DISPLACEMENT-BASED SEISMIC DESIGN OF MULTI-DEGREE-OF-FREEDOM BRIDGE STRUCTURES

The concept of displacement-based design is attractive for seismic design, primarily because it places the focus of design directly on displacement demand, and hence damage, rather than on force-reduction or behaviour factors. A procedure is presented which extends the simple concept of displacement-based design to complex multi-degree-of-freedom (MDOF) bridge structures. The procedure is based on the assumption of a displaced shape for the structure, and the subsequent reduction of the system to an equivalent single-degree-of-freedom (SDOF) system. The process is shown to work well for the design of a symmetrical bridge, while suffering some shortcomings when applied to a highly irregular bridge. The topic of design-oriented displacement response spectra is also briefly addressed.