Methods for Controlling Stresses and Distortions in Stage-Constructed Steel Bridges

Abstract

Widening and staged construction of steel bridges are becoming more frequent with today’s heavy traffic demands, right-of-way restrictions, and environmental constraints. Both construction practices require the addition of new girders to an existing structure. When new girders are added to an existing structure, inherent constructibility problems arise. The completed structure requires that the new girders, after placement of the new concrete deck, be aligned in both elevation and cross slope with the existing structure. Problems occur when the loading over the new girders is unbalanced, causing a torsional moment and twisting of the bridge. The twisting of the new girders may add undesirable vertical and horizontal displacements. Six design and construction methodologies for staged construction or widening of straight, steel girders are discussed. Research was initiated in response to construction problems experienced by the Washington State Department of Transportation (WSDOT). Several state highway agencies were surveyed, and the survey revealed that the problems experienced by WSDOT were not unique. The six methods are presented and the advantages, disadvantages, and applicable situations are discussed. A finite-element model was developed and used to compare calculated deflections with actual WSDOT case study field measurements. The model was then used to investigate the stresses and deformations for the six methods. A design paradigm is also presented for use in determining the appropriate method to be used for each particular situation.