Experimental and Theoretical St.udy on Maximum Reinforcement Ratios of High Strength Concrete Flexural Beams

Abstract

In the current study, experimental and analytical analysis were carried out to propose models for the maximum reinforcement ratios for high strength concrete flexural beams and to compare the behavior of HSC beams with normal strength concrete beams with respect to this point of view. The behavior is represented by failure mode, ultimate load, deflection and strain. The failure mode of HSC beams is relatively different than that of normal strength beams and this is mainly due to the higher degree of brittleness of HSC. High strength beams require more quantity of steel reinforcement to achieve the ductility. Using HSC leads to an increase of the cracking and ultimate loads of beams and to a decrease of ductility. The steel reinforcement of HSC beams should be increased in such a way that yielding of steel should occur first before crushing of concrete to avoid brittle failure. From the given results of failure mode, load deflection relations and from recording the propagation of cracks and failure mode of beams and following the concept of the required steel reinforcement which is given by the code for normal strength concrete, the required reinforcement of HSC flexural beams is determined and given by equations 4 and 5 in the text. The equations are applicable to all grades of concrete (normal and high strength concrete). Analytical analysis is carried out to consider the effect of size of cross section on the required reinforcement. Nonlinear plane stress finite element model is utilized to give the required steel reinforcement considering the size effect. Based on experimental and theoretical results and by using parametric analysis and curve fitting, a model of the maximum required steel reinforcement of high strength concrete flexural beams considering the effect of size is recommended and represented by equation 15 in the text. The model is recommended to be used in the design of beams.