PSI - Issue 18

Bilal L. Khan et al. / Procedia Structural Integrity 18 (2019) 108–118 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Under Lomaprieta earthquake excitation, figure 6 shows that transmission of earthquake forces and acceleration are significantly reduces as the damping ratio increases, which means transmissibility has been lower than 1. Maximum reduction was measured for lead rubber bearing (54 %) followed by high damping rubber (52 %) and low damping rubber system (44%). Figure 7 shows that transmission of earthquake forces and acceleration significantly reduces under the influence of far field earthquake excitation. Maximum reduction in transmissibility was measured for high damping rubber (47%) followed by lead rubber bearing (45%) and low damping rubber (35%). The reason for maximum reduction transmissibility ratio for high rubber damping as compared to lead rubber bearing can be that the if damping ratio increases from certain limit the transmissibility starts to increase. Figure 6: Transmissibility Co parison of Passive Base Isolators under Lomaprieta Excitation (Near Field)

2.5

2.1 0% Reduction

2.0

1.37 35% Reduction

1.16 45% Reduction

1.5

1.10 47% Reduction

1.0

0.5

Transmissibility Ratio

0.0

Fig. 7. Transmissibility Comparison of Passive Base Isolators for Lander Excitation (Far Field).

4.3. Relative Peak Displacement

The trend observed in global peak displacement for various base isolated systems also varied for near and far field earthquakes. Under the influence of near field earthquake excitation, peak global displacement/ drift measured for Lead rubber bearing isolation system (290 mm) was almost similar to that of high damping rubber isolation system (300 mm) and was much lesser than low damping rubber isolation system (390 mm) as represented in figure 8. For far field earthquake excitation, peak global displacement was measured to be smallest for lead rubber bearing (150 mm) followed by high damping rubber isolation system (180 mm) and low damping rubber isolation system (250 mm) as represented in figure 9. This shows that the presence of high damping values can decrease the peak displacements in the structure efficiently. During the analysis under the influence of far field earthquake excitation, the peak displacement measured for low damping rubber bearing system was more than that of an un isolated system, this shows that low damping base isolator had adverse effect on the dynamic response of the structure under far field earthquake excitation. Figure 7: Transmissibility Comparison of Passive Base Isolators for Lander Excitation (Far

Fig. 8. Comparison of Relative Displacement between Passive Base Isolators under Lomaprieta Earthquake (Near Field)