Resolving Restraint Moments: Designing for Continuity in Precast Prestressed Concrete Girder Bridges

Abstract

This paper presents analytical studies of Washington State Department of Transportation (WSDOT) standard precast, prestressed concrete bridge girders and their design for continuity. These studies indicate that deeper girders with longer spans, such as the new W83G girder, do not develop large positive restraint moments from creep and shrinkage effects. Without these large positive restraint moments, it is possible to design the girders for full or near-full continuity for superimposed loads. This continuity reduces the moment induced in each girder and leads to significant economic advantages. This paper also introduces the computer program RMCalc, developed by the authors, which simplifies the calculation of restraint moments. With the aid of this program and the potential for low restraint moments, engineers can design prestressed concrete girder spans for continuity, thereby providing greater structural efficiency in the bridge and significant cost savings to the taxpaying public.