Integrated Superstructure-Substructure Load Rating for Bridges with Foundation Movements

Abstract

Superstructures of highway bridges are load rated regularly as a part of the National Bridge Inspection Standards (NBIS). It is well known that the load-carrying capacity of a superstructure is affected by foundation movements; however, the current load rating framework does not explicitly include these effects. In the current framework, foundation movement could be treated as structural condition change and considered as a permanent load. In this paper, the authors propose an integrated framework for load rating of superstructures and substructures in the presence of continuing foundation movements and geohydraulic hazards. The approach is based on the modification of the load rating equation to include foundation movements and effects of loads other than dead and live loads that can affect the load capacity of a bridge. A methodology for load rating elements loaded in biaxial moment and axial load, commonly experienced by piers, columns, and piles, has also been proposed. The term substructure functionality index (SFI) has been proposed to account for the effect of foundation movement on the functionality of critical elements such as bearings. Applications of the proposed integrated superstructure-substructure load rating and SFI have been demonstrated through two examples of actual bridges. It has been demonstrated that the load rating produced can be nonconservative if the effects of foundation movement are neglected.