Shear Capacity of Prestressed and Reinforced Concrete Members: Modeling and Experimental Validation

Despite more than a century of continuous research effort, the problem of determining the shear capacity of a structural concrete member still remains open for discussion. The main reason for the aforementioned dispute can be attributed to the complex nature of shear in structural concrete elements. Near failure, the state of stress of a cracked concrete member generally deviates significantly from the behavior as predicted by the theory of linear elasticity. After the occurrence of inclined cracks, different shear carrying mechanisms are simultaneously activated to resist the applied shear force. The intricacy is furthermore increased due to the vast amount of parameters affecting the aforementioned shear transfer mechanisms. The complexity of the shear phenomenon impedes a straightforward modeling strategy. Hence, a variety of modeling approaches can be found in literature. However, none of the existing modeling procedures are able to fully explain the mechanics behind shear failure. Due to our incomplete knowledge and the brittle failure modes typically associated with shear, current codes of practice tend to propose highly conservative design equations, specifically in the case of prestressed concrete members.The present research therefore assesses the mechanical behavior of shear-critical prestressed and reinforced concrete members based on experimental research, nonlinear numerical simulation and analytical modeling. An extensive experimental dataset was obtained containing the results of 24 full-scale structural tests on prestressed and reinforced concrete elements. The constructed dataset not only covers the failure properties of all specimens but also includes a vast amount of discrete displacement and deformation data obtained from two advanced optical measurement methods, i.e. 3D CDD-LED Coordinate Measurement Machine (CMM) and Stereo-vision digital image correlation (DIC). Based on the performed experimental research, a large discrepancy was found between the experimentally observed and analytically predicted failure load and failure mode using current Eurocode 2 shear design equations. To further investigate on the aforementioned discrepancy, a nonlinear finite element model was constructed which was validated with the obtained experimental results. A good correlation was found between the experimentally observed and numerically predicted failure properties (i.e. failure load and failure mode), displacement and deformation data. Based on the numerical results, the mechanical behavior of the reported test specimens was thoroughly investigated. It was found that direct strut action is the main bearing mechanism for the vast majority of the reported experimental test beams.The identified structural behavior is finally converted into comprehensible analytical engineering models. It was found that the proposed analytical modeling approaches perform much better in estimating the experimentally observed failure load and failure mode if compared to the performance of current Eurocode 2 shear design equations. Based on the performed analytical work, a code proposal is derived in the case of concrete elements with a point load close to the support and a solution procedure for a forward analysis is presented. Additionally, a general theoretical framework is presented for shear in slender structural concrete members based on a thorough analytical study of all shear carrying mechanisms.status: publishe