Evaluation of highway bridge strength considering parapets

Abstract

This paper describes a study evaluating increase in design strength, performance and capacity when including bridge parapets in a bridge analytical model. Traditionally, concrete parapets are treated solely as superimposed dead load in an overall bridge structural design. Parapets are detailed from a safety standpoint to resist impact forces from vehicle loading. However, in the global design models, the inherent strength of the parapets is not considered as a contributing factor to the overall strength of the bridge structure as a system. As part of an evaluation of global performance of bridge structures, the authors have prepared a set of three-dimensional finite element models of a simple span, composite concrete – steel stringer bridge. These models evaluate the overall strength and deflections under standard traffic loadings, with and without the stiffness contribution of the concrete parapets. These models predict a substantial increase in strength when including the parapets as a structural element rather than merely a superimposed dead load. Furthermore, standard details and construction procedures commonly in use to provide adequate strength for current code requirements seem to also provide sufficient strength to enable composite action between parapets and the bridge deck. The preliminary results from this analytical study indicate that current design practices are perhaps overly conservative in that they do not account for the system strength of the parapet. In some cases, ignoring the strength and stiffness contribution of parapets may be under-conservative, for example in pre-stressed concrete butted box beam bridges, longitudinal shear key joints may be adversely impacted by difference in stiffness in the adjacent box sections. This paper will investigate the advantages of including the evaluation of parapet strength, initial load rating and analysis during the life history of the bridge structure.