Influence of Ground Motion Characteristics on the Seismic Performance of Scoured Bridge Piers

This paper investigates the seismic performance of scoured bridge piers, focusing on the combined effect of ground motion characteristics and scouring conditions. Numerical analyses were conducted using a finite element framework based on a caisson-pier model embedded in a layer of coarse-grained material. Three numerical models were developed to simulate different hydraulic scenarios: (i) unscoured (NS), (ii) general scour (GS), and (iii) local scour (LS). A set of seven spectrum-compatible recorded inputs were employed, varying in ground motion parameters such as Peak Ground Acceleration, Cumulative Absolute Velocity, and Arias Intensity. Seismic demand is considered in terms of instantaneous measures, i.e., maximum acceleration at the deck, and cumulative measures, i.e., normalized residual horizontal deck displacement and foundation settlement. The results of the study indicate that the maximum acceleration at the deck correlates with the spectral acceleration at the pier fundamental period, increasing and being always larger in NS scenarios, followed by GS and LS scenarios, respectively. Dynamic analyses also show that the seismic amplification occurring in the range of vibration periods of the pier is strongly influenced by scouring conditions, with the GS scenario responsible for the largest base isolation effect. Such beneficial effect is however counterbalanced by the trends observed for the residual displacements. The results of the analyses show indeed that energy-based parameters, such as Arias Intensity and Cumulative Absolute Velocity, are well correlated with the residual displacements, but significantly differ according to the scour scenario, with horizontal displacement being more relevant in the LS scenario and the settlement accumulation in the GS scenario.