A STUDY ON THE BEHAVIOR OF RC BEAMS PROVIDED WITH WELDED WIRE MESH AS A CORE ZONE REINFORCEMENT

Abstract

It is a known fact that the Reinforced Concrete (RC) due to its inherent advantages, occupies a prominent place among several materials used in building construction. While carrying the different building loads the reinforced concrete members are subjected to flexure, shear and torsional affects. In the design of concrete structures, it is generally desirable to ensure that ultimate strengths are governed by flexure rather than shear. Hence from the point of structural safety, the RC members are designed primarily to flexure and are normally engineered to fail in flexure rather than in shear at ultimate. This is because the shear failures are characterized by sudden and brittle in nature compared to the ductile modes of failure due to flexure. Shear failures, which in reality are failures under combined shear forces and bending moments, are characterized by small deflections and lack of ductility. Several research studies conducted in the past have investigated about the factors affecting shear failure and developed numerous models, theories and designs to understand the same. For resisting different loads, the RC members are normally reinforced with both longitudinal and transverse reinforcement to take care of flexure and shear respectively. The resistance to shear in RC members is in general contributed by (i) Shear strength of concrete and (ii) Shear strength due to transverse reinforcement. The different types of reinforcement used for resisting shear in RC members include bent up / cranked bars, transverse reinforcement in the form of vertical or inclined stirrups. The bent-up bar capacity towards shear resistance in RC members is in general limited due to their in-effectiveness in the event of load reversals. In general, the Reinforced concrete (RC) beams subjected to transverse loading create non-uniform bending accompanied by internal shear forces. With the result the Reinforced concrete beam cross-section experiences the normal and flexural shear stresses. In homogeneous rectangular cross sections, the intensity of flexural shear stress becomes zero in the outer edges and reaches maximum at the neutral axis i.e., near the core zone of the cross- section The stirrups go around near to the periphery. This kind of placement of stirrups in reinforced concrete beams leaves the core of the cross section where there is existence of high transverse stress (shear stress), unreinforced. At present, the RC beams are provided with rectangular stirrups (having required diameter, spacing and number of vertical legs) for resisting shear force. Further the stirrups provide resistance against diagonal tension due iii to shear only in discrete manner. This leads to sudden appearance and propagation of cracks, leading to brittle failures under shear. Hence, a hypothesis is made that by providing any form of effectively anchored reinforcement in the core zone that intersects these shear cracks will improve the performance of RC members under the influence of transverse stresses. Keeping the hypothesis in mind, a novel means of resisting shear and simultaneously improving the performance of reinforced concrete members by using a prefabricated mesh such as Welded Wire Mesh (WWM) as a core zone reinforcement is presented in this investigation. In this investigation, the welded wire mesh is used either as transverse reinforcement replacing totally the conventional stirrups or as longitudinal core reinforcement apart from conventional rectangular stirrups /ties to resist against diagonal tension due to shear. An experimental and numerical investigation was carried out in four different phases to ascertain the efficacy of the core zone reinforcement in the form of Welded Wire Mesh (WWM) used either as transverse reinforcement replacing totally the use of conventional stirrups or as longitudinal core reinforcement apart from conventional rectangular stirrups, in improving the performance of RC beam in shear. The effect of WWM as a core zone reinforcement was quantified by introducing a parameter termed as ‘Mesh Index’. Further the usefulness of ‘mesh index’ was studied in RC beams with different shear span to depth ratio, provided with WWM as a core zone reinforcement. Also, the numerical simulation of RC beams provided with welded wire mesh as shear reinforcement using ABAQUS is made and the results were compared with the experimental shear strength. The investigation concluded that for the similar spacing of transverse steel, even the less quantity of transverse steel in the form of WWM will be able to provide similar or better performance of RC beams compared to that of RC beams having conventional stirrups. Further the nature of failure / behavior of the RC beam remained more or less similar with the replacement of conventional stirrups with welded wire mesh as a core zone transverse reinforcement for the same spacing of transverse steel in the form of mesh / stirrups.