PSI - Issue 18

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

115

Bilal L. Khan et al. / Structural Integrity Procedia 00 (2019) 000 – 000

8

Under excitation due to Lander’s Earthquake as shown in Figure 5, that inter -storey drifts are also significantly controlled after applying base isolators of different damping ratio. Lead core rubber bearing (LCRB) has shown the least inter-storey drift (5 mm) and deformations followed by high damping rubber (30 mm) and low damping rubber (60 mm). The presence of vertical irregularity enabled us to evaluate the effectiveness of various passive base isolators. If there was no irregularity present in structure, all passive base isolators would have shown similar performance.

Fig. 5. Inter-storey Drift Comparison between Base Isolated Structure and Fixed Structure for Landers earthquake (Far Field).

4.2. Transmissibility ratio

The ratio of acceleration transmitted to the mass and amplitude of ground acceleration is known as the transmissibility (TR) of the system. The un-isolated structure with fixed base has Multi Degree of Freedom (MDOF), whereas in the base isolated structure due to passive base isolators the relative inter-storey drifts are insignificant and the structure performs like a Single Degree of Freedom (SDOF). Hence, the concept of transmissibility can be applied. Transmissibility is concept from which it can be determined that how much accelerations/forces are being transferred from the base to the top of structure due to an earthquake. If the transmissibility ratio is kept very low, we can reduce the forces/accelerations from the ground to structure (Chopra, 2001). The transmissibility ratio comparison is made to investigate the acceleration response of different types of dampers.

Fig. 6. Transmissibility Comparison of Passive Base Isolators under Lomaprieta Excitation (Near Field).