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The effects of combinations of different types of irregularities have not been studied in details in the past and current seismic design codes do not address this issue appropriately. In this research, 76 regular and irregular bridges with irregularities in both superstructure and substructure were designed and evaluated to investigate the impact of combinations of irregularities on the seismic ductility demands. The irregularity parameters considered in this study include irregularities in span arrangement, different lengths of columns, different abutments support conditions and different stiffness of superstructure. The bridges were designed and checked according to AASHTO provisions. Inelastic time history analysis was conducted using OpenSees software and ductility demands in bridge columns for different bridge configurations were predicted. Predictions of ductility demands were based on the mean responses obtained using a number of ground motion records. Finally, the effect of considering displacement directions in predicting the mean bridge response (i.e., using different methods for predicting the mean response) for irregular and regular bridges was investigated. The results indicate that the combinations of irregularities can significantly increase the ductility demands in some cases compared to the case of regular bridges.

Seismic behaviour of a total of 76 bridges, including 4 regular and 72 irregular continuous RC bridges with irregularities in both superstructure and substructure are investigated in this study. Bridges with different span arrangements, various column heights, different support conditions at abutments, different superstructure transverse stiffness were considered in this study. The influence of different seismic intensity levels on the seismic response was also investigated. The bridges were designed and detailed according to American Association of State Highway and Transportation Officials (AASHTO) regulations. Seismic response of bridges was predicted using different methods of analysis including elastic multi-mode and inelastic time history analyses. To investigate the sufficiency of code provisions for predicting the seismic behaviour of irregular bridges, a comparison was made between the results obtained using linear and non-linear analyses in the longitudinal and transverse directions of the bridges and a new relationship was proposed to predict when the results from elastic analyses are not appropriate. The results indicate that in some cases significant deviations can occur between the predictions obtained using linear and nonlinear analyses, when simultaneous irregularities in both superstructure and substructure were considered. Current code provisions do not consider this issue in design of irregular bridges.