Shear Capacity of Concrete Beams without Shear Reinforcement under Sustained Loads

Abstract

Concrete is one of the oldest and most widely used construction materials in the world and possesses many unique qualities such as versatility, aesthetic appeal, eco-friendliness, cost-effectiveness and availability. Increasingly, architects and engineers are making concrete their material of choice. Its strength, durability and natural thermal mass result in structures that require low maintenance, offer high durability and have high operating energy efficiency. Well designed and well placed concrete offers exceptional durability and long life in any structure. Concrete structures built over 100 years ago, indeed as long ago as the Romans, are still in active service today. Infrastructures like underwater tunnels that are built in 1960’s and 1970’s are under sustained loading. At this point, the question is “are these structures as safe as the construction day or there is any reduction in the capacity (Shear or bending)?”. 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 when subjected to long-term 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 inplane loading conditions. In spite of substantial experimental and theoretical efforts in the past, the shear transfer mechanism in concrete in case of sustained loading is not well known. When a concrete beam is under high sustained loading, flexural crack 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 the 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 propagate 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 high sustained loading, the crack length and therefore the crack width will increase. The aim of this research is to predict the time-dependent mechanical behaviour of concrete beams subjected to sustained loads. The results should enable the designer to quantify the failure load (Ultimate load) and deformations and the propagation of the cracks of beams under sustained shear loads.