specified by deterioration, damage, or faulty construction of the design-basis code before application of any members or systems of a structure. factor. Commentary: the definition of repair from ACI nonstructural concrete—any element made Concrete Terminology is “to replace or correct of plain or reinforced concrete that is not required deteriorated, damaged, or faulty materials, to transfer gravity load, lateral load, or both, components, or elements of a structure.” The 24 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) definition of repair from IEBC is “The repair system—the combination of existing reconstruction or renewal of any part of any part and new components, which may include existing of an existing building for the purpose of its reinforcement, repair materials, supplementary maintenance or to correct damage.” The reinforcement and supplemental structural definition herein is adapted from the IEBC and is members specific for repair of materials, components, or retrofit—modification of an existing member, elements of existing concrete structures where system, or structure to increase its strength, structural repair or durability is addressed. ductility, or both as a means of improving the Faulty materials, components, or elements of a seismic performance of the structure. structure are interpreted to be faulty construction Commentary: typically used to refer to seismic resulting from errors or omissions in design or modifications to increase resistance in an construction. existing structure per ASCE/SEI 41. The repair reinforcement—reinforcement used to definition is adapted from ASCE/SEI 41 – provide additional strength, ductility, “Improving the seismic performance of confinement, or any combination of the three, to structural or nonstructural components of a the repaired member. building.” repair, structural—restoring a damaged or serviceability—structural performance under deteriorated structure or increasing the capacity service loads. of a structure. shoring—props or posts of timber or other Commentary: this definition is adapted from material in compression used for the temporary ACI Concrete Terminology – “increasing the support of excavations, formwork, or unsafe load-carrying capacity of a structural component structures; the process of erecting shores. beyond its current capacity or restoring a specialty engineer—a licensed design damaged structural component to its original professional retained by a contractor to design a design capacity.” Herein, the definition delegated portion of the project. addresses increasing the capacity to include Commentary: The term specialty engineer is enhancements such as ductility of existing used in Chapter 9. In this code, the specialty concrete members. Repairs to nonstructural engineer will typically be a licensed design members, whose failure would cause or result in professional that is retained by the contractor to unsafe structural conditions are considered design specific types of components such as structural repairs. precast or shoring members.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
stability, global—stability of the overall proposed use.” Herein, assessments should be existing structure with respect to uplift, limited to the work area and may include: overturning, sway instability, or sliding failure. a) investigation of the in-place condition of the stability, local—the stability of an individual existing structure by: member or part of an individual member. i. collection and review of field data for strengthening—process of increasing the the structure, such as geometry, load-resistance capacity of an existing structure material strengths, conditions, or a portion thereof. symptoms of distress, extent of structural analysis—process of using damage, measurement of engineering mechanics to determine internal displacements, environmental factors demands on, and capacities of a structure, and reinforcement sizes and placement member or system. ii. collection of background data, such as structural concrete—plain or reinforced plans, construction records, original, concrete in a member that is part of a structural current, and code governing existing system required to transfer gravity loads, lateral buildings, and historical events loads, or both, along a load path to the ground. b) evaluation of an existing structure, member structural assessment—the process of or system of the work area (see commentary investigating by systematically collecting for structural evaluation) information that affects the performance of an c) detail findings and conclusions of the existing structure; evaluating the collected investigation and evaluation include: information to make informed decisions i. define the existing structure, member, regarding the need for repair or rehabilitation; or system rehabilitation category using detailing of findings as conclusions and reporting the assessment criteria of this code recommendations for the examined structural ii. identify the work area, scope of work concrete work area (member, system, or and likely cause or mechanism of structure). damage, distress and deterioration Commentary: This definition with specific iii. identify faulty construction limitations details for existing concrete is adapted from iv. appraise test results to determine ASCE/SEI 11 – “Systematic collection and cause of failure and predict future analysis of data, evaluation, and performance. recommendations regarding the portions of an d) determine repair and rehabilitation concepts, existing structure which would be affected by its strategies, alternates and recommendations 26 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
i. develop cost-impact or economic study structural adequacy of the structure or as necessary to appraise remedial component for its intended use and/or work and maintenance performance. Evaluation by its nature implies the ii. describe repair and rehabilitation use of personal and subjective judgment by those work recommendations functioning in the capacity of experts.” An e) report conclusions and recommendations evaluation should determine, to the best of the include: license design professional’s knowledge, the level i. work area limits and limitations of of quality (structural adequacy, serviceability, or information collected and evaluated durability) of an existing structure based upon a ii. assessment criteria and work of the measured criteria and the judgment of the evaluation such as calculations, tests licensed design professional. An evaluation may and analyses require professional judgment to gage structural iii. details of findings (conclusions) and adequacy. Structural analyses may be required to recommendations determine possible ranges of existing structure iv. safety issue requirements capacities and variations in demands. The goal of (recommendation for any temporary the evaluation process is to appraise the in-place shoring etc.) condition to determine adequacy for current or proposed future use. Structural appraisal A structural assessment is the processes of requires determining capacity and demand, acquiring knowledge of the existing structure which may vary widely depending on the used for the purpose of judging the future acquired information, tests, models, and performance. The results of the investigation and analyses; determining the demand-capacity evaluation are used to make decisions on the ratios; and judging structural reliability limits, appropriate course of action regarding the future which may be open to interpretation based on use of the structure and the suitability of the project requirements, structural experience, structure to continue in service. knowledge, and past performance. structural evaluation—the process of Evaluation activities may include: determining, and judging the structural adequacy a) tests to confirm reinforcement location, of a structure, member, or system for its current strength of material properties or structural intended use or performance objective. capacity of existing members or systems or Commentary: This definition is adapted from for presence of contaminants. ASCE/SEI 11 – “The process of determining the 27 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) b) Analysis of test results to establish 2. The capacity of any vertical gravity load- reinforcement, statistical equivalent material carrying component, or any group of such properties, limits of faulty construction, and components, that supports more than 30 percent structural capacity of the total area of the structure’s floor(s) and c) Screening of observations and tests for roof(s) has been reduced more than 20 percent mechanisms and causes of damage, distress, from its predamage condition and the remaining and deterioration capacity of such affected elements, with respect d) establishing the assessment criteria to all dead and live loads, is less than 75 percent e) calculating demand loadings, serviceability of that required by this code for new buildings of limits, lateral displacements, and durability similar structure, purpose and location. requirements When using this code as a stand-alone code, f) analysis of the structure to determine the substantial structural damage shall be as defined capacity of the structure to withstand current in A.4. or future load demands and comply with Commentary: the definition of substantial serviceability limits structural damage is from IEBC and has been i. determination of demand-capacity modified as noted in A.4 when using this code as ratios to appraise structural adequacy, a stand-alone code. ascertain classifications, and judge the temporary bracing—temporary supplemental need for repair and rehabilitation members added to an existing structure to prevent ii. determination of maintenance local or global instability during assessment and requirements necessary for the service repair construction. life of the structure undercutting—concrete removal above or substantial structural damage—Except below reinforcement to allow for existing when using Appendix A, substantial structural reinforcement to be encapsulated in repair damage per the IEBC shall be - A condition material. where one or both of the following apply: unsafe structural condition—structural state 1. In any story, the vertical elements of the of an individual structural member, structural lateral force resisting system have suffered system, or structure with instability, potential damage such that the lateral load-carrying collapse of overhead components or pieces capacity of the structure in any horizontal (falling hazards), noncompliance with fire direction has been reduced by more than 33 resistance ratings or demand to capacity ratio percent from its predamage condition. 28 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) limits above acceptable limits defined in this code. Commentary: this definition is adapted from the IEBC and modified for strength design to be consistent with concrete requirements.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 3—REFERENCED Strengthening of Concrete and STANDARDS Masonry Structures
C Both current, past and withdrawn standards American Institute of Steel Construction are referenced. Standards that are referenced in ANSI/AISC 360-10 Specification for the design basis code are applicable for the Structural Steel Buildings assessment of existing structures. These standards may have been withdrawn by the American Welding Society developing organization; however, they provide D1.4/D1.4M:2011 Structural Welding Code— information on the materials used at the time of Reinforcing Steel original construction. Refer to 4.3.3 and Chapter 6. ASTM International American Concrete Institute ASTM A15 Specification for ACI 216.1-14 Code Requirements for Billet-Steel Bars for Concrete Determining Fire Resistance of Reinforcement (withdrawn 1969) Concrete and Masonry ASTM A16 Specification for Construction Assemblies Rail-Steel Bars of Concrete ACI 318-14 Building Code Requirements for Reinforcement (withdrawn 1969) Structural Concrete and ASTM A61 Specification for Commentary Deformed Rail Steel Bars for Concrete ACI 437.2-13 Code Requirements for Load Reinforcement with 60,000 psi Testing of Existing Concrete Minimum Yield Strength (withdrawn Structures and Commentary 1969) ACI 440.6-08 Specification for Carbon and ASTM A160 Specification for Glass Fiber-Reinforced Polymer Axle-Steel Bars for Concrete Bar Materials for Concrete Reinforcement (withdrawn 1969) Reinforcement ASTM A370-14 Standard Test ACI 440.8-13 Specification for Carbon and Methods and Definitions for Glass Fiber-Reinforced Polymer Mechanical Testing of Steel Products (FRP) Materials Made by Wet ASTM A408 Specification for Layup for External Special Large Size Deformed Billet-
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Steel Bars for Concrete Reinforcement ASTM A955/A955M-15 Standard (withdrawn 1968) Specification for Deformed and Plain ASTM A431 Specification for Stainless Steel Bars for Concrete High-Strength Deformed Billet-Steel Reinforcement Bars for Concrete Reinforcement with ASTM A1061/A1061M-09 Standard Test 75,000 psi Minimum Yield Strength Methods for Testing Multi-Wire Steel (withdrawn 1968) Strand ASTM A432 Specification for ASTM A1064/A1064M-14 Standard Deformed Billet Steel Bars for Concrete Specification for Carbon-Steel Wire and Reinforcement with 60,000 psi Welded Wire Reinforcement, Plain and Minimum Yield Point (withdrawn Deformed, for Concrete 1968) ASTM C42/C42M-13 Standard Test ASTM A497/A497M Standard Method for Obtaining and Testing Specification for Steel Welded Wire Drilled Cores and Sawed Beams of Reinforcement, Deforme4d, for Concrete Concrete (Withdrawn) ASTM C823/C823M-12 Standard Practice ASTM A615/A615M-14 Standard for Examination and Sampling of Specification for Deformed and Plain Hardened Concrete in Constructions Carbon-Steel Bars for Concrete ASTM C1583/C1583M-13 Standard Test Reinforcement Method for Tensile Strength of ASTM A616/A616M-96a Standard Concrete Surfaces and the Bond Specification for Rail-Steel Deformed Strength or Tensile Strength of Concrete and Plain Bars for Concrete Repair and Overlay Materials by Direct Reinforcement (withdrawn 1999) Tension (Pull-off Method) ASTM A617/A617M-96a Standard ASTM D4065-12 Standard Practice Specification for Axle-Steel Deformed for Plastics: Dynamic Mechanical and Plain Bars for Concrete Properties: Determination and Report of Reinforcement (withdrawn 1999) Procedures ASTM A706/A706M-14 Standard ASTM E329-14a Standard Specification for Low-Alloy Steel Specification for Agencies Engaged in Deformed and Plain Bars for Concrete Construction Inspection, Testing, or Reinforcement Special Inspection 31 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
American Society of Civil Engineers ASCE/SEI 7-10 Minimum Design Loads for Buildings and Other Structures ASCE/SEI 37-14 Design Loads on Structures during Construction ASCE/SEI 41-13 Seismic Evaluation and Retrofit of Existing Buildings
International Code Council IEBC 2015 International Existing Building Code
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 4––CRITERIA WHEN USING using ASCE/SEI 41. Provisions of ASCE/SEI 41 THIS CODE WITH THE may or may not be applicable to nonbuildings. INTERNATIONAL EXISTING BUILDING Section 4.3.2 provides minimum assessment CODE (IEBC) criteria for seismic safety provisions. 4.1.3 It shall be permitted to use the current 4.1—General building code as the design-basis criteria for all damage states, deterioration, faulty design, or 4.1.1 This chapter applies if a jurisdiction has faulty construction. adopted the International Existing Building Code 4.1.4 Alternately, this code in conjunction with as the existing building code. When this chapter the IEBC shall be used to determine the is used, Appendix A does not apply. rehabilitation category of work as shown in Table 4.1.1C Appendix A is used when this code is 4.1.4. used for existing concrete structures as a stand- 4.1.4C Unless the local jurisdiction provides alone code without the IEBC. more restrictive requirements, this Chapter with 4.1.2 The design-basis code criteria of the the IEBC should be used to determine the project shall be based on requirements set forth in assessment and design-basis criteria based on the this Chapter. rehabilitation category of Table 4.1.4. 4.1.2C Structures constructed under previously adopted codes or before the adoption of a building code may not satisfy all current building code requirements. This code and the IEBC contain specific requirements that determine if existing structures should be rehabilitated or retrofitted to satisfy the requirements of the current building code. Local ordinances may also require that a structure be rehabilitated to satisfy the current codes. These requirements should be reviewed at the start of a project. An evaluation and remediation of unsafe seismic resistance is excluded from IEBC. The licensed design professional should determine if seismic evaluation and retrofits are necessary
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Table 4.1.4—Design-Basis Code Criteria a) The structure is in seismic design References for Rehabilitation Categories categories A, B, or C and deterioration is
Design-Basis Code addressed; Rehabilitation Category Criteria Reference b) The repaired structure shall have Unsafe structural conditions 4.3.2 for gravity and wind loads capacity equal to or greater than demand Unsafe structural conditions for seismic forces in regions 4.3.3 per 5.2.2 using the original building of high seismicity Substantial structural code; IEBC Chapter 2 damage, definition c) No unsafe structural conditions were Substantial structural damage to vertical elements IEBC Section 404.2 or determined to be present; of the lateral-force-resisting 606.2.2 system d) The structure has demonstrated historical Substantial structural damage to vertical elements IEBC Section 404.3 or structural reliability. of the gravity-load-resisting 606.2.3 system 4.1.6C The licensed design professional Damage less than substantial structural 4.5 should determine if structural distress as damage with strengthening identified by observations, testing or Damage less than substantial structural 4.6 measurements is proportional to that predicted damage without strengthening based on historical data of the loads the structure Deterioration and faulty construction with 4.5 has experienced and if this demonstrates strengthening Deterioration and faulty statically acceptable past performance. Where construction without 4.6 the structural performance indicates adequate strengthening IEBC Section 402 or Additions behavior based on historical data, such as 1103 IEBC Section 403; acceptable resistance of previous loads which Sections 503 and 707; Alterations Sections 504 and 807; or equal or exceed the loads that would be predicted Sections 505 and 907 IEBC Section 407 or for the remaining life of the structure, the licensed Changes in Occupancy 1007 design professional may judge the structure to
have demonstrated historical structural 4.1.5 This code shall be used to design repairs reliability. ACI 224.1R-07, ACI 437R-03 and ACI of existing structures. ACI 318-14 shall be used 437.1R-07 provide guidance in judging to design new members and connections between acceptable performance. new members and existing construction.
4.1.6 The detailing of the existing 4.2—Compliance Method reinforcement need not comply with ACI 318-14 if the following conditions are satisfied:
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
4.2.1 The assessment and repair and current building code. Unsafe structural rehabilitation design shall be performed in conditions shall be reported in accordance with accordance with the prescriptive method, the 1.5.2. work area method, or the performance method of If the demand-capacity ratio does not exceed the IEBC. The compliance method selected and 1.5 for structures, 4.4 through 4.9 shall be used to the design basis code shall be used consistently determine the design-basis criteria. for all assessment and rehabilitation design, 4.3.2C In assessing unsafe structural excluding other options. conditions the strength design demand of Eq. (4.3.2) combines current building code nominal 4.3—Unsafe structural conditions gravity loads (dead, live and snow) and lateral 4.3.1 A structural assessment shall be wind forces, excluding seismic forces, using the performed to determine if unsafe structural factored load combinations of ASCE/SEI 7. A conditions are present. demand to capacity ratio greater than 1.5, 4.3.2 For gravity and wind loads, unsafe calculated using Equation 4.3.2, represents a structural conditions include instability, potential condition with limited to no margin of safety collapse of overhead components or pieces against failure. (falling hazards), or structures where the demand- In the assessment of unsafe structural capacity ratio is more than 1.5, as shown in Eq. conditions, the licensed design professional (4.3.2).\ should determine if it may be appropriate to include structural redundancies, alternate load U paths, primary and secondary supporting c 1.5 R cn (4.3.2) elements, redistribution of loads, collapse mechanisms, reduced live loads, measured
In Eq. (4.3.2), the strength design demand (Uc) displacements (listing, leaning and tilting), shall be determined for current building code second-order effects, and other loads specific to nominal dead, live, snow and wind loads, the structure, such as drifting snow, lateral earth excluding earthquake using factored load pressures, self-straining loads, ice, and floods. combinations of ASCE/SEI 7 and the strength References for unsafe structural conditions reduction factors () of 5.3 or 5.4 shall apply. include: commentary to Chapter 1 of ASCE/SEI If the demand-capacity ratio exceeds 1.5 for 7-10, Galambos, T.V., Ellingwood, B.R., structures, the design-basis criteria shall be the MacGregor, J.G., and Cornell, C.A., 1982, “Probability Based Load Criteria: Assessment of 35 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Current Design Practice,” Galambos, T.V., 78, the IEBC and ASCE 41 appendices for Ellingwood, B.R., MacGregor, J.G., and Cornell, guidance. C.A., 1982,“Probability Based Load Criteria: Load Factors and Load Combinations,” and 4.4—Substantial Structural Damage Ellingwood, B. R., and Ang, A. H-S., 1972, “A 4.4.1 Substantial structural damage shall be Probability Study of Safety Criteria for Design.” assessed and rehabilitated as referenced in Table These references provide target reliability 4.1.4. indexes, basic probability theory and concepts for an evaluation using the specific details of the 4.5—Conditions of Deterioration, Faulty demand as it relates to the capacity with the Construction or Damage Less than Substantial Structural Damage strength reduction factors of Chapter 5 for concrete structures. 4.5.1 If a structure has damage less than 4.3.3 Assessment criteria for unsafe structural substantial structural damage, deterioration, or conditions of seismic resistance is limited to contains faulty construction, and there is a reason structures in seismic design category D, E, and F to question the capacity of the structure, it shall of ASCE/SEI 7 and shall be determined using be assessed by checking the demand-capacity ASCE/SEI 41 and this code. The design-basis ratio using the original building code demand criteria for rehabilitation design and construction (Uo) with nominal loads, factored load of unsafe structures shall be this code and combinations and capacities of the original ASCE/SEI 41. building code to determine if it exceeds 1.0, as 4.3.3C Compliance with ASCE/SEI 41 for shown in Eq. (4.5.1). Structural Performance Level, Collapse U Prevention using an applicable Earthquake o 1.0 Rcn Hazard Level should be as determined by the (4.5.1) local jurisdictional authority for the assessment of unsafe structural conditions. Assessment of In Equation 4.5.1, strength reduction factors unsafe structural conditions for seismic () of original building code shall be used. If the resistance is not required for structures in demand-capacity ratio exceeds 1.0, then that regions of low or moderate seismicity. If no member or system strength shall be restored requirements for unsafe structural conditions are using the original building code. If the demand- provided by the local jurisdictional authority, the capacity ratio does not exceed 1.0, then licensed design professional should refer to ATC strengthening is not required. 36 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Repairs shall be permitted that restore a considered in the selection of an applicable member or system to the capacity of the original assessment criteria. building code based on material properties of the Beyond using the current building code, the original construction. assessment criteria should address if the demand 4.5.1C Most existing concrete structures with or capacity of the original structure or member is damage less than substantial structural damage, significantly inconsistent with current standards deterioration, or containing faulty construction, and results in unacceptable structural safety. An will provide acceptable safety if restored to the increase in load intensity, added loads, change in strength of the original building code. load factors, strength-reduction factors or load The demand-capacity ratio limit of 1.0 as combinations, modification of analytical provided in this section allows strengthening that procedures, or changes in the determined restores the structural reliability of the existing capacity between the original and current structure to the level prior to damage and building codes [such as a change from ASD to deterioration, or as intended in the original strength design] or the benefits received versus building code. the costs incurred should lead the licensed design Historical performance is often an acceptable professional to question the applicability of using indicator of adequate safety if the structure has the original building code for assessment of an been subjected to known loads. existing structure. Engineering principles used to If the capacity of the structure is not in determine acceptable structural safety are to use question, such as indicated by the commentary either a probabilistic evaluation of loads and provisions of 1.7.1C, assessment checks are not capacities to show adequate structural reliability required. indices or an evaluation procedure using 4.5.2 Alternative assessment criteria for demand-capacity ratios that is derived from the deterioration, faulty construction, or damage less basic engineering principles as presented in than substantial structural damage shall be current standards. permitted. The selected alternative assessment An assessment criterion for a structure that has criterion shall substantiate acceptable structural damage less than substantial structural damage, safety using engineering principles for existing deterioration, or faulty construction excluding structures. seismic forces that is based on the demand- 4.5.2C An alternative assessment criterion capacity ratios of IEBC is the following: may be use of the current building code and a) If the current building code demand (Uc) ASCE/SEI 41. The references of 4.3.2C should be exceeds the original building code 37 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
* strength should be restored using the demand ()Uo increased by 5 percent original building code demand. If the (1.05)UU * , check the demand- co demand-capacity ratio does not exceed capacity ratio using the current building 1.05, then strengthening is not required. code demand (U ) to determine if it c Strength reduction factors () of sections 5.3 exceeds 1.1, as shown in Eq. (4.5.2a). or 5.4 in Eq. (4.5.2a) and (4.5.2b) apply. If the original building code demand is used, the repair U c 1.1 design should be supplemented for existing Rcn (4.5.2a) members or systems by this code. In this assessment criterion, the current If the demand-capacity ratio exceeds 1.1, building code strength design demand (Uc) then that system or member should be combines current building code nominal gravity strengthened using the current building loads (dead, live, and snow) and lateral wind code demand. If the demand-capacity loads excluding earthquake loads using the ratio does not exceed 1.1, then no factored load combinations of ASCE/SEI 7. The strengthening is required. original building code strength design demand b) If the current building code demand (Uc) ()U * o combines original building code nominal does not exceed the original building
* gravity loads (dead, live, and snow) and lateral code demand ()Uo increased by 5 wind loads excluding earthquake loads using the * percent (1.05)UUco , check the factored load combinations of ASCE/SEI 7. demand-capacity ratio using the original Consideration should be given as to if it may be U * appropriate to include ASCE/SEI 41 seismic building code demand ( o ) to provisions, redistribution of loads, reduced live determine if it exceeds 1.05, as shown in loads, measured displacements (listing, leaning, Eq. (4.5.2b). and tilting), second-order effects, and other loads
specific to the structure, such as drifting snow, U * o 1.05 lateral earth pressures, self-straining loads, ice, Rcn (4.5.2b) and floods. The use of structure-specific data is If the demand-capacity ratio exceeds acceptable, if substantiated by the licensed 1.05, then that system or member design professional. For these assessment 38 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) criteria, the demand-capacity ratio provisions of wind forces including seismic forces using the part (1) may be used in the assessment regardless load combinations of original building code. of the whether the current building code demand Displacements (listing, leaning, and tilting), does or does not exceed the original building second-order effects, and other loads specific to code demand increased by 5 percent. the structure, such as drifting snow, lateral earth 4.5.3 If the concrete design regulations of the pressures, self-straining loads, ice, and floods original building code only used allowable stress should be considered. design and design service loads, the demand - Using allowable stress design is inconsistent capacity ratio shall be based on service load with the reliability principles of current strength demand (US) and resistance calculated using design provisions. To adequately address safety, allowable stresses (Ra) as shown in Eq. (4.5.3). consideration should be given to verification using 4.5.2 and a check of seismic resistance U using ASCE/SEI 41. s 1.0 R a (4.5.3)
If the demand-capacity ratio exceeds 1.0, then 4.5.4 Existing structures other than those to be that member or system strength shall be restored strengthened per 4.3 through 4.5 shall use 4.6 using the original building code. If the demand- through 4.9 to determine the design-basis criteria. capacity ratio does not exceed 1.0, then strengthening is not required. Repairs shall be 4.6—Conditions of Deterioration, Faulty Construction, or Damage Less than permitted that restore the member or system to its Substantial Structural Damage without pre-damage or pre-deteriorated state. Repair of Strengthening existing structural concrete is permitted based on 4.6.1 If no damage or less than substantial material properties of the original construction. structural damage is present, structures damaged, 4.5.3C Before 1963 the “Building Code deteriorated, or containing faulty construction Requirements for Reinforced Concrete” (ACI that do not require strengthening in accordance 318-63), the design of reinforced concrete with 4.5 shall use Chapters 7 through 10 of this structures was based upon allowable stress, or code as the design-basis criteria. working stress, design principles. Original 4.6.2 Deflections building code demands should include nominal 4.6.2.1 The effects of floor levelness, gravity loads (dead, live, and snow) and lateral vibrations, and deflections on the performance of
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) the existing structure shall be assessed. 4.9.1 The existing structure shall be assessed Deflections exceeding those allowed by the and rehabilitated in accordance with structural original building code shall be permitted requirements of the IEBC per Table 4.1.4 for provided those deflections do not adversely affect Changes of occupancy. structural performance. 4.6.2.1C The effect of floor levelness, vibrations, and deflections on the structural performance should be investigated by the licensed design professional to determine if the performance of the structure is acceptable to the owner and users of the structure. Acceptable performance criteria will need to be established for an individual structure based upon the intended use of the structure.
4.7—Additions 4.7.1 The existing structure shall be assessed and rehabilitated in accordance with structural requirements of the IEBC per Table 4.1.4 for Additions.
4.8—Alterations 4.8.1 The existing structure shall be assessed and rehabilitated in accordance with structural requirements of the IEBC per Table 4.1.4 according to Alteration level 1, 2, or 3. 4.8.1C Alterations in this section exclude the remedial work of 4.3 through 4.6.
4.9—Change of Occupancy
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 5—LOADS, FACTORED LOAD factors and load combinations from this Chapter COMBINATIONS, AND STRENGTH- with strength-reduction factors from the original REDUCTION FACTORS building code. 5.1.3C Mixing of load factors and load 5.1—General combinations from one code with strength- 5.1.1 Applicable loads used in the assessment reduction factors from a different code may result of the existing structure and the design of in an inconsistent level of reliability and safety. rehabilitation shall be determined to verify code Sections 4.5.2 and A.5.2 use nominal load from compliance. the original codes with factored load 5.1.2 If this code is part of the design-basis code combinations and strength-reduction factors for the assessment or rehabilitation design, the from this code. load factors, load combinations and strength- 5.1.4 Loads during the construction period shall reduction factors in this Chapter shall be used. be in accordance with the design basis code. If the 5.1.2C Load factors, load combinations, and building is unoccupied during the construction strength-reduction factors are intended to period, it shall be permitted to determine loads in achieve acceptable levels of safety against failure accordance with ASCE/SEI 37. If portions of the based on the accuracy of the strength prediction building are restricted to construction-only access model and on maximum expected loads during during the construction period, it shall be the service life of the rehabilitated structure. permitted to determine loads on only those In some instances, a building may need to be portions in accordance with ASCE/SEI 37. upgraded to satisfy current building code 5.1.4C These provisions permit the less requirements in accordance with the provisions stringent loads in ASCE/SEI 37 to be applied for of Chapters 4 and 6 or Appendix A and Chapter the construction-access only case. 6. Applicable loads are determined in 5.1.5 When assessing an existing structure, accordance with the existing-building code and consideration shall be given to effects caused by standards such as ASCE/SEI 7, ASCE/SEI 37, loads or imposed deformations that the structure and ASCE/SEI 41. is subjected to, if required by the jurisdictional 5.1.3 It shall not be permitted to use load factors authority, even if such effects may not have been and load combinations from the original building specified in the original building code. code with strength-reduction factors from this 5.1.5C Examples of such loads include Chapter. It shall not be permitted to use load vibration or impact loads. Examples of such imposed deformations include unequal settlement 41 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) of supports, and listing, leaning and tilting, and 5.2.3 Required strength U shall equal or exceed those due to prestressing, shrinkage, temperature the effects of factored load combinations as changes, creep. specified in the design-basis code. 5.2.3C The required strength U is expressed in 5.2—Load factors and load combinations terms of factored loads, which are the product of 5.2.1 Design of rehabilitation shall account for specified nominal loads multiplied by load existing loads and deformations of the structure; factors. the effects of load redistribution due to damage, 5.2.4 Required strength U shall include internal deterioration, or load removal; and the load effects due to reactions induced by sequencing of load application, including prestressing with a load factor of 1.0. construction and shoring loads, during the 5.2.5 For post-tensioned anchorage zone design rehabilitation process. or evaluation, a load factor of 1.2 shall be applied 5.2.2 Rehabilitation design shall confirm that to the maximum prestressing jacking force. structural members and connections have design 5.2.5C The load factor of 1.2 applied to the strengths at all sections at least equal to the maximum tendon jacking force results in a design required strengths calculated for factored loads load that exceeds the typical prestressing yield and forces in such combinations as stipulated in strength. This compares well with the maximum this code. Structural evaluation shall consider attainable jacking force, which is limited by the whether the design strengths of such members anchor efficiency factor. For jacking loads less and connections at all sections are sufficient. than the maximum tendon jacking force, or for 5.2.2C The basic requirement for strength jacking loads applied to nonmetallic prestressing design or assessment is expressed as: tendons, design of the anchorage for 1.2 times the design strength (for example, anticipated jacking force is appropriate given capacity)≥required strength (for example, that the jacking load is controlled better than demand) typical dead loads.
5.3—Strength reduction factors for (Rn) ≥ U rehabilitation design
5.3.1 Design strength provided by a member, The design strength is the nominal strength its connections to other members, and its cross multiplied by the strength-reduction factor . sections, in terms of flexure, axial load, shear, and torsion, shall be taken as the nominal strength 42 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) calculated in accordance with requirements and 5.3.2.C For a steel yield strength of 60 ksi, the assumptions of this code, multiplied by the steel tensile strains corresponding to the tension- strength-reduction factors in 5.3.2 and 5.3.4. and compression-controlled limits are 0.005 and 5.3.2 The strength-reduction factor shall be as 0.002, respectively. Because the compressive follows: strain in the concrete at nominal strength is Tension-controlled sections (steel typically assumed to be 0.003, the net tensile tensile strain at failure exceeding strain limits for compression-controlled members
2.5y where y is the yield may also be stated in terms of the ratio c/dt, where strain) ...... 0.90 c is the depth of the neutral axis at nominal Compression-controlled sections strength, and dt is the distance from the extreme (tensile strain at failure not compression fiber to the centroid of extreme
tension reinforcement. The c/dt limits for tension- exceeding y) (a) Members with spiral and compression-controlled sections are 0.375 reinforcement ...... 0.75 and 0.6, respectively. The 0.6 limit for (b) Other reinforced compression-controlled sections applies to members...... 0.65 sections reinforced with Grade 60 steel and to For sections in which the net tensile strain in prestressed sections. For other grades of steel,
c/dt should change with y, where c/dt = the extreme tension steel at nominal strength, t, is between the limits for compression-controlled 0.003/(0.003+y), where y is the yield strain of and tension-controlled sections, linear the steel reinforcement. interpolations of shall be permitted. 5.3.3 Computation of development lengths do Shear and torsion, and interface not require a -factor. shear ...... 0.75 5.3.4 For flexure, compression, shear, and Bearing on concrete (except for post- bearing of structural plain concrete, shall be tensioned anchorage zones and strut- 0.60. and-tie models) ...... 0.65 Post-tensioned anchorage zones 0.85 5.4—Strength-reduction factors for assessment Strut-and-tie models and struts, ties, nodal zones, and bearing areas in 5.4.1 If the required structural element such models ...... 0.75 dimensions and location of reinforcement are determined in accordance with Chapter 6, and
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) material properties are determined in accordance 5.4.3C The resistance factor for assessment of with 6.4, it shall be permitted to increase from plain concrete is the same as that specified for those specified in 5.3, but shall not exceed: design in 5.3.4. Material properties for plain Tension-controlled section ...... 1.0 concrete determined in accordance with 6.3.5 Compression-controlled sections: may increase its nominal resistance, but the Members with spiral strength-reduction factor remains unchanged reinforcement ...... 0.9 because plain concrete failures are usually Other reinforced members ...... 0.8 brittle. Shear and/or torsion, interface shear ...... 0.8 5.5—Additional load combinations for structures rehabilitated with external Bearing on concrete ...... 0.8 reinforcing systems Strut-and-tie models and struts, 5.5.1 For rehabilitation achieved with ties, nodal zones, and bearing unprotected external reinforcing systems that are areas in such models ...... 0.8 susceptible to damage by fire, vandalism or 5.4.1C Strength-reduction factors given in collision, the required strength of the structure 5.4.1 are larger than those in 5.3.1. These without rehabilitation shall equal or exceed the increased values are justified by the improved effects of the load combinations specified in reliability due to the use of accurate field- 5.5.2, and 5.5.3. obtained material properties, actual in-place 5.5.1C For rehabilitation achieved with dimensions, and well-understood methods of external reinforcing systems, such as externally analysis. They have been deemed appropriate for bonded fiber-reinforced polymer, externally use in ACI 318-14, Chapter 27, and have had a bonded steel plates, or external post-tensioning lengthy history of satisfactory performance. systems, the unrehabilitated structure requires a 5.4.2 If an evaluation of members with no minimum strength without the participation of the observed deterioration is based on historical external reinforcing system. Section 7.9 gives material properties as given in Tables 6.3.1a requirements for protected and unprotected through 6.3.1c, the -factors not exceeding those external reinforcing systems with respect to fire in 5.3 shall apply. and elevated temperatures. 5.4.3 For flexure, compression, shear, and 5.5.2 The required strength of the structure bearing of structural plain concrete, shall be without external reinforcement shall satisfy Eq. 0.60. (5.5.2) 44 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
where ex = 1.0; Rex is the nominal resistance of
Rn 1.1D + 0.75L + 0.2S (5.5.2) the structure computed using the probable material properties after the extraordinary event; where D, L and S are the effects due to the and S is the specified snow load. For cases where specified dead, live and snow loads, respectively, the design live load acting on the member to be calculated for the rehabilitated structure, is the strengthened has a high likelihood of being strength-reduction factor in 5.3 or 5.4, as present for a sustained period of time, a live load applicable, and Rn is the nominal strength. factor of 1.0 shall be used in place of 0.5 in Eq. 5.5.2C This load combination is intended to (5.5.3). minimize the risk of overload or damage to the 5.5.3C This load combination is intended to unstrengthened structure in the case where, minimize the risk of overload or damage to a during normal operating conditions, the external strengthened structure when the external reinforcement is damaged. Such damage may not reinforcement is damaged by an extraordinary be detected immediately and so the structure (or event such as fire, impact, or blast. Wind and structural component) may remain in service earthquake forces are not considered until the damage is identified. This combination extraordinary events for this load combination, also provides a desirable upper limit on the as they are unlikely to result in damage that additional strength that can be utilized using specifically affects the capacity of the external reinforcing systems. unprotected external reinforcing systems. The 5.5.2.1 If the applied live load has a high minimum limit of Eq. (5.5.3) should allow the likelihood of being sustained the live load factor structure to maintain sufficient structural in Eq. 5.5.2 shall be increased from 0.75 to 1.0. strength until the damaged rehabilitation system 5.5.2.1C Examples include library stack areas, has been repaired. Guidance concerning heavy storage areas, warehouses, and other probable material properties during the occupancies with a live load exceeding 100 lb/ft2. extraordinary event may be obtained from ACI 5.5.3 The required strength of the structure 216.1. without external reinforcement after an 5.5.3.1 If the applied live load has a high extraordinary event shall satisfy Eq. (5.5.3). likelihood of being sustained, the live load factor in Eq. 5.5.3 shall be increased from 0.50 to 1.0. 5.5.3.1C Refer to 5.5.2.1C exRex 1.2D + 0. 5L + 0.2S (5.5.3)
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 6—ASSESSMENT, deterioration and distress in the structural EVALUATION, AND ANALYSIS members should be identified, inspected, and recorded as to the type, location, and degree of 6.1—Structural assessment severity. Procedures are referenced in ACI 6.1.1 A structural assessment shall be 201.1R, ACI 228.1R, ACI 228.2R, ACI 364.1R, performed before rehabilitation of an existing ACI 437R, ASCE/SEI 11, ASCE/SEI 41 and structure. The structural assessment shall FEMA P-154. The affected structural members comprise 1) an investigation to establish the in- are not only members with obvious signs of place condition of the structure in the work area, distress but also contiguous members and including environment, geometry, material connections in the structural system. strengths, reinforcing-steel sizes and placement, The data gathered to determine the existing and signs of distress; 2) an evaluation to define capacity should include the effects of material the causes of distress, goals of the rehabilitation, degradation, such as loss of concrete strength and criteria for selection of rehabilitation from chemical attack; freezing and thawing; and solution(s); and 3) appropriate rehabilitation loss of steel area due to corrosion or other strategies. causes, or misplaced reinforcement; and effects of damaging events, such as earthquakes or fire. 6.2—Investigation and structural evaluation The effect of deterioration on the ductility of the 6.2.1 An investigation and structural evaluation member should be considered in the evaluation. shall be performed if an existing structure 1) The strength or serviceability of a member or exhibits signs of damage, displacement, structure may be compromised by spalling, deterioration, structural deficiency, or behavior excessive cracking, large deflections, or other that is inconsistent with available design and forms of damage or degradation. Seismic construction documents or code requirements in evaluation references for undamaged buildings effect at the time of construction, or 2) include FEMA P-58, FEMA P-154 and preliminary evaluation indicates strengthening is ASCE/SEI 41 and for damaged buildings include required. ATC 20, FEMA 306 and FEMA 307. 6.2.1C Field investigations in support of the 6.2.2 An investigation and structural evaluation structural evaluation may include visual shall be performed when there is a reason to observations, destructive testing, and question the capacity of the structure and nondestructive testing (NDT). Areas of known insufficient information is available to determine
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) if an existing structure is capable of resisting (c) As-built information required to determine design demands. appropriate strength reduction factors in 6.2.3 Where repairs are required to an accordance with Chapter 5. individual member in a structure, it shall be (d) Structural members’ orientation, determined if similar members throughout the displacements, construction deviations, and structure also require evaluation. physical dimensions. 6.2.3C If there is no evidence of damage, (e) Properties of materials and components distress or deterioration of similar members from available drawings, specifications, and elsewhere in a structure to those that required other documents; or by testing of existing repair, there is no need to perform an evaluation materials. of similar members unless unsafe conditions are (f) Additional considerations, such as present. Unsafe conditions may be a concern if proximity to adjacent buildings, load-bearing there are significant variances from the original partition walls, and other limitations for design intent such as lower-strength concrete or rehabilitation. insufficient reinforcement. In addition, if the (g) Information needed to assess lateral-force- similar members are in an environment that resisting systems, span lengths, support could foster deterioration, then repairs with conditions, building use and type, and strengthening or durability enhancements may be architectural features. required, as opposed to a similar member in a The construction documents may not represent less severe environment. as-built conditions. Therefore, the licensed 6.2.4 An investigation shall document design professional is encouraged to research conditions as necessary to perform a structural and verify that the material properties obtained evaluation. from record documents are accurate. Material 6.2.4C Conditions which may need to be testing may be required to verify these values. documented include (a) through (g): 6.2.5 If an analysis is performed, the structural (a) The physical condition of the structural evaluation shall document the requirements of members to examine the extent and location of 6.2.4 and (a) through (c). The analysis shall be degradation or distress. performed in accordance with 6.5. (b) The adequacy of continuous load paths a) As-measured structural member through the primary and secondary structural dimensions. members to provide for life safety and structural b) The presence and effect of alterations to the integrity. structural system. 47 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
c) Loads, occupancy, or usage different from documents. If such documents do not provide the original design. sufficient information to characterize the material properties, such properties shall be obtained from 6.3—Material properties the historical data provided in Tables 6.3.1a 6.3.1 Material properties shall be obtained from through 6.3.1c, or in accordance with 6.4, or both. available drawings, specifications, and other
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Table 6.3.1a—Default compressive strength of structural concrete, psi
Time frame Footings Beams Slabs Columns Walls
1900-1919 1000 2000 1500 1500 1000
1920-1949 1500 2000 2000 2000 2000
1950-1969 2500 3000 3000 3000 2500
1970-present 3000 3000 3000 3000 3000 Note: Adopted from ASCE/SEI 41-06.
Table 6.3.1b—Default tensile and yield strength properties for steel reinforcing bars for various periods*
Structural† Intermediate† Hard† Grade 33 40 50 60 65 70 75 Minimum yield, psi 33,000 40,000 50,000 60,000 65,000 70,000 75,000 Year Minimum tensile, psi 55,000 70,000 80,000 90,000 75,000 80,000 100,000 1911-1959 X X X — X — — 1959-1966 X X X X X X X 1966-1972 — X X X X X — 1972-1974 — X X X X X — 1974-1987 — X X X X X — 1987-Present — X X X X X — Note: Adopted from ASCE/SEI 41-06. *An entry of “X” indicates the grade was available in those years. †The terms “structural,” “intermediate,” and “hard” became obsolete in 1968.
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Table 6.3.1c—Default tensile and yield strength properties of steel reinforcement for various ASTM specifications and periods* Structural Intermediate Hard
† † † Grade 33 40 50 60 65 70 75 50,00 60,00 65,00 70,00 Minimum yield, psi 33,000 40,000 75,000 0 0 0 0 Minimu ASTM Steel Year m 80,00 90,00 75,00 80,00 100,00 Designation 55,000 70,000 type range tensile, 0 0 0 0 0 ‡ psi 1911- A15 Billet X X X — — 1966 1913- A16 Rail§ — — X — — 1966 1963- A61 Rail — — — X — 1966 1936- A160 Axle X X X — — 1964 1965- A160 Axle X X X X — 1966 1936- A185 WWF — — — — X present 1957- A408 Billet X X X — — 1966 1959- A431 Billet — — — — — X 1966 1959- A432 Billet — — — X — — 1966 1964- A497 WWF — — — — — X — present 1968- A615 Billet — X — — — X 1972 1974- A615 Billet — X — X — — 1986 1987- A615 Billet — X — X — X present 1968- A616-96|| Rail — — — X — — present 1968- A617 Axle — X — — — — present Low- 1974- A706# — — — X — X — alloy present Stainl 1996- A955 — X — X — X ess present Note: Adopted from ASCE/SEI 41-06. *An entry of “X” indicates the grade was available in those years. †The terms structural, intermediate, and hard became obsolete in 1968. ‡ASTM steel is marked with the letter W. §Rail bars are marked with the letter R. ||Bars marked with “s!” (ASTM A616-96) have supplementary requirements for bend tests. #ASTM A706 has a minimum tensile strength of 80 ksi, but not less than 1.25 times the actual yield strength.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
6.3.1C Material properties required for seismic e) Internal cracking (especially adjacent to evaluation and rehabilitation are discussed in and under previous repairs). ASCE/SEI 41. Where the as-built conditions and f) Degradation of stiffness and strength due properties of historical buildings require to bar slip in cracked sections and joints evaluation and rehabilitation, care should be damaged in seismic events. taken to minimize the impact of design and Other tests for material properties, including investigation procedures (U.S. Department of the petrographic examination, are often used. These Interior 1995). Material properties include all tests can be highly variable and dependent on the physical and chemical properties of the concrete structure, member type(s), and distress and reinforcement, and includes all references to mechanism. ASTM standards and other methods of Chloride penetration can cause steel determining physical and chemical properties. reinforcement corrosion, which can lead to 6.3.2 Concrete compressive strength and steel cracking and spalling. The depth of a spall will reinforcement yield strength shall be determined affect the effective area of concrete section. for the structure if a structural evaluation is Concrete degradation will affect its compressive required. If tests are used to determine material strength. properties, test methods shall be in accordance 6.3.3 Nominal material properties shall be with 6.3.5. determined by (a), (b) or (c): 6.3.2C Additional factors and characteristics a) Historical material properties in affecting materials that may be required to be accordance with Tables 6.3.1a through evaluated include: 6.3.1c. a) Ductility of the member based on the b) Available drawings, specifications, and stress-strain curves of the material. previous testing documentation. b) Presence of corrosion of embedded steel c) Physical testing in accordance with 6.4. reinforcement, including carbonation, 6.3.3C The construction documents may not chloride intrusion, and corrosion-induced represent as-built conditions. Therefore, the spalling. evaluation of material properties should verify, c) Presence of other degradation, such as using material testing as required, that the alkali-silica reaction, sulfate attack, or material properties obtained from record delayed ettringite formation. documents are representative. d) Degradation due to cyclic freezing and 6.3.4 The material properties provided in the thawing. original construction test reports or material test 51 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) reports shall be permitted to be used unless place materials. The focus of the prescribed known deterioration that can affect performance material testing should be on the principal has occurred. structural members and specific properties 6.3.4C If the results of material testing from needed for analysis. The licensed design original construction are available, these results professional should determine the appropriate may be used in the analysis. Additional testing number and type of testing needed to evaluate the could be required to confirm these material test existing conditions. results if degradation has occurred. Care should be taken in selecting the location 6.3.5 If material properties are determined by for sampling concrete. Core drilling should in-place testing in accordance with 6.4, the minimize damage of the existing reinforcement locations and numbers of material samples shall and should generally occur at locations where be defined to characterize the materials. The the coring will least affect the member strength. number of samples shall be determined during 6.3.6 If historic data are not given in either evaluation. Table 6.3.1b or 6.3.1c, the historic default value
6.3.5C Review of available records from the for yield strength, fy shall be taken as 27,000 psi. original construction may be used to guide 6.3.6C Additional guidance regarding the use testing. Evaluation, historical research, and of the historic lower bound default value is given documentation of the geometry, material in 6.4.4.1C properties, and detailing used in the construction are invaluable and may be used to reduce the 6.4—Test methods to quantify material and amount of required in-place testing. The data member properties gathered to determine strength should include the 6.4.1 General effects of material degradation, such as loss of 6.4.1.1 Destructive and nondestructive test concrete strength from chemical attack and loss methods used to obtain in-place mechanical of steel area due to corrosion. The impact of properties of materials and member properties deterioration on the expected strength and shall be in accordance with this section. ductility of the section also should be considered Compressive strength of sound concrete shall be in the evaluation. determined by taking and testing core samples or The minimum number of tests is influenced by by a combination of cores and by the use of site the data available from the original construction, specific nondestructive testing. Steel the type of structural system, the desired reinforcement properties shall be determined by accuracy, and the quality and condition of the in- 52 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) removal of reinforcement samples and destructive testing. Table 6.4.3.1—Coefficient of variation
6.4.2 Core sampling of concrete for testing modification factor kc 6.4.2.1 It shall be permitted to determine the n kc compressive strength of sound concrete by taking 2 2.4 cores from the members being evaluated. Steel 3 1.47 reinforcement shall be located before locating the cores to be extracted. 4 1.28 6.4.2.1C NDT may be used to locate existing 5 1.20 reinforcement and to avoid damage to 6 1.15 reinforcement during coring. Guidelines for core 8 1.10 sampling and evaluating core strength data are 10 1.08 given in ACI 214.4R. 12 1.06 6.4.3 Concrete 6.4.3.1 The cores shall be selected and removed 16 1.05 in accordance with ASTM C42 and ASTM C823. 20 1.03
The equivalent specified concrete strength fceq 25 or more 1.02 shall be calculated by: 6.4.3.1C The equivalent specified strength 2 ()kVc determined using this procedure can be used in ffceq0.9 c 1 1.28 0.0015 n (6.4.3.1) strength equations with the strength reduction factors from Chapter 5. The strength value obtained using this procedure is an estimate of f where c is the average core strength, as the 13 percent fractile of the in-place concrete modified to account for the diameter, length to strength. Equation 6.4.3.1 is a simplification of diameter ratio and moisture condition of the core; criteria given in ACI 214.4 that gives similar V is the coefficient of variation of the core results because it accounts for the impact and strengths (a dimensionless quantity equal to the uncertainty of strength correction factors for sample standard deviation divided by the mean); length-to-diameter ratio, core diameter, and n is the number of cores taken, and k is the c drilling damage. This approach is specified in the coefficient of variation modification factor, as Canadian Highway Bridge Design Code obtained from Table 6.4.3.1. 53 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
(CAN/CSA S6-06 2006) and is based on the corresponding to the structure’s age should be approach proposed by Bartlett and MacGregor used. If no information is available, the lower
(1995). When the testing requirements of ASTM bound value of fy equal to 27,000 psi may be used C42/42M are not met, the user should consult instead of testing, provided it is conservative. In ACI 214.4. some instances assuming higher yield strengths 6.4.3.2 Nondestructive strength testing to may be more conservative. Where the demand on evaluate in-place strength of concrete shall be one member is governed by the capacity of a permitted if a valid correlation is established with connected member, it is appropriate to assign core sample compressive strength test results and higher yield strengths to the connected member. nondestructive test results. Quantifications of For example, in seismic analysis at beam column concrete compressive strength by NDT alone joints, the moment strength of the columns should shall not be permitted as a substitute for core exceed the moment strength of the beams. When sampling and testing. assessing this requirement it is more conservative 6.4.3.2C ACI 228.1R provides information on to assume a higher yield strength for the beam NDT methods for evaluation of concrete reinforcement than for the column reinforcement. compressive strength and development of 6.4.5 Reinforcement sampling and testing statistical correlations between NDT and core 6.4.5.1 Coupon samples for the determination test results. of the yield and tensile strength for steel 6.4.4 Steel reinforcement reinforcement shall be obtained in accordance 6.4.4.1 The size, number, and location, with ASTM A370. A minimum of three sample including effective depth of steel reinforcing bars coupons, taken from different segments of or elements shall be established. If the original reinforcement shall be obtained from the construction documents are not available and if members being evaluated. the properties of the reinforcing bars are 6.4.5.1C Often the steel reinforcement in a unknown, historical values provided in 6.3.6 shall structure is of a common grade and strength. be permitted in place of testing. If the grade of Occasionally, more than one grade of steel is material is unknown, the lowest grade provided used, for example, smaller diameter (#3 and 4) in Table 6.3.1b for a given historic period shall be stirrups and other complex bent bars were often used. fabricated with lower strength material than the 6.4.4.1C The age of the structure may be known longitudinal bars. but the grade of reinforcement is unknown. In this CRSI (2014): Vintage Reinforcement in Concrete case, the lowest grade of reinforcement Structures contains supplemental information on 54 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
mechanical properties of the reinforcement used 30 or more 1.00 in different construction eras. Steel reinforcement information includes 6.4.6C The equivalent specified yield strength square, rectangular, and round bars with and determined using this procedure can be used in without deformations, prestressing wire, bars, strength equations with the strength reduction multi-wire strands, and structural shapes. factors from Chapter 5. The yield strength value Historically, wire rope and chain have also been obtained using this procedure is an estimate of used as reinforcement. the 10 percent fractile of the static steel strength. 6.4.6. The equivalent specified yield strength It is assumed that the yield strength measured during a coupon test exceeds the static yield fyeq used for analysis shall be calculated by: strength by 3500 psi. This approach is specified in the Canadian Highway Bridge Design Code f f = ( y – 3500)exp(–1.3k V) (6.4.6) yeq s (CAN/CSA S6-06 2006). N as presented above
represents the number of strength tests performed f where y is the average yield strength value from for a given set of tested reinforcement. the tests, in psi; V is the average coefficient of The factors in Table 6.4.6 reflect the variation determined from testing; n is the uncertainty of the sample standard deviation for number of strength tests; and ks is the steel a small sample size. They are the 95 percent one- coefficient of variation modification factor, as sided tolerance limits on the 10 percent fractile, obtained from Table 6.4.6. and they have been reduced by a constant factor to be equal to 1.0 for n = 30 specimens. Table 6.4.6—Steel coefficient of variation
modification factor, ks 6.4.7 If the properties of the connector steel are
n ks unknown, strength shall be determined by (a), (b), 3 3.46 or (c): 4 2.34 a) Testing of coupons taken from the 5 1.92 6 1.69 connector steel. 8 1.45 b) Documentation giving connector steel 10 1.32 properties in the original construction 12 1.24 16 1.14 documents. 20 1.08 c) Use of historic default values in accordance 25 1.03 with 6.3.6. 55 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
6.4.7C The historic default value is obtained 6.5.1 The gravity and lateral-force-resisting from ASCE/SEI 41. structural systems shall be analyzed for the 6.4.8 Coupon specimens for the determination maximum effects on the affected members. of yield and tensile strengths of structural steel Loads and load combinations shall be determined shall be tested in accordance with ASTM A370. in accordance with this code. A minimum of three specimens shall be taken 6.5.1C Structural evaluation and analyses are from representative elements. conducted to verify strength and serviceability.
The equivalent specified yield strength fy of The analytical methods of 6.5 are used with each specimen shall be its reported yield strength. factored loads to determine strength
The fyeq used for analysis shall be calculated by: requirements for a combination of flexure, shear, torsion, and axial loads of pertinent structural members. A service-load analysis may be f y fyeq = ( – 4000)exp(–1.3ksV) (6.4.8) required to evaluate serviceability issues such as
deflection and cracking. f where y is the average yield strength value from 6.5.2 Analysis of the structure shall use tests, in psi; V is the average coefficient of accepted engineering principles that satisfy force variation determined from testing; n is the equilibrium and the principles of compatibility of number of strength tests; and ks is the steel deformations and strains. coefficient of variation modification factor, as 6.5.3 Analysis shall consider material obtained from Table 6.4.6. properties, member geometry and deformation, 6.4.9 The sampling of prestressing steel lateral drift, duration of loads, shrinkage and reinforcement for strength testing shall be creep, and interaction with the supporting required if strength and historical data are not foundation. available. Testing of the prestressing 6.5.3C The licensed design professional is reinforcement shall be in accordance with ASTM responsible for determining the appropriate A1061/1061M. method of analysis. Appropriate methods include 6.4.10 If welding of reinforcement is required, linear elastic analysis, nonlinear analysis, and carbon equivalent shall be determined in other traditionally accepted engineering analysis accordance with D1.4/D1.4M:2011. methods. If a linear elastic analysis method is used, the effects of cracking, second-order and 6.5—Structural analysis of existing structures other nonlinear effects should be included in the analysis using engineering approximations. 56 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
The analysis may include the effects of the size analysis adequately represents the part of the and member geometry to determine the forces on structure being evaluated. individual members of a structure. The analysis 6.5.5C The evaluation of load effects requires should consider external effects, including consideration of both the load paths through the prestressing, material volume changes, structure and how the forces are distributed in temperature variations, and differential members. foundation movement. 6.5.6 Analysis shall consider the effects of 6.5.4 Members shall be analyzed considering previous repairs and of any previous structural the effect of any material degradation, bond loss, modifications on the behavior of the structure. and the redistribution of forces in members and in 6.5.6C Modifications to structures in the form the structural system as a whole. of repairs, alterations, or additions may affect the 6.5.4C Member deterioration and damage may force distribution and load path in a structure. result in distribution of internal forces different 6.5.7 The analysis shall be based on available than the distribution of forces of the original documentation, as-built dimensions, and the in- structural design. The strength and integrity of place properties of the structure including section prestressed structures with damaged prestressing loss. The determination of in-place material reinforcement requires careful consideration to properties shall be in accordance with 6.3. assess the impact of the damage. Actual 6.5.7C Available documentation may include redistribution of moments in existing structures original drawings, specifications, shop drawings, may exceed the moment redistribution permitted structural assessments, testing, and geotechnical in ACI 318-14. The state of the structure should reports. Deviations between the existing be accurately modeled to determine the construction and construction documents are to distribution of forces. Redistribution of forces be identified and recorded. If section loss has may be determined using material nonlinear occurred, a more accurate analysis may be analysis, by load tests described in ACI 437.2, or developed by direct measurement of the section, by linear analysis, which bounds the limits of and by calculation of section properties based on redistributed forces. actual conditions. Additional information may be 6.5.5 Analysis shall consider the load path from obtained in ACI 364.10T. the load application through the structure to the foundation. Three-dimensional distribution of 6.6—Structural serviceability loads and forces in the complete structural system shall be considered unless a two-dimensional 57 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
6.6.1 If serviceability problems have been applied loads may be due to prestressing, identified in accordance with 6.2, the licensed vibration, material volume changes (such as design professional shall perform a serviceability creep and shrinkage, or temperature changes), evaluation based on the existing geometry and effect of shoring, and unequal deformation of properties of the structure. supports. 6.6.1C Structural serviceability problems may 6.7.2 Structural analysis shall account for include deflections, vibrations, leakage, and repairs where the materials change through the objectionable cracking. The data gathered to section. determine serviceability should include the 6.7.2C The intent of this section is to address effects of material degradation, such as loss of differences in stiffness between repair material concrete strength from sulfate attack or loss of and existing substrate. In these situations, steel area due to corrosion. localized deformation may occur in the material The specific performance criteria and the with the lower modulus of elasticity, affecting the intended function of the structure should be force distribution in the repaired structure. considered. Floor deflection criteria can be 6.7.3 Section analysis shall use principles of found in ACI 318.-14. Vibration criteria are mechanics and shall assume (a), (b), or (c) as given in Murray et al. (1999). appropriate: a) full composite action with no slip at 6.7—Structural analysis for repair design interfaces between repair materials and 6.7.1 The structural analysis used for repair existing materials design shall consider the structural repair process. b) separate action with full slip between repair The analysis shall consider the effects of the and existing materials sequence of load application and material c) partial composite action with friction at removal during the anticipated phases of the interfaces between repair and existing evaluation and repair process. materials 6.7.1C The construction process may involve 6.7.3C Depending on the repair construction the application, removal and replacement of process and the selection of repair materials, the loads. The analysis needs to consider the effects repair materials and the existing concrete or of the application and removal of construction reinforcement may not act compositely. The loads to determine the maximum loading during analysis should model the anticipated degree of anticipated construction phases. The additional composite action of the repaired structure. An example of partial composite behavior are beams 58 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) that contain shear studs to develop nominal strength, yet lack bond between the overlay and 6.8—Strength evaluation by load testing substrate. In this situation, the overlay and 6.8.1 Load testing in accordance with ACI substrate do not maintain strain compatibility. 437.2-13 shall be permitted to supplement an 6.7.4 Seismic analysis of repaired structure analysis or to demonstrate the strength of the 6.7.4.1 The interaction of structural members original or repaired structure and nonstructural components that affect the 6.8.1C Information obtained during a response of the structure to seismic motions shall structural evaluation may be insufficient to be considered in the analysis. determine the strength or serviceability of 6.7.4.2 Existing, repaired, and added deteriorated or repaired structural members. supplementary members assumed not to be a part Structural condition assessments, including of the seismic-force-resisting system shall be destructive testing, can provide some of the permitted, provided their effect on the response information required, but the costs for these of the system is considered and accommodated in assessments can be significant. Further, the the repair design. Consequences of failure of results of a structural evaluation may still be structural members that are not a part of the inconclusive due to unknown effects of existing seismic-force-resisting system and nonstructural conditions or interaction with the repair. In such components shall be considered. cases, load testing may provide the most effective 6.7.4.3 The method of analysis shall consider means of verifying the strength of a structure or the structural configuration and material member. Load testing can also be a valuable tool properties after repair. for evaluating the effectiveness of structural 6.7.4.3C Procedures for seismic rehabilitation repairs. For example, load testing, as defined in of concrete buildings, including analysis, are ACI 437, can be performed to determine if the provided in ASCE/SEI 41 and supplemented in service load deflection and cracking are ACI 369R. These references provide details for acceptable. forces, rehabilitation methods, analysis and 6.8.2 Model analysis shall be permitted to modeling procedures, and seismic rehabilitation supplement calculations. design. Additional references for repair of 6.8.2C This code permits model analysis to be building damage by a seismic event and used to supplement structural analysis and design rehabilitation of concrete buildings include calculations. Model analysis involves the FEMA 308, FEMA 395 through FEMA 400, and construction and experimental testing of full or FEMA 547. 59 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) scale models of structure components, assemblages, or systems. Documentation of the model tests and subsequent interpretation should be provided with the related calculations. Model analysis should be performed by an individual having experience in this technique. References are provided in Harris and Sabnis, (1999), ACI SP-24 (1970).
6.9—Recommendations 6.9.1 Recommendations shall be developed based upon the results of the evaluation. Repair and rehabilitation design, if performed, shall be in accordance with this code.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 7—DESIGN OF STRUCTURAL deformations that adversely affect strength or REPAIRS serviceability of a structure. 7.2.1C Adequate stiffness needs to be 7.1—General determined on a project-specific basis and is a 7.1C Repair and rehabilitation, as defined in function of the structure type, the desired Chapter 2, are processes in which deficiencies performance of the structure, and loading and damage in a structure or member are conditions and use. corrected. The methods used to correct 7.2.2 Repair design and construction deficiencies and damage in structures will be the procedures shall consider loading, internal forces, same for both repair and rehabilitation projects. and deformations in both the existing and For the purposes of this chapter, design repaired structure during the repair process. requirements for repair and rehabilitation can be 7.2.2C During the repair process, it may not be considered to be equivalent. possible or practical to relieve existing stresses Durability requirements for repairs are in or deformations. Consideration should be given Chapter 8. to the in-place internal forces and deformations 7.1.1 Repaired structures and connections shall present in the structure during the repair and the have design strengths at all sections at least equal subsequent internal forces from the design loads to the required strengths calculated using the that the repaired section will resist. Internal factored loads and forces in such combinations as forces and deformations caused by existing loads stipulated in this code. may be locked in by the repair. 7.1.1C Loads include those from externally Analysis to evaluate the effects of structural applied loads and those from imposed modifications should verify that strength is deformations, from such actions as prestressing, adequate and that serviceability conditions are and shrinkage of repair materials, temperature met. As an example, creating a large opening in changes, creep, unequal settlement of supports, structural slabs may necessitate cutting and listing, leaning and tilting displacements. reinforcement, which can significantly influence the global behavior of the structure. 7.2—Strength and serviceability Supplementary strengthening may be required to 7.2.1 Repaired structures shall be designed to address force redistribution that can exceed the have adequate stiffness to limit lateral and existing strength. Slab punching shear strength vertical deflections, vibrations, cracking, or any should be evaluated for openings at the intersection of column strips to verify that the 61 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) slab is adequate. This is especially critical near designed to transfer design forces between new corner and edge columns where the slab shear members and the structure. stress is typically highest. New members may need to be separated from adjacent members to prevent or minimize 7.3—Behavior of repaired systems interaction that may result in damage to adjacent 7.3.1 Repairs to sections, components, portions of the structure. Transfer of forces reinforcement, connections of members, or between new and existing members should not systems, or incorporating new members shall be compromise the performance of the structural designed to be integrated with the existing system. structure, creating a structural system capable of 7.3.2 Repairs to members shall account for sharing and transferring loads. force transfer at the interface between the 7.3.1C Repair of a structure may be achieved member and the repair material or repair system. by improving the global behavior of the structure It shall be permitted to use ACI 318-14 to design by adding new structural members that act the force transfer mechanism between new and integrally with the existing structural system or existing concrete. improving the behavior of the existing members. 7.3.2C In a repaired member, induced forces Load sharing and load transfer should exist on the repaired member are shared between the between the structure and the new members so member and the repair material or system. The that the assumed load path and force distribution repair should be designed to allow for transfer of can occur. The effects of adding new members on forces between the components. the global stiffness and force distribution should The requirements for composite behavior be considered. between the repair and the member may vary 7.3.1.1 The design of the repair shall consider depending on the type of repair (structural or the structural interaction between the structure nonstructural), the performance criteria at and new members. The effect of the new service, and the required strength at the ultimate members on the structure shall be evaluated limit states. While certain designs require according to the design-basis code. composite behavior up to an ultimate limit state, 7.3.1.1C The design of the repair should others may be limited to service conditions. consider connections of new members to the Composite behavior can be achieved by chemical structure. Connections of new members should be bonding, mechanical means, or a combination thereof. The design should specify the repair materials and techniques that will develop the 62 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) level of composite behavior to achieve the shall use factored loads in addition to internal intended performance of the repaired member. forces resulting from restrained volume change to Specific reference is made to ACI 318-14, 16.4 calculate the resultant interface stress demand and 22.9, for force transfer requirements between (vu) from the transfer of tension and shear. new and existing concrete. Techniques other than 7.4.1C The forces acting on the interface shear-friction may be acceptable. between repair material and existing substrate Design provisions for fiber-reinforced polymer can include tension, shear, or a combination of (FRP) are provided in ACI 440.1R, 440.2R and tension and shear depending on repair geometry 440.7R (Design provisions for composite and the applied loads. The tensile and shear structural steel sections are provided in the Steel demand at an interface between a repair material Construction Manual (AISC 360-10 Chapter I). and the substrate from applied loads and from 7.3.2.1 Structural repairs required for strength volume changes that occur as a result of or stiffness shall maintain composite behavior shrinkage or thermal movement can be under service load. The repaired system shall calculated using principles of structural have sufficient redundancy to mitigate the mechanics, but these calculations can be potential for falling hazards in the event that bond complex. Guidance on designing the interface for between the repair and the substrate is lost. horizontal shear can be found in Chapter 16 of 7.3.2.1C Non-structural repairs intended to ACI 318-14, AISC 360-10, Chapter I and Bakhsh improve durability or aesthetics might not (2010). Repair materials include cementitious require composite behavior under service loads. and polymer concretes, fiber reinforced concrete, Redundancy of the repair material can be and mortar. provided by the encapsulation of the existing steel Where the required nominal interface shear reinforcement with the repair material, by stress is lower than 80 psi, and where good installing new anchors within the repair or by surface preparation, placement and curing other means. techniques, and adequate repair materials are provided, satisfactory composite behavior will 7.4—Interface Bond likely be achieved without interface 7.4.1 Repair design shall include an analysis to reinforcement. determine the interface shear and tension stresses 7.4.1.1 Interface shear stress shall be designed across bonded interfaces between repair materials based on: and the existing substrate. The interface analysis
vu ≤ φvni (7.4.1.1) 63 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
that tensile bond test values less than 175 psi that where vni is nominal interface shear stress and φ fail at the bond interface or superficially within is in accordance with 5.3.2. the existing concrete substrate may indicate a 7.4.1.2 Testing requirements shall be in partially damaged, contaminated, or otherwise accordance with Table 7.4.1.2 inadequate bond surface. EN 1504-10 suggests minimum direct tension strengths of 100 psi for Table 7.4.1.2—Testing requirements where non-structural repair and 175 to 215 psi for
vu is partially or totally resisted by the structural repairs. Interface reinforcement may concrete be needed if sufficient interface capacity cannot Testing be achieved through bond. vu Reference Requirements Bond integrity testing can consist of various Less than 30 7.4.2 Bond-integrity testing qualitative test methods such as sounding in psi Between 30 Quantitative bond accordance with ASTM D4580, nondestructive 7.4.3 and 60 psi strength testing methods such as ground penetrating radar or Greater than Quantitative bond impact-echo described in ACI 228.2R or ICRI 7.4.4 60 psi strength testing 210.4.
7.4.3 If vu is between 30 psi and 60 psi, interface 7.4.2 If v does not exceed 30 psi, interface u reinforcement is not required. Quantitative bond reinforcement shall not be required. Bond- strength testing shall be performed to verify integrity testing as specified in the construction performance. Direct tension pull-off tests (ASTM documents shall be performed. C1583) or other similar quantitative test methods 7.4.2C The 30 psi bond stress specified by this shall be specified. The frequency of tests and code is based on half of a nominal shear stress of acceptance criteria shall be specified, but the 80 psi multiplied the strength reduction in 5.3.2. number of tests on a project shall be at least three A properly prepared substrate is achieved by (3). removing existing deteriorated, damaged, or 7.4.3C The 60 psi bond stress is based on a contaminated concrete. The exposed sound nominal shear stress of 80 psi multiplied by the concrete is then roughened and cleaned to allow strength reduction in 5.3.2 for adequate bond of a repair material. ICRI No. Testing to verify the bond of repair materials to 210.3 presents a discussion of achievable tensile the substrate is recommended as part of a quality bond strengths, suggests a minimum value of 100 assurance program on most concrete repair psi for less critical applications, and indicates projects. ICRI No. 210.3 provides guidance on 64 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) the number of tests that should be performed surface preparation can be found in ACI 546R based upon the repair area and acceptance and ICRI 310.2R. criteria. 7.4.4. If vu exceeds 60 psi, interface Bond capacity has primarily been evaluated reinforcement shall be provided. using direct tension pull-off tests, as defined in 7.4.5 If vu is completely resisted by interface ASTM C1583 and as described in ICRI No. 210.3. reinforcement, quantitative bond strength testing In some instances, laboratory slant shear tests in is not required. accordance with ASTM C882 of cores made in 7.4.5C This provision provides an alternative to the lab or cores taken from mockups in the field bond strength testing. have been used to assist the licensed design 7.4.6 Interface reinforcement shall be designed in professional to make informed design decisions. accordance with ACI 318-14, 16.4.4 through Slant shear test results typically exceed direct 16.4.7. tension pull-off test results, but the slant shear 7.4.7 Construction documents shall specify strength is greatly influenced by the compressive testing requirements for interface reinforcement stress the test setup introduces across the in the repair applications. interface and may not be directly comparable to 7.4.7C Testing to verify the performance of the field conditions. Typically direct shear strengths interface reinforcement to transfer horizontal are larger than direct tension strengths. shear can be performed in accordance with the Comparisons of these tests and other tests, for the recommendations contained in ACI 355.2 and purpose of achieving adequate bond is discussed 355.4. Specific requirements for testing of ties in Bakhsh (2010). It generally is adequate to should be included in a quality assurance plan. assume that the repair to substrate bond will Direct tension testing of post-installed interface resist an interfacial shear equal to the direct reinforcement is recommended to provide tensile pull-off test result. verification of the installation. Guidance to If failure during direct pull-off testing occurs at determining the number of tests and acceptance the bond line, it may indicate inadequate surface criteria of the direct tension testing is similar to preparation of the concrete substrate or the principles used in developing direct tension pull- substrate surface was damaged by the surface off testing requirements described in ICRI 210.3. preparation method (bruising of the substrate) Modifications to the surface preparation 7.5—Materials procedures may improve the tensile bond strength. Discussion of proper methods for 65 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
7.5.1 Design of the repair system shall consider combined in a repair system. An example of this the properties and installation of the repair is where materials with differing thermal materials and systems. These include, but are not coefficients of expansion may be used, provided limited to: physical properties of the repair that the overall performance of the system is not materials, type of application, adhesion, volume affected by thermal changes. stability, thermal movement, durability, Volume stability is often estimated as changes in corrosion resistance, installation methods, curing a linear dimension of the repair and should be requirements, and environmental conditions. considered in the design of a repair system. 7.5.1C Physical properties include mechanical, Autogenous shrinkage, chemical shrinkage, chemical, and electrical properties. degree of restraint, environmental conditions, Documentation should be obtained for properties drying shrinkage, creep, thermal changes, of each repair material. The stated properties moisture absorption, and other factors all affect should be verified that they satisfy the project volume stability. Experience has shown that requirements. ACI and ICRI provide guidelines volume change of repair materials has often been for the selection of repair materials (ACI 301, the cause of poor performance of repairs. ACI 318-14, ACI 503R, ACI 503.5R, ACI 503.6R, Properties of repair materials should be selected ACI 506R-05 ACI 546.3R, ICRI No. 320.2R, ICRI for volume stability with the structure to reduce No. 320.3R, ICRI No. 330.1, and ICRI No. 340.1). the probability of cracking caused by volume The design of a repair should consider the changes. compatibility of the repair materials and the Volume stability is discussed in ACI 209R, ACI materials of the existing structure. Compatibility 209.1R, ACI 546.3R, and ICRI No. 320.2R. of repair materials and systems include volume Repair materials such as portland-cement stability, bond compatibility and durability, concrete, portland-cement mortar, polymer- mechanical compatibility, and electrochemical cement concrete, polymer concrete, fiber- and permeability compatibility. Generally, the reinforced concrete, resin-based materials, and intent is to use a repair material or repair system similar products are commonly used. Repair that has physical, mechanical, and other materials might not necessarily contain portland properties that are as close as possible to those cement, but should be selected to achieve the of the parent material to provide long-term necessary service, strength, and durability performance. requirements. Individual repair materials may have different The selection of reinforcement material should properties yet will perform satisfactorily when consider the durability, performance at elevated 66 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) temperatures, and ductility. Electrical and 7.6.1 Repair design shall be based upon the chemical reactivity between the reinforcement, member conditions in Chapter 6. the repair material, and the existing 7.6.2 Concrete—The in-place properties of the reinforcement should also be considered. concrete, in accordance with Chapter 6, shall be Refer to ACI 440.1R for internal FRP used in the repair design. reinforcement, ACI 440.2R for externally bonded 7.6.2C The extent and cause of deterioration FRP reinforcement, and ICRI No. 330.1 and ACI and the concrete strength and quality should be SP-66 (ACI Committee 315 2004) for steel assessed, including compressive strength, reinforcement. chlorides, carbonation, sulfate attack, alkali- Required properties of the repair silica reaction, physical damage, corrosion- reinforcement should be specified in the induced spalling, and cracking. construction documents. Specified reinforcement Chloride penetration can cause corrosion that properties are dependent on the requirements of can lead to cracking and spalling. The depth of a the repair and may include physio-chemical (for spall reduces the effective area of concrete example, glass transition temperature, and section. Degradation of the concrete affects the coefficient of thermal expansion) as well as concrete compressive strength. mechanical properties (for example, ultimate 7.6.3 Reinforcement strength, tensile modulus, and ultimate 7.6.3.1 Reinforcement that is damaged or elongation). corroded shall be permitted to remain. The 7.5.2 Materials in a structure shall be permitted effective cross-sectional area of remaining to remain if such materials are performing reinforcement shall be permitted to be used in the satisfactorily. repair design in accordance with the design basis 7.5.3 Materials permitted by ACI 318-14 or code. The effect of corrosion damage on permitted by this code shall be used for repairs development of steel reinforcement shall be and alterations. considered; where original deformations are no longer effective, reinforcing bars shall be 7.5.4 Alternate materials shall be permitted considered as smooth bars. following approval in accordance with 1.4. 7.6.3.1C Repair design should consider the in- place condition of the reinforcement, including 7.6—Design and detailing considerations the effective cross-sectional area of the reinforcing bars. The effective area is calculated
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) using the remaining effective diameter of the conditions. The design of the repair should reinforcing bar accounting for the loss of section evaluate the required development length. due to corrosion. Further considerations may Detailing of the repair should include the proper also include the location of the corroded areas, development of new reinforcement to achieve the loss of confinement, the loss of bond, and the design force. ACI 318-14 provides development effect of corrosion on member strength. If the equations and requirements for detailing of steel structure is fire damaged, steel reinforcement reinforcement. ACI 440.1R and ACI 440.2R may be annealed, and the yield strength reduced. provide detailing guidance for internal FRP Refer to ACI 216.1R for additional guidance. reinforcement and externally bonded FRP Durability requirements related to corroded reinforcement, respectively. Additional reinforcement are addressed in 8.4 and ACI information can be found in FIB Bulletin No. 10. 364.1R. CRSI (2014) provides information on 7.6.4 Prestressed structures older reinforcement systems 7.6.4.1 The effects of prestressing shall be 7.6.3.2 Design shall consider the location and included in the repair design. detailing of the reinforcement in accordance with 7.6.4.1C Requirements for repair of structures the evaluation requirements of Chapter 6. with bonded and unbonded prestressing are 7.6.3.2C The location and detailing includes different. Post-tensioned structures (with bonded the horizontal and vertical positions, orientation, and unbonded tendons) are often cast-in-place geometry of the reinforcement, development of monolithic structures, whereas pretensioned reinforcement, and the presence of hooks and structures (with bonded strands) are often single- crossties. Field examination to locate span precast structures. Each system is unique reinforcement may be required. and should be individually considered. The 7.6.3.3 Both existing and new reinforcement repair of prestressed structures requires a shall be adequately developed. Development condition assessment of the existing tendons. length shall be permitted to be calculated based Repair of unbonded tendons may require tendon upon development in both the existing concrete detensioning. Guidance for analysis, evaluation and new materials and in accordance with the methods and repair techniques of unbonded post- design basis code. tensioned structures is provided in ACI 423.4R, 7.6.3.3C Reinforcement development may be ACI 222.2R, ICRI No. 210.2, ICRI No. 320.4, and inadequate due to corrosion, mechanical PTI DC80.2-10 and DC 80.3-12. damage, insufficient or loss of concrete cover, 7.6.4.2 The effects of modifications to existing delaminated concrete, concrete strength, or other structure geometry, damage conditions, loss of 68 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) prestressing force, and repair sequence shall be damage or discontinuity of a tendon at one included in the repair design. location will reduce the strength for the entire 7.6.4.2C Analysis to evaluate the effects of length of the tendon. structural modifications should verify that If unbonded tendons are severed, the strength is adequate and that all serviceability prestressing force is assumed to be lost for the full conditions (for example, deflection limits) are length of the tendon. Releasing or cutting tendons satisfied. may affect multiple spans and may require Analysis of prestressed structures is required to shoring beyond the area where cutting or evaluate the effect of damaged or severed releasing of tendons occurs. Adjacent spans may prestressing reinforcement on structural strength require temporary shoring depending on the and performance. The effect of a severed bonded number of tendons severed at one time and the tendon is typically localized because the severed applied loads. Analysis based on actual loading tendon is effective after a development length is at the time of the modification may show shoring achieved and the full strength of the tendon is to be unnecessary. reestablished. For structures with bonded Repair and structural modification may require tendons, shoring, if necessary, may only be detensioning of prestressing tendons. Unbonded required locally at the repair area. tendons should be detensioned in a controlled Review of grouting quality assurance and manner to ensure performance and safety. Unless supervision documents should be performed to not needed based on analysis, unbonded tendons evaluate grouted tendons in advance of any should be reanchored and restressed to restore repair or rehabilitation of bonded post- required structural strength. Cut or damaged tensioning systems. The presences of voids, unbonded tendons can be restored by splicing or moisture in ducts, chlorides or extent of by installing new tendon with anchors at carbonation need to be identified in the existing intermediate locations, at the end of the grout. Methods for evaluation of chloride-ion structural member or the edge of any new content are listed in ASTM C1152M, ASTM openings. C1218, and AASHTO T260. Field evaluation of The stressing force in a repaired tendon grout may be required even if documentation of depends on the condition and type of the repaired the original construction is available. post-tensioned system and in certain cases this Unbonded tendons are designed to be force can be less than the original force if permanently debonded from the member and considered acceptable by structural analysis. often extend over multiple spans. As a result, 69 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Further discussion of this topic can be found in Bartlett (2004). ICRI No. 320.4 provides PTI DC80.3-12/ICRI 320.6 (2012) guidance for removing concrete around anchors Corrosion on prestressing strands for bonded and splices to prevent catastrophic loss of and unbonded post-tensioned systems may have anchor. an effect on strand integrity and strength. 7.6.5 Anchoring to concrete—Post-installed Prestressing strands require examination for anchors and dowels shall be designed to transfer conditions such as corrosion pitting and design forces to the substrate considering hydrogen embrittlement (refer to ICRI No 210.2 possible anchor failure modes and the condition and ACI 222.2R). of the substrate into which the anchor is installed. If repairs to prestressed slabs or beams result The design of post-installed anchors shall be in in increased concrete tensile stress (i.e. changing accordance with ACI 318-14. the classification of the prestressed flexural 7.6.5C The design of post-installed anchors member as defined in ACI 318-14), impacts of the requires careful consideration of the loads to be repair scheme on serviceability should be resisted. Anchors should have adequate strength evaluated. to transfer design forces across all interfaces and 7.6.4.3 Stresses in remaining section after into the existing member. All possible anchor concrete removal during repair shall not exceed failure modes should be considered to determine the limits established in the design basis code. the design strength. Anchors should be selected 7.6.4.3C Removing surface concrete from a considering the expected concrete substrate prestressed member may cause excessive cracking condition. For example, post-installed compressive and tensile stress in the remaining anchors used in the tension zone of concrete concrete section and may alter secondary forces members and in structures located in regions of and moments due to prestressing in indeterminate moderate or high seismic risk should be able to structures. This condition is more critical for transfer the design seismic forces assuming a prestressed joists and girders that have a cracked concrete condition. relatively small section and large prestressing Design of post-installed anchors is provided in force. Slabs are less critical due to the relatively ACI 318-14, Chapter 17, which includes small initial precompression. This change is provisions that require performance of post- acceptable as long as durability and strength are installed anchors in both cracked and uncracked addressed as part of the repair design. The concrete. ACI 355.2 and 355.4 provide the impact of removing concrete from a post- standard required for qualifying post-installed tensioned structure is addressed in Scollard and anchors in cracked and uncracked concrete. 70 American Concrete Institute Copyrighted Material -- concrete.org
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Specifications for post-installed anchors should The shape of the repair should be considered to include installation, testing, and inspection reduce stress concentrations and possible procedures. cracking. Methods discussed in ICRI No. 310.1R For post-installed expansion or undercut provide guidance to reduce cracking in concrete anchors, manufacturer’s installation instructions repairs including providing a uniform depth of specify procedures for drilling, hole cleaning, edges and substrate, repair geometry, surface installation, torque magnitude, and procedures to preparation, concrete removal below engage the anchor. reinforcement (undercutting) and elimination of For adhesive anchors and dowels, hole feather edge repairs. cleaning and moisture conditions are critically important. Manufacturer’s printed installation 7.7—Repair using supplemental post- instructions should specify procedures for tensioning drilling, hole cleaning, installation, and the care 7.7.1 Supplemental post-tensioning shall be to be taken until the adhesive has cured. permitted for repair of structures. Testing and inspection of post-installed 7.7.1C Supplemental post-tensioning can be anchors should be specified in the construction applied to the structure externally, internally, or documents. Many building codes require that both. adhesive anchors be installed under special 7.7.2 Design of the repair shall include the inspection procedures to ensure that the effects of the supplemental post-tensioning on the installation is correctly performed in accordance behavior of the structure. with the design and manufacturer’s procedure. 7.7.2C Supplemental post-tensioning can Refer to ACI 318-14 Chapters 17 and 26 for introduce moment, shear, and axial forces within specific inspection requirements for post- the structure that should be considered in the installed anchors design and detailing of the repair. The internal 7.6.6 Repair geometry—Configuration of forces induced by the supplemental post- repairs shall consider the potential for stress tensioning can be significant. For statically concentrations and cracking in both the existing indeterminate structures, restraint to post- structure and the repair area. tensioning deformations can result in significant 7.6.6C Repair shapes with sharp reentrant internal forces. Refer to ICRI 330.1 for selecting corners can cause stress concentrations that may strengthening systems for concrete structures. result in cracking. Long, slender (high aspect 7.7.2.1 Stresses due to supplemental post- ratio) repair areas also may result in cracking. tensioning shall be combined with existing 71 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) stresses and the total shall not exceed the limits in long-term deformations, deflections, changes in the design basis code. length, and rotations due to prestressing. 7.7.2.1C Adding supplemental post-tensioning 7.7.3C The post-tensioning may be restrained to a prestressed member may cause excessive by adjacent stiff members such as walls, and compressive and tensile stress and may alter reduce the effect of the prestressing on the secondary forces and moments. External post- intended member or have unintended effects on tensioning may result in changing the the adjacent construction. classification of prestressed flexural members as 7.7.4 Post-tensioning losses shall be included defined in ACI 318-14 Section 24.5.2. This in the design of supplemental post-tensioning change is acceptable as long as durability and systems. strength are addressed as part of the repair 7.7.4C Losses include wedge seating in the design. anchor; elastic shortening; creep of original 7.7.2.2 Design of supplemental post-tensioning concrete; shrinkage of original concrete; creep of shall provide for the transfer of post-tensioning repair material; shrinkage of repair material; forces between the post-tensioning system and prestressing relaxation; and friction and wobble the structure. Design of concrete supplemental between the post-tensioning reinforcement and post-tensioning anchor zones shall be in ducts, bearings, or deviators. Assessment of accordance with ACI 318-14. Design of steel losses of supplemental post-tensioning force brackets and supplementary structural steel shall should consider the existing conditions of the be in accordance with ANSI/AISC 360-10. repaired elements, as the members may have 7.7.2.2C Anchors for new post-tensioned already experienced time-dependent creep and reinforcement should be designed and detailed shrinkage. for the transfer of post-tensioning forces to the 7.7.5 Construction documents shall specify the existing structure. Bearing, spalling, and repair sequence, including tendon placement, bursting forces created at anchor zones should be anchors, and stressing of the post-tensioned considered. Strut-and-tie modeling, as given in system. ACI 318-14 Section 25.9, may be used to design 7.7.5C Repair design using supplemental post- post-tensioning anchor zones. tensioning systems should include construction 7.7.3 Provisions shall be made for effects of documents for installation sequence including post-tensioning, temperature, and shrinkage on shoring, removal of concrete, placement of new adjoining construction, including immediate and material and reinforcement, additional anchor requirements, horizontal shear transfer 72 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) requirements, curing, and stressing. Installation of externally bonded FRP systems should be of supplementary post-tensioning involves consistent with ACI 440.2R. Particular attention application of significant forces, which may should be given to strength increase limits, require project safety and protection procedures service limits, and determination of FRP material by the installer. Refer to 8.4.1 for corrosion design properties. protection requirements. Design and detailing of internal FRP 7.7.6 Structural members repaired or modified reinforcement should be consistent with ACI with externally installed unprotected post- 440.1R. Particular attention should be given to tensioning shall have adequate unrepaired service limits and determination of FRP material strength, in accordance with 5.5. design properties. 7.7.6C Unless protection of the post-tensioning If internal prestressed FRP reinforcement is strengthening system is provided to prevent used, the design and detailing should be sudden failure of the member in case the external consistent with ACI 440.4R. post tensioning reinforcement is damaged or FRP systems should only be installed in or on becomes ineffective (such as in an extraordinary sound concrete. Concrete distress, deterioration, event like fire or impact), the structural member and corrosion of reinforcing steel should be should have adequate strength without the post- evaluated and addressed before the application tensioning reinforcement to support factored of the FRP system. Surface preparation loads, as defined for extraordinary events in requirements should be based on the intended Chapter 5. application of the FRP system. FRP applications can be categorized as bond-critical or contact- 7.8—Repair using fiber-reinforced polymer critical. Bond-critical applications, such as (FRP) composites flexural or shear strengthening of beams, slabs, 7.8.1 Fiber-reinforced polymer composites in columns, or walls, require an adhesive bond conformance with ACI 440.6-08 and ACI 440.8- between the FRP system and the concrete. 13 shall be permitted to repair concrete structures. Contact-critical applications, such as 7.8.1C Fiber-reinforced polymer fabrics, bars, confinement of columns, only require intimate or shapes can be used as externally bonded contact between the FRP system and the reinforcement, internal reinforcement, and as concrete. Contact-critical applications do not internal or external prestressed reinforcement. require an adhesive bond between the FRP FRP shapes may be used as additional stand- system and the concrete substrate, although one alone structural members. Design and detailing is often provided to facilitate installation. ACI 73 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
440.2R provides descriptions of FRP substrate and epoxy polymer. Surface moisture applications and surface preparation and repair should not exceed the limits established by the requirements. manufacturer. Testing for presence of moisture For bond critical applications, the concrete should be done in accordance with substrate should possess the necessary strength manufacturer's written recommendations or one to develop the design forces of the FRP system of the following: ASTM D4263 – Standard Test through bond. The substrate, including all bond Method for Indicating Moisture in Concrete by surfaces between repaired areas and the original the Plastic Sheet Method; AASHTO Guide concrete, should have sufficient direct tensile and Specifications for Design of Bonded FRP Systems shear strength to transfer force between the for Repair and Strengthening of Concrete Bridge existing substrate and FRP system. The tensile Elements, 1st Edition; ACI 548.1R; ASTM F1869 strength of the substrate should be at least 200 psi – Standard Test Method for Measuring Moisture as determined by a pull-off type adhesion test per Vapor Emission Rat (MVER) of Concrete ASTM D7522. Contact-critical applications are Subfloor Using Anhydrous Calcium Chloride; not required to meet this minimum bond value as ASTM F2170 – Standard Test Method for the design forces of the FRP are developed by Determining Relative Humidity in Concrete deformation or dilation of the concrete section. Floor Slabs Using In Situ Probes; or ASTM For bond-critical applications, the concrete F2420 Standard Test Method for Determining surface should be prepared to a minimum Relative Humidity on the Surface of Concrete concrete surface profile (CSP) 3 as defined by the Floor Slabs Using Relative Humidity Probe ICRI 310.2. In contact-critical applications, Measurements and Insulated Hood. surface preparation should promote continuous The surfaces to receive moisture testing and the intimate contact between the concrete surface testing equipment should be acclimated near the and the FRP system. Surfaces to be wrapped relative humidity levels and temperatures that the should, at a minimum, be flat or convex to design is anticipated to have in service. Variation promote proper loading of the FRP system. between testing and in-service conditions may FRP systems should not be applied to damp or provide inaccurate or misleading testing results wet surfaces unless the epoxies are formulated by 7.8.2 Structural members repaired or modified the manufacturer for such applications. Moisture with externally-applied FRP composites shall content of the concrete substrate should be have adequate unrepaired strength, in accordance evaluated before application of the FRP system with 5.5. as it may inhibit bonding between the concrete 74 American Concrete Institute Copyrighted Material -- concrete.org
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7.8.2C Unless protection of the strengthening spread and smoke density should also be system is provided, to prevent sudden failure of considered in accordance with the general the member in case the FRP system is damaged existing building code and ASTM E84. or becomes ineffective (such as in an 7.9.2 It shall be permitted to design a repair extraordinary event like fire or impact), the without supplemental fire protection if the structural member should have adequate strength unrepaired member has adequate strength without the FRP reinforcement to support considering the reduced material properties due factored loads, as defined for extraordinary to fire exposure in accordance with 5.5. events in Chapter 5. The design and use of 7.9.2C A repair system can be selected without externally bonded FRP may be limited by the additional fire protection provided that the service requirements of the repaired member. existing unrepaired member has adequate strength to support the loads, as defined in 5.5, 7.9—Performance under fire and elevated during a fire event. Fire performance temperatures requirements and evaluation procedures are 7.9.1 Design of the repair system shall consider outlined in ACI 216.1, ACI 318-14, ACI 440.2R, elevated temperature performance and shall ASCE/SEI/SFPE 29-05, and AISC Design Guide comply with the fire resistance ratings of the 19 (Ruddy et al. 2003). structural members and other fire safety 7.9.3 The properties of the specified repair requirements in accordance with the design basis materials at elevated temperatures shall be code. considered. 7.9.1C Regardless of the repair system, 7.9.3C Repair material specifications should performance of the repaired element under fire comply with the requirements of relevant fire and elevated temperatures should be evaluated regulations valid at the project location. If there and the system should be detailed and material is a conflict between the properties of specific selected to provide adequate protection. The products or systems and fire regulations, repaired elements should comply with applicable alternative repair principles or methods should building code requirements and relevant fire be used to avoid such a conflict. In general, regulations valid at the project location. polymer mortar and polymer concrete have Structures renovated for different use or higher coefficients of thermal expansion and strengthened to support higher loads may require higher resistance to water vapor transmission a more stringent fire rating than the original and lower resistance to fire and elevated structure. Other requirements such as flame 75 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) temperatures compared to cementitious 7.9.5 Supplemental fire protection to improve alternatives. the fire rating of repaired systems shall be 7.9.4 Repairs using adhesives shall consider permitted. their performance at elevated temperatures. 7.9.5C Standard fire protection systems can be 7.9.4C ACI 440.2R reports that the physical used to increase the fire rating of repaired and mechanical properties of the resin systems. National codes and professional components of FRP systems are influenced by organizations list generic ratings for concrete temperature and can degrade at temperatures structural members, giving the minimum close to and above their glass-transition thickness of concrete cover needed to protect the temperature Tg. An acceptable service main steel reinforcement from fire effects (IBC temperature for FRP is established by ACI 2015; NFPA 5000 2015; PCA 1985, 1994). In
440.2R as Tg – 27F. This value accounts for addition to increasing the cover thickness, fire typical variation in test data for dry environment performance of reinforced and prestressed exposures. Adhesive-bonded FRP reinforcement concrete members may be enhanced by fire should not be used if the maximum service protection systems as proven by fire testing or temperature exceeds Tg – 27F. A service analytical methods (ACI 216.1). Concrete cover temperature exceeding this limit temperature for nonmetallic reinforcement may need to should be addressed using an adhesive system exceed cover for steel reinforcement to achieve with a higher Tg value, using heat protection or the same fire resistance rating. insulation systems or using alternate repair 7.9.6 Fire rating of repaired systems, based on systems. ACI 216.1, shall be permitted. Adhesive-based repair systems can be 7.9.6C The fire rating of a repaired system or considered effective during a fire event if a fire assembly can be determined in accordance with protection system with an established fire rating ACI 216.1, which requires the application of the is used that maintains the temperature of the expected service load to the test specimen. The adhesive-based system below its glass transition applied load should reflect the use of the tested temperature. In the absence of an established fire member in terms of magnitude and layout. rating, detailed fire analysis may be used to The criteria for evaluating a structure for fire establish a fire rating of the repaired system. safety are different than those for strength design and typically incorporate lower material strengths and load factors, and may not require the use of strength reduction factors. The licensed 76 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) design professional should verify that the fire- reduced strength of the member exceeds the force demand due to expected service loads during the fire event. The fire-reduced strength should be based on reduced material strengths for the maximum expected temperature in a fire event, which can be determined in accordance with ASTM E119 and ACI 216.1. Section 1.2 of ACI 216.1 allows alternative methods to assess the fire resistance of assemblies. The fire reduced strength as well as the effect of fire protection system on the overall performance and fire rating of an existing and repaired element can also be determined utilizing available design models and finite element numerical procedures. Descriptions of the detailed analytical methods can be found in Buchanan, (2001) and Technical Report No. 68 (2008) by the Concrete Society.
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the specified repair materials, is it possible to CHAPTER 8—DURABILITY achieve the design service life. The design service life of the structure and repaired members, 8.1—General including maintenance requirements, should be 8.1.1 Durability of materials incorporated into estimated by considering the durability of the a repair shall be considered for individual repairs, materials. Such design service life should be the overall durability of the repaired structure, reflected in the repair design and maintenance and the interaction of the repair system with the requirements, as well as be incorporated into the structure. construction documents. A repaired section is 8.1.1C The durability of materials considered to be the combination of the installed incorporated into a repair depends on their repair material(s) and the substrate material(s). ability to withstand the environment where they Service life is discussed in ACI 365.1R. are installed. The durability of repairs is Some examples of end-of-service life include: dependent on the compatibility between repair a) Structural safety is unacceptable due to materials, the structure, and the surrounding material degradation or the nominal environment. To achieve compatibility, the repair strength is less than the required strength. and the structure need to interact on several b) Maintenance requirements exceed levels without detriment, including chemical, resource limits. electrochemical, and physical behavior. c) Aesthetics become unacceptable. 8.1.2 Repair materials and methods shall be d) Structural functionality is no longer selected that are intended to be compatible with sufficient. the structure, and are durable within the service e) Deformation capacity of the structure has environment. Anticipated maintenance shall be been degraded due to a seismic event. considered in the selection. The cause of degradation should be determined 8.1.2C The design service life of a structure and as a first step in predicting each type of service repaired members is established by the licensed life. Causes of degradation include: design professional in consultation with the a) Mechanical (abrasion, fatigue, impact, Owner to achieve an economical repair that overload, settlement, explosion, vibration, satisfies strength, safety, and serviceability excessive displacement, loads, or ground requirements. Only through satisfactory repair motion from a seismic event) construction practices, including application of
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b) Chemical (alkali-aggregate reaction, environment. ASTM C666 may be used to sulfate attack, acid dissolution, soft water define a durability factor. A durability leaching, or biological action) factor exceeding 80 percent has generally c) Physical (freezing and thawing cycles, been found to be acceptable in many scaling, differing coefficients of thermal locations for resistance to freezing and expansion, salt crystallization, radiation thawing for cementitious materials (refer exposure [ultraviolet light], fire, or to ACI 546.3R). differential permeability between d) Scaling if exposed to salts. materials) e) Exposure to ultraviolet or other radiation d) Reinforcement corrosion (carbonation, degradation within the repair environment corrosive contaminants, dissimilar metals, unless other means are provided to address stray currents, or stress corrosion such degradation. cracking) f) Fatigue resulting from loading cycles and Preparation methods, materials, placement, load reversal. For example, fatigue and installed systems should be defined in the resistance may be needed in repair areas construction documents to reflect the design subject to many cycles of repeated loading. intent and requirements to achieve compatibility. g) Impact, erosion, and vibration effects if Repaired sections should be resistant to exposed to conditions causing expected service conditions that can result in deterioration by these mechanisms. degradation, including the causes of degradation h) Abrasion resistance of repaired sections listed previously within the design service life, subject to heavy traffic, impingement of and combinations of these causes. abrasive particles, or similar conditions. Repaired sections should be resistant to: i) Chemical exposure may include sulfate a) Chlorides and other corrosive attack, acids, alkalis, solvents, leaching of contaminants that are present in the cementitious materials due to soft water, concrete or the penetration of corrosive salt crystallization, and other factors that contaminants into the concrete (such as are known to attack or deteriorate the chlorides) that lead to corrosion of repair material or concrete substrate. reinforcement or other embedments (8.4). Water penetration into concrete is b) Thermal exposure and cycles. associated with many types of chemical c) Freezing-and-thawing damage if subject to attack and other deterioration saturation and a freezing-and-thawing mechanisms. 79 American Concrete Institute Copyrighted Material -- concrete.org
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j) The carbonation susceptibility, depth, and protection are used, anchorage and development rate of both the existing concrete and the lengths should be reviewed. repair material in repairs containing 8.2.2 Corrosion—Where concrete cover for reinforcement or other embedments existing reinforcement is insufficient to provide requiring alkaline passivation of the metal corrosion protection for the design service life of for protection from corrosion (refer to 8.4). the structure, additional concrete cover or an k) Alkali-aggregate reactions. alternate means of corrosion protection shall be l) Differential permeability between the provided to mitigate corrosion of reinforcement repair and existing concrete if the repair within the repair area. material or the substrate concrete is 8.2.2C Alternative means of protecting vulnerable to deterioration due to trapped reinforcement include the application of moisture, such as freezing-and-thawing waterproof membranes (ACI 515.2R Guide to damage of saturated concrete, corrosion of Protective Systems), corrosion inhibitors, and embedded steel reinforcement, alkali- various forms of cathodic protection. aggregate reactions, or sulfate attack Reinforcement corrosion, chloride (refer to ACI 546.3R). contamination, and carbonation should be considered when evaluating the maintenance 8.2—Cover requirements and design service life of 8.2.1 Concrete cover shall be in accordance alternative methods for corrosion protection. with the design basis criteria. For alternative Ongoing metal corrosion may create distress and materials and methods, an equivalent cover that deterioration beyond the limit of the repair area. provides sufficient corrosion protection shall be The design service life requirements should be approved in accordance with 1.4.2. Sufficient reviewed when widespread durability issues are anchorage and development for the considered. Issues related to concrete cover need reinforcement shall be provided regardless of to be addressed in a timely manner. methods used to provide corrosion protection. 8.2.1C The code language is intended to allow 8.3—Cracks materials that provide equivalent cover to be 8.3.1 The cause(s) of cracks shall be assessed, used if they can be demonstrated to be effective and mitigating cracking shall be considered in the according to the approval procedure detailed in rehabilitation design. 1.4.2. If alternative methods of corrosion
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8.3.1C Cracks can reduce the protection Consideration should be given to post-repair provided by the effective cover over steel cracking and the need for protection of the reinforcement and lead to water and deleterious existing concrete and repair material from the material ingress, which accelerates the ingress of deleterious materials. ACI 224.1R deterioration of embedded reinforcement and can provides guidance for the prevention and control cause other concrete deterioration issues such as of cracks. freezing-and-thawing deterioration, alkali- There are a variety of different materials that aggregate deterioration, and chemical attack. have been used for crack repair, and their correct Identification of their cause(s) and evaluation of specification for a given application will govern their impact on a structure or a concrete the design service life of the repair. For cracks component is described in ACI 224.1R. that are essentially acting as a joint or are active, As part of a repair design, cracking mitigation one type of effective repair is to seal the crack methods should consider the causes, movement, with an elastomeric sealant. Materials used for size, orientation, width, and complexity of the crack injection include, epoxy, polyurethane, network of cracks. The characteristics of the latex in a cement matrix, microfine cement, and substrate, location, and evidence of water polymethacrylate. For repair by crack injection, transmission should be determined to assess the the process and material should be appropriate appropriate method of repair. Active water to the site conditions. Crack injection should not infiltration should be corrected as required for be used to repair cracks caused by corrosion of the durability of the structure. steel reinforcement and alkali aggregate reaction 8.3.2 The design of repairs shall consider the unless supplemental means are employed to effects of cracks on the expected durability, mitigate the cause of the cracks. performance, and design service life of the repair and structure as a whole. 8.4—Corrosion and deterioration of 8.3.2C Not all cracks need to be repaired, reinforcement and metallic embedments however, all cracks have the potential to become 8.4.1 The corrosion and deterioration of active cracks. Cracks in concrete structures can reinforcement and embedded components shall be detrimental to the long-term performance of a be considered in the durability design. Repair structure if the cracks are of sufficient size to materials shall not contain intentionally added allow for the ingress of deleterious materials into constituents that are corrosive to reinforcement the structure, and guidance for critical crack within the repair area. sizes is provided in ACI 224R, Table 4.1. 81 American Concrete Institute Copyrighted Material -- concrete.org
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8.4.1C Untreated reinforcement corrosion fire and other forms of damage and deterioration limits the life expectancy of repair areas, repair shall be considered. materials, and repaired structures. ICRI No. 8.4.3C Water and chemical penetration into the 310.1R provides guidelines on removal of concrete can cause corrosion of metallic damaged concrete and cleaning of reinforcing embedments and damage to nonmetallic steel. Repairs that do not address reinforcement reinforcement. Where concrete cover over corrosion may negatively impact the design reinforcement is insufficient to provide corrosion service life and require more intensive protection for the design service life of the monitoring. The structural design considerations structure, additional concrete cover or an for corroding reinforcing steel on repairs are alternate means of corrosion protection should described in 7.6.3.1. be provided to mitigate reinforcement corrosion. 8.4.2 The impact on the design service life of The corrosion of embedded metals adjacent to the the repaired structure shall be considered if it is repair may be accelerated due to differing anticipated that corrosion products cannot be electrical potential between electrically removed during repair. continuous reinforcement in the repair area and 8.4.2C Ideally corrosion products should be external to the repair area. This form of removed from reinforcing steel in repairs. In corrosion is commonly referred to as the "anodic some situations, due to congestion of steel ring" or "halo effect", and is discussed in ACI reinforcement, access limitations, load 546R, ACI 364.3T, and ACI RAP BULLETIN 8 considerations, or other factors, it is not possible (Whitmore 2006). The rate of anodic ring to remove corrosion products from the steel corrosion depends upon the chloride content, reinforcement. Situations exist where corroding internal relative humidity, and temperature. reinforcement that cannot be adequately cleaned The anodic ring effect that can be induced by or repaired will remain in the repaired structure. certain repairs should be addressed by The effects of uncleaned reinforcing steel on incorporating appropriate corrosion mitigation the long-term durability of the repaired structure strategies such as cathodic protection or should be considered in these situations. corrosion inhibitors. ACI 222R, ACI 222.3R, ACI Supplemental corrosion mitigation strategies 364.3T, ACI 546R and the Concrete Society may be needed in these situations. Technical Report 50 and FAQ sections from 8.4.3 The quality of existing concrete and its Concrete International (2002a, b, c) provide ability to protect reinforcement from corrosion, guidance for corrosion prevention, mitigation and inhibition. Both carbonation and chloride 82 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) contamination may require consideration and accelerate the deterioration of the installation are discussed in ACI 546R. (refer to ACI 222R). Aesthetics may be affected by different means 8.4.6 Corrosion protection of bonded and of protection and may also require consideration. unbonded prestressing materials and prestressing Damage due to fire and fire protection system components shall be addressed during the requirements are discussed in 7.9. repair design. 8.4.4 Existing steel reinforcement and added 8.4.6C The presence of prestressing force in the reinforcement shall be protected from corrosion, steel and the need to transfer the prestressing fire and other forms of damage and deterioration force into the concrete makes corrosion damage to satisfy durability requirements. in prestressed concrete members more critical 8.4.4C Reinforcing steel in concrete than traditionally reinforced structures (refer to construction is usually protected by concrete ACI 423.4R). Section 7.6.4 addresses the cover from deleterious materials and also structural requirements for the repair. provides fire protection. The minimum cover is The bonded or unbonded nature of the typically required by the design basis criteria. prestressing steel, the condition of the steel at the Adequate protection may be provided by repair area, the attachment of the steel to the increased section thickness and appropriate structure, the as-designed corrosion protection coatings, such as sealers, intumescent coatings, measures, the existing corrosion condition, and or electrochemical methods. the continuity of the prestressing steel need to be 8.4.5 Galvanic corrosion between considered to address corrosion protection of the electrochemically dissimilar materials shall be structure. Refer to ICRI 320.4, and 222.2R. considered. Hydrodemolition and other types of material 8.4.5C Reinforcement or metallic embedments removal methods should be used cautiously if the in the repair area with differing electrochemical structure contains unbonded prestressing steel potentials, environments, or both, should be reinforcement. In these situations, water can be isolated from the existing reinforcement, or the introduced into the corrosion protection existing reinforcement and metal embedments (sheathing) surrounding the steel (refer to ICRI should be protected to minimize galvanic No. 310.3), affecting the long-term durability of corrosion. For example, rail or post-pocket the prestressing steel reinforcement. repairs that use dissimilar metals from 8.4.7 If electrochemical protection systems are conventional steel reinforcement could used to protect steel reinforcement in repair areas and structures, the interaction of the protection 83 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) system with the repaired elements, the entire a) In certain situations such as exposure to structure, and environment shall be considered. high temperatures, polyvinyl chloride 8.4.7C Structures using impressed current (PVC) and other polymer-based materials electrochemical protection or mitigation systems can deteriorate, releasing decomposition should have continuous reinforcement, separate products found to cause corrosion. zones, or provisions should be made to make the b) Even if the conventional steel steel electrically continuous. Impressed current reinforcement becomes more noble in electrochemical protection systems should be electrical contact with a dissimilar metal designed and maintained to not promote an (for example, embedded aluminum conduit alkali-aggregate reaction (AAR) and to avoid in the presence of chlorides), considerable embrittlement of prestressing steel. concrete damage can arise (Monfore and Impressed current electrochemical protection Ost 1965). systems should include a monitoring and c) Fiber-reinforced polymer (FRP) wrapping maintenance plan developed by a licensed design should not be used as a corrosion repair professional specializing in the design of strategy on members experiencing corrosion protection systems (refer to NACE corrosion of embedded reinforcement SP0290, NACE SP0390, NACE 01105, NACE unless the concrete is repaired and 01102, NACE 01101, NACE 01104, and NACE corrosion mitigated. Appropriate sections SP0107). within this code and referenced documents 8.4.8 Repair materials and reinforcement shall concerning FRP repairs should be be selected and detailed to be compatible such consulted (refer to ACI 440.2R). that the characteristics of each material do not adversely affect the durability of the other 8.5—Surface treatments and coatings materials or of the existing concrete and 8.5.1 Moisture transmission through the reinforcement. structure and the influence of the surface 8.4.8C Incompatibilities can arise from the use treatment on the durability of the structure shall of inappropriate materials or components, or be considered. dissimilar electrochemical characteristics or 8.5.1C Surface treatments, coatings, sealers, or physical properties, which can negatively impact membranes are commonly used to limit the the concrete and reinforcement. Some examples ingress of deleterious materials and moisture into include: the structure to reduce future deterioration of the
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) structure. Surface treatments, coatings, sealers, and membranes may have a shorter service life than the concrete and can be considered as consumable or requiring periodic replacement or repair to maintain effective protection of the concrete (ACI 515.1R). In some situations, encapsulation of moisture and deleterious materials by a surface treatment has been found to cause or accelerate deterioration. The condition of the concrete should be appropriate to receive a specific surface treatment, coating, or membrane (ICRI No. 310.2). 8.5.2 The selection of surface treatments applied to concrete surfaces shall consider concrete cracks and their anticipated expansion and contraction, or surface deflections on the repair system durability, the surface treatment, and the anticipated design service life of the structure. 8.5.2C Crack development and propagation provide an accelerated mechanism for ingress of moisture and deleterious materials and may also cause a surface treatment to become ineffective.
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CHAPTER 9—CONSTRUCTION 9.2—Stability and temporary shoring requirements 9.1—General 9.2.1 Construction documents shall specify: Construction documents shall specify: a) Portions of the work that require temporary a) Contractor has the responsibility to shoring and bracing during the period construct the project in accordance with the before the repair implementation for safety construction documents and with purposes and during construction. appropriate standards. b) Design loads and spacing requirements for b) Contractor shall provide the necessary the temporary shoring and bracing. resources and access for inspection, testing, c) Contractor responsibilities to install, field observations, and quality control of provide quality control, and properly the work. maintain the temporary shoring and c) Specific temporary shoring and bracing bracing. requirements. 9.2.1C Project-specific design criteria for the d) Specific jacking requirements temporary shoring and bracing in the e) Project-specific inspection, testing, and construction documents should include, as field observation requirements of Chapter necessary: loads, displacements, spacing, 10. placement, and quality control requirements 9.1C The information to be presented in during construction. construction documents is described in 1.6.1. 9.2.2 Temporary shoring and bracing design Specific to the construction process, the shall consider: construction documents should indicate that the a) accommodation for in-place conditions and contractor is responsible for construction changes in conditions over the period of the consistent with the project plans and repair phases, per 9.2.7 specifications, and convey project specific b) effects from measured lateral and vertical shoring, bracing and jacking requirements. displacements, tilting or listing, secondary During the work, the contractor should make the effects, and superimposed loads work available for inspection and observations c) impact of the temporary shoring and by the licensed design professional, repair bracing on the structure inspectors, and other quality assurance d) effects of deformation compatibility of the personnel. shoring system with the supported and
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supporting structural members and 9.2.3 Shoring and bracing design shall be systems, in accordance with 9.2.6 performed by a licensed design professional. e) structural stability of members, systems, 9.2.3C Shoring and bracing design is not and the structure in accordance with 9.2.5 usually performed by the licensed design and 9.2.6 professional of record for the repair design. The f) effects of damage or deterioration of contractor will usually retain a specialty existing members and systems in engineer to prepare the temporary shoring design accordance with 9.2.8 details and shoring-plans, showing loads, 9.2.2C Temporary shoring and bracing member type, spacing, and placement sequence members should be designed to consider changes for temporary shores and braces at the phases of in bracing and shoring conditions during repair planned repairs. construction and as required to support 9.2.4 The licensed design professional of construction operations. Design of temporary record for the repair design shall review shoring and bracing members should be based on temporary shoring and bracing design and details the in-place loads and forces on the structure, to determine if they comply with the deformations of the structure, and anticipated requirements of the project repair design and the superimposed loads during construction. temporary shoring and bracing criteria. Secondary effects that may need to be examined 9.2.4C Temporary shoring and bracing design in shoring and bracing design include geometric and installation details should be reviewed by the and material nonlinear response, member and licensed design professional for the repair foundation displacement, and internal member project to assess the impact of the shoring on the forces developed due to placement and alignment structure, and to verify conformance of the of shoring and bracing elements. proposed shoring with project-specific Anticipated loads, such as snow, seismic, wind, requirements. Refer to 5.1.4 for load and construction and occupancy live loads, requirements associated with shoring and should be considered in the design criteria of the temporary construction. Review of the shoring temporary shoring and bracing. Design design by the licensed design professional for the requirements for shoring are contained in repair design does not normally include a ASCE/SEI 37. Shoring design guidelines are comprehensive review of the shoring design contained in AISC Steel Design Guide Series 10 prepared by the specialty engineer and should (Fisher and West 2003) and ACI SP-4 (ACI SP- not be considered a validation of the specialty 4). engineer’s design. 87 American Concrete Institute Copyrighted Material -- concrete.org
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9.2.5 The shoring and bracing shall maintain specified by the licensed design professional for the global structural stability of the structure the repair in the construction drawings. before remedial construction and during the 9.2.6 Supplemental bracing for compression repair phases. members may be required if the cross section or 9.2.5C The assessment of global structural unbraced length of a compression member is stability includes the overall structure, members modified during the repair process. Compression and systems affected by repair, and temporary members include columns, walls, beam flanges, lateral bracing elements that contribute to and other members, such as chords of overall stability. Stability of these elements diaphragms, that resist compressive loads. The should be considered during the phases of the design of bracing members is described in repair process. Temporary measures may be various publications (AISC 2006; ANSI/AF&PA needed to provide lateral bracing and shoring of NDS 2005). The design load for a bracing affected members and systems. If necessary, the member should be based on the existing dead and criteria to temporarily preload members should live loads, construction loads, and other loads be included in the construction documents. that may be resisted by the compression member. Review and redesign for variations in the A lateral force of 2 percent of the axial load in the construction proposed by the contractor with member being braced is commonly used as a changes in temporary shoring and bracing design minimum load in the design of bracing members and detailing should be addressed in the (ANSI/AISC 360-10). construction documents. 9.2.7 The design of shoring and bracing 9.2.6 The shoring and temporary bracing shall members to accommodate in-place conditions maintain the structural stability of members and and changes in conditions during construction systems before construction and during the repair shall include consideration of the changes in load phases. paths, construction loads, unbraced lengths, and The lateral forces for temporary bracing design the redistribution of loads and internal forces that shall be determined using generally accepted result from removal of existing adjacent framing engineering principles or as required by the or changes in applied loads on structural design basis code. Temporary shoring and members. bracing shall be designed to provide sufficient 9.2.7C Removal of column, beam, wall, and stiffness to prevent excessive vertical and lateral floor slab elements or parts thereof during repair displacement of the shored or braced members as construction and the placement of shoring and bracing can result in the redistribution of loads 88 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) and internal forces within the building structure. 9.3.1 Load and load factors during the The removal of framing members, diaphragms, or assessment and construction processes shall be in slabs can also affect the unbraced length of the accordance with 5.1.4. framing members in the removal area. Effects of 9.3.1C During the assessment and repair the removal of elements should be considered in process, a temporary reduction in design load assessing the structure and shoring and bracing may be allowed, except if prohibited by design. jurisdictional authorities or local building codes. 9.2.8 Where structural members support the Reduction in the design load intensity should be structure and superimposed loads before repair determined using the in-place condition of the and during construction, the structural capacity of structure and the time required for the damaged or deteriorated members shall be completion of stabilization measures or repairs. evaluated. The evaluation shall consider the ASCE SEI 37 provides information on reductions actual cross section of the member and in loads based upon the duration of a project. If reinforcing at the time of the repair including a change in the length of the project or a delay losses of capacity due to damage and occurs, the reduced design loads may no longer deterioration. Unless the in-place strength of the be appropriate. member exceeds the required strength for all superimposed loads, including construction 9.4—Environmental issues loads, temporary shoring and bracing shall be 9.4.1 Construction documents shall specify the specified in the construction drawings to be contractor or other designated party is responsible installed and maintained in place until the for implementing specified environmental member is repaired. remediation measures, reporting new conditions 9.2.8C Design of shoring and bracing members encountered, and controlling construction debris, and the -evaluation of members should be based including environmentally hazardous materials on the member cross sections before and during and conditions. the time of repair implementation. To account for 9.4.1C Assessment and repair of a structure unknown conditions, the evaluation by the can result in the exposure of workers and the licensed design professional should consider the public to potentially hazardous materials and importance of the member to the overall stability conditions. Hazardous materials may be exposed, of the structure. dislodged, carried into the air, or discharged as effluent into surface drainage during the 9.3—Temporary conditions assessment and repair process. Hazardous 89 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) conditions include noise, nuisance dust, misdirected drainage, and falling debris. The owner should have an environmental assessment performed during the structural assessment and repair process in the areas to be repaired before any work to identify hazardous materials with the potential to present health issues to the workers and public, unless the owner can attest that the structure is free of hazardous materials. During the repair project, the contractor normally is responsible for the implementation of repairs and, accordingly, the control of construction debris, dust, and other materials. Any new conditions uncovered during the repair process should be reported to the owner and licensed design professional.
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CHAPTER 10—QUALITY ASSURANCE construction. Inspection is necessary to verify repairs and rehabilitation work are completed in 10.1—General accordance with construction documents. 10.1.1 Quality assurance requirements of this Construction documents should specify chapter supplement the current and existing- inspection requirements for concrete repair and building code provisions and shall be used for rehabilitation construction during the various repair and rehabilitation construction. work stages. The licensed design professional 10.1.1C The construction documents for repair should recommend that the owner retain a and rehabilitation projects should include a licensed design professional, a qualified project-specific quality assurance and inspection inspector, a qualified individual, or some program. The quality assurance program should combination thereof for the necessary include: inspections. a) Review of the contractor’s quality 10.2.2 The construction documents shall assurance program include testing and inspection requirements b) Quality control procedures during the applicable to the project. repair process 10.2.2C Required testing and inspections may c) Review of conditions during the project include (a) through (j): d) Testing of materials used and material a) Delivery, placement, and testing reports installation procedures documenting the identity, quantity, Usually, the quality control requirements are location of placement, repair materials specified in the construction documents and the tests, and other tests as required owner retains the quality control personnel. The b) Construction and removal of forms and contractor is responsible for the work quality, reshoring including the quality of materials and c) Concrete removal and surface preparation workmanship. of the concrete and reinforcement d) Placing of reinforcement and anchors 10.2—Inspection e) Mixing, placing, and curing of repair 10.2.1 Concrete repair and rehabilitation materials construction shall be inspected as required by the f) Sequence of erection and connection of construction documents. new members 10.2.1C The quality of concrete repairs is g) Tensioning of tendons largely dependent upon the workmanship during 91 American Concrete Institute Copyrighted Material -- concrete.org
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h) Review and reporting of construction loads with construction documents, documentation and on floors, beams, columns, and walls report of the work inspected as conforming or i) General progress of work nonconforming, and whether corrections were j) Installation and testing of post-installed made and verified or are still needed. Inspection anchors and testing of post-installed anchor installation Inspection and test results should be submitted should be performed as required by the to the licensed design professional and the owner. construction documents and in accordance with Repair construction should be inspected to Chapters 17 and 26 of ACI 318-14. verify the quality of materials, quality of Repair inspections should determine workmanship, and for compliance with the intent compliance with the intent of the contract of the construction documents. Inspection should documents, document the inspection, and report be provided by either repair inspectors, the the inspection results. If the inspection shows licensed design professional, or a combination of conformance with the contract documents and no repair inspectors and the licensed design corrections are necessary, then the inspected professional. Responsibilities for performing the work should be documented as conforming and inspections should be clearly delineated at the reported to the licensed design professional and start of a project. contractor, noting no corrections. If the Repair inspector qualifications for inspection inspection shows readily correctable issues and of concrete repairs should be demonstrated by the issues are corrected by the contractor, then certification or previous work history and as the inspected work should be documented as required by the jurisdictional authority before conforming and reported to the licensed design being retained. An individual who has been professional and contractor with corrections certified as an ICRI Concrete Surface Repair noted and verified as completed. Nonconforming Testing Technician (ICRI Concrete Surface or deficient components, processes, and Repair Technician - Grade 1) or as an ACI procedures including the parts of the repairs not Construction Inspector (ACI C630) are examples passing inspection should be reported to the of qualified inspectors. The licensed design licensed design professional for review. Actions professional may provide inspection services. should be made to correct the process before Inspection of concrete repair construction as resuming the repair construction and inspection specified in the construction documents should process. Nonconforming repair construction may include review of the work in the field, review of include: construction documents, comparison of the work 92 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
a) Existing construction that differs from g) Mixing, placing, and curing of repair the repair documents materials b) Deterioration, distress, or levels of h) Sequence of repair construction distress beyond those anticipated in the i) Tensioning of tendons design of repairs j) Construction loads c) Deficiencies in repair components k) General progresses of the repair work d) Deficiencies in construction processes and procedures 10.2.3 The construction documents shall Material data sheets indicate the establish inspection requirements of existing manufacturer’s stated material properties that conditions and reinforcement before concealing should satisfy the required properties of each with materials that obscure visual inspection. specific repair. The manufacturing date and shelf 10.2.3C Removal of deteriorated concrete and life of the repair material provide information reinforcement often uncovers unanticipated that the material is within the manufacturer’s conditions that should be examined. Visual recommended time limits for installation. inspection and verification of existing conditions Existing conditions describe the nature and may require review of project specific conditions extent of damage or deterioration, and size and before continuing the construction process and condition of the members. Those conditions need thus require pauses in the construction processes to be verified for conformance to the design so as not to conceal components of the work assumptions. The following are some items where before completing necessary inspections and inspections are beneficial: verifications. If unanticipated conditions are a) Location of repairs identified by the repair inspector, the licensed b) Surface preparation of existing concrete design professional should be informed. The and reinforcement licensed design professional should examine c) Placement of reinforcement and anchors these conditions and determine what measures d) Specific materials used in the repairs are to be implemented before placement of new e) Delivery, placement, and testing reports repair materials. The construction should specify documenting the quantity and location of the locations where inspection is necessary placement, repair material tests, strength, before concealment and provide for possible and other tests of all repair materials changes in these locations due to unforeseen f) Construction and removal of forms and conditions. In some projects, all locations will not shoring 93 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) need to be inspected and representative locations confirm that their material achieves the published will provide suitable inspection. values that they provided for the project. Refer to ACI 546.3R and ICRI 320.2R for guidance. Tests 10.3—Testing of repair materials of repair materials’ bond to existing materials 10.3.1 Repair material tests and test frequencies should comply with requirements of the contract shall be specified in the construction documents. documents. Results of tests shall be reported as required by Concrete repair materials testing personnel the construction documents and the design-basis should be qualified by demonstrating competence code. Test records shall be retained by the testing to the satisfaction of the licensed design agency as required by the design-basis code. In professional and building code official for testing the absence of record retention requirements in types required of concrete repair and the design-basis code, the construction rehabilitation work. documents shall require that the test records be As a minimum level of record keeping, the retained by the testing agency for a minimum of testing agency should maintain a record of the 3 years beyond completion of construction. tests performed and the results consistent with the 10.3.1C Tests of repair materials should requirements for records of ASTM E329. comply with testing and test frequency of new concrete construction, unless otherwise specified 10.4—Construction observations in the contract documents and approved by the 10.4.1 Construction observation shall be jurisdictional authority. It is generally not performed as required by the construction practical to verify all manufacturers’ listed documents. properties of proprietary materials, such as 10.4.1C A primary purpose of construction shrinkage, compressive and tensile creep, observation of rehabilitation work is to verify that thermal expansion coefficient, and modulus of the exposed existing construction is as assumed elasticity. In such cases, the licensed design in the design and that the work detailed in the professional should seek independent testing data contract documents will fulfill the design intent. from the manufacturer or others to verify specific Construction observations are in addition to the manufacturer’s listed properties that are critical inspection requirements described in 10.2. to the application for the specific lots (or batches) Construction observations should be performed of material to be used. The licensed design by the licensed design professional that designed professional should evaluate the data and, if the work or other designated representative to necessary, have manufacturers perform testing to provide these services. 94 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
If the existing construction differs from the design assumptions, requiring modification of the design, changes should be documented and the work modified as necessary. The licensed design professional or designated person responsible for construction observations should report design changes in writing to the owner, rehabilitation inspector, contractor, and jurisdictional authority resulting from existing construction, nonconforming rehabilitation work, and observed construction deficiencies. When construction observations are made by a party designated by the licensed design professional, design changes (construction deviations from the repair design) should also be reported to the licensed design professional. Revised design or construction work necessary to correct these deficiencies, and the construction corrections, should be observed.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
CHAPTER 11—COMMENTARY ACI 222.3R-11 Design and Construction REFERENCES Practices to Mitigate Corrosion of Reinforcement in American Association of State Highway Concrete Structures Transportation Officials ACI 224R-01 Control of Cracking in AASHTO T 260-97 (2011) Standard Method Concrete Structures of Test for Sampling and Testing for ACI 224.1R-07 Causes, Evaluation, and Chloride Ion in Concrete and Concrete Repair of Cracks in Concrete Raw Materials Structures ACI 228.1R-03 In-Place Methods to Estimate American Concrete Institute Concrete Strength ACI 201.1R-08 Guide for Conducting a Visual ACI 228.2R-98 Nondestructive Test Methods Inspection of Concrete in for Evaluation of Concrete in Service Structures ACI 201.2R-08 Guide to Durable Concrete ACI 301-10 Specifications for Structural ACI 209R-92 Prediction of Creep, Concrete Shrinkage, and Temperature ACI 318-63 Building Code Requirements Effects in Concrete Structures for Reinforced Concrete ACI 209.1R-05 Report on Factors Affecting ACI 318-14 Building Code Requirements Shrinkage and Creep of for Structural Concrete and Hardened Concrete Commentary ACI 214.4R-10 Guide for Obtaining Cores and ACI 355.2-07 Qualification of Post-Installed Interpreting Compressive Mechanical Anchors in Strength Results Concrete and Commentary ACI 216.1-14 Code Requirements for ACI 355.4-11 Qualification of Post-Installed Determining Fire Resistance Adhesive Anchors in Concrete of Concrete and Masonry and Commentary Construction Assemblies ACI 364.1R-07 Guide for Evaluation of ACI 222R-01 Protection of Metals in Concrete Structures before Concrete against Corrosion Rehabilitation ACI 222.2R-14 Corrosion of Prestressing Steels 96 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
ACI 364.3T-14 Treatment of Exposed Epoxy- Bonded FRP Systems for Coated Reinforcement in Strengthening Concrete Repair Structures ACI 364.10T-14 Rehabilitation of Structure ACI 440.4R-04 Prestressing Concrete with Reinforcement Section Structures with FRP Tendons Loss (TechNote) ACI 440.7R-10 Guide for the Design and ACI 365.1R-00 Service-Life Prediction Construction of Externally ACI 369R-11 Guide for Seismic Bonded Fiber-Reinforced Rehabilitation of Existing Polymer Systems for Concrete Frame Buildings and Strengthening Unreinforced Commentary Masonry Structures ACI 423.4R- 14 Corrosion and Repair of ACI 503R-93 Use of Epoxy Compounds Unbonded Single-Strand with Concrete Tendons ACI 503.5R-92 Guide for the Selection of ACI 437.2-13 Code Requirements for Load Polymer Adhesives in Testing of Existing Concrete Concrete Structures and Commentary ACI 503.6R-97 Guide for Application of ACI 437R-03 Strength Evaluation of Epoxy and Latex Adhesives Existing Concrete Buildings for Bonding Freshly Mixed ACI 437.1R-07 Load Tests of Concrete and Hardened Concrete Structures: Methods, ACI 503.7-07 Specification for Crack Repair Magnitude, Protocols, and by Epoxy Injection Acceptance Criteria ACI 506R-05 Guide to Shotcrete ACI 440R-07 Report on Fiber-Reinforced ACI 515.2R-13 Guide to Selecting Protective Polymer (FRP) Reinforcement Treatments for Concrete for Concrete Structures ACI 546R-14 Concrete Repair Guide ACI 440.1R-15 Guide for the Design and ACI 546.3R-14 Guide for the Selection of Construction of Structural Materials for the Repair of Concrete Reinforced with FRP Concrete Bars. ACI 548.1R ACI 440.2R-08 Guide for the Design and ACI C630 Construction Inspector Construction of Externally Certification 97 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
ACI SP-4 Formwork for Concrete, 8th Applied Technology Council Edition ATC 20-89 Procedures for Post-Earthquake ACI SP-6604 ACI Detailing Manual Safety Evaluation of Buildings ATC 45-04 Field Manual: Safety Evaluation of American Institute of Steel Construction Buildings after Windstorms and AISC 2006 Standard for Steel Building Floods Structures ATC-58 Seismic Performance Assessment of ANSI/AISC 360-10 Specification for Structural Buildings Steel Buildings ATC 78 Project Mitigation of Nonductile Concrete Buildings American Society of Civil Engineers ATC 78-1 Evaluation of the Methodology to ASCE/SEI 7-05 Minimum Design Loads for Select and Prioritize Collapse Buildings and Other Structures Indicators in Older Concrete ASCE/SEI 7-10 Minimum Design Loads for Buildings Buildings and Other Structures ASCE/SEI 7-16 Minimum Design Loads for ASTM International Buildings and Other Structures ASTM C666/C666M-03(2008) Standard ASCE/SEI 11-99 Guideline for Structural Test Method for Resistance of Concrete Condition Assessment of Existing to Rapid Freezing and Thawing Buildings ASTM C1152/C1152M-04(2012) Standard Test ASCE/SEI 37-14 Design Loads on Structures Method for Acid-Soluble Chloride in during Construction Mortar and Concrete ASCE/SEI 41-13 Seismic Rehabilitation of ASTM C1218/C1218M-99(2008) Standard Test Existing Buildings Method for Water-Soluble Chloride in ASCE/SEI/SFPE 29-05 Standard Calculation Mortar and Concrete Methods for Structural Fire Protection ASTM C1581/C1581M-09 Standard Test Method for Determining Age at American Forest and Paper Association Cracking and Induced Tensile Stress ANSI/AF&PA NDS-2014 National Design Characteristics of Mortar and Concrete Specification (NDS) for Wood under Restrained Shrinkage Construction ASTM C1583/C1583M-13 Standard Test Method for Tensile Strength of 98 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Concrete Surfaces and the Bond Relative Probe Measurement and Strength or Tensile Strength of Concrete Insulated Hood Repair and Overlay Materials by Direct Canadian Standards Association Tension (Pull-off Method) CAN/CSA S6-14 Canadian Highway Bridge ASTM D4263-83(2012) Standard Test Method Design Code and for Indicating Moisture in Concrete by Commentary the Plastic Sheet Method ASTM D7522/D7522M-09 Standard Test Concrete Reinforcing Steel Institute Method for Pull-Off Strength for FRP Vintage Steel Reinforcement in Concrete Bonded to Concrete Substrate Structures ASTM E84-15 Standard Test Method for Surface Burning Federal Emergency Management Agency Characteristics of Building Materials FEMA P-58 Seismic Performance Assessment ASTM E119-14a Standard of Buildings: Volume 1 & 2 Test Methods for Fire Tests of Building FEMA P-695 Quantification of Building Construction and Materials Seismic Performance Factors ASTM E329-13a Standard FEMA 306 Evaluation of Earthquake Specification for Agencies Engaged in Damaged Concrete and Masonry Construction Inspection, Testing, or Wall Buildings Special Inspection FEMA 307 Evaluation of Earthquake ASTM F1869-11 Standard Damaged Concrete and Masonry Test Method for Measuring Moisture Wall Buildings Vapor Emission Rate of Concrete FEMA 308 The Repair of Earthquake Subfloor Using Anhydrous Calcium Damaged Concrete and Masonry Chloride Wall Buildings ASTM F2170-11 Standard Test Method for FEMA 395 FEMA Risk Assessment Determining Relative Humidity in Database Concrete Floor Slabs Using in situ FEMA 396 Risk Management Series: Probes Incremental Seismic ASTM F2420-05 Standard Test Method for Rehabilitation of Hospital Determining Relative Humidity on the Buildings Surface of Concrete Floor Slabs Using 99 American Concrete Institute Copyrighted Material -- concrete.org
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FEMA 397 Risk Management Series: IBC-2015 International Building Code Incremental Seismic IEBC-2015 International Existing Building Rehabilitation of Office Code Buildings FEMA 398 Risk Management Series: International Concrete Repair Institute Incremental Seismic ICRI No. 210.2-02 Guideline for the Rehabilitation of Multifamily Evaluation of Unbonded Post- Apartment Buildings: Providing Tensioned Concrete Structures Protection to People and ICRI No. 210.3-13 Guide for Using In-Situ Buildings Tensile Pull-Off Tests to Evaluate FEMA 399 Risk Management Series: Bond of Concrete Surface Materials Incremental Seismic ICRI No. 310.1R-08 Guide for Surface Rehabilitation of Retail Preparation for the Repair of Buildings: Providing Protection Deteriorated Concrete Resulting from to People and Buildings Reinforcing Steel Corrosion FEMA 400 Risk Management Series: ICRI No. 310.2-13 Selecting and Specifying Incremental Seismic Concrete Surface Preparation for Rehabilitation of Hotel and Motel Sealers, Coatings, and Polymer Buildings Overlays FEMA 547 Techniques for the Seismic ICRI No. 310.3-14 Guide for the Preparation of Rehabilitation of Existing Concrete Surfaces for Repair Using Buildings Hydrodemolition Methods FEMA P-154 Rapid Visual Screening of ICRI No. 320.2R-09 Guide for Selecting and Buildings for Potential Seismic Specifying Materials for Repair of Hazards: A Handbook. Third Concrete Surfaces Edition ICRI No. 320.3R-12 Guideline for Inorganic Repair Material Data Sheet Protocol FIB ICRI No. 320.4-06 Guideline for the Repair of FIB Bulletin 10 Bond of Reinforcement in Unbonded Post-Tensioned Concrete Concrete Structures
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ICRI No. 330.1-06 Guideline for the Selection Atmospherically Exposed Existing of Strengthening Systems for Concrete Steel-Reinforced Concrete Structures Structures ICRI No. 340.1-06 Guideline for the Selection Post-Tensioning Institute of Grouts to Control Leakage in PTI DC80.2-10 Guide for Creating Concrete Structures Openings and Penetrations in Existing ICRI Concrete Surface Repair Technician - Slabs with Unbonded Post-Tensioning Grade 1 PTI DC80.3-12/ICRI 320.6 Guide for evaluation and repair of unbonded post- NACE International tensioned concrete structures NACE 01101 Electrochemical Chloride Extraction from Steel-Reinforced Authored documents Concrete—A State-of-the-Art Report Bakhsh, K. N. 2010, “Evaluation of Bond NACE 01102-02 State-of-the-Art Report: Strength between Overlay and Substrate in Criteria for Cathodic Protection of Concrete Repairs,” KTH Royal Institute of Prestressed Concrete Structures Technology, Stockholm, Sweden. Petersen, C. NACE 01104 Electrochemical G., 1990. Realkalization of Steel-Reinforced Bartlett, F. M., and MacGregor, J. G., 1995, Concrete—A State-of-the-Art Report “Equivalent Specified Concrete Strength from NACE 01105-05 Sacrificial Cathodic Core Test Data,” Protection of Reinforced Concrete Buchanan 2001: Structural Design for Fire Elements—A State-of-the-Art Report Safety, Andrew H. Buchanan, 2001, Wiley NACE SP0107-07 Electrochemical Publishing Realkalization and Chloride Extraction Concrete International, V. 17, No. 3, Mar., pp. for Reinforced Concrete 52-58. NACE SP0290-2007 Standard Recommended Concrete International, 2002a, “FAQ,” V. 24, Practice—Cathodic Protection of No. 3, Mar., p. 82. Reinforcing Steel in Atmospherically Concrete International, 2002b, “FAQ,” V. 24, Exposed Concrete Structures. No. 6, June, p. 90. NACE SP0390-09 (formerly RP0390) Concrete International, 2002c, “FAQ,” V. 24, Maintenance and Rehabilitation No. 7, July, p. 91. Considerations for Corrosion Control of 101 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Fisher, J., and West, M., 2003, “Erection Bracing NFPA 5000, 2009, “Building Construction and of Low-Rise Structural Steel Buildings,” Steel Safety Code,” National Fire Prevention Design Guide Series 10, American Institute of Association, Quincy, MA. Steel Construction, Milwaukee, WI, 83 pp. PCI, 2010, PCI Design Handbook, seventh Ellingwood, B. R., and Ang, A. H-S., 1972, “A edition, Precast/Prestressed Concrete Institute, Probabilistic Study of Safety Criteria for Chicago, IL. Design,” University of Illinois, Urbana, IL Portland Cement Association (PCA), 1994, Harris, J. R., and Stevens, G. R., 1991, “Detailing “Assessing the Condition and Repair Reinforced Concrete Structures for Post-Elastic Alternatives of Fire-Exposed Concrete and Seismic Resistance,” Seismic Design of Masonry Members,” Model Code SR322, Reinforced Concrete Structures Inelastic PCA, Skokie, IL, 15 pp. Response and Design, SP-127, American Portland Cement Association (PCA), 1985, Concrete Institute, Farmington Hills, MI, pp. “Analytical Methods of Determining Fire 539-554. Endurance of Concrete and Masonry Harris, H.G., and Sabnis, G., 1999, “Structural Members—Model Code Approved Modeling and Experimental Techniques, 2nd Procedures,” Model Code SR267, PCA, Edition, CRC Press and Models for Concrete Skokie, IL. Structures (ACI SP-24) (1970). American Priestley, M. J. N.; Seible, F.; and Calvi, G. M., Concrete Institute, Farmington Hills, MI. 1996, Seismic Design and Retrofit of Bridges, Kahn, L. F., 1980, “Strengthening of Existing RC John Wiley & Sons, pp. 686. Columns for Earthquake Resistance,” Seventh PTI, 2006, Post Tensioning Manual, sixth World Conference on Earthquake Engineering, edition, Post-Tensioning Institute, Farmington Istanbul, Turkey. Hills, MI, 354 pp. Monfore, G. E., and Ost, B., 1965, “Corrosion of Ruddy, J. L.; Marlo, J. P.; Loanneides, S. A.; and Aluminum Conduit in Concrete,” Journal of Alfawakhiri, F., 2003, “Design Guide 19: Fire the PCA Research and Development Resistance of Structural Steel Framing,” Laboratories, V. 7, No. 1, pp. 10-22. American Institute of Steel Construction, Murray, T. M.; Allen, D. E.; and Ungar, E. E., Chicago, IL. 1999, “Floor Vibrations Due to Human Sabnis, G. M.; Harris, H. G.; White, R. N.; and Activity,” Steel Design Guide Series 11, Mirza, M. S., 1983, Structural Modeling and American Institute of Steel Construction, Experimental Techniques, Prentice-Hall Inc., Chicago, IL. Englewood Cliffs, NJ. 102 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Scollard, C. R., and Bartlett, F. M., 2004, “Rehabilitation Criteria for Post-Tensioned Voided-slab Bridges,” Canadian Journal of Civil Engineering, V. 31, No. 6, pp. 977-987. The Concrete Society, 1997, “Guide to Surface Treatments for Protection and Enhancement of Concrete,” Technical Report 50, The Concrete Society, Camberley, UK, 80 pp. The Concrete Society, 2008, “Assessment, Design and Repair of Fire-Damaged Concrete Structures,” Technical Report 68, The Concrete Society, Camberly, UK. Tuutti, K., 1980, “Service Life of Structures with Regard to Corrosion of Embedded Steel,” Performance of Concrete in Marine Environment, SP-65, American Concrete Institute, Farmington Hills, MI, pp. 223-236. U.S. Department of the Interior, 1995, “The Secretary of the Interior Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring, and Reconstructing Historic Buildings,” National Park Service, Department of the Interior, Washington, DC. (http://www.nps.gov/hps/tps/standguide/index. htm) (accessed February 5, 2013). Whitmore, D., 2005, “Installation of Embedded Galvanic Anodes,” Field Guide to Concrete Repair Application Procedures (ACI RAP Bulletin 8), American Concrete Institute, Farmington Hills, MI, pp. 26-31.
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
APPENDIX A – CRITERIA WHEN Provisions of ASCE/SEI 41 may or may not be USING THIS CODE AS A STAND-ALONE applicable to nonbuildings. Section A.3.3 CODE provides minimum assessment criteria for A.1—General seismic safety provisions. This appendix shall apply if a jurisdiction has A.2.2 It shall be permitted to use the current adopted this code by reference. When this building code as the design-basis code for all appendix is used, Chapter 4 shall not apply. damage states, deterioration, and faulty design A.1C This appendix is used when this code is and construction. used for existing concrete structures as a stand- A.2.2C The current building code per 1.2.2 alone code without the use of the IEBC. provides acceptable safety based on consistent statistical probabilities. When using the current A.2—Design-Basis Code Criteria building code the resulting demand-capacity ratios provide the limits that need not be A.2.1 Unless prohibited by the jurisdictional exceeded if assessing and designing remedial authority, the design-basis code criteria of the construction. project shall be based on requirements set forth in A.2.3 As an alternative to using the current this Appendix. building code, this Appendix shall be used to A.2.1C This code contains specific determine the rehabilitation category of work as requirements that determine if existing structures shown in Table A.2.3 and defined in A.3 through should be rehabilitated or retrofitted to satisfy the A.9. requirements of the current building code. Local A.2.3C Unless the local jurisdiction provides ordinances may also require that a structure be more restrictive requirements, this appendix rehabilitated to satisfy the current codes. These should be used to determine the assessment and requirements should be reviewed at the start of a design-basis criteria for the rehabilitation project. categories of A.3 through A.9 and as summarized The licensed design professional should in Table A.2.3. determine if seismic evaluation and retrofit of an existing concrete structure (buildings, members, Table A.2.3 –Assessment and Design-basis system, and, where applicable, nonbuilding Criteria for Rehabilitation Categories structures where the construction is concrete or Primary code of Sections of mixed construction with concrete and other Rehabilitation the design-basis this code to Category criteria used use for the materials) are necessary using ASCE/SEI 41. with this code 104 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
assessment the current criteria building code* *Current building code is as per 1.2.2. Unsafe structural †Original building code is as per 1.2.3. conditions for For unsafe A.3.2 gravity and wind structures, current loads building code* Unsafe structural supplemented by A.2.4 The detailing of the existing conditions for ASCE/SEI 41 for seismic forces in seismic if the reinforcement need not be in accordance with regions of high structure is A.3.3 seismicity seismic design ACI 318-14 if (a) through (d) are satisfied: (Seismic design category D or category D or higher a) The structure is in seismic design higher) Substantial categories A, B, or C and only deterioration structural damage current building is addressed; to vertical code* for A.4 members of the substantial b) The repaired structure shall have capacity lateral-force- structural damage resisting system equal to or greater than demand per 5.2.2 Substantial structural damage current building using the original building code; to vertical code* for A.4 members of the substantial c) No unsafe structural conditions were gravity-load- structural damage resisting system determined to be present; current building Damage less than d) The structure has demonstrated historical code* substantial unless compliant structural damage, structural reliability. with Sections deterioration and A.5 A.5.1, A.5.2 or faulty construction A.2.4C The licensed design professional A5.3 for the with capacity original building should determine if structural distress as increase code† Damage less than identified by observations, testing or substantial measurements is proportional to that predicted structural damage, this code, deterioration and A.6 Chapters 8 based on historical data of the loads the structure faulty construction through 10 without capacity has experienced and if this demonstrates increase current building statically acceptable past performance. Where code* unless compliant the structural performance indicates adequate Additions A.7 with Section A.7 for the original behavior based on historical data, such as † building code acceptable resistance of previous loads which current building code* equal or exceed the loads that would be predicted unless compliant Alterations A.8 with Section A.8 for the remaining life of the structure, the licensed for the original building code† design professional may judge the structure to Changes in If rehabilitation is A.9 Occupancy required then use have demonstrated historical structural reliability. ACI 224.1R-07, ACI 437R-03 and ACI 105 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
437.1R-07 provide guidance in judging If the demand-capacity ratio does not exceed acceptable performance. 1.5 for structures, A.4 through A.9 shall be used A.2.5 This code shall be used for design of to determine the design-basis criteria. repairs to existing structures. ACI 318-14 shall be A.3.2C In assessing unsafe structural used for design of new members and connection conditions the strength design demand of of new members to existing construction. Eq.A.3.2 combines current building code nominal gravity loads (dead, live, and snow) and lateral A.3—Unsafe structural conditions wind forces excluding earthquake loads using A.3.1 A structural assessment shall be factored load combinations (strength design) of performed to determine if unsafe structural ASCE/SEI 7. A demand to capacity ratio greater conditions are present. than 1.5, calculated using Equation A.3.2, A.3.2 For gravity and wind loads, unsafe represents a condition with limited to no margin structural conditions include: instability, of safety against failure. potential collapse of overhead components or In the assessment of unsafe structural pieces (falling hazards), or structures where the conditions, the licensed design professional demand-capacity ratio is more than 1.5, as shown should determine if it may be appropriate to in Eq. (A.3.2). include: structural redundancies, alternate load paths, primary and secondary supporting U elements, redistribution of loads, collapse c 1.5 R cn (A.3.2) mechanisms, reduced live loads, measured displacements (listing, leaning, and tilting), In Equation A.3-2, the strength design demand second-order effects, and other loads specific to the structure, such as drifting snow, lateral earth (Uc) shall be determined for current building code nominal dead, live, snow and wind loads, pressures, self-straining loads, ice, and floods. excluding earthquake using factored load References for unsafe structural conditions combinations of ASCE/SEI 7, and the strength include: commentary to Chapter 1 of ASCE/SEI reduction factors () of 5.3 or 5.4 shall apply. 7-10, Galambos, Ellingwood, MacGregor and If the demand-capacity ratio exceeds 1.5 for Cornell 1982, “Probability Based Load Criteria: structures, the design-basis criteria shall be the Assessment of Current Design Practice,” current building code. Unsafe structural Galambos, T.V., Ellingwood, B.R., MacGregor, conditions shall be reported as described in 1.5.2. J.G., and Cornell, C.A., 1982, “Probability Based Load Criteria: Load Factors and Load 106 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
Combinations,” and Ellingwood and Ang 1972, Structures in regions of low and moderate “A Probability Study of Safety Criteria for seismicity are not required to assess unsafe Design.” These references provide target structural conditions for seismic resistance. reliability indexes, basic probability theory and concepts for an evaluation using the specific A.4—Substantial Structural Damage details of the demand as it relates to the capacity A.4.1 Substantial structural damage shall be with the strength reduction factors of Chapter 5 assessed using current building code demands. for concrete structures. Substantial structural damage to vertical A.3.3 Assessment criteria for unsafe structural members of the lateral-force-resisting system conditions of seismic resistance is limited to shall be where in any story, the shear walls or structures in seismic design category D, E, and F columns of the lateral-force-resisting system are of ASCE/SEI 7 and shall be determined using damaged such that the lateral-load-resisting ASCE/SEI 41 and this code. The design-basis nominal capacity of the structure in any criteria for rehabilitation design and construction horizontal direction is reduced more than 33 of unsafe structures shall be this code and percent from its predamage condition, as shown ASCE/SEI 41. in Eq. (A.4.1a). A.3.3C Compliance with ASCE/SEI 41 for Structural Performance Level, Collapse RR ncn 0.33 Prevention using an applicable Earthquake R n (A.4.1a) Hazard Level as determined by the local jurisdictional authority for the assessment of Substantial structural damage to vertical unsafe structural conditions. Additional research elements of the gravity-load-resisting system on the appropriate seismic hazard level for safety shall be where for any wall or column or group of is needed to set local requirements. If no vertical members of the gravity-load-resisting requirements for unsafe structural conditions are system whose tributary area is more than 30 provided by the local jurisdictional authority, the percent of the total area of the structure's floor(s) licensed design professional should reference the and roof(s) are damaged such that the total IEBC and ASCE 41 appendices for guidance. vertical nominal capacity is reduced more than 20 ATC-78 provides the most up to date percent from its predamage condition, as shown documentation of the earthquake resistance in Eq. (A.4.1b) necessary for the safety of existing concrete structures. 107 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
RR load combinations that include earthquake ncn 0.2 R effects. The seismic design provisions of n (A.4.1b) ASCE/SEI 41 shall be Earthquake Hazard Level,
BSE-1E with the Basic Performance Objective of and concurrently where the current building code “Life Safety” for Risk Category I, II, or III factored gravity (dead, live, and snow) load (ASCE/SEI 7) and of “Immediate Occupancy” demand to in-place vertical design capacity ratio for Risk Category IV. of these damaged members is more than 1.33, as The design of new structural members and shown in Eq. A.4.1c. connections to members supporting load from
vertical members of the gravity-load-resisting U c 1.33 R system that have substantial structural damage cn (A.4.1c) from gravity loads shall be in accordance with
provisions of the current building code. Capacities according to Chapter 6 and A.4.1C The assessment criteria for substantial strength-reduction factors per 5.3 or 5.4 shall be structural damage are specific to existing used in equations A.4.1a through A.4.1c. The concrete structures, which were adapted from the design-basis criteria shall be the current building IEBC. code demands, supplemented by requirements of In Eq. A.4.1c the demand load has been this code for the existing structure and ASCE/SEI modified from the IEBC’s limit of only dead and 41 for seismic design provisions for the live loads to include snow load. Further, the following: current building code factored gravity load a) lateral-force-resisting system in both demand used in Eq. A.4.1c should include other directions for the case of substantial gravity loads judged to be applicable to the structural damage in either direction from structure, such as drifting snow. lateral forces Supplemental requirements of this code for the b) vertical members of the gravity-load- design-basis criteria include strength reduction resisting system for the case of substantial factors per Section 5.3 or 5.4, capacities structural damage from gravity loads. according to Chapter 6, repairs per Chapter 7, Structures assigned to Seismic Design durability per Chapter 8, repair construction per Category D, E, and F per ASCE/SEI 7 with Chapter 9, quality assurance per Chapter 10 for substantial structural damage caused by existing structures. The referenced seismic design earthquake shall be assessed or rehabilitated for
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Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) provisions of ASCE/SEI 41are adapted from code based on material properties of the original those defined in the IEBC. construction. A.4.2 The design-basis criteria for structures A.5.1C Most concrete structures with damage without substantial structural damage shall be less than substantial structural damage, determined in accordance with A.5 through A.9. deterioration, or containing faulty construction will provide acceptable safety if restored to the A.5—Conditions of Deterioration, Faulty strength of the original building code. Construction or Damage less than Substantial The demand-capacity ratio of limit of 1.0 as Structural Damage provided in this section allows strengthening that A.5.1 If a structure has damage less than restores the structural reliability of the existing substantial structural damage, deterioration, or structure to the level prior to damage and contains faulty construction and there is a reason deterioration, or as intended in the original to question the capacity of the structure, it shall building code. be assessed by calculating the demand-capacity Historical performance is often an acceptable ratio using the original building code demand indicator of adequate safety if the structure has (Uo) with nominal loads, load combinations, and been subjected to known loads. capacities of the original building code, as shown If the capacity of the structure is not in in Eq. (A.5.1). question, such as indicated by the commentary
provisions of 1.7.1C, assessment checks are not U o 1.0 R required. cn (A.5.1) A.5.2 Alternative assessment criteria for,
deterioration, faulty construction, or damage less In Eq. (A.5.1a), strength reduction factors () than substantial structural damage shall be of original building code shall be used. If the permitted. The selected alternative assessment demand-capacity ratio exceeds 1.0, then that criterion shall substantiate acceptable structural member or system strength shall be restored safety using engineering principles for existing using the original building code. If the demand- structures. capacity ratio does not exceed 1.0, then A.5.2C An alternative assessment criterion to strengthening shall not be required. consider is use of the current building code and Repairs shall be allowed that restore a member ASCE/SEI 41. The references of A.3.2C should be or system to the capacity of the original building considered in the selection of an applicable assessment criterion. 109 American Concrete Institute Copyrighted Material -- concrete.org
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Beyond using the current building code, the capacity ratio using the current building assessment criteria should address if the demand code demand (Uc) to determine if it or capacity of the original structure or member is exceeds 1.1, as shown in Eq. (A.5.2a). significantly inconsistent with current standards and results in unacceptable structural safety. An U c 1.1 R increase in load intensity, added loads, change in cn (A.5.2a) load factors, strength-reduction factors or load combinations, modification of analytical If the demand-capacity ratio exceeds 1.1, procedures, determined capacity change between then that system or member should be the original and current building codes [such as strengthened using the current building a change from ASD to strength design], or the code demand. If the demand-capacity benefits received versus the costs incurred should ratio does not exceed 1.1, then no lead the licensed design professional to question strengthening is required. the applicability of using the original building b) If the current building code demand (Uc) code for assessment of an existing structure. does not exceed the original building
Engineering principles used to determine * code demand (U o ) increased by 5 acceptable structural safety are to use either a percent (1.05)UU * , check the probabilistic evaluation of loads and capacities co to show adequate structural reliability indices or demand-capacity ratio using the original * an evaluation procedure using demand-capacity building code demand (U o ) to ratios that is derived from the basic engineering determine if it exceeds 1.05, as shown in principles as presented in current standards. Eq. (A.5.2b). An assessment criterion for a structure that has damage less than substantial structural damage, U * o 1.05 deterioration, or faulty construction excluding R cn (A.5.2b) seismic forces that is based on the demand- capacity ratios of the IEBC is the following: If the demand-capacity ratio exceeds a) If the current building code demand (Uc) 1.05, then that system or member exceeds the original building code strength should be restored using the * demand (U o ) increased by 5 percent * original building code demand (U o ). If (1.05)UU * , check the demand- co the demand-capacity ratio does not 110 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard)
exceed 1.05, then strengthening is not current building code demand does or does not required. exceed the original building code demand Strength reduction factors () of sections 5.3 increased by 5 percent. or 5.4 in Eq. (A.5.2a) and (A.5.2b) apply. If the A.5.3 If the concrete design regulations of the original building code demand is used, the repair original building code used only allowable stress design should be supplemented for existing design and design service loads, the demand members or systems by this code. capacity ratio shall be based on service load
In this assessment criterion, the current demand (US) and resistance calculated using building code strength design demand (Uc) allowable stresses (Ra) as shown in Eq. (A.5.3) combines current building code nominal gravity loads (dead, live, and snow) and lateral wind Us/Ra > 1.0 (A.5.3) loads excluding earthquake loads using the factored load combinations of ASCE/SEI 7. The If the demand-capacity ratio exceeds 1.0, then original building code strength design demand that member or system strength shall be restored * using the original building code. If the demand- ()Uo combines the original building code capacity ratio does not exceed 1.0, then nominal gravity loads (dead, live, and snow) and strengthening shall not be required. Repairs shall lateral wind loads excluding earthquake loads be allowed that restore the member or system to using the factored load combinations of its pre-damage or pre-deteriorated state. Repair of ASCE/SEI 7. Consideration should be given to structural concrete is permitted based on material inclusion of ASCE/SEI 41 seismic provisions, properties of the original construction. redistribution of loads, reduced live loads, A.5.3C Before 1963 and the “Building Code measured displacements (listing, leaning, and Requirements for Reinforced Concrete (ACI 318- tilting), second-order effects, and other loads 63),” the design of reinforced concrete structures specific to the structure, such as drifting snow, was based upon allowable stress or working lateral earth pressures, self-straining loads, ice, stress design principles. Original building code and floods. demands should include nominal gravity loads Using structure-specific data is acceptable, if (dead, live, and snow) and lateral wind forces substantiated by the licensed design professional. including seismic forces using the load For these assessment criteria, the demand- combinations of original building code. capacity ratio provisions of part (1) may be used Consideration should be given to inclusion of in the assessment regardless of the whether the measured displacements (listing, leaning, and 111 American Concrete Institute Copyrighted Material -- concrete.org
Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562) and Commentary (Provisional Standard) tilting), second-order effects, and other loads A.6.2C The effect of floor deflections, levelness specific to the structure, such as drifting snow, and vibrations on the structural performance lateral earth pressures, self-straining loads, ice, should be investigated by the licensed design and floods. Using allowable stress design is professional to determine if the performance of inconsistent with the reliability principles of the structure is acceptable to the owner and users strength design. To adequately address safety, of the structure. Acceptable performance criteria consideration should be given to verification will need to be established for an individual using A.5.2 and a check of seismic resistance structure based upon the intended use of the using ASCE/SEI 41. structure. A.5.4 Existing structures other than those to be strengthened per A.3 through A.5 shall use A.6 A.7—Additions through A.9 to determine the design-basis A.7.1 For existing gravity-load-resisting criteria. systems and members where the gravity load demands of the current building code with the A.6—Conditions of Deterioration, Faulty addition are more than the original building code Construction, or Damage less than increased by 5 percent, the design-basis criteria Substantial Structural Damage without Strengthening shall be the current building code, with this code A.6.1 If no damage or less than substantial for existing systems and members and ACI 318- structural damage is present, structures damaged, 14 for new members. deteriorated, or containing faulty construction Existing gravity-load-resisting systems and that do not require strengthening in accordance members whose calculated capacity using this with A.5 shall use the provisions of Chapters 7 code is decreased as part of an addition shall be through 10 of this code as the design-basis shown to have an in-place capacity exceeding the criteria. current building code demand. A.6.2 Deflections—The effects of floor If the addition is not independent of the levelness, vibrations and deflections on the existing building for lateral-force resistance, the performance of the structure shall be assessed. design-basis criteria for the existing lateral-force- Deflections exceeding those allowed by the resisting system with the addition shall be the original building code shall be permitted current building code supplemented by provided those deflections do not adversely affect ASCE/SEI 41 for seismic assessment and design. structural performance.
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Exception: The licensed design professional If the existing gravity-load-resisting system or shall be permitted to use the original building member capacity is to be reduced as part of an code load demands and capacities for any alteration, the reduced capacity shall not be less lateral-force-resisting member where the than the current building code demand. If the demand-capacity ratio, with the addition using alteration increases design lateral loads resulting the current building code, does not exceed the in a structural irregularity per ASCE/SEI 7, or demand-capacity ratio without the addition decreases the lateral capacity, the design-basis using the original building code increased by criteria shall be the current building code 10 percent. supplemented by ASCE/SEI 41 for seismic A.7.1C The exception permits the licensed assessment and design. The seismic design design professional to use the original building provisions of ASCE/SEI 41 shall be Earthquake code for the assessment and design-basis Hazard Level, BSE-1E with the Basic criteria of existing lateral-force-resisting Performance Objective of “Life Safety” for Risk members when the members of the existing Category I, II, or III (ASCE/SEI 7) and of lateral-force-resisting system comply with “Immediate Occupancy” for Risk Category IV. equation A.7.1. Exception: The licensed design professional shall be permitted to use as an alternative to the U original building code load demands and c withtheaddition R n (A.7.1) capacities for any lateral-force-resisting 1.1U o without theaddition member where the demand-capacity ratio with Rn the alteration using the current building code is
not more than the demand-capacity ratio A.8—Alterations without the alteration using the original A.8.1 For existing gravity-load-resisting building code increased by 10 percent. systems and members where the gravity load A.8.1C The exception permits the licensed demands of the current building code with the design professional to use the original building alterations are more than the original building code for the assessment and design-basis code increased by 5 percent, the design-basis criteria of existing lateral-force-resisting criteria shall be the current building code, with members when the members of the existing this code applicable for existing systems and lateral-force-resisting system comply with members and ACI 318-14 applicable for new equation A.8.1. members.
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U c withthealteration R n (A.8.1) 1.1U o without thealteration Rn Alterations in this section exclude the remedial work of A.3 through A.6.
A.9—Change of Occupancy A.9.1 The use or occupancy of a structure shall not be changed if it increases the demand on the structure using the current building code as compared with the original building code, unless the structure is evaluated and shown to comply with the current building code or rehabilitated using the current building code supplemented by this code for existing members, ACI 318-14 for new members and ASCE/SEI 41 for seismic design as the design-basis criteria.
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Key changes from ACI 562-13 to ACI 562- 16 include: a) Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (ACI 562-16) and Commentary”. These changes were made for consistency in the hierarchy of terminology used in ISO, ASCE and other documents related to existing structures, and for consistency with ACI 318. b) Definitions were added to Chapter 2 that reflect the hierarchy of terminology. c) Revisions to Chapters 1-4 to include specific criteria requirements for assessment and design of repair and rehabilitation for varying levels of damage, deterioration, or faulty construction. d) Revisions to the document to allow for use of document with the International Existing Building Code (see Chapter 4) and as a stand-alone code (Appendix A). e) Revisions to the load combinations in Chapter 5 used to define the minimum strength of a structure with unprotected external reinforcement. f) Revisions to the interface bond provisions in Chapter 7. g) Revisions to the commentary in Chapter 8 to simplify the text.
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