Evaluation of Properties of Steel Reinforcing Bars for Seismic Design

Capacity design procedure for the earthquake-resistant reinforced concrete (RC) structures is effective when actual member capacities do not greatly exceed the assumed design capacities. Moreover, RC members are expected to undergo large inelastic deformations for adequate seismic energy dissipation. Since flexural capacity and post-yield behavior of an RC member is largely controlled by steel reinforcing bars, it places certain special requirements on their properties, such as, yield strength (YS), ultimate tensile strength to yield strength ratio (UTS/YS ratio) and elongation, which are sensitive to the method of rebar manufacturing. Flexural tests on thirty RC beams which used rebars of carefully controlled properties was conducted and it was observed that for dependable flexure behaviour, YS and UTS values should lie in a narrow band around values used in the member design. If these values are greater than the specified value, it may cause brittle shear failure instead of more ductile and desirable flexure mode of failure. Moreover, a high UTS/YS ratio equal to 1.25 is necessary to have dependable peak strength which is larger than the yield strength.