Shear Capacity of Concrete Beams without Shear Reinforcement under Sustained Loads

Abstract

Concrete is a multiphase granular material consisting of aggregate particles of various sizes and irregular shape, embedded in hardened cement paste. The physicochemical processes during the hardening of the cement cause air voids, micro cracks and interfacial bond micro cracks. As a consequence of this heterogeneous structure, concrete displays a non-linear and time-dependent deformation response under sustained loading. A challenging topic was and still is the failure behaviour of concrete beams without shear reinforcement. The behaviour of cracked reinforced concrete panels can now be satisfactorily predicted for monotonic short-term shear loading conditions. In spite of substantial experimental and theoretical efforts in the past, the shear transfer mechanism in concrete in the case of sustained shear loads is not well known. When a concrete beam is under sustained high loads, a flexural cracking pattern appears along the span. Here, various shear-carrying mechanisms may be developed by a beam, e.g. aggregate-interlock and dowel action. These mechanisms induce tensile stresses in concrete near the crack tip and at the level of the reinforcement. Once the tensile strength of the concrete in these regions is reached, the existing flexural cracks progress in a diagonal direction or new ones are created. The development of the critical shear crack, however, does not necessarily imply the collapse of the member but in case of sustained high loads, the crack width and therefore the crack length will be increased. The aim of this research is to predict the time-dependent mechanical behaviour of cracked concrete beams subjected to sustained shear loads. The results should enable the designer to quantify the failure load (ULS) and deformations and the propagation of the cracks (SLS) of beams under sustained shear loads.