Effect of material properties on ductility factor of singly rc beam sections

Abstract

Ductility may be defined as the ability to undergo deformations without a substantial reduction in the flexural capacity of the member. The ductility of reinforced concrete beams depends mainly on the shape of the moment-curvature relationship of the sections. The constituents of reinforced concrete are very complex due to its mechanical properties. The stress-strain behavior of concrete is considered parabolic and that of the steel is elastic plastic. Concrete and reinforcing steel are represented by separate material models that are combined together to describe the behavior of the reinforced concrete sections. The end displacements of the steel element are assumed to be compatible with the boundary displacements of the concrete element which implied perfect bond between them. The curvature ductility factor of singly reinforced concrete rectangular beams is derived taking into account the possible nonlinear behavior of the unconfined compressed concrete and reinforcing steel. Effects of material properties such as concrete compressive strength, reinforcement ratio and yield strength of reinforcement on the curvature ductility factors are derived analytically. From the analyses it is observed that an increasing steel content decreases the curvature ductility of a singly reinforced concrete section and this pattern is valid for any concrete strength. On the other hand, for the same reinforcement content curvature ductility increases as the concrete strength is increased.