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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 Building. 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 buildings. Prior to adoption of the that is not similar to International Building Code (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 towers 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 tower. 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.

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