Experimental research on the capacity of bridge shear keys

Abstract

Conceptual design of bridges has evolved rapidly during the last ten years and new, efficient and cost effective design schemes have been introduced in practice. Use of shear keys, as an active seismic link, is not prohibited in current codes. However, the major concern of having the shear keys damaged one-by-one due to their asynchronous participation still remains an open issue. As such, shear keys are typically used to prevent potential span unseating. Shear keys, also known in European literature as seismic links or stoppers, are stub RC structural elements. A capacity design procedure is provided for these elements, to safeguard the support of the deck. Design of shear keys engineering is an open issue in contemporary bridge. Current state-of-the-art deals with the efficient use of reinforcements, while practitioner engineers dealt with the seismic role of these elements and have proposed different materials for the design of stoppers and/or different reinforcement materials, since sacrificial shear keys can respond as structural fuses to limit the demand of the piers. Shear keys, whether they receive seismic actions or not-the last referring to the case in which keys are utilized to avoid the common unseating of the spans-have peculiar response and unconventional reinforcement requirements due to their loading. Simultaneously, their geometry and size is restricted due to bridge's esthetics. Hence, stoppers are relatively small and stub concrete "blocks", which are expected to receive reliably and safely large pounding forces. In this framework, two alternative reinforcement layouts with transverse hairpin bars were assessed. The efficiency of the proposed reinforcement was assessed by comparing the above rebar with the state-of-practice shear key reinforcements. The required hairpin reinforcement ratio was then evaluated through an analytical procedure that accounted for the relation between the reinforcement hairpin ratio vs the capacity of the shear keys. The procedure indicated the most appropriate reinforcement ratio for a required capacity of the stopper. The study proposes the reinforcement of the stoppers with additional diagonal rebar. Conclusions are drawn based on the analytical models and the experimental campaign.