Report - PEER - University of California, Berkeley

The IN2 curve can be used in the probabilistic seismic assessment method (Cornell etal. 2002). In such a case, the dispersion has to be known. Dispersion measures fordifferent types of structural systems can be determined by parametric studies andsubsequently used as predetermined values in analyses. For example, for infill frameswe assumed that the same dispersion as observed for the R-µ-T relation applies alsofor top displacement.A four-storey infilled RC frame (Fig.3b), representing an existing building andtested pseudo-dynamically in full-scale in ELSA, will be used for illustration of theN2 method for infilled frames and the IN2 method. Ground motion is defined by anNewmark-Hall type spectrum, which represents the idealized mean spectrum of a setof 20 recorded accelerograms. Pushover curve and the capacity diagram are shown inFigs. 6a and 7a, respectively. The reduction factors, corresponding to the idealizedpushover curve and to the applied ground motion, are presented in Fig.6b.Determination of seismic demand for ground motion normalized to PGA = 0.45 g andof a point of the IN2 curve is shown in Fig.7a. In Fig.7b a comparison of the meanIN2 curve with the mean IDA curve, as well as the mean ± σ curves are presented.Note that displacement of the equivalent SDOF system and top (roof) displacementare plotted on the x-axis in Figs.7a and 7b, respectively. The value of 0.7 was used forthe coefficient of variation related to IN2 analysis (as suggested in Dolšek and Fajfar2004a), and the “exact” coefficient of variation was used in the case of IDA analysis.A fair agreement of results can be observed. Additional results are presented in(Dolšek and Fajfar 2004b).6. CONCLUSIONSSimplified non-linear design and assessment methods based on pushover analysis andinelastic spectrum approach represent a rational and effective tool for practicalapplications. However, the limitations of their applicability should be observed.ACKNOWLEDGEMENTSThe results presented in this paper are based on work continuously supported by the Ministryfor Science and Technology of the Republic of Slovenia and, more recently, by the EuropeanCommission within the 5 th Framework programs.REFERENCESCEN (2003). Eurocode 8 — Design of structures for earthquake resistance, Part 1,European standard prEN 1998-1, Stage 49 Draft, October 2003, European Com.for Standardisation, Brussels.Clough, R. W., J. Penzien (1975). Dynamics of structures, 1 th edition, McGraw-Hill.367