12.07.2015 Views

Report - PEER - University of California, Berkeley

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in X-direction pushover curves practically overlap. Target displacements <strong>of</strong> theMDOF model, obtained by the N2 method, amount to about 12 cm in the X-directionand to 11.4 cm in the Y-direction. The values obtained by non-linear time-historyanalysis amount to 10.6 and 10.4 cm in X- and Y- direction, respectively. Thecorresponding coefficients <strong>of</strong> variation are about 0.10 and 0.25. The comparison <strong>of</strong>results suggests that the N2 method is conservative in both steps, i.e. whendetermining target displacement in CM and when determining the torsionalamplifications.u/uCM1.41.31.21.11.00.90.80.7X-directionPGA [g]0.050.100.200.300.50Y-directionN2 0.30 gElastic SpectralPushover 0.30 gStiff CM Flex. Stiff CM Flex.Figure 4. Envelopes <strong>of</strong> the normalised displacements at the top <strong>of</strong> theSPEAR building in the horizontal plane.0.80.70.60.5X-directionY-direction+ −Sa [g]0.40.30.20.1µ −Y = 3.0µ +X = 4.0µ +Y = 3.80.00 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 7 8 9 10 11 12Sd [cm]Figure 5. Capacity diagrams and demand spectra (PGA = 0.3 g).4. EXTENSION TO INFILLED FRAMESSd [cm]In order to employ the N2 method to infilled RC frames, a specific R-µ-T relation isneeded. The basic characteristic <strong>of</strong> the pushover curve <strong>of</strong> infilled RC frames is asubstantial decrease in strength and stiffness after the infill has begun to degrade. The363

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