Report - PEER - University of California, Berkeley

Base Shear (kN)Base Shear (kN)400020000OpenSees-20001FPhase1, Test No.3, LP89g04(10/50)-40000 5 10 15 20 25 30 35 40Time (sec)4000TESTPhase1OpenSEESPISA3D20000-2000-40001FTESTPISA3DTest No.5,TCU082(2/50)0 5 10 15 20 25 30 35 40 45Time (sec)Figure 15. Base shear history in Tests No. 3 and No. 5.In the Test No. 2, braces started to experience plastic deformation at the first and thesecond floors. As shown in Table 4, by computing the linear responses between theaxial force versus core displacement of braces before yielding, it is confirmed that theinitial stiffness of the BRBs of the specimen is rather close to the design value. Thissuggests that the unbonding mechanism of the BRBs is effective in these BRBs. Afterthe application of six earthquake effects in Phase 1 tests, it is found that the UBs andBRBs performed rather satisfactorily without evident failure. Furthermore, the BRBsdissipated most of hysteretic energy absorbed by the structure in different levels ofearthquake intensities (Fig. 16). In each case, the energy dissipated by the north BRBis almost the same as that by the south BRBs in each floor suggesting the accuratetransformation of the strain gauge readings into the brace axial forces. In themeantime, the ultimate story drift of the BRB composite frame was controlled rathereffectively under the effects of the design earthquakes.Table 4. Effective stiffness of BRBs or UBsExperiment Analysis error (%)N (kN/mm) S (kN/mm) N (kN/mm) S (kN/mm) N S3BRB 91.5 88.0 87.35 87.4 4.7 0.72UBB 183.0 181.4 191.1 191.1 4.2 5.11BRB 193.0 184.3 185.9 185.9 3.8 0.8254