Numerical Load Rating of Reinforced Concrete Compression Members: Demonstration with Connecticut Arch Bridges

Abstract

As the reinforced concrete arches and columns built over a century ago begin to deteriorate, the load rating of these structures becomes increasingly important because decisions about bridge rehabilitation, replacement, and capacity are based on the value of the load rating. Compression members can be load rated to determine the effect of their structural condition on their live-load carrying capacity. Methods for the analysis of compression members based on the formulation of an interaction diagram are useful for the design of compression members but have theoretical and analytical limitations in their use for load rating. After a survey of the theory and inadequacies of this solution for load rating, procedures for analysis of compression members were developed that can be efficiently and accurately applied to load rating. This load-rating technique is combined with a standard structural analysis tool and a spreadsheet application for efficient rating of all compression members in a standardized format. As demonstration, the method was applied to load rating of the Bulkeley Arch Bridge in Hartford, Connecticut, which carries I-84 over the Connecticut River, and of the Housatonic Bridge in Milford, Connecticut, which carries US-1 over the Housatonic River. The technique used to rate these bridges was generalized for a wide variety of compression members, including those in biaxial bending, slender columns, and members with deterioration, using both load factor design and load and resistance factor design. Only with a proper understanding of our bridges gained through a standardized method of rating can their safety, function, and form be maintained.