Use of Internal Structural Steel Strip Bands as Shear Reinforcement in Concrete Beams

Abstract

A new method of lateral shear reinforcement is investigated in which a reinforced concrete (RC) beam is transversely reinforced by Internal Structural Steel Strip Bands (ISSSBs), instead of conventional stirrups. The steel strip bands are cut to a specified width from structural steel squares or rectangular tubes of desired thickness, and the size of the bands depends on the cross-section of the RC beam. This method has the potential of improving the strength and ductility characteristics of RC beams subjected to shear without increasing the amount of steel reinforcement and congesting the steel rebar cage. With the use of ISSSBs, it is believed that the beam reinforcement will be less congested and the concrete core of the beam will be better confined; thus, delaying the formation of cracks and increasing the ductility. A comprehensive literature review on the subject has revealed no published work on this new type of transverse reinforcement; hence, no established design guidelines are in place for such a system. The purpose of the study is to check the applicability of current structural design codes to concrete beams reinforced with ISSSBs and develop appropriate recommendations and design guidelines. To achieve objectives of the study, an experimental testing program was implemented in the laboratory on half-scale beam specimens to compare the performance of ISSSB reinforced beams with the corresponding performance of stirrups reinforced beams in terms of shear strength, stiffness and ductility. The experimental program was complemented with a theoretical analysis. The study considered various cross-section dimensions, shear-span-to-depth ratios, transverse steel volumetric ratios, and strip band thickness-to-width ratios. Results of the study showed that the shear strength of strip reinforced beams matched the corresponding stirrups reinforced beams at the low shear span-to-depth ratio and exceeded the stirrups reinforced beams at the high shear-span-to-depth ratios. For the considered shear span to depth ratios, the beams transversely reinforced with strips exhibited higher ductility and residual strength than the corresponding beams that were reinforced with stirrups. In general, the ACI 318 code, Modified Compression Field Theory, and Eurocode2 can be safely used to predict with reasonable accuracy the shear strength of ISSSB reinforced beams.