The assessment of reinforced concrete bridge decks

Abstract

The current program of bridge assessments in the United Kingdom has presented bridge owners with a substantial problem as conventional analysis techniques have suggested that many structures have insufficient capacity for current highway loading. With their general application, improved assessment techniques, which more accurately reflect the true capacity of structures, can prove highly cost effective in extending the useful life of structures. The Wood-Amer equations were derived for the design of reinforced concrete slabs subject to complex loadings. The equations ensure that the capacity of a slab is not exceeded in flexure by an imposed loading, wile minimizing the total amount of reinforcement required. However, the use of these equations for assessment leads to a conservative estimate of structural capacity in all cases where steel is not distributed optimally. The optimality condition is a constraint in design problems that is not relevant to assessment problems, and its use can lead to adequate structures being condemned as unsafe. The present analysis is based on the same fundamental principles as those set out by Hillerbourg, which were extended by Wood and Amer in the derivation of the Wood-Amer equations, but it assumes that the reinforcement arrangement is already known. The methodology provides a systematic approach to assess whether a reinforced concrete slab has sufficient capacity to withstand an imposed loading, quantified by determination of the factor of safety on that loading. Examples are presented demonstrating how the method can readily be applied to the assessment of reinforced concrete bridge decks.