Displacement Based Design for transverse response of rc bridges: evaluation of iterative and direct procedures

Transverse response prediction for continuous rc bridges in a displacement-based framework presents some critical issues related to representativeness of the equivalent SDOF structure in respect to the original MDOF system, particularly the estimation of the design displacement profile for irregular bridges. This paper investigates the accuracy of the current iterative Direct Displacement-Based procedure: parametric analyses were carried out considering multiple configurations of regular and irregular continuous girder bridges with 3 to 5 spans, designed with target drift limits of 1% to 4%, and subsequently checked with non linear time history analyses. It can be seen that for regular bridges the DDBD method can be applied with satisfactory reliability for both low and high ductility design cases, while for irregular bridges the method leads to high overstimations in some cases. At the same time a non-iterative method based on the effective stiffness and ResponseSpectrumAnalysis is proposed, with the aim of simplifying the current iterative procedure for everyday design use, while maintaining the required accuracy.