Behaviour of beams with exposed reinforcement: systematic literature review

Abstract

The issue of exposed reinforcement, especially in bridges subjected to aggressive environmental conditions, truck impacts, and patch repairs, is an important concern of the civil engineering community due to the increasing number of ageing reinforced concrete infrastructures and the important economic resources directed to bridge repairs. This paper presents a comprehensive review of the current research focused on the structural performance of reinforced concrete beams with exposed or unbonded reinforcement. It evaluates experimental investigations, analytical modelling efforts, and finite element simulations to understand the effects of bond loss on flexural strength, stiffness, ductility, and failure mechanisms. Results from over 20 key studies indicate that flexural strength can be reduced by up to 55% when the length of exposed reinforcement exceeds 80–90% of the beam span particularly in simply supported beams tested under a central point load, and especially in beams with a high reinforcement ratio of approximately 1.5%. In contrast, lightly reinforced beams under similar exposure conditions have shown strength reductions ranging from 0% to 30%, highlighting the importance of reinforcement ratio and test setups. The ductility of beams with 50% exposed length has been reported to decrease by as much as 60%, and stiffness losses were found to be approximately proportional to the exposed length. A comprehensive review of the current literature reveals that in certain configurations where exposed bars remain adequately anchored, the beams maintained an appropriate proportion of their original flexural capacity, suggesting that conservative assumptions in design may lead to unnecessary and costly interventions. The findings emphasise the need for improved predictive models and design guidelines to assess performance and ensure safety during repair and continued service. This systematic review integrates more than twenty key studies, identifies the principal parameters influencing the flexural behaviour of beams with exposed reinforcement, and highlights the current lack of normative provisions, hence offering a consolidated foundation for future experimental research and code development.

Keywords

Exposed reinforcement / Unbonded reinforcement / Bridge

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