A sliding seismic isolator that, due to its sliding property, cuts off the inertia force acting on the bridge pier is actively being developed. However, some concerns have been expressed about the performance of this isolator under the effect of vertical ground motions. As it is well known, the sliding bearings are velocity and vertical-load dependent; therefore, under the effect of vertical ground motions, the friction coefficient is expected to change greatly, affecting the horizontal earthquake response. In this study, pseudo-dynamic tests and numerical simulations are performed to analyze the effect of vertical seismic loads on the horizontal earthquake response characteristics of this sliding seismic isolator. The isolation system consists of a sliding bearing that generates the friction damping, and of a rubber bearing that generates the restoration force. A hybrid on-line earthquake response test is performed, in which the sliding bearing is exposed to a pseudo-dynamic loading test with vertical load variation. The sliding bearing is composed of a Teflon plate and a stainless steel plate on each sliding surface. The JMA Kobe record of the Hyogo Ken Nanbu Earthquake of January 17, 1995 is used as input load. Furthermore, a numerical analysis is also performed to confirm the effect of the vertical seismic load on the sliding seismic isolator. From the results, it becomes clear that, although the friction force changes remarkably when the vertical ground motion is applied, the horizontal earthquake response presents little influence and almost no change is observed on it. The same behavior is observed even in the case where the vertical seismic load is scaled to larger peak values. The results also show that a better isolation performance is obtained reducing the rubber bearing stiffness of the isolator, since the cut off effect of the sliding bearing becomes more relevant. With the experimental results, implementation of the bearing to different type of bridge structures is investigated through numerical simulation.
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