Numerical study of seismic response of irregular multi-frame reinforced concrete bridges

In-span hinges can facilitate construction processes and diminish the adverse consequences of creep, shrinkage and thermal phenomena, but can also bring about detrimental effects such as impacts, unseating issues and large displacements. The seismic behaviour of concrete bridges has been addressed in previous studies, but it remains unclear how in-span hinges affect the seismic response of irregular bridges. The aim of this research was to determine the seismic performance of irregular multi-frame bridges. To consider a wide range of irregularity, four classes of single- and multi-frame bridges with low to high regularity indices were considered. An innovative parameter, the adjacent frame lateral stiffness ratio (AFSR), was introduced to determine the appropriate position of in-span hinges and investigate the performance of multi-frame bridges. The results showed that the beneficial or damaging effects of in-span hinges on the seismic behaviour of a bridge depend on its level of irregularity. The seismic demands of piers in multi-frame bridges are typically lower than those of single-frame bridges. The results also showed that the piers adjacent to an in-span hinge are more affected by the hinge. It is recommended that in-span hinges are located such that the AFSR approaches unity so as to avoid out-of-phase vibration of adjacent frames and unseating issues.