Report - PEER - University of California, Berkeley

As the first step in understanding their lateral load behavior, both hybrid buildingmodels were subjected to pushover analyses. Figure 7 compares the base shear-lateraldisplacement responses, in which the increased stiffness and strength of HFB2 areapparent. Another interesting observation is that both buildings had yielddisplacements of about 1.5 inches despite using different methods to deign the hybridbuildings. Due to the increased stiffness, the first mode of the HFB2 was 0.21 secondsless than the fundamental period of 0.99 seconds for HFB1.Base shear (kips)25020015010050HFB2 (FBD)HFB1 (DBD)00 1 2 3 4 5 6 7 8 9 10 11 12Roof displacement (in.)Figure 7. Pushover analysis results from HFB1 and HFB2 models.When the HFB1 and HFB2 models were subjected to 0.5EQ-1 and theearthquake input sequence shown in Figure 5, the maximum average inter-story driftsand base moment resistance shown in Figures 8 and 9 were obtained. As seen inFigure 8, the residual drifts calculated for both buildings at the end of each earthquakesegment were negligibly small and satisfied the acceptance criteria. Table 3 lists themaximum transient inter-story drifts obtained during the analyses of the buildings,which confirmed that the inter-story drifts of both buildings were below theacceptable transient drift limits for the EQ-II, EQ-III and EQ-IV input motions. ForEQ-1, the calculated maximum transient drifts exceeded the acceptable drift for bothbuildings, which should not be of a concern for three reasons. First, the crackedsection properties selected for the beam-column members in the buildings were morerepresentative for seismic assessment at EQ-II or greater intensity. Next, the analysesare based on specified rather than probable material properties, and finally, it has beensuggested that the spectral ordinates of EQ-I spectrum in the SEAOC Blue Book maybe too large (Performance-Based Seismic Engineering Ad Hoc Subcommittee 2003).Therefore, it is concluded that both HFB1 and HFB2 are acceptable solutions for thedesign of the prototype building despite the design base shear force of HFB1 being40% less than that obtained for HFB2.453