Numerical study of seismic performance of irregular continuous reinforced concrete rigid-frame bridges

This study presents a comprehensive numerical investigation into the seismic performance of continuous reinforced concrete rigid-frame (CRCR) bridges with geometric irregularities. Based on a real case study in Iran, several bridge models were developed in OpenSees by systematically varying span length ratios, pier height ratios, and pier skew angles. Both modal and nonlinear analyses were conducted, and the modeling approach was validated using experimental data. Results indicate that increasing the pier height ratio reduces seismic capacity, with the most critical configuration (B16) showing approximately a 45% reduction in the longitudinal direction and 40% in the transverse direction compared to the reference bridge (B0). Conversely, reducing the difference between adjacent span lengths improves the lateral load-bearing capacity by up to 55% longitudinally and 45% transversely. Increasing skew angles leads to longer natural periods—by as much as 50%—due to torsional effects. These findings highlight the significant impact of geometric irregularities on dynamic behavior and point out the need for advanced seismic design strategies and targeted retrofitting measures to improve the resilience of irregular CRCR bridges in earthquake-prone regions.