Report - PEER - University of California, Berkeley

Fig. 5 shows the actual applications of the ground motions in the PDTs for theCFT/BRB frame specimen. As noted above, four earthquake ground accelerationsscaled to three different PGAs were planned for the PDT of the CFT/BRB framespecimen. However, some unexpected events encountered during the testing. In theTest No. 1, due to the buckling of the gusset plate occurred at the brace to beamconnection in the first story, the test stopped at the time step of 12.3 second. Thenstiffeners were added at the free edges of all the gusset plates underneath the threefloor beams. Then test resumed using the same ground accelerations as Test No.1 butin reversed direction. Until Test No.4, the PDT test was stopped at the time step of12.54 second as the crack on the top of concrete foundation near the gusset plate forthe south BRB-to-column joint were observed. After one pair of angles was installedbracing the stiffener to the two anchoring steel blocks, the test resumed again byapplying the same earthquake acceleration as that proceeded in Test No. 4. After all, atotal of six PDTs were conducted, and all the BRBs were not damaged. Therefore,cyclic increasing uniform story drifts were imposed until the failure of the BRBs.Since the scheduled PDT and cyclic tests were completed with failures only inbracing components including the BRBs, UBs and the gusset plates, it was decidedthat Phase-2 tests be conducted after repairing the damaged components. It adoptedthe same two earthquake records but scaled to match the spectral acceleration at thefirst mode period to the specified earthquake hazard levels. The ground motionaccelerations applied in Phase 2 PDTs are also shown in Fig. 5 (Chen et al. 2004). Allthe key analytical predictions and the experimental responses were broadcasted froma website (http://cft-brbf.ncree.gov.tw).Acceleration (m/sec 2 )8Test No.14 50/50-12.62 secTCU082EW0-4Test No.250/50TCU082EWTest No.310/50-ILP89g04NSTest No.42/50-12.54 secTCU082EWTest No.52/50TCU082EWTest No.610/50-IILP89g04NS-80 50 100 150 200 250 300Time (sec)Acceleration(m/sec 2 )1050-5-10Test No.1TCU08210/50Phase2Figure 5. Ground acceleration time history in PDTs.Test No.2LP89g042/500 25 50 75Time (sec)5. ANALYTICAL MODELS5.1 PISA3D ModelIn the application of PISA3D, all BRBs were modeled using the two-surface plastic(isotropic and kinematic) strain hardening truss element (Fig. 6). All the beammembers were modeled using the bi-linear beam-column elements (Fig. 7).Considering the strength degrading behavior of the concrete, all the CFT columnswere modeled using the three-parameter degrading beam-column elements as shown250