Analysis and experiment of isolated bridges using Polynomial Rocking Bearings

This paper is aimed to study the effectiveness of Polynomial Rocking Bearing (PRB), a various-frequency sliding isolator, in decreasing the seismic responses of isolated bridges. Although sliding isolators have been widely used to mitigate seismic hazard, it may be not effective in decreasing the seismic responses of isolated structures subjected to near-field ground motions. Near-field ground motions are of a pulse period which may be close to the natural periods of the isolated structures so as to lead the isolated structures to be resonant. Various-frequency sliding isolators could regulate the natural periods of the structures to avoid resonance under near-field ground motions. However, the key issue is how to choose the geometric shape and friction materials in design of various-frequency sliding isolators. This study adopts PRB to be the various-frequency sliding isolator whose rocking surface consisting of six-order polynomial. The restoring stiffness of the PRB possesses softening section as well as hardening section. The structural acceleration response can be decreased by decreasing the restoring stiffness in softening section while the structural displacement response can be decreased by increasing the restoring stiffness in hardening section. Since the PRB equivalent horizontal friction coefficient can be adjusted via the various geometric shapes, the friction material can be then arbitrarily chosen to increase the bearing reliability and durability. PSO-SA hybrid algorithm is used to find out the optimum parameters of the PRB in this study. A series of shaking table tests are conducted to demonstrate the effectiveness of the PRB in mitigating the dynamic responses of bridges under strong earthquakes. Numerical analysis is also performed to make comparison with the experiments. It shows the numerical results agree with the experimental results very well.