Verification of spectral reduction factors for seismic assessment of bridges

Within a nonlinear static analysis procedure perspective for the assessment of structures, one of the key issues is the employment of a demand spectrum that takes also into account, through an adequate reduction of its spectral ordinates, the hysteretic energy dissipation capacity of the structure being assessed. There are certainly a relatively large number of past parametric studies dedicated to the validation of different approaches to translate such structural energy dissipation capacity into spectral reduction factors, however such studies have focused mainly, if not exclusively, on single-degree-of-freedom (SDOF) systems. It seems, therefore, that verification on full structural systems, such as complete bridges, is conspicuously needed in order to verify the adequacy of using existing SDOF-derived relationships in the assessment of multiple-degree-of-freedom (MDOF) systems. In this work, eleven different spectral reduction proposals, involving diverse combinations of previously proposed equivalent damping and spectral reduction equations, are evaluated, for various intensity levels, using a preliminarily validated nonlinear static procedure. A wide set of bridges, covering regular and irregular configurations as well as distinct support conditions, is used. The accuracy of the results is checked by direct comparison with Time-History Analyses performed with ten real ground motion records. Overall conclusions are then presented with the purpose of providing practitioners and researchers with indications on the most adequate spectral reduction schemes to be employed in nonlinear static analysis of bridges.