The Ingenieur Vol 59 July-Sept 2014 The Ingenieur Vo. 59, July-Sept 2014 | Page 34

INGENIEUR Response Spectrum Analysis The response spectrum loading was imposed on two different directions (transverse and longitudinal). The internal moment shows obvious effects and will be taken as an indicator to be looked into in this study. Tables 4 and 5 show the maximum moment of a bridge pier due to self weight and earthquake response spectrum in transverse and longitudinal directions for three types of models (fix-based, rubber bearing pad and seismic isolator bearing model). In general, the usage of rubber bearing pad and seismic isolator bearing increases the overall performance of the bridge. Table 4: Maximum Moment (M3) at Pier (Earthquake in Transverse Direction) Pier No Pier 1 Pier 2 Pier 3 Pier 4 Response Spectra Return Period (Years) Moment (kNm) TR=500 TR=2500 TR=500 TR=2500 TR=500 TR=2500 TR=500 TR=2500 459 882 1530 2900 1497 2835 1912 3744 Fix-based Model Rubber Bearing Pad Model 339 486 1165 1953 1142 1909 1329 2557 Seismic Isolator Model 380 831 1269 1532 1260 1517 588 978 Table 5: Maximum Moment (M2) at Pier (Earthquake in Longitudinal Direction) Pier No Pier 1 Pier 2 Pier 3 Pier 4 6 32 ingenieur 2014-July-FA.indd 32 Response Spectra Return Period (Years) TR=500 TR=2500 TR=500 TR=2500 TR=500 TR=2500 TR=500 TR=2500 Bridges with seismic isolator models have a reduction in moment up to 60% compared with a bridge with normal rubber baring pads. However, at Pier 1 the moment was observed to be different with a slight increment but it is expected this will become lower if the effect of approached bridge is taken into account. Time History Analysis The performance levels of a bridge due to earthquake time history refer directly to FEMA 356 and are described as Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP) level. Meanwhile, B level is a transition from safe level to damage level. The nonlinear behaviour of reinforced concrete piers is modelled using the fibre beam theory. The result clearly shows that serious damage levels will not occur on the Second Penang Bridge due to expected ground earthquakes time histories for Penang Island under long distant great Sumatera and subduction zone fault. The actual time history at bedrock for Penang in 500TR and 2500TR are shown in Figure 7. Figure 7a Moment (kNm) Fix-based Model Rubber Bearing Pad Model Seismic Isolator Model 873 478 7127 9843 7125 9841 1944 2456 297 495 1257 2423 1190 2286 2243 3220 966 1210 584 992 558 946 1724 2003 Figure 7b Figure 7: The Time History (TH) of Penang due to Sumatera Earthquake at bedrock for (a) 500TR and (b) 2500TR VOL 59 JULY –2013 VOL 55 JUNE SEPTEMBER 2014 7/9/14 10:37 AM