Estimating Inelastic Displacements for Design: Extended Pile-Shaft-Supported Bridge Structures

Accurate estimation of inelastic displacements is important for the evaluation of the seismic performance of structures with desired ductile response. In this paper, nonlinear dynamic analyses results from a companion numerical study investigating the response of ductile-designed bridge structures, were compared with a commonly applied inelastic displacement estimation approach and an alternative approach. The extended pile-shaft-supported bridge structures considered are susceptible to amplified response under long-period velocity pulses, and hence an evaluation of design methods for estimating inelastic displacement demands is warranted. In this case, force-reduction–displacement-ductility–period (R−μ_Δ−T) relations and a mean spectral displacement approach are investigated. The alternative approach estimates inelastic displacement demand using the mean elastic spectral displacement between two spectral periods that are important for the structure's response. Results support the conceptual merits of using the mean spectral displacement method, indicating that the approach is capable of reducing the uncertainty in predicting inelastic displacement demands for the types of structures considered when subjected to near-fault ground motions.