Reinforced High-Strength Concrete Beams in Flexure

Abstract

An important design issue is the ductility or the ability of a reinforced concrete (RC) member to deform at or near the ultimate load without significant strength loss. This article reports on a study of reinforced high-strength concrete (HSC) beams in flexure. The study included flexural test results generated on 16 reinforced concrete beams. Test parameters considered include concrete compressive strength, ratios of tensile and compressive reinforcements, and spacing of lateral ties. The authors found that the current code provisions for serviceability requirements of maximum crack width and ultimate strength are adequate up to a concrete strength of approximately 130 MPa. The authors express concerns regarding the adequacy of current code provisions, however, for cracking moment and service load deflection. They show that stresses generated by shrinkage of concrete and the creep associated with it can significantly affect the cracking moment and service load deflection of reinforced HSC beams. The authors recommend that the ACI Code specification for maximum spacing of ties in RC flexural members need to be reduced to d/4, particularly at critical sections. This will prevent premature disintegration of the confined concrete core in the compression zone due to buckling of compression reinforcement.