Direct displacement-based design of seismically isolated bridges

A Displacement-Based Design (DBD) procedure for bridges equipped with different seismic Isolation Systems (IS’s) is proposed. It has been derived from the Direct DBD method recently developed by Priestley and co-workers. The key aspect of the proposed procedure is the definition of a uniform target displacement of the deck, which is assigned by the designer to accomplish a given performance level, expressed through limit values of the maximum IS displacement and of the pier drift, respectively. The proposed design procedure has been developed for four different idealized force-displacement cyclic behaviours of IS’s, which can be used to describe the response of a wide variety of IS’s, including: (i) Lead-Rubber Bearings (LRB), (ii) High-Damping Rubber Bearings (HDRB), (iii) Friction Pendulum Bearings (FPB), (iv) Combinations of either Low-Damping Rubber Bearings (LDRB) or FPB and Viscous Dampers (VD), (v) Combinations of lubricated Flat Sliding Bearings (FSB) and LDRB, (vi) Combinations of FSB and Steel Yielding Devices (SYD), (vii) Combinations of FSB, Shape Memory Alloy (SMA)-based Re-centring Devices and VD. In the paper, the background and implementation of the design procedure is presented first, then some validation studies through nonlinear time-history analyses on different configurations of continuous deck and multi-span simply supported deck bridges are illustrated.