Flexural Ductility Assessment and Concurrent Flexural Strength and Ductility Design of Reinforced Concrete Beams

Abstract eng:
Due to its higher strength-to-weight ratio, high-strength concrete is increasingly adopted in the construction of tall buildings and long span bridges. However, apart from better utilising its strength potential, there was only little attention paid to the ductility design of HSC members. Currently, the ductility design of HSC beams rely on some deemed-to-satisfy rules to provide a nominal level of ductility. The main drawback of this method is that it would not provide the same level of ductility, and most importantly much lower ductility, to HSC beams. This is dangerous because the lower ductility in beams would disallow the moment redistribution to occur during earthquake, and eventually lead to brittle collapse. In this regard, a new method that would enable the design of HSC beams with a minimum ductility not less than that provided in the past for normal-strength concrete beams is advocated in this paper. With this fixed minimum ductility set as a nominal requirement in the beams design, a maximum limit of tension steel ratio or neutral axis depth is imposed. These limits are subsequently evaluated using a new method of nonlinear moment-curvature analysis taking into account the stress-path dependence of steel reinforcement. The associated flexural strength that can be designed while achieving the recommended minimum ductility are also evaluated and presented in the form of design charts for practical application.

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