Is It a Nonstructural Component or a Nonbuilding Structure? By Robert Bachman, S.E., and Susan Dowty, S.E.

This article provides guidance to code users on how to determine whether or not an item should be treated as a nonstructural component or a nonbuilding structure for purposes of seismic design. In order to explain the differences ® between nonstructural components and nonbuilding struc- tures, many generalizations need to be made so that the discussion can be simplified as much as possible. Common sense also needs to be exercised, as these generalizations don’t always apply. Also, it should be noted, that the guid- ance provided herein represents only the collective opinion of the authors at this point in time. It is hoped that as the nonstructural component and nonbuilding structure code Figure 1: Nonbuilding Structure Similar to . provisions evolve, some of these guidelines will become ob- solete as the code will directly address theseCopyright issues.

Nonstructural Components Traditionally, nonstructural components system similar to build- have been identified as architectural, me- ings and the other type chanical and electrical components found has a structural system in . Prior to adoption of the that is not similar to International (IBC), the buildings (Figures 1 and focus had been on the design of anchor- 2). The focus of this age and bracing of these components article is on nonbuild- and not the components themselves. The ing structures which are Figure 2: Nonbuilding Structure Not Similar to Building. components themselves had been treated not similar to build- as a “black box” and whatever was inside ings, and the determination of when “big” now need to be described in a more the “black box” was not required to be the design rules of ASCE 7-05 Chapter definitive way. Mechanical and electrical designed for seismic loads. Exceptions 15 apply and when the design rules of equipment components are typically to this “black box” approach were items ASCE 7-05 Chapter 13 apply. small enough to fit within a building; such as on tops of buildingsmagazine (radio Figure 3 provides a visual illustration something on the order of less than 10 and cell towers), heavy cladding, battery that shows: feet tall. There are, of course, exceptions Sracks, billboardsT and signageR attached toU 1) those itemsC which shouldT Uto the 10 feet, suchR as signs attachedE to buildings. Current IBC seismic code re- be treated as nonstructural buildings and very large generators and quirements for anchorage and bracing components; turbines. The 10-foot height is obviously requirements for nonstructural compo- 2) those items which should be treated an arbitrary height. The basis for select- nents are found in ASCE 7-05 Chapter as nonbuilding structures; and ing 10 feet is twofold:

tandards 13. It should be noted that, starting with 3) those items, such as tanks, that 1) it represents a story height which the 2000 IBC, when the component is appear to be ambiguous since will allow installation within a determined to have an importance factor they are permitted to be treated S building, and of 1.5, the “black box” itself now generally either way. 2) the weight of the component is

needs to be designed, or qualified, to resist It should be noted that most, if not likely small relative to the weight the effects of seismic forces. all, nonbuilding structures support at- of the supporting structure. tached nonstructural components of Another obvious difference between Nonbuilding Structures some type. One item not shown on the nonstructural components and nonbuild- list that is of interest is skid mounted

and Self-supporting nonbuilding structures ing structures is whether they are factory equipment modules. assembled or field erected. Nonstructural

are structures other than buildings that carry gravity loads and resist the effects components are typically factory as- of earthquakes. The concept of provid- Differentiating Between sembled in that they are transported in ing specific seismic design requirements Nonstructural Components one piece on a truck and require no as- for nonbuilding structures was first in- sembling at the jobsite. Obviously there troduced into code requirements in the and Nonbuilding Structures are many nonstructural components that 1988 Uniform Building Code (UBC). The There are a number of obvious differ- are assembled on the site in pieces such

odes most current seismic design requirements ences between nonstructural components as ceilings, partition walls, exterior curtain for nonbuilding structures are found in and nonbuilding structures. First is size. walls, exterior siding, masonry veneer, updates and discussions related to codes standards C ASCE 7-05 Chapter 15. To say it simply, nonstructural compo- cable trays, piping systems, ductwork, There are two types of nonbuilding nents are typically small, and nonbuilding large roof mounted roof handlers, eleva- structures. One type has a structural structures are typically big. “Small” and tors etc. Fortunately, there is no question

STRUCTURE magazine 18 July 2008 of the structure. For nonstructural components, the period of the item affects the determina- Nonstructural Components tion of the a factor. Because of differences in Chapter 13 p the form of the two sets of equations and the Access floors Escalator components Air conditioning units Evaporators defined parameters, as shown in the box below, Air distribution boxes Furnaces Air handlers Generators they may yield quite different results. Air separators Heat exchangers Nonbuilding Structures Battery racks HVAC Not Similar to Buildings Boilers Inverters Penthouses: Are They Really® a Cabinet heaters Lighting fixtures Billboards & Signs Chapter 15 Cabinets Manufacturing equipment Bins Nonstructural Component? Cable trays Motor control centers Ceilings Chimneys Motors Conveyors Amusement structures Chillers Panel boards There is one item listed as a nonstructural Communication equipment Cooling Towers Hoppers (elevated) Parapets Stacks Monuments component in Figure 3 that may come as a Compressors Penthouse (except where Tanks Silos (cast-in-place Computers framed by an extension of surprise: penthouses (except where framed Ductwork Towers concrete having walls the building frame) to foundation) Electrical conduit Piping Vessels by an extension of the building frame). A Elevator Plumbing penthouse is typically a structure on a roof for Engines Process equipment Switch gear Pumps housing elevator machinery, equipment, water Transformers Wall panel Tubing Walls tanks, etc. It can easily be more than 10 feet Turbines Water heaters in height, and it is most likely constructed at Veneer Vibration isolated components Copyright and systems the jobsite. Because penthouses are typically located at the roof level, are of a small mass and footprint size compared to the structure Figure 3: Intersection of Nonstructural Components and Nonbuilding Structures. as a whole thus not affecting the dynamics that these all should be treated as nonstructural equation in ASCE 7-05 Chapter 15, and of the entire structure, they are classified as components and the design criteria in ASCE using the most conservative design. nonstructural components provided they are 7-05 Chapter 13 apply. Nonbuilding struc- The design force equation for nonstructural not part of the building frame. One could tures are most likely field erected, as they are components is indirectly dependent on the pe- argue that their framing system is similar to constructed at the jobsite. Exceptions to this riod of the item (is it flexible or rigid?) whereas that of a building; however, they also can be rule would be large vertical vessels, hoppers the design force equation for non-building viewed as a small appendage to a structure and bins which can be shipped on trucks or structures is directly dependent on the period similar to a . If the penthouse is framed railcars to the site. Essentially every by an extension of the building frame, other type of nonbuilding structure then it needs to be designed as part of is constructed at the jobsite. Nonstructural Components: the building as a whole. Another major difference between z 0.4a S W 1 + 2 a nonstructural component and a p DS p Fp = ( h ) Nonbuilding Structures nonbuilding structure is the basis Rp Supported Within a for its design and construction. magazine Ip Nonstructural components are typ- ( ) Building or icallyS constructed toT function forR Fp shall notU be taken as less than:C Fp = 0.3 SDSITpWp U OtherR Structures E architectural, mechanical or elec- Fp is not required to be taken as greater than: Fp = 1.6SDSIpWp Sometimes a nonbuilding structure trical purposes. The primary func- needs to have its seismic design forces tion of nonbuilding structures is to Nonbuilding Structures S determined using the same equations DS for T T maintain structural stability, and Not Similar to Buildings: Cs = ≤ s used to determine forces as specified R they are typically constructed to for a nonstructural component. This resist gravity and lateral loads and ( I ) happens when, rather than being sup- the structural system is typically ported on the ground, the nonbuilding very carefully designed for seismic SD1 Cs = for TL ≥ T > Ts structure is supported within a building loads. For example, a communica- R or by another nonbuilding structure. tions tower is designed to maintain T I ASCE 7-05 Section 15.3 provides clear structural stability whereas a motor ( ) instructions for this condition. is primarily designed for mechanical SD1TL Where the weight of the supported functionality and seismic design Cs = for T > TL R nonbuilding structure is “relatively may be inherent and therefore not T 2 small” compared to the weight of the rigorously evaluated (other than ( I ) supporting structure, the assumption is for anchorage). For nonbuilding systems that have an R value provided in that the supported nonbuilding struc- ture will have a relatively small effect Table 15.4-2, Cs shall not be taken as less than: Designer’s Option on the overall nonlinear earthquake C = 0.03 When in doubt, the designer s response of the primary structure dur- always has the option of calculating For nonbuilding structures located where S1 ≥ 0.6g, Cs shall ing design level ground motions. In the force demand in accordance not be taken as less than: 0.8S1 these cases, the code allows such struc- Cs = with the nonstructural component R tures to be considered as nonstructural components and they can therefore equation in ASCE 7-05 Chapter I 13 and the nonbuilding structure ( ) utilize the requirements for Chapter

STRUCTURE magazine 19 July 2008 13 for their design. The code equates “rela- tively small” to weighing less than 25 percent Mechanical and Electrical Components ap Rp of the combined weight of the nonbuilding Wet-side HVAC, boilers, furnaces, atmospheric tanks and bins, chillers, structure and supporting structure. water heaters, heat exchangers, evaporators, air separators, manufacturing Where the weight of the supported structure 1.0 2.5 or process equipment, and other mechanical components constructed of is large as compared to the weight of the high deformability materials. supporting structure (greater than or equal ® to 25 percent of the combined weight of Figure 4: From ASCE 7-05 Table 13.6-1 the nonbuilding structure and supporting structure), it is expected that the combined because of transportation loadings. It is the Design of Items Which Can response could be significantly affected by authors’ opinion that transportation design Be Either a Nonstructural the combined response of the supported and loads are usually sufficient to assure adequate supporting nonbuilding structure. There are seismic performance in lower areas of seis- Component or a two analysis options that are permitted to be micity (structures assigned to Seismic Design Nonbuilding Structure Categories A, B or C) if the module is not used for this situation, and they are set forth Now that the differences between nonstruc- stiffened or braced in anyway for transporta- in ASCE 7-05 Section 15.3.2. tural components and nonbuilding structures tion. In higher areas of seismicity (structures have been described, it is appropriate to take assigned Copyrightto Seismic Design Categories D, E Equipment Modules a look at the apparently ambiguous items (the or F), seismic design of the primary structural overlap items in Figure 3, page 19). Table 1 (Equipment Skids) frame of the modular unit should be demon- provides discussion on these items. Equipment modules are currently not ex- strated. Obviously if a modular unit doesn’t plicitly (but implicitly) covered by ASCE weigh much, for example 400 pounds, it does 7-05, and therefore a suggested seismic design not make sense to require a design. On the Conclusion approach is provided in this article. Some- other hand, if a modular unit weighs 2000 The foregoing article provides guidance on times these modules have exterior coverings pounds, it is prudent to design for seismic how the authors believe items that could be and one could consider them as very large loads. In such a case, the primary support identified as either nonstructural components “black boxes”. There’s a certain inherent rug- members should be designed in accordance or nonbuilding structures can be treated from gedness of equipment modules because these with ASCE 7-05 Chapter 13, and ap and Rp a seismic design perspective. Because of the preassembled modular units are typically values should be the same as that for the en- wide variety of items, it is extremely difficult transported on a truck and therefore must try from ASCE 7-05 Table 13.6-1 shown in to write all-inclusive definition rules within have a certain level of inherent ruggedness Figure 4. the code. It is hoped that the guidance pro- vided along with the application of a good dose of common sense will lead users to the magazineappropriate treatment.▪ S T R U C T BobU Bachman, S.E., isR a licensed StructuralE Engineer with offices in Laguna Niguel, California. He chaired the American Society of Civil Engineers ASCE 7 Seismic Task Committee during the development .org of ASCE 7-02 and ASCE 7-05. He is a member of the NEHRP Recommended Provisions Update Committee and chaired STRUCTUREmag the NEHRP Recommended Provisions TS- www. 8 subcommittee. Ms. Dowty, S.E., a registered civil and in the State of California, is a project manager with S.K. Ghosh Associates, Inc. She has over twenty years experience in the administration and development of building code provisions. In Wayne Lyman Morse U.S. Courthouse | Eugene, Oregon recent years she has played an active role in

ADVERTISEMENT - For Advertiser ADVERTISEMENT Information, visit the development of structural provisions for the International Building Code, serving as the Structural Committee Secretariat. She come work with us | www.kpff.com served as the consultant for the reformat of the ASCE 7-05 seismic provisions and is currently serving on the California

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STRUCTURE magazine 20 July 2008

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Inside_Cover_Outside_Cover_Perfe1 1 5/29/2008 10:42:58 AM Table 1: Discussion of Items Which Can Be Either Nonstructural Components or Nonbuilding Structures.

Ch 13 Ch 15 Item Discussion Rp-value R-value Billboards If the item is attached to a structure, then it is considered a nonstructural component and 2.5 3.5 and Signs Chapter 13 is used. If the item is attached and supported by another structure, it may be of such a size and weight that it needs to be treated as a nonbuilding structures supported by ® other structures with the seismic design forces determined in accordance with Section 15.3 Bins 1.0 2 or 3 which refers back to Chapter 13. If the item is assembled and is a free standing, ground- supported structure, then it should be treated as a nonbuilding structure and Chapter 15 should be used. There are many types of chimneys ranging from residential to industrial chimneys. A attached to a structure may be of such a size and significance that it can be considered an architectural nonstructural component and designed in accordance with Chapter 13. Industrial, institutional and commercial chimneys that are attached and Chimneys varies 3 supportedCopyright by other structures may be of such a size and weight that they need to be considered nonbuilding structures supported by other structures with the seismic design forces determined in accordance with Section 15.3 which refers back to Chapter 13. Freestanding industrial, institutional, and commercial chimneys, on the other hand, are typically of a size that they are considered nonbuilding structures and designed in accordance with Chapter 15.

They are usually The support structures for conveyors which are used in large industrial complexes such as considered surface mining facilities typically qualify as nonbuilding structures similar to buildings. There “nonbuilding are, however, smaller manufacturing, processing and material handling conveyors which can Conveyors 2.5 structures similar be transported in a truck in one piece and would qualify as a nonstructural component. In to buildings” the case where conveyors are designed as nonbuilding structures in accordance with Chapter except for the 15, the bracing and anchorage for the actual mechanical workings should be designed in mechanical parts. accordance with Chapter 13. If the is shop fabricated and transported in a truck, it is considered a nonstructural component and designed in accordance with Chapter 13. If it is self- Cooling Tower 2.5 or 1.0 3.5 supporting and field erected, then it is considered a nonbuilding structure and designed in accordance with Chapter 15. Stacks that are supported by or attached to a structure are considered nonstructural magazinecomponents and are designed in accordance with Chapter 13. Stacks that are free standing or Stacks 2.5 or 1.0 3 guyed-supported at grade are considered nonbuilding structures and designed in accordance S T R withU Chapter 15. C T U R E It is recommended that tanks which are small (5 feet or less in diameter), shop fabricated and transported to the site in one piece be considered nonstructural components and designed in accordance with Chapter 13. It is recommended that tanks which are larger in size (greater Tanks 1.0 varies than 5 feet in diameter) and constructed at the jobsite be considered nonbuilding structures and designed in accordance with Chapter 15. Should such a larger tank be installed within a building or on the roof, then design forces may need to be determined in accordance with Section 15.3 which refers back to Chapter 13. A tower is typically shop fabricated and shipped to a site in pieces to be field erected. As such, they are considered nonbuilding structures. But there are times when a tower is small enough and transported in one piece that it qualifies as a nonstructural component. If the Towers 2.5 or 1.0 varies tower is attached and supported by another structure, it may be of such a size and weight that design forces may need to be determined in accordance with Section 15.3 which refers back to Chapter 13.

If the vessel is less than 10 feet tall, it can typically fit within a building and is considered a nonstructural component. If the vessel is more than 10 feet tall, it most likely should be considered a nonbuilding structure. Vessels that are power boilers typically qualify as a Vessels 2.5 or 1.0 varies nonbuilding structure. Free standing vessels should typically be considered nonbuilding structures. If the vessel is attached and supported by another structure, it may be of such a size and weight that design forces may need to be determined in accordance with Section 15.3 which refers back to ASCE 7-05 Chapter 13.

Reprinted with permission from ICC Building Safety Journal, April/May 2008.

STRUCTURE magazine 21 July 2008