floor response spectra for seismic design of …2011/04/30 · floor response spectra for seismic...
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Floor response spectra for seismic design ofoperational and functional components ofconcrete buildings in Canada
M. Shooshtari, M. Saatcioglu, N. Naumoski, and S. Foo
Abstract: It has been observed during previous earthquakes that the damage to operational and functional components ofbuildings often result in more injuries, fatalities and property damage than those inflicted by structural damage. Opera-tional and functional components of a building include architectural components, mechanical and electrical equipment, aswell as building contents. A rational approach to designing these elements against seismic excitations involves the use offloor design spectra. The development of such design spectra for buildings in Canada constitutes the objective of the pa-per. This objective was achieved by conducting comprehensive analyses of selected reinforced concrete buildings, with dif-ferent lateral force resisting systems and building heights, under code compatible earthquake records for an eastern and awestern Canadian city. It was observed that the floor response was significantly amplified, especially for buildings withshort periods. Generally, the higher floors showed higher amplifications with differences in spectra between the floorsbeing more pronounced in low-rise buildings and shear wall buildings with short fundamental periods. The results provideda large volume of data to generate floor response spectra for the design of operational and functional components of build-ings in Canada. The details of the approach and the design spectra are presented in the paper.
Key words: earthquakes, floor response spectra, frames, nonlinear analysis, non-structural components, operational andfunctional components, response spectra.
Resume : Lors de seismes anterieurs, il a ete observe que les dommages aux composantes operationnelles et fonctionnellesdes batiments resultent souvent en plus de blessures, de deces et de dommages a la propriete que ceux causes par les dom-mages structuraux. Les composantes operationnelles et fonctionnelles d’un batiment comprennent les composantes archi-tecturales, les equipements mecaniques et electriques ainsi que le contenu des batiments. Une approche rationnelle pour laconception de ces elements pour resister aux seismes implique l’utilisation de spectres de reponse au niveau du plancher.L’objectif de cet article est le developpement de tels spectres de conception pour les batiments du Canada. Cet objectif aete atteint en realisant des analyses completes de batiments en beton arme selectionnes comportant differents systemes derenfort contre les forces laterales et differentes hauteurs de batiments, selon les enregistrements sismiques compatibles auxcodes pour une ville canadienne de l’Est et une de l’Ouest. Il a ete remarque que la reponse au niveau du plancher etaitgrandement amplifiee, particulierement pour les batiments a courtes periodes. Regle generale, les planchers plus hautsdans la structure ont montre de plus grandes amplifications et les differences entre les spectres etaient plus prononcees en-tre les planchers dans les batiments de faible hauteur et dans les batiments comportant des murs de contreventement acourtes periodes fondamentales. Les resultats ont engendre un grand nombre de donnees afin de generer les spectres de re-ponse au niveau des planchers pour la conception des composantes operationnelles et fonctionnelles des batiments au Ca-nada. Cet article presente les details de la methode et des spectres de conception.
Mots-cles : seismes, spectres de reponse au niveau des planchers, cadres, analyse non lineaire, composantes non structura-les, composantes operationnelles et fonctionnelles, spectres de reponse.
[Traduit par la Redaction]
IntroductionPerformance of buildings and their contents during pre-
vious earthquakes have clearly indicated the vulnerability ofoperational and functional components (OFC) of buildingsto seismic damage and life safety. Operational and func-tional components in buildings consist of (i) non-structuraland architectural components, such as infill walls, partitions,claddings, parapets, stairways, suspended ceilings, lightingsystems etc.; (ii) mechanical and electrical equipment, suchas pipes and ducts, escalators, central control panels, trans-formers, emergency power systems, fire protection systems,machinery, etc.; and (iii) building contents, including bookshelves, furniture, file cabinets, storage racks, etc. Poor per-formance of these components claims more injuries, fatal-
Received 03 February 2009. Revision accepted 12 August 2010.Published on the NRC Research Press Web site at cjce.nrc.ca on22 October 2010.
M. Shooshtari. Department of Civil Engineering, Bu-Ali SinaUniversity, Hamedan, Iran.M. Saatcioglu1 and N. Naumoski. Department of CivilEngineering, the University of Ottawa, Ottawa, ON K1N 6N5,Canada.S. Foo. Public Works & Government Services Canada,Gatineau, QC K1A 0S5, Canada.
Written discussion of this article is welcomed and will bereceived by the Editor until 30 April 2011.
1Corresponding author (e-mail: [email protected]).
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Can. J. Civ. Eng. 37: 1590–1599 (2010) doi:10.1139/L10-094 Published by NRC Research Press
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ities, property and financial losses during damaging earth-quakes than those inflicted by structural damage. Therehave been many incidences that a building, which sustainedonly minor structural damage, was deemed unsafe and unus-able as a result of extensive damage to its OFCs. Failure ofsuch components also poses serious problems for search andrescue operations after an earthquake, resulting in additionaland unnecessary increases in casualties. Equipment failuresand the debris caused by falling objects could critically af-fect the performance of vital facilities such as emergencycommand centres, fire and police stations, hospitals, powerstations and water supply plants. Furthermore, there may beadditional seismic risks associated with fire or leakage ofhazardous materials triggered by failures of OFCs.
Operational and functional component failures during pastearthquakes have been reported extensively in previousearthquake reconnaissance reports, including those byMcKevitt et al. (1995), Filitrault et al. (2001) and FEMA-74 (1994) with specific emphasis on the subject. Only abrief summary of previous observations from these publica-tions is presented here. The collapse of unreinforced brickparapets and exterior walls during the 1906 San Francisco,1925 Santa Barbara, and 1933 Long Beach earthquakes re-sulted in heavy casualties. Similar failures, including thefailures of interior fixtures were observed during the 1952Bakersfield, 1971 San Fernando, 1987 Whittier-Narrows,1989 Loma Prieta, and 1994 Northridge earthquakes. The1964 Alaska Earthquake exposed the vulnerability of mod-ern exterior precast wall panels, elevators and suspendedceilings. The 1971 San Fernando Earthquake triggered col-lapses of metal library shelving, failures of suspended ceil-ings, light fixtures and ducts for heating, ventilation and airconditioning. The 1989 Loma Prieta Earthquake resulted inthe collapse of heavy ceiling plasters and ornamentation,lighting grids and their suspended fixtures. This earthquakealso resulted in severe economic losses caused by damagedwater supply systems. During the 1994 Northridge Earth-quake, several major hospitals had to be evacuated, not be-cause of structural damage, but because of the failure ofemergency power systems, air control units, falling ceilingsand light fixtures. McKevitt et al. (1995) reported that fail-ure of most OFCs during the Northridge Earthquake couldbe attributed to lack of seismic restraints. They also reportedthat approximately 20% of deaths during the same earth-quake occurred because of poor performance and failure ofOFCs. In Canada, the 1988 Saguenay earthquake, the stron-gest event in eastern North America recorded within the last50 years, caused very little structural damage, but resulted ininjuries, property damage, and economic loss associatedwith the failures of OFCs in buildings.
Past experiences with OFC performances during previousearthquakes prompted research to develop asesimic designmethodologies, tools, guidelines, standards and codes forearthquake resistant OFCs. In the United States, several ap-proaches were developed and published. The InternationalBuilding Code (ICC-IBC 2006) requires the computation ofseismic forces applied on OFCs as well as maximum lateraldeflections to ensure survivability of these components. TheUS Federal Emergency Management Agency (FEMA) pub-lished design requirements for OFCs in new (FEMA-3021997; FEMA-303 1997) and existing buildings (FEMA-273
1997; FEMA-274 1997), as well as the seismic evaluation(FEMA 1998) and seismic rehabilitation (FEMA 1992,1994) of OFCs in buildings.
Research work related to this topic was conducted bySankaranarayanan and Medina (2007) and Medina et al.(2006). The focus of these studies was to determine the ef-fects of various parameters on the floor acceleration re-sponse spectra, i.e., the effects of the height of the buildingstructure, the floor level for which the spectra are calculated,the damping value for the response spectra, the fundamentalperiod of the building, and the level of the inelastic behav-iour of the building. The structural models used in the anal-ysis consisted of single-bay frames. Additional research wasconducted by Uma et al. (2010), Rodriguez et al. (2002),Chaudhuri and Villaverde (2008), and Marsantyo et al.(2000) for developing floor response spectra. A state of theart paper was published by Villaverde (1997) on the topic.
In Canada, the Canadian Standards Association (CSA)published the first edition of CSA S832 ‘‘Guideline for Seis-mic Risk Reduction of Operational and Functional Compo-nents (OFCs) of Buildings’’ in 2001 (CSA-S832 2001). TheStandard was subsequently revised in 2006 and was pub-lished under the title of ‘‘Standard for Seismic Risk Reduc-tion of Operational and Functional Components (OFCs) ofBuildings’’ (CSA-S832 2006). The CSA 832–2006 includestwo methods for evaluating the OFC behaviour: (i) prescrip-tive method and (ii) analytical method. The prescriptivemethod provides general concepts for design and perform-ance, including the details for fastening OFCs to prevent orminimize seismic movements, but otherwise relies on guide-lines published by the industry for specific equipment orcomponent manufactured. In the analytical method, theforces and (or) displacements of OFCs are calculated usinga simple method, such as the equivalent static force method,or a refined method involving response spectrum or timehistory analyses. The refined methods are mandatory forOFCs with a mass greater than 20% of that of the floor or10% of the total building mass.
The current National Building Code of Canada 2005(NRC 2005) addresses the design of non-structural compo-nents against seismic effects by classifying them into 21 cat-egories and by suggesting an empirical approach.Accordingly, these components must be designed to carry alateral force Vp defined in eq. [1] and applied at the centreof mass.
½1� Vp ¼ 0:3FaSað0:2ÞIESpWp
where, Wp is the weight of non-structural component, IE isimportance factor, Fa is acceleration-based site coefficientand Sa (0.2) is the spectral response acceleration value at0.2 s. The horizontal force factor Sp is computed by eq. [2],with minimum and maximum values of 0.7 and 4.0, respec-tively.
½2� Sp ¼ CpArAx=Rp
where Cp, Ar, Ax and Rp are component, component forceamplification, height and component response modificationfactors where the latter reflects the available ductility in thecomponent. These factors are defined for each of the 21 ca-tegories of OFCs specified in the code. For most OFCs, Vp
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is applied in the horizontal direction, except for horizontallycantilevered floors, balconies and other similar elementswhere the lateral force is to be applied in the vertical direc-tion as an upward and downward force. The code also em-phasizes that the lateral deflection of an OFC, computedusing an elastic analysis, should be multiplied by Rp/IE toobtain a realistic deflection within the inelastic range of de-formations.
While empirical methods have been developed in the pastand are used currently, a more rational approach may beused for designing OFCs in buildings, utilizing floor designresponse spectra. The NBCC-2005 reflects the most recentseismic hazard data for building designs in the form of uni-form hazard spectra (UHS). However, floor design spectrafor OFCs, compatible with NBCC 2005, are currently notavailable for use in design. The current research program isan effort towards filling this gap and meeting the needs ofthe design profession.
The NBCC-2005 compatible floor response spectra weregenerated by Saatcioglu et al. (2008) for reinforced concreteframe buildings in Canada, as part of an earlier phase of thecurrent research program. The current phase includes addi-tional concrete frame buildings, as well as shear wall build-ings. A total of 180 nonlinear dynamic response historyanalyses were conducted for this purpose, using 30 code-compatible earthquake records for eastern and western Can-ada. The analyses provided acceleration time histories foreach floor of each building, which were then used to con-duct a statistical analysis to obtain floor response spectra atmean and mean plus one standard deviation. Floor designresponse spectra were then generated for the design of earth-quake resistant OFCs. Note that no dynamic interaction be-tween the OFCs and the floors was considered in thedevelopment of the floor response spectra, i.e., it was as-sumed that the masses of the OFCs are substantially smallerthan the mass of the supporting floor. The details of the pro-cedure are presented in the following sections.
Buildings selected for analysisA total of 12 reinforced concrete buildings, designed on
the basis of the seismic provisions of NBCC-2005, were se-lected. The buildings consisted of 5, 10, and 15 storeyheights. Both moment resisting frame and shear walls struc-tural systems were considered as lateral force resisting sys-tems. Consequently, three moment resisting frame buildingsand three shear wall buildings with three different buildingheights were considered in Vancouver and Ottawa, sepa-rately. The Vancouver buildings represented structures inwestern Canada, and the Ottawa buildings represented struc-tures in eastern Canada. The frame buildings in Vancouverincluded cases where the buildings were designed withoutdue considerations given to current drift limitations, andhence includes structures that may be representatives ofolder buildings built prior to the enactment of modern build-ing codes. Figures 1 through 3 show the floor plan and ele-vation views of buildings. The floor plans were selected tobe symmetrical to minimize the effects of torsion.
The analyses were conducted in the short direction ofplan. The participation of non-structural elements, such asarchitectural and masonry enclosures, and (or) partition
walls were not accounted for in seismic analysis. Therefore,the computed fundamental periods of buildings may be lon-ger than those with significant stiffening effects of non-structural components. The periods were computed with dueconsiderations given to the cracking of concrete, as per CSAStandard A 23.3 requirements (CSA A23.3 2004). Accord-ingly, the horizontal element (beam) and vertical element(column and wall) stiffness were reduced to 35% and 70%of their elastic, uncracked values, respectively. The build-ings in Vancouver were designed for full ductility, whereasthose in Ottawa were designed for nominal ductility, withelastic design force levels reduced by appropriate forcemodification factors. Within the NBCC-2005 requirements,this corresponds to the use of Rd = 4.0 and Ro = 1.7 forframe buildings and Rd = 3.5 and Ro = 1.6 for shear wallbuildings in Vancouver; and Rd = 2.5 and Ro = 1.4 for framebuildings and Rd = 2.0 and Ro = 1.4 for shear wall buildingsin Ottawa. Consequently, a higher reduction of forces wasapplied to Vancouver buildings relative to those in Ottawa.However, the design spectral values for Vancouver wereproportionately higher than those for Ottawa, resulting in es-sentially the same seismic design forces and element dimen-sions for buildings with the same heights in Vancouver andOttawa. The primary difference in design between the build-ings in western and eastern Canada was in the design anddetailing of reinforcement, reflecting different levels of duc-tility. This resulted in the same fundamental period for thesame structural type and height of buildings in Vancouverand Ottawa. The fundamental period values were 1.75 s,3.47 s, and 5.11 s, for 5, 10, and 15-storey frame buildingsand 0.44 s, 1.30 s, and 2.34 s for 5, 10, and 15-storey shearwall buildings, respectively.
All buildings were assumed to be located on firm soil(Class ‘‘C’’ in NBCC-2005), without the amplification ef-fects of soft soils. The force levels were based on buildingperiods computed by the empirical expressions suggested inthe code, increased to 150% and 200% of the empiricallycomputed values as permitted by the code because of thelonger periods computed by dynamic analyses.
Selection of ground motionsGround motion records for dynamic analysis were se-
lected to match the UHS given by NBCC-2005 for Vancou-ver and Ottawa. A total of 15 synthetic records, generatedby Atkinson and Beresnev (1998), were selected for eachcity with a probability of occurrence of 2% in 50 years, re-flecting different earthquake distance and magnitude rela-tionships. The magnitudes of records selected for Ottawawere 6.0 on the Richter scale for short events and 7.0 forlong events; and for Vancouver, 6.5 for short events and 7.2for long events. The distance for the short events varied be-tween 25 km and 50 km; and for long events between 50 kmand 100 km for both cities. Table 1 shows the characteristicof the synthetic records considered. Figure 4 shows the re-sponse spectrum for each earthquake record relative toUHS. Each record is labeled to reflect its magnitude and dis-tance. For example, M6-R25-1 indicates a record with mag-nitude 6 and distance 25 km. The short events are intendedto govern in the short period range, whereas the long eventsare intended to govern in the long period range.
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Dynamic inelastic response history analysesComputer software DRAIN-2DX (Prakash et al. 1993)
was used to carry out nonlinear time history analysis ofbuildings to generate floor response spectra. DRAIN-2DX isa general purpose dynamic analysis program that utilizes thestiffness method of structural analysis. Dynamic equation ofmotion is solved numerically through the step-by-step linearacceleration method. Three degrees of freedom were used ateach node, consisting of X and Y translations and R rotationabout the Z-axis. Flexural yield strengths for all structuralelements are defined as part of the parameters that definedthe hysteretic model. The element stiffness was definedwith due considerations given to concrete cracking. Theflexural rigidities were taken as 70% and 35% of those com-puted based on gross cross-sectional properties of vertical(columns and walls) and horizontal (beams) elements, re-spectively. Takeda’s hysteretic model (Takeda et al. 1970)was employed to describe the element stiffness during load-ing, unloading and reloading under earthquake excitations.Structural mass was assumed to be concentrated at eachfloor level and was specified at each node. Damping wasspecified as 5% of critical damping, consisting of stiffnessand mass dependent components.
The lateral force resisting systems were modeled as seriesof plane frames in the short direction, linked together withrigid links, ensuring equal horizontal displacements at joints
of the same storey. This implies that the floors were as-sumed to be infinitely rigid. Each building had 6 frames inthe short direction. All the interior frames were identical instrength and stiffness, and hence were lumped together as asingle frame, representing total strength and stiffness of allinterior frames. Similarly, the two exterior frames havingthe same properties were lumped together to form a singleframe representing total strength and stiffness of the exteriorframes. These two model frames were then linked to ensureequal displacements at floor levels. Each element of themodel was provided with a flexural spring at each end, al-lowing it to yield beyond the member yield capacity, whilealso incorporating the rules of the hysteretic model (stiffnessduring loading, unloading and reloading beyond the elasticrange). The elements were assumed to have sufficient ca-pacity to remain elastic in shear.
The model for each structure was subjected to the se-lected earthquake records to conduct dynamic inelastic re-sponse history analysis. The results indicated that thebuildings in Ottawa, representing eastern Canada, remainedelastic at all times, even though they were designed for in-elasticity and moderate levels of ductility. The maximumstorey drift ratios remained within 2.3% for frame buildingsand 1% for shear wall buildings. The frame buildings inVancouver developed inelasticity in some columns andbeams under the majority of earthquake records. The shearwall building in Vancouver only developed inelasticity in
Fig. 1. Typical floor plans for selected buildings: (a) moment resisting frame building; (b) shear wall frame building.
Fig. 2. Elevation views of interior and exterior frames of momentresisting buildings as well as interior frames of shear wall build-ings: (a) 15-storey; (b) 10-storey; (c) 5-storey.
Fig. 3. Elevation views of exterior frames of shear wall buildings:(a) 15-storey; (b) 10-storey; (c) 5-storey.
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the walls, under some of the ground motion records. Figure5 shows examples of hysteretic response in selected struc-tural elements. The analyses results provided response timehistories of floor accelerations for use in generating designfloor response spectra.
Floor response spectra
Dynamic analyses of 12 buildings under 15 earthquake re-cords resulted in a total of 180 analyses and 1800 floor re-
sponse spectra for frame and shear wall buildings located inOttawa and Vancouver, one spectrum for each floor of eachbuilding. The spectra for each floor were used to computethe mean spectrum. Floor response spectra were also con-structed for mean plus one standard deviation values to de-velop design floor spectra. Design spectra are commonlyspecified at mean plus one standard deviation level (Rose-nblueth 1980) to ensure that there is a relatively small prob-ability that the response will be above the specified designlevel. The mean plus one standard deviation level corre-
Table 1. The characteristic of 15 records selected for Ottawa and Vancouver.
Recordnumber
Ottawa Vancouver
M R (km)Peak acceleration(cm/s2) Scale factor M R (km)
Peak acceleration(cm/s2) Scale factor
1 6 25 582.79 0.58 6.5 25 586.84 0.722 6 30 422.13 0.80 6.5 30 523.51 1.003 6 30 512.36 0.80 6.5 30 526.83 1.004 6 30 461.16 0.80 6.5 30 567.54 1.005 6 30 430.94 0.80 6.5 30 380.05 1.006 6 40 299.81 1.26 6.5 40 335.38 1.497 6 40 231.14 1.46 6.5 40 288.34 1.458 7 50 498.89 0.58 7.2 50 357.06 0.559 7 50 619.76 0.42 7.2 50 366.64 0.55
10 7 70 295.3 0.80 7.2 70 241.55 1.0011 7 70 280.46 0.80 7.2 70 254.33 1.0012 7 70 335.54 0.80 7.2 70 225.94 1.0013 7 70 286.07 0.80 7.2 70 247.14 1.0014 7 100 237.81 0.92 7.2 100 146.82 1.3815 7 100 256.25 0.70 7.2 100 117.13 1.50
Note: M is Richter magnitude, R is distance and the scale factor is used to match the UHS (Atkinson and Beresnev 1998).
Fig. 4. Spectral accelerations for synthetic records: (a) short events in Ottawa; (b) long events in Ottawa; (c) short events in Vancouver;(d) long events in Vancouver.
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sponds to 84% of all spectral values being below the speci-fied level. This level was deemed appropriate for the devel-opment of design spectra. Figures 6–9 show spectral valuesfor all buildings.
The examination of response spectra indicates that there isa progressive increase in response going from the first floorto upper floors. The rate of response amplification is higherin low-rise buildings as compared to companion mediumand high-rise buildings. The 5-storey frame buildingsshowed an amplification of approximately a factor of 4 forthe roof response relative to that of the first-storey. Howeverthis amplification factor was approximately 3 and 2 for 10-storey and 15-storey buildings. It was further observed thatthe shear wall buildings analyzed developed higher flooramplifications than the companion frame structures having
the same height. This may be explained by the dependenceof the amplification factor on the fundamental period. In-deed, the amplification in floor response was higher forshort period structures. The response spectra further indi-cated higher amplifications for buildings in Vancouver,which were subjected to stronger ground motions relative tothose in Ottawa.
Figures 6 through 9 also include the UHS for respectivecities, depicting the amount of amplification observed ateach floor relative to ground. In general, the UHS was rep-resentative of the floor response spectra for lower stories,though in certain buildings, especially in shear wall build-ings, the UHS was above the floor spectra for lower floors.However, it was deemed appropriate to use the UHS as rep-resentative of the first floor response spectrum for design
Fig. 5. Sample hysteretic relationships for exterior frame elements of the 10-storey building in Vancouver: (a) first storey column, (b) firststorey exterior beam.
Fig. 6. Floor response spectra for frame buildings in Ottawa — mean plus one standard deviation values: (a) 5-storey building; (b) 10-storeybuilding; (c) 15-storey building.
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Fig. 7. Floor response spectra for frame buildings in Vancouver — mean plus one standard deviation values: (a) 5-storey building; (b) 10-storey building; (c) 15-storey building.
Fig. 8. Floor response spectra for shear wall building in Ottawa — mean plus one standard deviation values: (a) 5-storey building; (b) 10-storey building; (c) 15-storey building.
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purposes. A relationship was then derived for the amplifica-tion of roof response relative to UHS as a function of funda-mental period. This relationship is given as
½3� C ¼ 5:0� 0:5Ta
where Ta is the fundamental period of building housing theOFC in seconds, computed by an accepted method of me-chanics; and C is the response amplification factor for roof
spectral values relative to the UHS. The application of theamplification factor C provides roof design spectral accel-erations for buildings on firm ground, Sf(T). The amplifica-tion factor may vary with different soil conditions. The roofspectra established by the amplification factor specified ineq. [3] were observed to overestimate response in the shortperiod range. Hence a cut-off value was derived as
½4� SfðTÞ ¼ CSðTaÞ � BSð0:2Þ for T s < T � 2:0 s
where T is the period of OFC in the building, S(Ta) is the
Fig. 9. Floor response spectra for shear wall building in Vancouver — mean plus one standard deviation values: (a) 5-storey building;(b) 10-storey building; (c) 15-storey building.
Fig. 10. Comparisons of proposed roof design response spectra forbuildings considered for Vancouver in the current investigation.
Fig. 11. Proposed roof design spectra for buildings with a funda-mental period of 1.5 s.
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UHS value specified in NBCC-2005 for firm ground, C isthe amplification factor computed using eq. [3] and B is acoefficient that defines the maximum cut-off value. B = 1.5for buildings with lateral force resisting systems (LFRS)consisting of frames, and B = 2.5 for buildings with shearwall LFRS. Ts is equal to 0.04 s for Ottawa, representingeastern Canada, and 0.2 s for Vancouver, representing wes-tern Canada. The UHS values in NBCC for very short per-iod structures, corresponding to T < 0.2 s, is constant andequal to the UHS at T = 0.2 s. This is a conservative as-sumption, which may not have much effect on building de-sign, since there would be very few buildings with peirodsof less than T = 0.2 s. However, this is not the case forOFCs. Operational and functional components may be quiterigid, with periods of less than 0.2 s. Therefore, further re-finements were introduced to eq. [4] to reflect the computedfloor response spectra more accurately. Accordingly, thevariation of design spectra was suggested to change linearlybetween Sf(0.01) = D S(0.2) at T = 0.01 s and Sf(Ts) at T = Ts(where, Ts is defined above as 0.04 s for Ottawa and 0.2 s.for Vancouver). The coefficient D is defined as 2/3 forframe buildings and 1.0 for shear wall buildings. A linearinterpolation can be made for in-between floors between theroof design spectrum and the UHS representing the firstfloor spectrum. However, the design spectral values for in-between floors need not exceed the value specified for theroof.
The UHS is assumed to remain constant beyond 2.0 s.This was found to overestimate structural response in thelong period range. Further amplification of floor response inthis range was found to be overconservative. Therefore, it isrecommended that for T > 2.0 s, the floor response spectrachange linearly from Sf(2.0) at T = 2.0 s to the UHS valueat T = 5.0 s.
It is important to note that the floor spectra developed inthis study are intended for determining seismic forces actingon OFCs that are attached to the floors. Also, the floor spec-tra developed correspond to nonlinear response of the sup-porting structure under seismic motions compatible with thedesign spectrum for the location.
The proposed floor design spectra are compared inFig. 10 for the 6 buildings considered for Vancouver. Thecomparison indicates substantially higher amplification forshear wall buildings, relative to frame buildings, with theamplification being more sensitive to building height inframe buildings. The relative impact of eastern and westernseismicity on proposed roof design spectra is illustrated inFig. 11 for selected frame and shear wall buildings.
ConclusionsThe following conclusions can be derived from the re-
search project presented in this paper:
� Floor response spectra show amplified spectral accelera-tions relative to the ground spectral accelerations as de-scribed by UHS.
� The amplification of floor spectral accelerations is thehighest at the roof level, gradually decreasing towardsthe first floor. The UHS is representative of lower storeyspectra, and may be used approximately as the designspectrum for the first floor of a multistory building.
� Floor-to-floor amplification of spectral accelerations ismore pronounced in low-rise buildings and shear wallbuildings. The building period appears to play a dominantrole on floor amplification. Buildings with longer periodsshow lower values of amplification, indicating that floorresponse spectra at different floor levels may be ap-proaching each other for tall frame buildings with longperiods. The opposite is true for low-rise shear wallbuildings, for which higher amplification of floor re-sponse may occur between the first floor and the roof.
� Equation [4] developed as part of the current researchproject can be used for the type of buildings and loca-tions considered in Canada on firm ground, to generatefloor response spectra from UHS. The amplification maybe scaled down within the short and long period ranges,as UHS in these regions tend to over-estimate structuralresponse.
ReferencesAtkinson, G.M., and Beresnev, I.A. 1998. Compatible ground-mo-
tion time histories for new national seismic hazard maps. Cana-dian Journal of Civil Engineering, 25(2): 305–318. doi:10.1139/cjce-25-2-305.
Chaudhuri, S.R., and Villaverde, R. 2008. Effect of building nonli-nearity on seismic response of nonstructural components: Aparametric study. Journal of Structural Engineering, 134(4):661–670. doi:10.1061/(ASCE)0733-9445(2008)134:4(661).
CSA-S832. 2001. Guideline for seismic risk reduction of opera-tional and functional Components (OFCs) of buildings. Cana-dian Standards Association, Rexdale, Ont., Canada.
CSA A23.3. 2004. Design of reinforced concrete buildings. Cana-dian Standards Association, Rexdale, Ont., Canada.
CSA-S832. 2006. Standard for seismic risk reduction of operationaland functional components (OFCs) of buildings. Canadian Stan-dards Association, Rexdale, Ont., Canada, pp. 104.
FEMA-172. 1992. NEHRP handbook of techniques for the seismicrehabilitation of existing buildings. Federal Emergency Manage-ment Agency, Washington, D.C., pp. 208.
FEMA-74. 1994. Reducing the risks of nonstructural earthquakedamage. Federal Emergency Management Agency, Washington,D.C., pp. 139.
FEMA-273. 1997. NEHRP guidelines for the seismic rehabilitationof buildings. Emergency Management Agency, Washington,D.C., pp. 435.
FEMA-274. 1997. NEHRP commentary on the guidelines for theseismic rehabilitation of buildings. Emergency ManagementAgency, Washington, D.C., pp. 48.
FEMA-302. 1997. NEHRP recommended provisions for seismicregulations for new buildings and other structures, Part 1: Provi-sions. Emergency Management Agency, Washington, D.C.,pp.335.
FEMA-303. 1997. NEHRP recommended provisions for seismicregulations for new buildings and other structures, Part 2: Com-mentary. Emergency Management Agency, Washington, D.C.,pp. 366.
FEMA-310. 1998. Handbook for the seismic evaluation of build-ings: A prestandard. Emergency Management Agency, Washing-ton, D.C., pp. 288.
Filitrault, A., Christopoulos, C., and Stearns, C. 2001. Guidelines,specifications, and seismic performance characterization of non-structural building components and equipment. PEER Report2002/05, Pacific Earthquake Engineering Research Center, Uni-versity of California, Berkeley, Calif.
1598 Can. J. Civ. Eng. Vol. 37, 2010
Published by NRC Research Press
Can
. J. C
iv. E
ng. D
ownl
oade
d fr
om w
ww
.nrc
rese
arch
pres
s.co
m b
y 75
.86.
130.
80 o
n 04
/19/
11Fo
r pe
rson
al u
se o
nly.
ICC-IBC. 2006. International Building Code (IBC-2006), Interna-tional Code Council, U.S.A., p. 679.
Marsantyo, R., Shimazu, T., and Araki, H. 2000. Dynamic responseof nonstructural systems mounted on floors of buildings. Pro-ceedings of the 12th World Conference on Earthquake Engineer-ing, Paper No. 1872, Auckland, New Zealand.
McKevitt, W.E., Timler, P.A.M., and Lo, K.K. 1995. Nonstructuraldamage from the Northridge earthquake. Canadian Journal ofCivil Engineering, 22(2): 428–437. doi:10.1139/l95-051.
Medina, R.A., Sankaranarayanan, R., and Kingston, K.M. 2006.Floor response spectra for light components mounted on regularmoment-resisting frame structures. Engineering Structures,28(14): 1927–1940. doi:10.1016/j.engstruct.2006.03.022.
National Research Council. 2005. National Building Code of Ca-nada. National Research Council, Ottawa, Canada.
Prakash, V., Powell, G.H., and Campbell, S. 1993. DRAIN-2DX:Base program description and user guide. Version 1.10. Univer-sity of California at Berkeley, Berkeley, Calif.
Rodriguez, M.E., Restrepo, J.I., and Carr, A.J. 2002. Earthquake-induced floor horizontal accelerations in buildings. EarthquakeEngineering & Structural Dynamics, 31(3): 693–718. doi:10.1002/eqe.149.
Rosenblueth, E. 1980. Design of earthquake resistant structures.Pentech Press Limited, Plymouth, United Kingdom.
Saatcioglu, M., Shooshtari, M., Naumoski, N., and Foo, S. 2008.Development of floor design spectra for operational and func-tional components of concrete buildings in Canada. Proceedingsof the 14th World Conference on Earthquake Engineering, 12–17 October, Beijing, China.
Sankaranarayanan, R., and Medina, R.A. 2007. Acceleration re-sponse modification factors for non-structural components at-tached to inelastic moment-resisting frame structures.Earthquake Engineering & Structural Dynamics, 36(14): 2189–2210. doi:10.1002/eqe.724.
Takeda, T., Sozen, M.A., and Nielsen, N.N. 1970. Reinforced con-crete response to simulated earthquakes. Journal of the Struc-tural Division, 96(ST12): 2557–2573.
Uma, S.R., Zhao, J.X., and King, A.B. 2010. Seismic actions onacceleration sensitive non-structural components in ductileframes. Bulletin of the New Zealand Society for Earthquake En-gineering. 43(2): 110–125.
Villaverde, R. 1997. Seismic design of secondary structures: stateof the art. Journal of Structural Engineering, 123(8): 1011–1019. doi:10.1061/(ASCE)0733-9445(1997)123:8(1011).
Shooshtari et al. 1599
Published by NRC Research Press
Can
. J. C
iv. E
ng. D
ownl
oade
d fr
om w
ww
.nrc
rese
arch
pres
s.co
m b
y 75
.86.
130.
80 o
n 04
/19/
11Fo
r pe
rson
al u
se o
nly.