DOCSLIB.ORG

Progressive Collapse Assessment of Multistory Irregular Reinforced Concrete Framed Structures Under Gravity Loads

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Progressive Collapse Assessment of Multistory Irregular Reinforced Concrete Framed Structures Under Gravity Loads 13TH ARAB STRUCTURAL ENGINEERING CONFERENCE UNIVERSITY OF BLIDA 1 DECEMBER 13-15, 2015 ALGERIA Progressive Collapse Assessment of Multistory Irregular Reinforced Concrete Framed Structures Under Gravity Loads Mohamed El-Bayomy* and Hamed Salem** *Assistant Lecturer, Structural Engineering Department, Faculty of Engineering, Cairo University [email protected] ** Prof. of Reinforced Concrete Structures, Faculty of Engineering, Cairo University [email protected] Abstract: Progressive collapse is a disastrous partial or total collapse which causes a massive number of causalities and injuries. It mainly occurs when a structure loses one or more of its main vertical carrying members such as columns or walls. In this research, the effect of plan structural irregularity on progressive collapse resistance was studied on multistory reinforced concrete framed structure subjected to gravity loads. The studied structure was designed according to the ‘Egyptian code of practice’ (ECP)[1] and the limits of elements' rotation were adopted from the ‘Unified Facilities Criteria’ (UFC)[2] guidelines. All the studied cases satisfied the UFC guidelines requirements for progressive collapse resistance of reinforced concrete structures. Key words: Progressive Collapse, Irregularity, Catenary action, UFC, AEM, ELS 1. INTRODUCTION Progressive collapse recently became an important point of research due to its catastrophic effect. In 1968, ‘Ronan Point apartment’, a 22-story building experienced partial collapse due to a gas explosion in the eighteenth floor which caused failure to corner load bearing walls[3]. In 1973, ‘Skyline Towers’, a 26-story building in Virginia, collapsed due to early shoring removal from an upper floor[3]. In 2013, ‘Savar building’, an eight-story building in Bangladesh, collapsed after appearance of several cracks in the columns of the ground floor[3]. The building was designed as an office building while it was used as a factory. The effect of machines weights and vibrations has caused the structure collapse. The aim of this research is to assess the effect of column sudden loss in a multistory irregular reinforced concrete framed structure under gravity loads, designed according to the Egyptian code of practice (ECP)[1], on progressive collapse according to the UFC guidelines[2]. Multiple cases of plan irregularity were studied with multiple column removal locations in each case. In the current study, a ten-story structure was modeled with slab and beam system. The Applied Element Method is used in this study with a fully nonlinear dynamic analysis scheme. The AEM is based on discrete crack approach which is capable of tracking the actual behavior of structure up to total collapse. The software used in analysis is ‘Extreme Loading for Structures’ (ELS)[4]. THE 13TH ARAB STRUCTURAL ENGINEERING CONFERENCE 2. THE APPLIED ELEMENT METHOD (AEM) The AEM is based on dividing the structure virtually into small elements. Each two adjacent elements are connected together at certain contact points which are distributed around the elements' surfaces. Each contact point is represented by one normal and two shear springs, these springs represent the stresses and deformations of a certain volume. The AEM is based on discrete crack approach. This method can track the structural behavior passing through all stages of loading; elastic stage, crack initiation, element separation, partial collapse of structure, and collision with the ground and other structures. The software used in the analysis is ‘Extreme Loading for Structures’ (ELS) which is an analytical tool which uses the Applied Element Method (AEM). The ELS uses an implicit method in numerical integration, which models structural collapse better than explicit solver software. The material models used in ELS are shown in Figure 1[5] and Figure 2[6]. Maekawa compression model is used for concrete modeling under compression as shown in Figure 1-a. For concrete shear springs, linear relation between shear stress and shear strain is assumed until cracking of concrete, then the shear stresses drop suddenly as shown in Figure 1-b. The level of drop depends on aggregate interlocking and friction at crack surface. For reinforcement springs, Figure 2 shows the model, presented by Ristic et al.[6], used in ELS. Several factors affect the calculation of tangent stiffness of reinforcement in this model such as: the strain from reinforcement spring, loading status (loading or unloading), and history of steel spring (which controls Baushinger's effect). ELS was proved to be capable of performing nonlinear, static and dynamic, analysis of structures subjected to extreme cases of loading through elastic and inelastic stages up to structural collapse including automatic detection of cracks' locations, formation of plastic hinges, and buckling of elements. The ‘ELS’ software was extensively validated [7][8][9][10][11][12][13][14][15][16][17][18] and had shown good agreement with real cases. Several validation cases including static, dynamic, and collapse cases were covered. Therefore, and since the goal of the current study is to assess the capability of multistory reinforced concrete framed structures to resist progressive collapse under gravity loads, it was decided that the AEM is the most suitable numerical tool for such assessment. (a) Concrete under axial force (b) Concrete undeer shear force Figure 1: Stresses in concrete springs due to relative displacement[5] Figure 2: Stresses in steel springs due to relative displacement[6] - 2 - THE 13TH ARAB STRUCTURAL ENGINEERING CONFERENCE 3. CASE STUDY The current study is an extension to the study by Helmy [21], where the progressive collapse of a regular reinforced concrete multi storey reinforced concrete structures was investigate. In the current study, effect of irregularity is investigated. 3.1 Details of Studied Structure The studied structure is a ten-story reinforced concrete residential building. The building consists of five bays in each direction, the typical span of each bay is five meters. The ground floor is a public area (uncontrolled area). The height of all stories is three meters. The structure is designed according to the Egyptian code for design and construction of reinforced concrete structures[1]. The Ultimate limits state design method was used for design of the structure members. All members were designed to resist both gravity loads and seismic loads. All columns were assumed fixed to the foundation. Figure 3 shows details of the master case of the studied structure. (b) Elevation of B1 and B2 (250X500) (c) Rft. details of B1 (d) Rft. details of B2 (a) Master case plan (All spans = 5m) Figure 3: Details of the master case of the studied structure 3.2 Earthquake Properties The design of the studied structure was checked against seismic loads using ACI318-08/IBC 2009[19][20] guidelines. The structure was assumed to be located in Cairo, Egypt (earthquake zone III according to the Egyptian code for loads). Therefore the peak ground acceleration was taken 0.15g and the response spectrum used is Type I. The importance factor of the building (γI) equals 1, the damping factor (η) equals 1, and the sub-soil group is assumed to be group (B). 3.3 Material Properties Nonlinear behavior of constituent materials are used in the models. The properties of concrete are shown in Table 1 and the properties of reinforcing steel are shown in Table 2. All the beams are assumed to be carrying masonry walls made of 25 cm width bricks, the density of bricks including plaster is assumed 1.8 t/m3. 3.4 Loads The loads considered in the analysis of all cases were as follows: The own weight of the structural members, the flooring load, the live load, and the masonry walls load. The flooring was assumed 0.15 t/m2 and the live load was assumed 0.3 t/m2. The load combination used in the study of column removal due to gravity loads was (1.2 D.L. + 0.5 L.L.) according to the UFC guidelines for nonlinear dynamic analysis of progressive collapse. The column in - 3 - THE 13TH ARAB STRUCTURAL ENGINEERING CONFERENCE each case was removed at (t = 0.0 seconds) without affecting the beam-column connection in order not to affect the continuity of the horizontal members. Table 1: Concrete Properties Young's Modulus 2213590 t/m2 Compressive Strength 2500 t/m2 Tensile Strength 200 t/m2 Specific Weight 2.5 t/m3 Table 2: Steel Properties Young's Modulus 20389000 t/m2 2 Yield Strength 36000 t/m Ultimate Strength 52000 t/m2 3.5 Mesh Sensitivity Mesh sensitivity analysis was carried out to obtain the optimum size of mesh to be used for each structural member in our case study, aiming to balance between the results preciseness and the required analysis time. The study was performed on a typical 5 m span building and the case of edge ground column removal was conducted. Four mesh groups were tested and mesh group (3) was chosen as shown in Table 3. Table 3: Properties of Mesh Group (3) Number of Mesh Group Beams Columns Slabs Elements 3 29586 16x3x3 12x3x3 14x14x2 3.6 Studied Parameters Four cases were chosen to study plan irregularity, where the typical plan consisting of five bays in each direction, each 5m span, is used as the master plan for each of the four cases. The chosen cases were as follows: a. Varying the span of the middle bay in one direction only. b. Varying the span of the external bay in one direction only. c. Varying the span of the middle bay in both directions. d. Varying the span of the external bay in both directions. Where the spans studied in each case were 5m, 7m, and 9m and the removal of ground column was studied in all cases from several locations. Removal of edge and interior columns was studied for case (a). Removal of corner, edge, and interior columns was studied for case (b).
Load more

Recommended publications
  • Recent Developments in Progressive Collapse Design
    RECENT DEVELOPMENTS IN PROGRESSIVE COLLAPSE DESIGN David Stevens1*, Eric Martin2, Eric Williamson3, Aldo McKay1 and Kirk Marchand1 1Protection Engineering Consultants, San Antonio, Texas 2US Army Corps of Engineers, Protective Design Center, Omaha, Nebraska 3University of Texas at Austin, Austin, Texas * Corresponding Author ([email protected]) Abstract The state-of-the-art in the design of buildings to resist Progressive Collapse (PC) has continued to advance, in North America and throughout the world. Recent developments include improved design guidance, cost assessments for implementing PC design requirements, research efforts to understand key structural mechanisms for collapse resistance, and growing experience in using commercially-available design tools to better design and analyze progressive collapse events. The goal of this paper is to report upon these recent developments. Keywords: Progressive Collapse Design, Extreme Events, Structural Testing. 1. INTRODUCTION Progressive collapse design of buildings continues to be an active area of research and development. Not only is the topic important in terms of protecting building occupants but it is also an intellectually-engaging issue, with a wide spectrum of views, ranging from those who feel progressive collapse design is not needed to those who have an obligation to protect the public. The range of technical issues is quite broad also, as there are many types of structural systems and materials, the structural response is typically complex and nonlinear, and there are a number of analysis and design approaches that can be taken. Finally, there is also passionate discussion generated by those who mistake progressive collapse design for hardened structure design, those who propose risk-based approaches when it is known that there is insufficient data to assess risk and those who feel progressive collapse design should not be employed until more research is done and all answers are known.
    [Show full text]
  • Progressive Collapse Design
    12/20/2017 Mitigating of Progressive Collapse in Structures Day 2 - 7 Hour Course Ahmed Khalil, Ph.D., P.E. [email protected] Ayman El Fouly, P.E. [email protected] www.appliedscienceint.com │ www.extremeloading.com ©2006‐17 Applied Science International, LLC Presenters Ahmed Khalil, Ph.D., P.E. Ayman Elfouly, P.E. • Structural Consultant • Structural Consultant • Applied Science International, LLC • Applied Science International, LLC • Member of SEI/ASCE • Member of SEI/ASCE • Member of Disproportionate • Member of Blast, Shock, & Impact Collapse Mitigation of Building Committee Structures Standards • Member of Disproportionate Collapse Technical Committee ©2006‐17 Applied Science International, LLC 1 12/20/2017 Morning Outline 1. Definition of Progressive Collapse 2. Progressive Collapse Historical Events & Evolution of Code Regulations 3. Historic Progressive Collapse Case Studies 4. Design Philosophy for Progressive Collapse Mitigation in Codes and Standards Day 2 ‐ 7 Hour Course ©2006‐17 Applied Science International, LLC What is progressive collapse? Europan Journal of Educational Studies 2(1), 2010 39 EARTHQUAKE EDUCATION IN CIVIL ENGINEERING DEPARTMENTS OF UNIVERSITIES OF TURKEY Mizan Doğan Department of Civil Engineering, Eskişehir Osmangazi University, TURKEY ©2006‐17 Applied Science International, LLC 2 12/20/2017 Definition of Progressive Collapse • Term is debated with respect to specific historical events • Was the collapse of Oklahoma City Federal Building progressive incident? • Was the collapse
    [Show full text]
  • Research and Practice on Progressive Collapse and Robustness of Building Structures in the 21St Century T ⁎ Jose M
    Engineering Structures 173 (2018) 122–149 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Review article Research and practice on progressive collapse and robustness of building structures in the 21st century T ⁎ Jose M. Adama, , Fulvio Parisib, Juan Sagasetac, Xinzheng Lud a ICITECH, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain b Department of Structures for Engineering and Architecture, University of Naples Federico II. Via Claudio 21, 80125 Naples, Italy c University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom d Key Laboratory of Civil Engineering Safety and Durability of Ministry of Education, Tsinghua University, Beijing 100084, China ARTICLE INFO ABSTRACT Keywords: Extreme events (i.e. terrorist attacks, vehicle impacts, explosions, etc.) often cause local damage to building Progressive collapse structures and pose a serious threat when one or more vertical load-bearing components fail, leading to the Accidental actions progressive collapse of the entire structure or a large part of it. Since the beginning of the 21st century there has Extreme events been growing interest in the risks associated with extreme events, especially after the attacks on the Alfred P. Robustness Murrah Federal Building in Oklahoma in 1995 and on the World Trade Center in New York in 2001. The accent State of the art is now on achieving resilient buildings that can remain operational after such an event, especially when they Codes Buildings form part of critical infrastructures, are occupied by a large number of people, or are open to the public. This Review paper presents an ambitious review that describes all the main advances that have taken place since the be- ginning of the 21st century in the field of progressive collapse and robustness of buildings.
    [Show full text]
  • Collapse Performance Assessment of Steel-Framed Buildings Under Fires
    Department of Civil and Environmental Engineering Stanford University Report No. The John A. Blume Earthquake Engineering Center was established to promote research and education in earthquake engineering. Through its activities our understanding of earthquakes and their effects on mankind’s facilities and structures is improving. The Center conducts research, provides instruction, publishes reports and articles, conducts seminar and conferences, and provides financial support for students. The Center is named for Dr. John A. Blume, a well-known consulting engineer and Stanford alumnus. Address: The John A. Blume Earthquake Engineering Center Department of Civil and Environmental Engineering Stanford University Stanford CA 94305-4020 (650) 723-4150 (650) 725-9755 (fax) [email protected] http://blume.stanford.edu ©2007 The John A. Blume Earthquake Engineering Center THIS PAGE LEFT BLANK ii ABSTRACT ABSTRACT The main objective of this research is to investigate the collapse performance of steel-framed buildings under fires and to contribute to the development of methods and tools for performance-based structural fire engineering. This research approach employs detailed finite element simulations to assess the strength of individual members (beams and columns) and indeterminate structural sub-assemblies (beams, columns, connections and floor diaphragms). One specific focus of the investigation is to assess the accuracy of beam and column strength design equations of the American Institute of Steel Construction (AISC) Specification for Structural Steel Buildings. The simulation results show these design equations to be up to 60 % unconservative for columns and 80-100 % unconservative for laterally unbraced beams. Alternative equations are proposed that more accurately capture the effects of strength and stiffness degradation at elevated temperatures.
    [Show full text]
  • Review on Quantitative Measures of Robustness for Building Structures Against Disproportionate Collapse
    International Journal of High-Rise Buildings International Journal of June 2020, Vol 9, No 2, 127-154 High-Rise Buildings https://doi.org/10.21022/IJHRB.2020.9.2.127 www.ctbuh-korea.org/ijhrb/index.php Review on Quantitative Measures of Robustness for Building Structures Against Disproportionate Collapse Jian Jiang1, Qijie Zhang1, Liulian Li2, Wei Chen1, Jihong Ye1, Guo-Qiang Li3,† 1Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, China University of Mining and Technology, Xuzhou 221116, China 2The First Construction Engineering Company Ltd. of China Construction Second Engineering Bureau, Beijing 100176, China 3State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China Abstract Disproportionate collapse triggered by local structural failure may cause huge casualties and economic losses, being one of the most critical civil engineering incidents. It is generally recognized that ensuring robustness of a structure, defined as its insensitivity to local failure, is the most acceptable and effective method to arrest disproportionate collapse. To date, the concept of robustness in its definition and quantification is still an issue of controversy. This paper presents a detailed review on about 50 quantitative measures of robustness for building structures, being classified into structural attribute-based and structural performance-based measures (deterministic and probabilistic). The definition of robustness is first described and distinguished from that of
    [Show full text]
  • Progressive Collapse Risk Analysis: Literature Survey, Relevant Construction Standards and Guidelines
    Progressive collapse risk analysis: literature survey, relevant construction standards and guidelines Administrative Arrangement No JRC 32253-2011 with DG-HOME Activity A5 - Blast Simulation Technology Development Seweryn KOKOT George SOLOMOS 2012 Report EUR 25625 EN European Commission Joint Research Centre Institute for the Protection and Security of the Citizen Contact information George Solomos Address: Joint Research Centre, Via Enrico Fermi 2749, TP480, 21027 Ispra (VA), Italy E-mail: [email protected] Tel.: +39 0332 78 9916 Fax: +39 0332 78 9049 http://ipsc.jrc.ec.europa.eu/ http://www.jrc.ec.europa.eu/ Legal Notice Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of this publication. Europe Direct is a service to help you find answers to your questions about the European Union Freephone number (*): 00 800 6 7 8 9 10 11 (*) Certain mobile telephone operators do not allow access to 00 800 numbers or these calls may be billed. A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server http://europa.eu/. JRC73061 EUR 25625 EN ISBN 978-92-79-27734-4 (pdf) ISBN 978-92-79-27735-1 (print) ISSN 1831-9424 (online) ISSN 1018-5593 (print) doi:10.2788/70141 Luxembourg: Publications Office of the European Union, 2012 © European Union, 2012 Reproduction is authorised provided the source is acknowledged. Printed in Italy Progressive collapse risk analysis: literature survey,
    [Show full text]
  • Best Practices for Reducing the Potential for Progressive Collapse in Buildings
    NISTIR 7396 Best Practices for Reducing the Potential for Progressive Collapse in Buildings National Institute of Standards and Technology • Technology Administration • U.S. Department of Commerce NISTIR 7396 Best Practices for Reducing the Potential for Progressive Collapse in Buildings Bruce R. Ellingwood Georgia Institute of Technology Robert Smilowitz Weidlinger Associates Donald O. Dusenberry Simpson Gumpertz & Heger Dat Duthinh H.S. Lew National Institute of Standards and Technology Building and Fire Research Laboratory Nicholas J. Carino Consultant February 2007 U.S. Department of Commerce Carlos M. Gutierrez, Secretary Technology Administration Robert C. Cresanti, Under Secretary for Technology National Institute of Standards and Technology William A. Jeffrey, Director ABSTRACT This document is intended to provide owners and practicing engineers with current “best practices” to reduce the likelihood of progressive collapse of buildings in the event of abnormal loading. The report includes a discussion of an acceptable risk approach to progressive collapse, which involves defining the threat, event control, and structural design to resist postulated event. Practical means for reducing risk for new and existing buildings are presented. An extensive review is provided of the design methods used to enhance a buildings resistance to progressive collapse. These include the indirect method (providing sufficient tie forces), the specific local resistance method (designing key elements to withstand abnormal loads), and the alternate load path method (allowing for redistribution of load in the event of the loss of a key member). Design considerations for different structural materials are summarized. The methodology for evaluating and mitigating progressive collapse potential in existing buildings is also discussed. Three appendices provide supporting information.
    [Show full text]
  • Abnormal Loading on Buildings and Progressive Collapse. an Annotated Bibliography NATIONAL BUREAU of STANDARDS
    AlllDQ NATL INST OF STANDARDS & TECH R.I.C. A1 11 00992794 /Abnormal loading on buildings and proar TA435 .U58 V67:ll76 C.I NBg-PUB-C 1876 BUILDING SCIENCE SERIES Abnormal Loading on Buildings and Progressive Collapse. An Annotated Bibliography NATIONAL BUREAU OF STANDARDS The National Bureau of Standards^ was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, and the Office for Information Programs. THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of the Office of Measurement Services, the Office of Radiation Measurement and the following Center and divisions: Applied Mathematics — Electricity
    [Show full text]
  • Blast and Progressive Collapse / Iii TABLE of FIGURES
    Facts for Steel Buildings number2 Kirk A. Marchand Blast and Walter P. Moore and Associates, Inc. Farid Alfawakhiri Progressive AISC, Inc. Collapse Copyright © 2004 By American Institute of Steel Construction, Inc. All rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the publisher. The information presented in this publication has been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed professional engineer, designer, or architect. The publication of the material contained herein is not intended as a representation or warranty on the part of the American Institute of Steel Construction or of any other person named herein, that this information is suitable for any general or particular use or of freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability arising from such use. Caution must be exercised when relying upon other specifications and codes developed by other bodies and incorporated by reference herein since such material may be modified or amended from time to time subsequent to the printing of this edition. The Institute bears no responsibility for such material other than to refer to it and incorporate it by reference at the
    [Show full text]
  • Progressive Collapse Analysis of Rc Building Frames with Different Seismic Design Levels
    The American University in Cairo School of Science and Engineering PROGRESSIVE COLLAPSE ANALYSIS OF RC BUILDING FRAMES WITH DIFFERENT SEISMIC DESIGN LEVELS A Thesis Submitted to The Construction and Architectural Engineering Department in partial fulfillment of the requirements for the degree of Master of Science in Engineering By Eng. Mohamed Foda Mohamed B.Sc. in Civil Engineering Under the supervision of Dr. Mohamed Abdel-Mooty Professor, Department of Construction and Architectural Engineering The American University in Cairo Fall 2012 ii ABSTRACT Progressive collapse prevention of buildings has recently become the focus of many researchers, design engineers, and officials all over the world particularly after the failure of the twin World Trade Center towers, New York City, USA in September 2001 and the increasing terrorist acts against governmental buildings. The progressive collapse is defined in the commentary of the American Society of Civil Engineers Standard 7-02 Minimum Design Loads for Buildings and Other Structures (ASCE 7-02) as “the spread of an initial local failure from element to element, eventually resulting in the collapse of an entire structure or a disproportionately large part of it”. To date, there is no design code for blast resistant building design and progressive collapse prevention, but only design guideline sexist which are prepared by different bodies like Departments of defense (DoD) in USA as well as other countries and the General Service Administration (GSA) and the Federal Emergency Management Agency (FEMA). While design for progressive collapse prevention is possible at design stage, it becomes more challenging for already existing buildings. On the other hand, almost all recently designed and constructed buildings are designed for seismic resistance according to the seismic zone they are located in according to existing codes.
    [Show full text]
  • 1 a Review of Progressive Collapse Research And
    A REVIEW OF PROGRESSIVE COLLAPSE RESEARCH AND REGULATIONS M. Byfielda, G. L. Kasima, C. Morisonb and E. Stoddarta aSchool of Civil Engineering and the Environment, University of Southampton, SO17 1BJ bSecurity & Explosion Effects Division, TPS Consult, Centre Tower, Croydon, CR9 0AU Abstract A series of historic events beginning with the Ronan Point apartment building collapse in 1968 and continuing in subsequent decades have shown that buildings designed in compliance with conventional design codes can lack the robustness necessary to withstand localised damage, partial collapse or, in some cases, complete collapse. The variable performance of different building forms has led to increased interest from governmental organisations in ensuring all buildings of significant size possess a minimum level of robustness. The research community have responded to this challenge by advancing the understanding of how structures behave when subjected to localised damage. Regulations and design recommendations have been developed to help ensure a more consistent level of resilience for all framed buildings of significant size and rigorous design approaches have been specified for buildings which are deemed potentially vulnerable to extreme loading events (e.g. vehicle borne improvised explosive devices). This paper summarizes some of the more important progressive collapse events in order to identify key attributes that lead to vulnerability to collapse. Current procedures and guidelines for ensuring a minimum level of performance are reviewed and the modelling methods developed for structures subjected to localised damage are described. These include increasingly sophisticated progressive collapse analysis procedures, starting with linear-static and non-linear static analysis and moving through to non-linear static pushover and linear dynamic methods.
    [Show full text]
  • Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions
    Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions Zdenfk P. Bažant, F.ASCE1; and Mathieu Verdure2 Abstract: Progressive collapse is a failure mode of great concern for tall buildings, and is also typical of building demolitions. The most infamous paradigm is the collapse of the World Trade Center towers. After reviewing the mechanics of their collapse, the motion during the crushing of one floor ͑or group of floors͒ and its energetics are analyzed, and a dynamic one-dimensional continuum model of progressive collapse is developed. Rather than using classical homogenization, it is found more effective to characterize the continuum by an energetically equivalent snap-through. The collapse, in which two phases—crush-down followed by crush-up—must be distinguished, is described in each phase by a nonlinear second-order differential equation for the propagation of the crushing front of a compacted block of accreting mass. Expressions for consistent energy potentials are formulated and an exact analytical solution of a special case is given. It is shown that progressive collapse will be triggered if the total ͑internal͒ energy loss during the crushing of one story ͑equal to the energy dissipated by the complete crushing and compaction of one story, minus the loss of gravity potential during the crushing of that story͒ exceeds the kinetic energy impacted to that story. Regardless of the load capacity of the columns, there is no way to deny the inevitability of progressive collapse driven by gravity alone if this criterion is satisfied ͑for the World Trade Center it is satisfied with an order-of-magnitude margin͒.
    [Show full text]