Low cycle fatigue effects in integral bridge steel h-piles under earthquake induced strain reversals

Abstract

Under the effect of medium and large intensity ground motions, the seismically-induced lateral cyclic displacements and ensuing bending strains in steel H-piles of integral bridges (IBs) could be considerable. As a result, the piles may experience cyclic plastic deformations following a major earthquake. This may result in the reduction of their service life due to low-cycle fatigue effects. Accordingly, low cycle fatigue in integral bridge piles is investigated under seismic effects in this study. For this purpose, an IB with two spans are considered. Three dimensional nonlinear structural models of this IB including dynamic soil-bridge interaction effects are built. Then, time history analyses of the IB models are conducted using a set of ground motions with various intensities representing small, medium and large intensity earthquakes. In the analyses, the effect of various properties such as soil stiffness, pile size and orientation are considered. The magnitude of cyclic displacements of steel H-piles are then determined from the analyses results. In addition, using the existing data from experimental tests of steel H-piles, a fatigue damage model is formulated. This fatigue damage model is used together with the cyclic displacement obtained from seismic analyses to determine the remaining service life of IBs under cyclic displacement due to thermal effects. The fatigue analyses results reveal that earthquakes with large intensity may reduce the service life of the piles with non-compact sections.