An Improved Displacement-Based Design Procedure for Concrete Bridges

Currently available displacement-based design (DBD) procedures for bridges are critically evaluated with a view to identifying extensions and/or modifications of the procedure, for it to be applicable to actual bridges wherein the simplifying assumptions made at various stages of the procedure do not hold. In the present study an improved direct displacement-based design procedure is presented, including i.a. a suite of design criteria leading to optimum design, and proper consideration of the degree of fixity to pier top provided by superstructure rigidity. A detailed case-study of the design of an overpass bridge (originally designed to a current European Code), applying the improved DBD procedure is presented and then assessed using non-linear response history analysis (NL-RHA) for a number of spectrum-compatible motions; comparisons are made in terms of both economy (reinforcement requirements) and seismic performance of the different designs (displacement- and force-based). It is seen that DBD provided a more rational base shear distribution among piers and abutments when compared to the force-based design (FBD) procedure. Moreover, the improved DBD was able to adequately capture the displacement pattern, closely matching the results of the more rigorous NL-RHA and to contribute to a ‘safe’ design, since demand quantities obtained from NL-RHA did not exceed the design ones. FBD (according to modern codes) on the other hand, still remains simpler to apply since it does not require iterations and it is fully implemented in currently available software packages.

Keywords:

displacement-based design , bridges , reinforced concrete , seismic codes