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EARTHQUAKE ACTIONS IN SEISMIC CODES: CAN CURRENTAPPROACHES MEET THE NEEDS OF PBSD?Julian J. BOMMER ∗ABSTRACTThe successful implementation of performance-based seismic design (PBSD) will require itsincorporation into seismic design codes in order to achieve application to all new constructionsand possibly also to existing buildings. Since PBSD has the objective of limiting structural andnon-structural damage under different levels of earthquake loading, the requirements for thespecification of design seismic actions inevitably exceed the current approach embodied innearly all design codes of an acceleration spectrum that approximates the uniform hazardspectrum for a return period of 475 years, modified to account for energy dissipation throughinelastic deformations. PBSD will require multiple levels of loading to be specified in codesand since the correlation between spectral acceleration and structural damage is poor theground motions will need to be represented in alternative formats, primarily displacements.Current code formats could be adapted to meet the needs of PBSD but the presentation of theseismic actions in this way could become rather cumbersome. At the same time, theintroduction of PBSD should be taken as an opportunity to review and improve the way inwhich earthquake ground shaking is characterized for design. Considering the requirements ofPBSD and the shortcomings in current code specifications, alternative formats for presentingseismic actions are proposed.Keywords: Seismic design codes; Earthquake actions; Performance-based seismicdesign.1. INTRODUCTIONPerformance-based seismic design (PBSD) is essentially the formalization of oftencited objectives of designing structures to withstand minor or frequent earthquakeshaking without damage, moderate levels of shaking with only non-structural damageand severe shaking without collapse and a threat to life safety (ATC, 1978). In theVision 2000 document (SEAOC, 1995) this is elegantly stated as the “coupling ofexpected performance level with expected levels of seismic ground motions”. Tworequirements regarding the representation of earthquake actions for PBSD are thenimmediately apparent: several levels of seismic shaking must be specified and the∗ Civil & Environ. Engineering, Imperial College London, SW7 2AZ, UK. Email:j.bommer@imperial.ac.uk469
ground motion must be given in a form that has a direct correlation with the behaviourof real structures, particularly in terms of the capacity to cause damage. This leads tothe question of whether current code formats for representing earthquake actions canbe directly adapted to the requirements of PBSD.The paper begins with a critical review of design code specifications of seismicactions, highlighting shortcomings even with regards to current design practice. Thethird section of the paper then briefly summarizes the requirements of PBSD in termsof earthquake actions. The fourth section then discusses possibilities for extendingcurrent code formats to cover the needs of PBSD and also explores alternative formatsthat could be used, both to address weaknesses in current approaches and to meetPBSD requirements.2. EARTHQUAKE ACTIONS IN CURRENT SEISMIC CODESMost earthquake-resistant design of structures is carried out by engineers withoutspecialist training in earthquake engineering by following the specifications andguidelines of design codes. To enable this, the codes must provide, in a simplified andaccessible manner, the nature of the ground shaking to be considered, the way theresponse of the structure to this shaking can be calculated, and the stress and/ordeformation criteria that the structure is required to meet under the specified actions.In the following sections, the way in which ground motions are specified for design incurrent codes — including a few recent innovations — are briefly reviewed.2.1 Design Levels of MotionThe first seismic design regulations to be based on a probabilistic seismic hazard mapappeared in ATC 3-06 (ATC, 1978). The hazard map for the USA, showing PGAvalues with a return period of 475 years, was taken from Algermissen and Perkins(1976). The return period of 475 years was the result of selecting 50 years as theexposure period, although it was acknowledged that “the use of a 50-year interval tocharacterize the probability is a rather arbitrary convenience, and does not imply thatall buildings are thought to have a design life of 50 years” (ATC, 1978). Algermissenand Perkins (1978) stated that “for structures which should remain operable afterlarge, damaging earthquakes, the 10 percent exceedance probability in 50 yearsseems reasonable”, although the choice of 10% was adopted on the rather arbitrarybasis of being a significance level often taken by statisticians “to be meaningful”(Perkins, 2004). A very interesting observation made in ATC 3-06 is that it was notdecided a priori to base the design seismic actions on the selected 475-year returnperiod: a map of effective peak acceleration was drafted for ATC 3-06 — “literallyhaving been drawn by a committee” (ATC, 1978) — and was found to be consistentwith the 475-year PGA map of Algermissen and Perkins (1976). On this basis the10% in 50 year map was adopted in ATC 30-6 and subsequently in the 1988 editionof UBC. The extensive commentary in ATC 3-06 provides a rational and honest470
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PERFORMANCE-BASED SEISMIC DESIGNCON
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CONTENTSTable of Contents..........
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REAL-TIME DYNAMIC HYBRID TESTING OF
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PREFACEThe workshop on “Seismic D
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LIST OF PARTICIPANTSSergio M. Alcoc
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RESOLUTIONSThe International Worksh
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CONCLUSIONS AND RECOMMENDATIONSThe
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nonlinear dynamic) and when they sh
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exists to develop testing protocols
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to be sent soon to the 28 members o
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factor γ I is 1.4 or 1.2 for essen
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i. The well-known relation µ θ -
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γ s =1.15. Values less than 1.0 me
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efore (factor α in Eq.(4)). Materi
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the force demand from the analysis,
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OVERVIEW OF A COMPREHENSIVE FRAMEWO
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ground motion Intensity Measure (IM
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2.2 Simulation of Engineering Deman
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describing the economic losses asso
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practice the localized gravity load
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Whereas financial and insurance org
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AN OUTLINE OF AIJ GUIDELINES FOR PE
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(7) a method of performance evaluat
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where, T: natural period of structu
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6. DAMAGE AND LIMIT DEFORMATIONSThe
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The limit inter-story deformations
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DirectionX-directionY-directionSkew
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HAZARD, GROUND MOTIONS AND PROBABIL
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of events with [X1>x 1 , X 2 >x 2 ,
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2.4 Option C: Sufficient IMs: Estim
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predictions and hence required samp
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PEER has put forward PBSA methodolo
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3.2.1 A DCF Displacement-Based Form
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parameter k (the slope of the hazar
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POST-EARTHQUAKE FUNCTION OF HIGHWAY
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ln( EDP) a b ln ( IM )= + (1)Probab
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terms of global and local bridge pe
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Figure 3. Bridge column component d
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5.2 Method B: MDOF Residual Displac
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calculated using a 2 dimensional mu
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MODELING CONSIDERATIONS IN PROBABIL
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location. Transverse reinforcement
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2.50.1000Spectral Accel. (g)2.01.51
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Results indicate that 33% of the re
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4.1.2 Elastic vs. Inelastic ModelsF
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The increased dispersion leads to h
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AN ANALYSIS ON THE SEISMIC PERFORMA
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The survey stood on the condition t
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who decide the design force levels
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It is interesting to clarify whethe
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concluded that the dependence of in
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Table 10. Problems of performance-b
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DEVELOPMENT OF NEXT-GENERATION PERF
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ground shaking hazard, probable str
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Vulnerability of buildings to losse
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Peak Interstory Drfit Ratio0.120.10
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Conditional Probability ofDamage St
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Probability of Non-Exceedance10.80.
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APPLICATIONS OF PERFORMANCE-BASED E
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PRACTICAL ADAPTATION FOR STAKEHOLDE
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cost premium for the more expensive
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The future techniques will improve
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Benefit-cost ratio(BCR) 2.5UC Berke
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motivation to change the way they w
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CHANGING THE PARADIGM FOR PERFORMAN
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Ideally, the preliminary design of
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ModelM1M2M3Table 1. Description of
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Sample results from the response-hi
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In FEMA 273/356, the intersection o
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(M8 and M9) and the isolated frames
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THE ATC-58 PROJECT PLAN FOR NONSTRU
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The development of next-generation
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for these flexible nonstructural co
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spectra is several times larger tha
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The variability is associated with
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functions for a wide variety of non
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SIMPLIFIED PBEE TO ESTIMATE ECONOMI
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One can show (Porter et al. 2004) t
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( )FDM| EDP= xdm = 1 −FRdm , + 1,
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1. Facility definition. Same as in
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Table 1. Approximation of seismic r
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The EAL values shown in Figure 3 mi
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ASSESSMENT OF SEISMIC PERFORMANCE I
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where e -λτ is the discounted fac
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IDR 3[rad]σPFAIDR34(g)σ PFA4media
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Figure 3a, shows an example of frag
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P(C LVCC i |IM )1.00.80.60.40.20.00
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E [ L T | IM ]$ 10 M$ 8 M$ 6 M$ 4 M
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SEISMIC RESILIENCE OF COMMUNITIES
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2. RESILIENCE CONCEPTSResilience fo
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quantification tools could be used
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structure remains elastic. This is
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of Figure 7a will be used. It is as
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Nigg, J. M. (1998). Empirical findi
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acceleration with a 475-year return
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limit states, the suggestions given
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∆NSLsi= SϑH(5)iTFor column-sway
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Pinto et al., 2004). The probabilit
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The main difficulty in assigning a
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Crowley, H., R. Pinho, and J. J. Bo
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analytical models generally have si
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Figure 2. Structure of the response
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can be used as a random variable of
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4. DERIVATION OF THE VULNERABILITY
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5. CONCLUSIONSDerivation of vulnera
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REFERENCESAbrams, D. P., A. S. Elna
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In general, these types of bench-mo
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where & x&(t ) = acceleration at th
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science building. The lateral load-
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emain the same, the magnitude of sl
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of sliding thresholds, are desirabl
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Retrofit of Nonstructural Component
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was developed to accommodate these
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tested by Meinheit and Jirsa are us
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where D is the maximum drift and N
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in predicting damage as well as rep
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4.2.2 Modeling the Data Using Stand
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that the defining demand using a no
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• The influence on the dynamic re
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deviations σ and correlation coeff
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The first three modes of vibration
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Details about the ten records selec
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to allow a quantitative assessment
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Cornell A. C., F. Jalayer, R. Hambu
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limited possibilities of overcoming
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uildings, up to five stories high (
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Efficiency η, %100806040203D-RWBW-
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Table 1. Performance criteria for c
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Because the analytical model strong
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REFERENCESAguilar, G., R. Meli, R.
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tests of its type ever conducted. T
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end work-point to work-point). And
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Fig. 5 shows the actual application
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3Roof Disp. (mm)250200150100500-50-
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Base Shear (kN)Base Shear (kN)40002
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8. CONCLUSIONSBased on the test and
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REAL-TIME DYNAMIC HYBRID TESTING OF
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:::::2004) can be formulated using
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The structure to be simulated is di
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measurements, to the modeling of th
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Figure 8. Two stories (left) and hy
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ROLES OF LARGE-SCALE TEST FOR ASSES
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mid-height in the third story, at w
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cycles were repeated for each ampli
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the tests with ALC panels were excl
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the relationship between the moment
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attachment details adopted for inst
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FULL-SCALE LABORATORY TESTING: STRA
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economic losses resulting from the
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4. OBJECTIVES AND OUTCOME OF STRUCT
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15001000500Shear [kN]0-8.0 -6.0 -4.
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5.1 3D Tests on a Torsionally Unbal
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Non-linear substructuring was recen
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PERFORMANCE BASED ASSESSMENT — FR
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4 x 50 m = 200 mC1 C2 C3h u = 7 mh
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some procedures are (contrary to th
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5 th floor disp. [cm]0.60.0-0.6CC =
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While the global drift of the build
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the use of such connections in eart
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I d = 0.25elastic limitmaximum resi
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As regards the influence of differe
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ON GROUND MOTION DURATION AND ENGIN
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time between the first and last acc
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FyFyFyFFFkk0.03kδδδcover a large
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T5b, T13a, T13b, T20a and T20b can
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Tabled results show that in the cas
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0 0.25 0.5 0.75 1Dkin PfSa[g]0 0.25
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ON DRIFT LIMITS ASSOCIATED WITH DIF
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BehaviourElasticInelasticCollapseDa
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Other factors such as the applied l
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4. MOMENT RESISTING FRAMES4.1 Ducti
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5Ductility factor432100 0.2 0.4 0.6
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5.1 Flexural Structural WallsAn exa
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MODAL PUSHOVER ANALYSIS: SYMMETRIC-
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Floor963SeattleNonlinear RHAFEMA1st
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The peak modal demands r n are then
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9BostonSeattleLos AngelesFloor63RSA
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5. EVALUATION OF MPA: UNSYMMETRIC-P
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Without additional conceptual compl
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AN IMPROVED PUSHOVER PROCEDURE FOR
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for a response governed by the fund
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2.2 Modal ScalingThe principal aim
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2.3 Pushover-History AnalysisSubsti
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(3) Calculate cumulative scale fact
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46.4 58 58 58 58 58 58 58 58 58 58
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EXTENSIONS OF THE N2 METHOD — ASY
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The strength reduction factor due t
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The relations apply to SDOF systems
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in X-direction pushover curves prac
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As an example, an idealized force-d
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The IN2 curve can be used in the pr
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HORIZONTALLY IRREGULAR STRUCTURES:
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Dutta and Das (2002, 2002b and refs
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They tested the procedure on three
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Table 1. Properties of the 4 WallsW
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The following is a summary of two s
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ectangular concrete deck supported
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REFERENCESAlmazan, J. L., and J. C.
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Rosenblueth, E. (1957). “Consider
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instantaneous period of vibration a
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value of the maximum plastic deform
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(a) elastic-perfectly plastic type(
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where a is the constant peculiar to
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Referring to Eq. (15), the natural
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-The effective period obtained by u
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eal damage data, rather than theore
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liquefaction-induced damage. This i
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Figure 5. Selected damage distribut
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Figure 6. Idealized capacity spectr
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I’ for the ductile case, as expec
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This study has shown that a modific
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thickness of the inner wall is usua
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4. EARTHQUAKE GROUND MOTION INPUT A
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5.2 Performance Levels and Limit St
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where λ I jis the occurrence rate
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Page 434 and 435: and thus are not considered in seis
Page 436 and 437: The values of the displacement modi
Page 438 and 439: constant amplitude loading (CA) or
Page 440 and 441: deterioration. These are the type o
Page 442 and 443: members, is the main feature of the
Page 444 and 445: RESULTS, DISCUSSIONS AND CONCLUSION
Page 446 and 447: systems, where FEMA estimations are
Page 448 and 449: The case study is a Hospital in the
Page 450 and 451: Table 1. Dimensions and amount of r
Page 452 and 453: 4.2 Incremental AnalysisBase shear
Page 454 and 455: When adding jackets to columns, the
Page 456 and 457: storyShear in interior Column [ton]
Page 458 and 459: PERFORMANCE-BASED SEISMIC ASSESSMEN
Page 460 and 461: 2. HYBRID FRAME BUILDINGSTwo precas
Page 462 and 463: 15’ - 0” 15’ - 0”Hybrid fra
Page 464 and 465: and maximum residual inter-story fr
Page 466 and 467: As the first step in understanding
Page 468 and 469: Table 3. Comparison of calculated m
Page 470 and 471: NEW MODEL FOR PERFORMANCE BASED DES
Page 472 and 473: (a) interior beam-column joint(b) k
Page 474 and 475: yxVN =VADjDBABLD jDOV cOVCN= VLV bV
Page 476 and 477: 3.3.2 B-modeThe equilibrium conditi
Page 478 and 479: 3.6 Failure ModeBased on the calcul
Page 480 and 481: Name ofSpecimenTable 2. Comparison
Page 484 and 485: examination of the risk implication
Page 486 and 487: Bozorgnia and Campbell (2004) find
Page 488 and 489: structure, the results of inelastic
Page 490 and 491: hazard curves will often vary throu
Page 492 and 493: large uncertainties associated with
Page 494 and 495: A PRAGMATIC APPROACH FOR PERFORMANC
Page 496 and 497: Relative Height20118160.8140.6 1210
Page 498 and 499: Yield Strength Coefficient, Cy2.01.
Page 500 and 501: Yield Strength Coefficient, Cy*1.61
Page 502 and 503: 2.6 Preliminary DesignIn the preced
Page 504 and 505: 4. CONCLUSIONSIn the space availabl
Page 506 and 507: EXAMINATION OF THE EQUIVALENT VISCO
Page 508 and 509: of the bilinear model with the ener
Page 510 and 511: 3. STUDY PARAMETERS AND ASSESSMENT
Page 512 and 513: decided to investigate the accuracy
Page 514 and 515: DISPLACEMENT(m)DISPLACEMENT (m)DISP
Page 516 and 517: The results for all 100 earthquake
Page 518 and 519: CONTRASTING PERFORMANCE-BASED DESIG
Page 520 and 521: Conceptual design is greatly facili
Page 522 and 523: 2. The availability of cost-of-repa
Page 524 and 525: There are many questions to be answ
Page 526 and 527: assess expected NSASS losses. For t
Page 528 and 529: 3.2.2 Design for Tolerable Mean Ann
Page 530 and 531: THE PERFORMANCE REQUIREMENTS IN JAP
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2.1 Law Enforcement and InspectionT
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Splices and development of reinforc
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as for the rising part of continuou
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compressive stress of concrete is t
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MOLIT Notification No. 1461 outline
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AUTHOR INDEXH. Akiyama.............
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F. Taucer .........................
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PEER 2003/06PEER 2003/05PEER 2003/0
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PEER 2001/13PEER 2001/12Modeling So
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PEER 1999/04 Adoption and Enforceme
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