07_may_282_298

228822 ✦✦ IIrroonn && SStteeeell TTeecchhnnoollooggyy

The current seismic design provisions inthe United States and Canada were writ-

ten predominantly to address commercial andinstitutional buildings. Industrial buildingshave geometries, framing systems, mass char-acteristics, load types and magnitudes, and

stiffness properties that may vary significantlyfrom those of typical commercial or institu-tional buildings. These characteristics mayinfluence the expected performance of thesebuildings when subject to a seismic event. Thenormal design procedures presented in thebuilding codes for both the United States andCanada do not fully acknowledge these differ-ences, creating uncertainty and problems forthe engineer designing these facilities.

Part One of this paper will focus on seismicdesign for industrial buildings. This willinclude:

• A brief description of current seismicbuilding design procedures in theUnited States and Canada. This discus-sion will be primarily a philosophicaldescription of these design procedures.It is assumed that the reader is some-what familiar with the seismic designrequirements in the referenced codes;therefore, this discussion will not beexhaustive.

• A discussion of the previously men-tioned characteristics of industrialbuildings and how they might affect the

performance of the primary structuralsteel system in a seismic event.

• A listing of publications that theauthors have found regarding or relat-ed to seismic design of industrial build-ings.

• Strategies for designing steel-framedindustrial buildings using the most cur-rent edition of the predominant build-ing code in the United States (IBC2003) and the Canadian Building Code(NBCC 1995). IBC was recently updat-ed, and a 2006 edition is now available.The NBCC has been updated, with a2005 edition recently made available tothe general public. Relevant changesincluded in these updates, which affectthese strategies, will be discussed.

• A brief discussion of current researchregarding seismic design for industrialbuildings, and a discussion of addition-al research and development necessarywith regard to this topic.

Part Two of this paper will focus on self-sup-porting, nonbuilding structures often encoun-tered in industrial facilities. This will includesilos and bins, elevated tanks and ground sup-ported conveyors. Included in this discussionwill be:

• A brief description of current seismicbuilding design procedures for thesestructures in the United States andCanada. Similar to Part One, the proce-dures discussed will be those presentedin IBC 2003 and NBCC 1995. Again, rel-evant revisions that are included in IBC2006 and NBCC 2005 will be men-tioned.

• A listing of standards available for thedesign of these nonbuilding structures(in addition to the provisions providedin IBC and NBCC).

Industrial Building Design —Seismic Issues

This paper discusses current seismic provisions for the

design and construction of steel-framed industrial

buildings. Also discussed are current design codes for,

and the design of, nonbuilding structures often

contained within these facilities.

Authors

JJoohhnn AA.. RRoollffeess (left), vice president, Computerized Structural Design, Milwaukee, Wis. ([email protected]), and RRoobbeerrtt AA.. MMaaccCCrriimmmmoonn (right), senior civil/structural consultant — industrial andregional projects, Hatch Acres, Niagara Falls, Ont., Canada ([email protected])

THIS ARTICLE IS AVAILABLE ONLINE AT WWW.AIST.ORG FOR 30 DAYS FOLLOWING PUBLICATION.

MMaayy 22000077 ✦✦ 228833

PPAARRTT OONNEE:: SSEEIISSMMIICC DDEESSIIGGNN FFOORRIINNDDUUSSTTRRIIAALL BBUUIILLDDIINNGGSS

SSeeiissmmiicc RReeqquuiirreemmeennttss ppeerr tthhee UU..SS..BBuuiillddiinngg CCooddee,, 22000033 EEddiittiioonnChapter 16 of the 2003 IBC addresses struc-tural design. Applicable design load combina-tions, seismic design loads and design criteriaare presented in this chapter. In manyinstances, IBC defers to design requirementsprovided in ASCE 7-02, Minimum Design Loadsfor Buildings and Other Structures. Seismicdesign in accordance with ASCE 7-02 is alsolisted as an accepted alternative.

The seismic design requirements in the2003 IBC and ASCE 7-02 are based primarilyupon the 2000 edition of the NationalEarthquake Hazards Reduction Program’s(NEHRP) Recommended Provisions for SeismicRegulations for New Buildings and OtherStructures (FEMA 368, Commentary is FEMA369). The start of discussion on seismic designrequirements as presented in theInternational Building Code and in FEMA 368should start with the purpose of these provi-sions. Specifically, as stated in FEMA 368 andin the Commentary to IBC 2003, the purposeof the provisions is:

1. To protect the health, safety and welfareof the general public by minimizing theearthquake-related risk to life.

2. To improve the capability of essentialfacilities and structures containing sub-stantial quantities of hazardous materialsto function during and after designearthquakes.

For most steel structures, inelastic behavioris expected if the building is subject to adesign-level earthquake. The ability of thestructure to withstand this inelastic behaviorwithout collapse is the premise for the majori-ty of the design criteria presented in these ref-erences. Essential facilities are designed forhigher forces and may have more stringentdesign requirements. Therefore, the expectedlevel of damage due to a design-level earth-quake for these facilities should be less andallow for the continued operation of that facil-ity. It is very possible that it may not be eco-nomically feasible to repair a building after adesign-level earthquake.

Understanding the premise that inelasticbehavior is expected in a structure designedto these provisions is paramount to under-standing the intent of the design require-ments. This behavior is acknowledged in thevarious analysis approaches prescribed to pre-dict earthquake forces in the building struc-ture. The most direct analysis approach forestimating both the dynamic and inelastic

responses of a building structure is to performa dynamic analysis (time history analysis),accounting for nonlinear or inelastic effects.Although this may be the most directapproach to predicting the expected behaviorof a structure to an earthquake event, mostengineers do not possess the analytical toolsand knowledge to perform such an analysis.Therefore, the most common approach is touse an Equivalent Lateral Force Analysis. Inthis approach, an elastic model of the build-ing structure is used, and the base shear asso-ciated with the design level earthquake (V) isapproximated as:

(Eq. 1)3

(Eq. 2)3

where

V = earthquake base shear,W = weight of structure considered during a

seismic event,R = response modification factor,T = fundamental period of the building struc-

ture,SDS and SD1 = earthquake spectral accelera-

tions associated with the building siteand

I = importance factor (used to prescribehigher forces for essential facilities).

In Equation 2, the response modificationfactor, R, represents an adjustment factorused with a linear analysis model to approxi-mate nonlinear dynamic response in thebuilding structure. Therefore, appropriatedetailing of the building structure is requiredto ensure that this approximation is justified.The nature of this “appropriate detailing” isthe design criteria included in IBC, ASCE 7and FEMA 368.

The response modification factor, R, incor-porates two effects: an overstrength factor anda ductility (or ductility reduction) factor. Theoverstrength factor accounts for the differ-ence in the force level required to collapse aframe and the seismic design force level forthat frame. This overstrength can be attrib-uted to the following:

1. Design efficiency — in general, membersare designed with capacities that areequal to or in excess of their design loads.

2. Drift limits for the building, imposed byseismic design criteria and/or serviceabil-ity limit states, result in larger member

(but not less than 0.44 S I)DS

CS

R

I

S

TR

I

sDS D=

⎛⎝⎜

⎞⎠⎟

≤⎛⎝⎜

⎞⎠⎟

1

V C Ws=


sizes than required for strength limitstates.

3. The nominal member strengths are larg-er than design strengths, due to factors ofsafety or resistance factors (Φ) and thefact that actual steel yield strengths aretypically higher than published for agiven grade of steel.

4. The building design may be governed byother load combinations, especiallywhere wind loads, gravity loads, andcrane loads (both vertical and horizon-tal) are high.

5. Elastic design methodologies define thestrength of a frame by the developmentof the strength of the weakest element (ascompared to the design force) in theframe. After the failure (flexural hinging,yielding, buckling, etc.) of this element,most frames have additional capacity andwill continue to resist load until enoughmembers have failed that the structurebecomes unstable and collapses. Thisanalysis is similar to plastic analysis meth-ods that have been used for years. Theexcess strength is expressed as the differ-ence between this collapse load and theload generating the first failure in anindividual element (hinging, yielding orbuckling).

The second effect included in the R factoris a ductility or ductility reduction factor. Thiseffect is associated with the following:

1. As the structure begins to yield anddeform inelastically, the natural periodof the building will increase. Thisincrease in period will result in decreasedmember forces for most buildings andwill prevent or reduce a resonantresponse in the building structure.

2. Inelastic action in members dissipatesenergy. This is often referred to as hys-teretic damping in the structure (where-as damping in the elastic model would beconsidered viscous damping).

The combination of these two effects wasconsidered in developing the R values thatare used today in the United States. The Rvalues currently used are based predominant-ly on engineering judgment (related princi-pally to commercial and institutional build-ings and framing systems common to thesebuildings) and the performance of variousmaterial and systems in past earthquakes.There has been discussion about quantifyingthese two effects individually and combiningthese two calculated values to establish amore refined approximation for an R valuefor a specific building. However, theCommentary to FEMA 368 states that insuffi-

cient research has been performed to allowimplementation of this type of philosophy,and the resulting complexity of design wouldbe problematic.

For steel buildings, Chapter 22 of IBC 2003requires that all buildings in Seismic DesignCategory D, E or F adhere to the requirementsof the 2002 AISC Seismic Provisions forStructural Steel Buildings (ANSI/AISC 341-02). For steel buildings in Seismic DesignCategory A, B or C, the engineer is given thechoice of using an R value of 3 and designingper the basic steel specification, or designingwith the higher R values provided in the seis-mic section of Chapter 16 and adhering to therequirements of ANSI/AISC 341-02. AISC hastypically advised the use of the former proce-dure, since seismic loads (even using thedecreased R value of 3) will oftentimes besmaller than lateral wind loads on the build-ing structures in the moderate or low seismicareas defined by these seismic design cate-gories. In addition, the increased complexityof design, fabrication and erection associatedwith the seismic provisions will oftentimes off-set any material savings obtained by the use ofthe higher R values.

Regarding changes included in the 2006IBC, the authors are aware of the followingmajor changes:

1. The 2006 IBC will completely defer toASCE 7-05 for seismic design require-ments.

2. ASCE 7-05 will incorporate changesincluded in the 2003 edition of FEMA368.

3. The 2005 AISC Seismic Provisions forStructural Steel Buildings will be refer-enced.

Although each of these changes may affectindividual design requirements, the basicdesign philosophy previously described hasnot changed.

SSeeiissmmiicc DDeessiiggnn RReeqquuiirreemmeennttss ppeerrtthhee NNaattiioonnaall BBuuiillddiinngg CCooddee ooffCCaannaaddaa,, 11999955 EEddiittiioonnThe basic design philosophy included in the1995 and 2005 National Building Code ofCanada (NBCC) parallels that used in theUnited States as discussed above, with a fewdifferences, as explained below.

The 1995 edition of this code approximatesearthquake loads using the following twoequations:

(Eq. 3)

VV

RUe= ⎛

⎝⎜⎞⎠⎟

MMaayy 22000077 ✦✦ 228855

(Eq. 4)

whereV = earthquake base shear,R = force modification factor,U = factor representing level of protection,

based on experience,v = zonal velocity ratio,S = seismic response factor,I = importance factor,F = foundation factor andW = weight of structure considered during a

seismic event.

In this equation, S is period-dependent andreflects spectral amplification of motion in thebuilding structure. R is oftentimes referred toas the “ductility factor” and is intended toreflect the capability of the structure to dissi-pate energy through inelastic behavior. The Ufactor incorporates overstrength and observa-tions on performance of various material andsystems in past earthquakes.

The 2005 edition of the NBCC incorporatesmany changes, bringing the approaches ofCanada and the United States closer together.The revised equation used to determine theearthquake base shear is as follows:

(Eq. 5)

whereV = earthquake base shear,S(T) = FaSa(T) or FvSa(T),Sa(T) = mapped spectral acceleration for

building location,Fa and Fv = functions of site class (soil type)

and intensity of ground motion,Mv = a function of T, type of system and

shape of response spectra curve, esti-mating higher mode effects in buildingstructures,

IE = importance factor,Rd = response modification factor associated

with ductility of frame andRo = response modification factor associated

with estimated overstrength of frame.

An explanation of many of the majorchanges in the 2005 edition is as follows:

1. Revised approach to incorporate newlymapped spectral accelerations, SDS andSD1 (same values as used in the UnitedStates). These spectral accelerationsdefine the shape of the site-specific, peri-od-dependent response spectra for agiven site.

2. Changed the basis for a design-level eventto a probability of exceedance of 2 per-

cent in 50 years (versus 10 percent in 50years in 1995 edition). This is similar tochanges introduced in the 2000 IBC inthe United States and is based on the goalof providing a more uniform basis for thefactor of safety against collapse. This oftenresults in higher seismic design forces inareas where significant earthquakes havehappened but are infrequent.

3. A more refined approach to evaluation ofthe site parameter (foundation factor)that takes into account the nature of thesupporting foundation material and themapped spectral accelerations. This issimilar to the approach used in theUnited States.

4. Delineation of the effects of overstrengthand ductility in developing a new expres-sion for the force or response modifica-tion factor. This is where the Canadiancode varies from the United States code.The Canadian approach independentlyquantifies both of these effects and usesthese independent values to calculate ajob-specific R value.

5. An elastic or inelastic dynamic analysis isrequired, except that an equivalent later-al force procedure is allowed for any ofthe following cases:

a. The building has a low seismic hazardas defined by the magnitude of SDS.

b. Regular structures less than 60 m(approximately 197 feet) in height.

c. Certain irregular structures less than20 m (approximately 66 feet) inheight.

The rationale for this criterion is thatdynamic analyses (especially linear, modalanalyses) are rather straightforward with cur-rent software used in the industry, and theseanalyses provide a much better approximationof the behavior of the structure in an earth-quake event. With regard to industrial build-ings, the majority of these buildings should beof a geometry that would allow the use of anequivalent lateral force procedure.

Since it has been demonstrated that theseismic design philosophies in the UnitedStates and Canada are very similar, and for thesake of brevity, the remaining discussion willreference only the United States designrequirements.

CChhaarraacctteerriissttiiccss ooff IInndduussttrriiaall SStteeeell--ffrraammeedd BBuuiillddiinnggss aanndd HHoowwTThheeyy MMiigghhtt AAffffeecctt tthhee SSeeiissmmiiccPPeerrffoorrmmaannccee ooff TThheessee BBuuiillddiinnggssThe following characteristics of a steel-framedindustrial building distinguish it from com-mercial and institutional buildings and affect

VS T M I W

R Rv E

d o

= ( )

( )

V v S I F We = ( )( )( )( )( )


the expected and/or required response ofthese structures to a design-level earthquake.

• Mass and stiffness properties of thebuilding frames.

• Building geometries.• Framing systems.• Bracing arrangements.• Loading considerations.• Lack of rigid diaphragm.• Lack of public exposure (sometimes).• Presence of hazardous material (some-

times).• Type of facade.

Each of these characteristics and the effectit has on the expected and/or requiredresponse of the structure to a design-levelearthquake is provided below.

Mass and Stiffness Properties of the BuildingFrame — Two types of industrial buildings areconsidered as follows. The first type is anindustrial building without heavy processloads supported on the building frame. Thesebuildings commonly have light metal wall androof panel systems and are therefore relativelylight. Examples of such buildings are typical“pre-engineered” metal buildings. Therefore,these types of industrial buildings have signifi-cantly less weight or mass (per unit volume) tobe considered in a seismic event as comparedto commercial or industrial buildings withsimilar footprints. Moreover, these buildingsmay be considerably more flexible than mostcommercial or institutional buildings, becausethe facade (metal skin) is less sensitive tobuilding movement than typical architecturalfacades. The net effect of these two differ-ences on the expected and/or requiredresponse of the structure to a design-levelearthquake is:

1. The calculated magnitude of seismic baseshears is smaller for these types of build-

ings. This is due to the relatively low seis-mic weight of the building and the high-er fundamental building period, posi-tioning the building structure on the lowend of the typical response spectra curve,as illustrated in Figure 1. Both of theseeffects are acknowledged in the currentseismic codes.

2. Seismic loads may still be overstatedand/or seismic design criteria may beoverly conservative for these types ofstructures. The rationale for this is, sincethe seismic loads are low, member sizes inthese frames are often governed by liveand wind load combinations; therefore,the overstrength component of theresponse modification factor may be sig-nificantly higher than that associatedwith a heavier building that would havehigher seismic shears. In addition, thefundamental period of these buildingsshould typically be larger than commer-cial or institutional buildings due to thehigher flexibility of these buildings.Building code requirements provide anestimated value for the fundamental peri-od of the building, Ta, based on empiri-cal studies and “typical” building massand stiffness characteristics. The calculat-ed period, T, to be used in design forstrength, is limited to Ta multiplied by afactor (Cu in IBC and 1.5 in NBCC). Thisupper limit on T for strength calculationsis based on the code committee’s desireto provide a conservative approximationof the period. For industrial buildings, itcould be argued that this limit is overlyconservative (see Figure 1 for a typicalresponse spectrum curve and variation ofseismic force with building period). Itshould be acknowledged that second-order effects are required to be includedin the design of the building structure. Itshould also be noted that seismic driftlimits provided in IBC 2003 (Table1617.3.1) do not apply to single-storybuildings if building facade and compo-nents have been designed or detailed toaccommodate the calculated drift.

The second type is an industrial buildingwith potentially high process loads on thebuilding structure. An example would be afossil-fueled power plant with a large boilerhung from the top deck of the structure.Another example would be a building sup-porting heavy cranes, where the weight of thecrane(s) is significant. In both of these cases,there is a large, relatively concentrated weightor mass positioned high on the structure. Thisweight or mass may exceed the weight of thesupporting building frame and facade. In thiscase, the predicted vertical distribution of the

Typical earthquake response spectrum curve.

Figure 1

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seismic shear over the height of the buildingmay be affected. This is really a mass irregu-larity. For example, in a building supportingheavy cranes with metal wall panels, the twopredominant mass elements on the buildingstructure are the cranes and the roof. The rel-ative height and magnitude of these two mass-es should influence the distribution of thedynamic earthquake forces over the height ofthe building structure. The equations used inthe building code to predict this distributionwere developed for typical mass and stiffnesscharacteristics in commercial and institutionalbuildings and may not be accurate for thistype of building. A dynamic analysis may bewarranted to more accurately predict this dis-tribution of forces.

Building Geometry — The primary differ-ences in geometry for industrial buildings dis-cussed in this section are the high floor-to-floor and floor-to-roof heights and the longroof spans that are often encountered inindustrial buildings. These geometries aredriven by process requirements in these facili-ties. The effect of this on the expected and/orrequired response of the structure to a design-level earthquake is:

1. Height requirements for various types ofindustrial buildings will often exceedheight limits imposed by the buildingcodes for common, less-expensive fram-ing systems (ordinary moment frame(OMF) systems and ordinary concentricbraced frame (OCBF) systems). Whetherthis consequence is warranted is ques-tionable. Commentary on the source ofthese height requirements is not readilyavailable, but is suggested to be based onengineering judgment of the code writ-ers. The mass and stiffness characteristicsof a one-story, 60-foot-tall industrialbuilding as compared to a five-story, 60-foot-tall commercial or institutionalbuilding are considerably different.Therefore, review of these height limitsfor industrial buildings is warranted.

2. Many industrial buildings have long roofspans that, for economical reasons, areframed with truss framing. The onlymoment frame system utilizing a trussthat is currently acknowledged by thebuilding code is a special truss momentframe, which utilizes a special interiorveirendeel or x-braced panel designedand constructed to force all inelasticbehavior into this panel (the fuse in thissystem), with the surrounding truss ele-ments not subject to inelastic behavior.The drawback to this system is that it islimited to trusses with spans less than or

equal to 65 feet and depths less than orequal to 6 feet. This still does not addressgeometry requirements for many indus-trial buildings. Therefore, the engineer isleft with the option of making the build-ing a braced building (may be difficultdepending on the aspect ratio of thebuilding and bracing restrictions) ordeveloping some other form of lateralload-resisting system that meets theintent of the code, and then explainingand defending that concept with localbuilding officials.

Framing Systems — As discussed in the previ-ous section, process requirements within anindustrial building structure will typicallydrive the geometry of the building structureand may also drive the type of framing systemused in the building structure. If the processrequirements and/or building geometry donot allow for the practical use of discreet brac-ing (either in plan and/or elevation), someform of rigid frame structure is often neces-sary to resist lateral loads in the building struc-ture. These rigid frame structures have certaincharacteristics that make them different fromrigid frame structures typically used in com-mercial and institutional buildings. Examplesare as follows:

1. The previously referenced “pre-engi-neered” metal building system, used inmany lighter industrial applications, typi-cally utilizes nonprismatic rigid framebuilding structures using members withslender elements (see Figure 2). Theexpected behavior of these types of rigidframes when subject to a design-levelearthquake does not necessarily matchthat of conventional steel rigid framesused in commercial and institutionalbuildings. Slender cross-section elementsmay buckle prior to developing full yieldstrengths of cross-sections, and, with non-prismatic frame profiles, expected loca-tions of flexural hinges in the frame maynot be obvious (similar to expectedbehavior for reduced beam sections inmoment frames). IBC 2003 precludes theuse of slender elements in specialmoment frames and requires tested con-nections for both special and intermedi-ate moment frames. Since the frame pro-files and member sizes vary considerablyfor the myriad of building geometriesand loadings included in metal buildingsystems, it is not practical to use testedconnections in these structures.Therefore, typical design methodologyused for buildings in Seismic DesignCategory D, E or F (where AISC Seismic


Provisions must be used) is to designthese frames as ordinary moment frames.With this approach, the building heightand roof dead load are limited by therestrictions applied to ordinary momentframes.

2. Crane runway systems are often includedin industrial building structures for use inmaterial handling. In these structures,the geometry of the building is common-ly defined by the dimensional character-istics of the crane. Examples of typicalbuilding geometries for crane buildingsare shown in Figures 3–5. When the mass

of the crane is supported on separatecrane columns that are independent ofthe lateral load-resisting system (seeFigure 3), the design of the rigid frame isrelatively straightforward, assuming that arational approach is provided for distrib-uting the lateral shear forces over theheight of the structure (see discussion in“Mass and Stiffness Properties of theBuilding Frame,” above). When thecrane vertical support system is integrat-ed with the rigid frame system, as shownin Figures 4 and 5, the column cross-sec-tion, stiffness and flexural strength vary

Typical metal building rigid frame.

Figure 2

Crane-supporting building with rigid frame and separate crane columns.

Figure 3

CL RIDGE

MMaayy 22000077 ✦✦ 228899

significantly both below and above thecrane runway. In these cases, the dynam-ic response of the structure will be affect-ed by the column properties, and thisshould be considered in the design of therigid frame. In heavy crane buildings, asshown in Figure 5, it is not uncommonfor the lateral load resistance to comesolely from the cantilevered, lacedcolumns. In first reviewing the various lat-eral load-resisting system classificationscontained in IBC 2003 (Table 1617.6.2),it would seem logical to classify this sys-tem as an inverted pendulum, can-tilevered column system, having a rela-tively low R value of 2.5. The resultingseismic forces in the building structuremay be significant (because of low Rvalue), and IBC and the AISC SeismicProvisions are not clear on detailingrequirements for this type of structure.

An additional consideration for crane-supporting buildings is the presence ofthe crane bridge and its effect on theresponse of the building structure.Specifically, beneficial or not, the cranebridge serves as an axial tie between thesupporting column lines that is limited byfrictional capacity of the crane wheel con-nection to the supporting rail and typesof crane wheels used, single-flange ordouble-flanged. (Single-flange wheels willrestrict relative movement in one direc-tion, whereas double-flanged wheels willrestrict relative movement in two direc-tions.) The presence of this axial tie inthe building structure may affect the

dynamic response of the building struc-ture to lateral seismic forces. The designengineer should consider this in thedesign of the building structure and, per-haps, if these forces are significant, com-municate these forces to the crane sup-plier responsible for the design of thecrane.

Crane-supporting building with stepped crane columns.

Figure 4

Heavy crane–supporting building with laced column system.

Figure 5


Bracing Arrangements — As mentioned earli-er, process layout within industrial buildingstypically dictates the framing geometry andsystems used in these structures. Similarly, thislayout affects where bracing can and cannotoccur. In multilevel industrial complexes(e.g., boiler buildings in power plants),acceptable bracing locations and configura-tions (both in elevation and plan) may varyfrom floor to floor, resulting in multiple brac-ing offsets and potentially other irregularitiesin the braced frame lateral load-resisting sys-tem for the building structure. In most com-mercial and institutional buildings, it is possi-ble to avoid or limit the extent of these irreg-ularities, whereas in industrial complexes, thismay be difficult if not impossible. In designingthese types of facilities, the design engineerneeds to be cognizant of these potential irreg-ularities, try to avoid them if possible, andaddress them if it is not possible to avoid.

Loading Considerations — When designingindustrial complexes for seismic loads, twoloading issues need to be considered. Thefirst issue is what masses or weights should beincluded in W, the effective seismic weight ofthe building structure used to calculate theseismic shear for the building structure. Asdefined in IBC 2003, the seismic weight is toinclude the weight of the building structure,25 percent of storage live loads, the weight ofpermanent equipment, and 20 percent of theflat roof snow load where this load exceeds 30psf. Some judgment is required from thedesign engineer regarding how much processloading should be included in the effectiveseismic weight and what crane loads shouldbe considered for single-aisle or multiple-crane-aisle conditions. The second issue iswhat load combinations are pertinent forthese building structures. In this context,process loadings are typically considered tobe live loads, and IBC specifies load combina-tions that are to be considered. For live loadsless than 100 psf, IBC allows a reduction oflive load when considered in conjunctionwith earthquake loads. If the process loadingis well-defined and is often present on thebuilding structure, this reduction is not war-ranted. With regard to crane loads in combi-nation with earthquake loads, IBC does notprovide clear direction.

Lack of Rigid Diaphragm — Most one-storyindustrial buildings have some form of metalroof deck (either a metal deck cladding or ametal roof deck supporting a weather-resistantmembrane or topping). With the exception ofa standing seam metal roof cladding, most ofthese decks have diaphragm capability, withthe strength and stiffness of the diaphragm

dependent upon the deck profile and gauge,support spacing, and type and number of fas-teners. Lateral deflections of thesediaphragms may be appreciable; therefore, anoften-questioned aspect of design is whetherthese diaphragms are rigid or flexible. Fromthe definition of a rigid diaphragm, thedeflections of the diaphragm are not consid-ered significant in comparison to the deflec-tions of the vertical lateral load-resisting sys-tem. A flexible diaphragm is defined as havingdeflections that are considered significant incomparison to the deflections of the verticallateral load-resisting system. IBC 2003 definesa flexible diaphragm as having a lateral deflec-tion of more than two times the average storydrift of the vertical elements of the lateralload-resisting system. For diaphragms catego-rized as rigid, the diaphragm is consideredrigid for the purpose of distribution of lateralstory shears and torsional moments. Fordiaphragms categorized as flexible, storyshears are distributed to vertical lateral load-resisting elements, assuming that thediaphragm is flexible and therefore a simplespan horizontal element between vertical lat-eral load-resisting elements.

Standing seam roofs are very popular inpre-engineered metal buildings and, in somecases, rehabilitation work, where they areapplied over existing deteriorated roofs.These roofs are a special type of metal deckcladding using formed metal sheets with side-laps joined together and supported on clipsconnected to the supporting roof structurebelow. The nature of this system allows forindependent movement parallel to the sheetbetween each sheet and between the sheetsand supporting clips. This independent move-ment is advantageous in that it allows for dif-ferential thermal movement between the roofpanel and supporting structure. Due to thenature of this system and the connectivitydescribed above, this roof does not typicallyprovide appreciable diaphragm strength orstiffness, and a separate discreet bracing sys-tem is required to transfer lateral loads to thevertical lateral load-resisting systems in thebuilding. In most instances, these roofs areassumed to have sufficient subdiaphragmstrength to span to loading points for the dis-creet bracing system.

Lack of Public Exposure (Sometimes) —Industrial buildings are often located in indus-trial parks, and the population of these build-ings may be considerably smaller than expect-ed in a commercial or institutional building.Therefore, a legitimate question is whether areduced level of design is warranted in thesestructures. Using the design approach cur-rently in building codes, this would be a

MMaayy 22000077 ✦✦ 229911

potential argument for a reduced importancefactor for these types of buildings. This wouldobviously be associated with number of occu-pants in the building structure, presence ofhazardous materials in the building structure,and whether the particular facility would beassociated with an essential operation after anearthquake event.

Presence of Hazardous Materials — As dis-cussed in the previous section, the presence ofhazardous materials in a facility is always aconsideration in design. The current buildingcode requirements assign more stringentdesign requirements (higher loads by virtue ofhigher importance factor) to facilities con-taining such substances. Chemicals and wasteproducts generated in these facilities are like-ly candidates for hazardous material. Section307 of IBC 2003 defines what materials areconsidered hazardous.

Type of Facade — Industrial buildings com-monly use metal wall panel systems that, whensubject to high distortions due to large drifts,do not present a life safety hazard due to bro-ken and falling debris. Excessive drift mayresult in elongated holes in the wall systemand failure of some fasteners, but this wouldnot typically pose a life safety problem.Conversely, architectural facades — includingconcrete, masonry and/or glass — may deteri-orate if the supporting building structuredeforms too much, and failure of these sys-tems may pose a life safety hazard to people inor near the building structure.

EExxiissttiinngg PPuubblliiccaattiioonnss RReeggaarrddiinnggSSeeiissmmiicc DDeessiiggnn ooff IInndduussttrriiaallBBuuiillddiinnggssPrevious sections of this paper have refer-enced design codes and standards, includingIBC 2003, ASCE 7-02, ASCE 7-05, FEMA 368and 369, ANSI/AISC 341-02, ANSI/AISC 341-05, NBCC-1995, NBCC-2005, CSA and CISC(specifically CSA Standard S16-01, whichaddresses limit state design of steel structures,including seismic design requirements).Additional references on seismic design ofindustrial buildings or related facilities thatthe authors have investigated include:

• Guidelines for Seismic Evaluation andDesign of Petrochemical Facilities, pub-lished by ASCE, 1997.

• Guidelines to Improved EarthquakePerformance of Electric Power Systems, pub-lished by ASCE, 1999.

• Seismic Design Guide for Metal BuildingSystems, published by the Metal BuildingManufacturers Association (MBMA),2000 IBC edition.

• Seismic Codes and Standard of EnergySupply Systems, published by the EnergyCommission, Ministry of EconomicAffairs, Taipei, China.

• Technical Report 13, Guide for the Designand Construction of Mill Buildings, pub-lished by the Association for Iron &Steel Technology, 2003.

SSttrraatteeggiieess ffoorr DDeessiiggnniinngg SStteeeell--ffrraammeedd IInndduussttrriiaall BBuuiillddiinnggssUUssiinngg CCuurrrreenntt BBuuiillddiinngg CCooddeessAs previously noted, the existing seismicdesign requirements were written predomi-nantly to address commercial and institution-al building structures. Previous discussionshave focused on characteristics of industrialbuildings that make the design of these struc-tures different for earthquake forces. Basedon these differences, it is clear that these pro-visions need to be amended to address thesetypes of building structures. Recognizing thatthese amendments are currently not availableand design engineers are faced with thedilemma of trying to apply the current seismicdesign requirements to industrial buildings,the following strategies and thoughts are pro-vided.

Characteristic 1 — Mass and StiffnessProperties of Industrial Buildings — The dis-cussion relative to R values and whether theyare appropriate to lighter industrial buildings(see earlier discussion) would need to beaddressed by future research and study. Sincethese structures are often more flexible thancommercial or institutional structures, itwould make sense to calculate a building peri-od (T), as opposed to using only the approxi-mate period (Ta) as calculated by the equa-tions in the building code. For a simple one-story building with the majority of the mass atthe roof level, the building period can be cal-culated as:

(Eq. 6)

where

m = mass at roof level = W/g (kips-sec.2/in.),g = acceleration due to gravity (386.4

in./sec.2) andk = frame lateral stiffness (kips/in.).

Further research and study may also focuson whether the code-prescribed limit on T(Tmax = CuTa) is necessary for these types ofstructures.

The mass characteristics of an industrialbuilding need to be evaluated to verify thatboth vertical and plan irregularities do not

Tm

k= 2π


exist. These irregularities could generateresponse (to a seismic event) in the buildingstructure that varies significantly from thatpredicted by the equations presented with theequivalent lateral force procedure in eitherIBC or ASCE 7. Both of these documentsdefine a vertical weight (mass) irregularity as astructure with an effective mass of any storymore than 150 percent of the effective masson an adjacent story (however, a roof that islighter than the floor below need not be con-sidered). If mass on an elevated floor or roofstructure is significantly heavier in one area ofthe building (as compared to the other areas),the building structure may be prone to poten-tial torsional irregularity. Both of these irregu-larities are defined in IBC and ASCE 7, withspecial analysis and design requirementsrequired if these irregularities exist. Specialconsideration should be provided to a crane-supporting building structure, where heavycranes contribute mass at an intermediateheight on the column. The equivalent lateralforce procedure provided in IBC and ASCE 7distributes the overall base shear to the vari-ous levels as a function of the mass and heightassociated with each of these levels per the fol-lowing equations:

(Eq. 7)

(Eq. 8)

where

V = total base shear,Fx = force at level x,wi and wx = the portion of the total effective

seismic weight of the structure (W) locat-ed or assigned to level i or x,

hi and hx = the height from the base to level ior x,

k = exponent = 1 for structures with funda-mental period (T) less than or equal to0.5 second, and 2 for structures with fun-damental period (T) less than or equalto 2.5 seconds. If T is between 0.5 and2.5 seconds, k can be taken as 2 or deter-mined by linear interpolation.

Equation 8 may generate erroneous resultsfor mass located at an intermediate level on acolumn, especially when a stepped or lacednonprismatic column profile is used, as previ-ously discussed and illustrated. A dynamicanalysis should be performed in theseinstances to better determine the distributionof seismic shears over the height of the build-ing structure. After a representative numberof models are evaluated, rules of thumb may

be developed that would alleviate the need forthe dynamic analysis.

Characteristic 2 — Building Geometry — Aspreviously discussed, many one-story industri-al buildings exceed height limits allowed forstandard OMF and OCBF framing systems inSeismic Design Categories D and E. IBC 2003and ASCE 7-02 limit the use of OMF systemsin these Seismic Design Categories to one-story buildings with building heights less thanor equal to 35 feet, and where the dead loadof the walls and roof do not exceed 15 psf.These documents allow an increase in build-ing height to 60 feet when field-constructedmoment joints use bolted end plates, the roofdead load remains limited to 15 psf, and thewall weights more than 35 feet above the baseof the building do not exceed 15 psf. Thisincreased height allowance would appear tobe in deference to the metal building indus-try, where bolted end plates are commonlyused for moment connections. Similarly,OCBF systems are limited in height to 35 feet,but this height limit is increased to 60 feet forone-story buildings with roof dead loads lessthan or equal to 15 psf. Large industrialbuildings may exceed these height limits. Inthese instances, the designer is left with adilemma of using a special steel momentframe or special concentric braced frame lat-eral load-resisting system. This may be prob-lematic because special steel moment framesrequire the use of tested connections. Deepercolumn profiles could very well be requireddue to strength and drift requirements andthe tall floor-to-floor heights. Tested connec-tions for these deeper column profiles are notreadily available. The use of a special concen-tric braced frame may also be problematicdue to poor building aspect ratios and inabil-ity to locate bracing along interior columnlines (due to process requirements). Largebracing connections requiring localized rein-forcement of the bracing member in thevicinity of the connection are typical for anSCBF system. These connections are costly. Aspreviously explained, for tall, one-story build-ings, seismic base shears may be considerablyless than wind loads, and the available over-strength in the building when subject todesign-level earthquake forces may be signifi-cantly larger than the same height multistorycommercial or institutional building (see pre-vious discussion on components of R values).Therefore, it may be argued that seismicdetailing requirements are overstated forthese buildings.

Another characteristic of industrial build-ings included in this category is long roofspans that, for economical reasons, areframed with truss framing. If the building

Cw h

w hvx

x xk

i ik

=Σ

F C Vx vx=

MMaayy 22000077 ✦✦ 229933

geometry and construction dictate that theseframe systems be designed as moment framesystems, the current building code require-ments are not explicit on how to address thesetypes of frames.

A number of strategies may be appliedwhen dealing with these issues within the con-straints of existing published design criteria. Afew of these strategies might be as follows:

1. For buildings in Seismic DesignCategories A, B or C, no height limitsexist for steel framing systems if thedesigner chooses to use an R value of 3,categorizing the system as a “steel systemnot specifically detailed for seismic resist-ance.” As previously stated, it is typicallyrecommended that this approach be fol-lowed when applicable.

2. ASCE 7-05 has changed height limitrequirements for OMF systems in SeismicDesign Categories D and E to 65 feet fora one-story building when the roof deadload is less than 20 psf. No restriction ontype of moment connection is includedin this height limit extension. AlthoughASCE 7-05 will not be enforced until IBC2006 is adopted, this document has beenballoted and accepted by the authoritiesresponsible for these documents, andbuilding officials may be willing to acceptvariances based on this document. Thisincreased height limit, coupled with theincreased dead load allowance, shouldencompass the geometry of a large major-ity of industrial buildings.

3. ASCE 7-05 has amended the height limitrequirements for OCBF systems in one-story buildings in Seismic DesignCategory D or E to extend to 60 feet(same as for ASCE 7-02), but with deadload allowance increased to 20 psf. Asstated in the previous paragraph, the useof this provision is not currently anadopted building code provision, but thebuilding official may be willing to accepta variance consistent with this provisionbased on this document.

4. The 2005 edition of the NBCC listsheight limits for various systems.However, the Commentary to this docu-ment indicates that certain one-storybuildings are excluded from height lim-its. Outside of Canada, this could be usedonly as a basis for seeking a variance toIBC requirements. This discrepancybetween IBC and NBCC should be stud-ied for future editions of these two codesto develop a consistent rationale for one-story buildings.

5. If the building qualifies for use of“Simplified Analysis Procedure” and thisanalysis method is used to derive seismic

forces, height limits are increased to 240feet for buildings in Seismic DesignCategory D or E (refer to IBC 2003,Section 1617.6.2.4.1). For the types ofbuildings discussed in this paper, thiswould require that the building lateralload-resisting system use braced frames(OCBFs allowed) in both directions. Thismay be difficult, depending on the build-ing aspect ratio and whether bracing atinterior frame lines would be allowed bythe building owner.

6. ASCE 7-05 provides a new seismic designmethodology for nonbuilding structuressimilar to buildings. This methodologyprovides three different R values for agiven structural system. The first, highestR value is the same as that provided forbuilding structures and has the sameheight limits and detailing requirementsrequired by ANSI/AISC 341 (SeismicProvisions) for building structures. Thesecond, somewhat smaller R value(resulting in higher design forces) hasexpanded height limits but maintains theANSI/AISC 341 detailing requirements.The third, lowest R value removes heightlimits altogether and requires design perthe AISC specification (ANSI/AISC 360)but does not require the special detailingrequirements from ANSI/AISC 341. Theauthors believe that this provides a veryrational and inclusive approach for allforms of industrial buildings. Again, thisis not currently an adopted code option,but a building official may be willing toaccept a variance based on this publisheddesign philosophy.

7. For one-story buildings with long-spanroof trusses incorporated into momentframes, the authors suggest categorizingthe frame as an OMF with a strongbeam/weak column system. Therefore,when this frame is subject to design-levelearthquake forces, flexural hingingshould occur in the column. IBC andANSI/AISC 341 do not prohibit thisbehavior for OMF systems in one-storybuildings. The truss should be designedfor both gravity load and lateral load endmoments obtained from an appropriateframe analysis. The roof truss should bedesigned for end moments (due to earth-quake forces) consistent with developingthe maximum expected flexural capacityof the supporting column (1.1 RyMp).The top and bottom chord of the trussmust be connected to the column totransfer the corresponding forces.Research at Georgia Institute ofTechnology (Georgia Tech) that wassponsored by the Steel Joist Institute


(SJI) supports this design approach. Thisdesign approach will be included in anew release of SJI Technical Digest 11,“Design of Joist-Girder Frames.”

Characteristic 3 — Framing Systems —Common framing systems used in industrialbuildings were previously discussed. Strategiesfor designing these framing systems within theconstraints of existing published design crite-ria are as follows:

1. The Metal Building Manufacturer’sAssociation produced the publication,Seismic Design Guide for Metal BuildingSystems Based on the 2000 IBC. This publi-cation addresses design of pre-engi-neered metal building structures per pro-visions consistent with IBC 2000. Themajority of these provisions are consis-tent with IBC 2003. Height limit con-straints were discussed in the previoussection of this paper.

2. Crane-supporting building framing sys-tems using stepped or nonprismatic col-umn arrangements are technically irreg-ular with regard to seismic performanceand should be analyzed using a dynamicanalysis procedure. This analysis will pro-vide a more accurate estimate of poten-tial dynamic magnification (of groundmotion) in the structure and offer insightwith regard to the distribution of seismicshears over the height of the structure.With this information, the designer canbetter understand where inelasticdemand can be expected in the struc-ture, and appropriate detailing and con-struction can be specified for these areas.A two-dimensional model should be suffi-cient to obtain the desired information.Inclusion of an axial tie in the model rep-resenting the crane bridge may affectresults if there is a large disparity in thelateral stiffness of different column lines.The authors suggest the followingapproaches for seismic design of variouscrane building systems:

a. For buildings in Seismic DesignCategories A, B or C, no height limitsexist for steel framing systems if thedesigner chooses to use an R value of 3,categorizing the system as a “steel sys-tem not specifically detailed for seismicresistance.” As noted before, it is rec-ommended that this approach be fol-lowed when applicable.

b. For crane-supporting buildings withseparate columns supporting theweight of the crane system and rigidbuilding frames providing lateral sta-bility (see Figure 3), design the rigid

frame using the provisions of the build-ing code and ANSI/AISC 341.Consider the crane level to be onelevel in the building structure and theroof level to be the other.

c. For rigid frames with stepped cranecolumns (see Figure 4) using standardwide flange shapes (or comparableplate girder sections), fixed connec-tions between the columns and roofbeams, and either fixed or pinned col-umn base, consider the frame to be anOMF. Design the connections recog-nizing where inelastic demand may berequired. This would include the roof-beam-to-column connection, whichshould be designed in accordance withANSI/AISC 341. In addition, the con-nection detail between the lower andupper column shafts (at the step inprofile) should be detailed to provideductile performance. This shouldinclude using weld metal that meetsthe notch-toughness requirements pro-vided in ANSI/AISC 341, providingCJP welds and developing maximumexpected material strengths (1.1 RyFy)of each column profile at the splicelocation, and using weld access holesthat conform to ANSI/AISC 341requirements. Furthermore, whenfixed-base columns are used, the col-umn bases should be designed to pro-vide ductile behavior limited either bythe maximum expected flexuralstrength of the column profile (1.1RyMp) or the flexural capacity associat-ed with the maximum expected yieldstrength of the anchor rods (1.1RyFyAe), whichever is less.

d. For heavy crane–supporting buildingsusing cantilevered, laced columns (seeFigure 5), the effective flexural stiff-ness of the laced columns is typicallysignificantly higher than the single col-umn shaft extended above the lacedcolumn to the roof. The low R valuesprescribed for an inverted pendulumsystem in the building code wereintended to apply to fixed-based col-umn or cantilevered systems that arerelatively flexible. Laced columncrane-supporting building systems areusually designed in this fashion to limitmovement due to crane and windloads; therefore, this system is usuallyvery stiff. Based on this and the previ-ous discussion relative to overstrengthof these systems, the authors suggestcategorizing this system as an OMF,subject to the same seismic design fac-tors (R, Ω, and Cd) presented in the

MMaayy 22000077 ✦✦ 229955

building code. Buildings framed in thisfashion are often very tall and mayexceed height limits for an OMF.Rationale explained in the discussionon building geometry may be used toextend these height limits.Recognizing the large disparity instrength and stiffness between thelower, laced column shaft and the sin-gle upper column shaft, the connec-tion of the single upper column shaftto the laced column shaft would be anobvious potential location for inelasticdemand under seismic loading.Therefore, this connection should bedesigned to develop the maximumexpected flexural capacity of the singleupper column shaft (1.1 RyMp). Theoverall building stability is dependenton the integrity of the column basedetails; therefore, the anchor rods andcolumn base details should bedesigned to provide ductile behavior atthis location. The authors suggestdesigning the anchor development inthe supporting foundation and the col-umn base detail for the maximumexpected yield strength of the anchorrods (1.1 RyFyAe). In addition, theauthors recommend using amplifiedseismic loads (Ω level forces) for thedesign of the axial lacing membersbetween column shafts to attempt toprevent buckling or yielding of thesemembers and their connections. Sincethese buildings use nonprismaticcolumns, a dynamic analysis may benecessary to more accurately predictthe magnitude and distribution of seis-mic shears. However, realizing that thelateral stiffness of the lower, laced col-umn is significantly higher than theframing above the lower laced column,an approximate and conservativeapproach would be as follows:

i. Analyze the structure as two inde-pendent elements. Analysis A wouldbe for the building structure (and sup-ported mass) above the laced column.This structure would be modeled as aone story, fixed-base frame, assumingthat its support (the laced column) isrigid and, therefore, motions at thebase of the single shaft column areapproximately the same as the groundmotions. Analysis B would consideronly the laced columns, supportingthe mass of the building structure andthe supported crane.

ii. A building period and seismic shearwould be developed for the struc-

ture included in Analysis A. Thisshear would be used to design theportion of the structure above thelaced columns.

iii. A period for the laced columnswould be calculated for Analysis B.This period would be used to deter-mine the seismic shear associatedwith the mass of the crane. Thisshear would be applied at the top ofthe laced columns. The lacedcolumns would be designed for theshear and overturning momentfrom the base of the columnsincluded in Analysis A and the sheardetermined in Analysis B.

A simple approach to the design of thesebuilding structures (especially those that areirregular) would be to use the approach fornonbuilding structures similar to buildingspresented in ASCE 7-05. By choosing to use avery low R value (resulting in higher seismicdesign forces), height limits and ANSI/AISC341 detailing requirements could be avoided.This is not currently an adopted code option,but a building official may be willing toaccept a variance based on this publisheddesign philosophy.

Characteristic 4 — Bracing Arrangements —Discontinuities or offsets in bracing over theheight of a building structure can result inboth vertical and plan irregularities in thebuilding structure. These irregularities are dis-cussed in both IBC and ASCE 7. The designershould be aware of design requirements andrestrictions associated with these irregularities.

Characteristic 5 — Loading Considerations— The design engineer must use judgmentin evaluating what portion of process loadingis to be included in the seismic dead load andthe subsequent calculation of seismic shear.These process loads should be what would beexpected under normal operating condi-tions. Cranes supported by a building struc-ture represent a special condition, in that themass of the crane is typically significant andcan move over the extent of the crane run-way. AIST’s Technical Report 13 suggests thatcrane weights include only the dead load ofthe crane (not lifted load), positioned to gen-erate the maximum seismic effect. For build-ings with multiple cranes and/or multiplecrane aisles, this document states that allcranes should be positioned to generate themaximum seismic effect on the buildingframe. The authors believe that this is overlyconservative. Unless there is a logical reasonfor all cranes to be positioned to produce thiseffect (e.g., crane access platforms located in


a particular building bay or a bay devoted tocrane maintenance), the authors suggest thatthe design engineer consider one crane inone building aisle, positioned to generate themaximum seismic effect for any given ele-ment in a frame.

Characteristic 6 — Lack of Rigid Diaphragm— Previous discussion adequately describesthis issue. IBC and ASCE 7 identify the perti-nent design requirements.

Characteristic 7 — Lack of Public Exposure— Previous discussion adequately describesthis issue. Further refinement of importancefactors for this condition could be a point ofdiscussion for code officials in the future.

Characteristic 8 — Presence of HazardousMaterial — Previous discussion adequatelydescribes this issue. IBC and ASCE 7 identifythe pertinent design requirements.

Characteristic 9 — Type of Facade — As pre-viously noted, industrial buildings often willhave facade systems that do not pose a safetyrisk if the building experiences large driftsduring a seismic event. As noted previously,IBC 2003 has no seismic drift limits for thesetypes of buildings if the exterior wall systemhas been designed to accommodate thesedrifts. However, the vertical load carryingcapacity of all components of the buildingstructure must not be compromised when thebuilding structure experiences these drifts.Furthermore, mechanical and electrical com-ponents of the building structure and any sup-ported equipment are to be designed to meetcode anchorage and performance require-ments when the building structure experi-ences these drifts.

CCuurrrreenntt aanndd NNeeeeddeedd RReesseeaarrcchhRReellaatteedd ttoo SSeeiissmmiicc DDeessiiggnn ooffIInndduussttrriiaall BBuuiillddiinnggssAs previously mentioned, research was recent-ly completed at Georgia Tech on seismicbehavior of steel joist girder structures. Theresults of this research indicate that one-storyrigid frame structures using joist girders (orconventional trusses) can be adequatelydesigned for seismic performance consistentwith an ordinary moment frame structure asdefined by IBC and ASCE 7. SJI intends topublish a technical digest outlining the designrequirements for such a system. As previouslydiscussed, this will assist design engineers withthe design of one-story industrial buildingstructures with larger clear spans where trussframing is more economical.

Research is currently being performed onseismic design for industrial buildings byProfessor Robert Tremblay at EcolePolytechnique, Montreal, Canada. The focusof this research is on simplifying and develop-ing industrial building seismic design criteria,taking into account a number of the distin-guishing characteristics of these buildings asdiscussed previously in this paper.

A number of ideas or thoughts that requirefurther research or study have been proposedin the previous discussions included in thispaper. These are summarized below:

• Appropriate R values for industrialbuildings.

• Appropriate height limit requirementsfor one-story building structures.

• Possibility of extrapolating ASCE 7-05design methodology for nonbuildingstructures for use in design of industri-al building structures.

• Dynamic seismic response of industrialcrane building structures that usestepped crane columns.

• Further refinement of importance fac-tors, specifically for industrial buildingswith limited public exposure.

AISC is in the process of forming an ad hoccommittee on design of industrial buildingstructures and nonbuilding structures. Theseconcerns or topics may be addressed by thiscommittee.

PPAARRTT TTWWOO:: SSEEIISSMMIICC DDEESSIIGGNN FFOORRNNOONNBBUUIILLDDIINNGG SSTTRRUUCCTTUURREESS OOFFTTEENNEENNCCOOUUNNTTEERREEDD IINN IINNDDUUSSTTRRIIAALL FFAACCIILLIITTIIEESSAs previously noted, this discussion will be lim-ited to silos and bins, elevated tanks andground-supported conveyors. Here, silos andbins are defined as ground-supported or ele-vated storage vessels that are used to store solid(or granular) material. A tank will be definedas a vessel used to store liquid material.

CCuurrrreenntt CCooddee RReeqquuiirreemmeennttssIBC 2003 references Section 9.14 of ASCE 7-02 for seismic design requirements for non-building structures. ASCE 7-02 allows the useof other design methodologies that are docu-mented in approved national standards, withthe following provisions: (1) the seismicground accelerations, including modificationsfor site factors (soil conditions), match thosederived from ASCE 7-02, and (2) the seismicbase shear and overturning moment are atleast 80 percent of those derived from ASCE 7-02. A number of these standards are refer-enced in ASCE 7-02. For the nonbuildingstructure types noted above, some useful rec-ognized standards include:

MMaayy 22000077 ✦✦ 229977

Silos and Bins — ACI (American ConcreteInstitute) 313, Design and Construction ofConcrete Silos and Stacking Tubes. It should benoted that, even if the silo or bin is construct-ed from steel rather than concrete, this docu-ment can assist in the determination of seis-mic forces associated with the stored material.

Tanks• ANSI/AWWA (American Water Works

Association) D100, 1997, Welded SteelTanks for Water Storage.

• ACI 350R-89, Environmental EngineeringStructures.

• API (American Petroleum Institute)620, 1998, Design and Construction ofLarge, Welded, Low Pressure Storage Tanks.

• API 650, Welded Steel Tanks for OilStorage.

ASCE 7-02 includes provisions for non-building structures that are supported directlyon grade and nonbuilding structures support-ed by other structures (for this discussion, thebuilding structure). If the weight of the sup-ported nonbuilding structure is less than 25percent of the weight of the building structureand nonbuilding structure, the supportednonbuilding structure is considered to be acomponent with design forces and require-ments determined from the building compo-nent equations. If the weight of the nonbuild-ing structure is more than 25 percent of theweight of the building structure and non-building structure, the nonbuilding structureis to be included as part of a combined systemcomposed of the supporting structure andnonbuilding structure. The designer mustthen choose the appropriate R value, consid-ering both elements of the system. However, ifthe nonbuilding structure is not rigid (naturalperiod of nonbuilding structure less than orequal to 0.06 seconds), the maximum R valueallowed is 3.0.

The design forces on nonbuilding struc-tures are determined using the equivalent lat-eral force procedure documented for build-ing design with an adjusted minimum limit forthe seismic response coefficient, Cs. A dynam-ic analysis procedure is required only for non-building structures located at a site where SDS≥ 0.50 g and that are judged to be irregularand cannot be accurately modeled as a singlemass system. Seismic coefficients (R, Ω andCd) and height limits (as a function of seismicdesign category) are provided for varioustypes of nonbuilding structures. Two cate-gories of nonbuilding structures are “non-building structures similar to buildings” and“nonbuilding structures not similar to build-ings.” Nonbuilding structures similar to build-ings are intended to be detailed consistent

with the comparable detailing requirementsfor building structures. No specific detailingcriteria are provided for nonbuilding struc-tures not similar to buildings. However, thedesign engineer should attempt to recognizewhat element(s) in the structure are intendedto be the ductile fuse for the structure or whatelements should be specifically protected(often, connections and/or anchorage detailsfor the structure). These elements should bedesigned to allow for the development of theintended fuse. Surrounding and protectedelements should be designed strong enoughto force the fuse to occur in the intended ele-ments. If uncertainty exists relative to detail-ing requirements for connections or the sur-rounding elements in the structure (nonfuseelements), the authors suggest using Ω-level(i.e., amplified) seismic forces for the designof these connections or elements.

As previously noted, ASCE 7-05 provides anew seismic design methodology for non-building structures similar to buildings. Thismethodology provides three different R valuesfor a given structural system. The first, highestR value is the same as that provided for build-ing structures and has the same height limitsand detailing requirements required byANSI/AISC 341 (Seismic Provisions) forbuilding structures. The second, somewhatsmaller R value (resulting in higher designforces) has expanded height limits but main-tains the ANSI/AISC 341 detailing require-ments. The third, lowest R value removesheight limits altogether and requires designper the AISC specification (ANSI/AISC 360),but does not require the special detailingrequirements from ANSI/AISC 341. Theauthors have already stated their appreciationof this design philosophy. This is especiallytrue in nonbuilding structures where theexpense of design fees and sophisticated fab-rication costs associated with the design ofhigh-ductile seismic systems may not be war-ranted (i.e., these costs exceed the increasedcosts associated with using a less-sophisticateddesign and higher design forces).

As mentioned earlier, the purpose of thissection is to make the reader aware of non-building structure seismic design criteria,design requirements for these structures pro-vided in the building code, and other stan-dards that may be applicable. The seismicdesign for each of these nonbuilding structuretypes is discussed at length in the documentsnoted above. Also as noted above, an ad hoccommittee is currently being formed by AISCon the design of industrial buildings and non-building structures. It is assumed that seismicdesign of steel-framed, nonbuilding structureswould be an included area of study and reviewfor this committee.


CCoonncclluussiioonnCurrent building codes provide seismic designcriteria for buildings that are based on char-acteristics of typical commercial and institu-tional buildings. Industrial buildings havemany characteristics that distinguish themfrom commercial and institutional buildings.Therefore, the design of these facilities forseismic loads can be problematic, with thedesign engineer and building officials uncer-tain of how to apply the provisions provided inthe building code to these structures. Thesecharacteristics have been defined in thispaper, and the authors have provided strate-gies and thoughts on how these structuresmay be designed, accounting for these char-acteristics. Definitive answers are not providedto all design issues discussed, but the intent ofthis paper is to define these issues with thehope of generating discussion and futurestudy on these issues. As noted, IBC 2006 andASCE 7-05 provide refinements that assist withsome of these issues.

Many industrial facilities include nonbuild-ing structures that also require considerationfor seismic loads. The design of these struc-tures is typically based on a combination ofbuilding code requirements and recognizedindustry standards. This paper provided acursory review of these design requirements,with references to applicable recognizedstandards.

RReeffeerreenncceess11.. IBC 2003, International Building Code and

Commentary, International Code Council.22.. NBCC 1995 and 2005, National Building Code

of Canada, National Research Council of Canada.

33.. ASCE 7-02 and -05, Minimum Design Loads forBuildings and Other Structures, American Society ofCivil Engineers.

44.. ANSI/AISC 341-02 and -05, Seismic Provisionsfor Structural Steel Buildings, American Institute ofSteel Construction.

55.. CAN/CSA-S16-01, Limit States Design of SteelStructures, Canadian Standards Association.

66.. Seismic Design Guide for Metal Building SystemsBased on the 2000 IBC, Bachman, Drake, Johnsonand Murray (published by MBMA).

77.. Guide to Improved Earthquake Performance ofElectric Power Systems (1999), ASCE.

88.. Guidelines for Seismic Evaluation and Design ofPetrochemical Facilities (1997), ASCE.

99.. ATC19, Structural Response ModificationFactors, Applied Technology Council.

1100.. Heidebrecht, Arthur C., “Overview of SeismicProvisions of the Proposed 2005 Edition of theNational Building Code of Canada,” Canadian Journalof Civil Engineering, 30:241–254 (2003).

1111.. Mitchell, Dennis; Tremblay, Robert;Karacabeyli, Erol; Paultre, Patrick; Saatcioglu, Murat;and Anderson, Donald, “Seismic Force ModificationFactors for the Proposed 2005 Edition of the NationalBuilding Code of Canada,” Canadian Journal of CivilEngineering, 30:308–327 (2003).

1122.. Technical Report 13, Guide for the Design andConstruction of Mill Buildings, Association for Iron &Steel Technology, 2003.

1133.. ACI 313, Design and Construction of ConcreteSilos and Stacking Tubes, American Concrete Institute.

1144.. ANSI/AWWA D100 (1997), Welded Steel Tanksfor Water Storage, American Water WorksAssociation.

1155.. ACI 350R-89, Environmental EngineeringStructures, American Concrete Institute.

1166.. API 620 (1998), Design and Construction ofLarge, Welded, Low Pressure Storage Tanks,American Petroleum Institute.

1177.. API 650, Welded Steel Tanks for Oil Storage,American Petroleum Institute. ✦✦

This paper was presented at AISTech 2006 — The Iron & Steel Technology Conference andExposition, Cleveland, Ohio, and published in the AISTech 2006 Proceedings.

07_may_282_298

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