Extent and hierarchy of seismic induced inelastic demands in the substructure system of bridges on piled foundation crossing waterways

Abstract

The effect of the exposed length of piles supporting bridges crossing waterways on the spread of inelasticity along the pile shaft compared with the extent of plasticity in the body of the column, and hence on the precedence of the formation of plastic hinges in the substructure system is of paramount importance. Plastic hinges may form ideally and preferably at the bottom of the column just above the pile cap, or undesirably either at the pile’s head or at any other section within the pile be it along its free/exposed length immersed in water or its embedded part in soil. A set of bridges are designed according to Eurocode for multiple configurations with various relative stiffness between the column and the group of piles featuring partly exposed shaft. Pushover as well as time history inelastic analyses under a set of ten earthquake records are performed accounting for soil-structure interaction. Results demonstrate that it is likely in some cases characterized by a remarkable increase in the flexural stiffness of the column relative to the group of piles to have spread of inelasticity and plastic hinges forming in piles prior to the column. This is undesirable for a robust, reliable and resilient seismic design as devised by universal design standards for bridges on piled foundation. While there is no clear consensus on the most effective corrective measure to such undesirable response, a few proposed remedial design actions have been formulated in order to preclude (or at least improve the behavior for the case featuring) plastic hinges deplorably forming in the piles prior to the base of the column.