Improving Redundancy of Two-Girder Bridges

Abstract

As the U.S. bridge inventory ages and traffic volumes increase, state highway departments are spending more on maintaining their current structures to extend the service life of the current bridge inventory. This includes two-girder bridges that are currently classified as fracture critical and nonredundant. Because of increased inspection costs associated with these fracture-critical bridges, many state highway departments are electing to evaluate alternate load paths and implement retrofit methods on existing bridge structures to avoid bridge replacement. Significant improvements to member and system redundancy can be achieved by using relatively straightforward retrofit methods and materials. Implementation of web reinforcement plate retrofits is discussed as a possible technique to improve redundancy and reduce the fracture potential of two-girder bridge structures. In each of two presented case studies, the bridge owner selected the design criteria of the redundancy retrofit (such as fracture environment, postfracture capacity, and postfracture performance). The industry lacks a clear, objective, and quantifiable definition of redundancy, and there is no rational minimum benchmark that can be quantified in the design standards.