Coupling Beams of Reinforced Concrete Shear Walls

The behavior of short and relatively deep reinforced concrete beams, which occur in shear walls of multistory structures, and the damage or failure of which has been observed in recent earthquakes, is examined. Experimental and analytical studies indicate that their ultimate flexural capacity is reduced by large shearing forces, even if a diagonal tension failure is prevented by adequate web reinforcement. After diagonal cracking, the distribution of internal forces radically differs from that observed in beams of normal proportions. The flexural reinforcement is found to be in tension in areas where compression is expected, and this affects the beam's ductility. Shear deformations of diagonally cracked coupling beams greatly overshadow those causd by flexure. With the aid of a model of the cracked beam its stiffness can be approximated. This satisfactorily agrees with observations which indicate that the stiffness after cracking is less than 20% of the stiffness of uncracked coupling beams.