Simulation of Behavior of Concrete Beams Reinforced by Plain Bars

Concrete buildings that have been built before 1960 are mainly reinforced by plain bars. Because of defective bond between plain bars and concrete, the response of such buildings to earthquakes is uncertain. Despite several experimental reports of cyclic behavior of such beams, their mechanical and physical modeling is vague, and little report on this issue can be found in the well-known literature. It is known that the displacement of concrete beams reinforced by plain bars consists of three components: slip, bending, and shear. In this paper, an attempt has been made to develop a model for flexural behavior of beams with plastic hinges, and to expand a formulation for slip of plain bars in concrete. The theoretical model has been verified by tests of three beams. The results show that the effective stiffness of plain-bar- beams is equal to 22% of that of gross section. In addition, displacement ductility of the beams is about 4.5. These properties vary with ratio of longitudinal reinforcement, ratio of sectional dimensions, and arrangement of reinforcements, where all these parameters have been assessed in the study.