Shear failure of prestressed girders in regions without flexural cracks

Abstract

In the design process of prestressed bridges and viaducts, the required amount of shear reinforcement is determined with a model that assumes the presence of flexural cracks. In order to keep the design process simple, this model is also prescribed to determine the amount of shear reinforcement for the regions of the structure in which, at the ultimate load, no flexural cracks are present. This is a conservative approach, as the conditions for shear transfer are more favourable in the regions without flexural cracks. From structural assessments of existing prestressed bridges and viaducts, it is found that the amount of shear reinforcement is frequently too low in the regions that remain free of flexural cracks. Accordingly, these structures are considered as unqualified, although the actual shear resistance could possibly be sufficient. This is the prime motivation for this research, in which the shear behaviour of prestressed girders in regions without flexural cracks is investigated.Two models are proposed in this dissertation for the determination of the shear resistance in the regions without flexural cracks: –a model for diagonal tension cracking and –a model that considers the contributions of stirrups, aggregate interlock and uncracked flanges after diagonal tension cracking. Depending on the amount of shear reinforcement and the level of prestressing, the governing resistance will be present in either one of these stages. With the proposed models it has become possible to determine the shear that can be resisted in regions without flexural cracks more accurately. The use of the proposed models will therefore prevent that numerous bridges and viaducts are strengthened or replaced while the actual shear resistance is sufficient.