Prediction of stiffness of reinforced concrete shearwalls under service loads

Reinforced concrete (RC) shearwalls are common structural components used in tall buildings for efficiently resisting lateral loads. Because of low tensile strength of concrete, reinforced concrete shearwalls tend to behave in a nonlinear manner with a significant reduction in stiffness, even under service load. The ratio of the area of the moment diagram segment over which the working moment exceeds the cracking moment S_cr, to the total area of moment diagram S is proposed as representing the probability of the occurrence of cracking. This probability is then used to calculate the effective moment of inertia for shearwalls loaded in the serviceability range. Verification of this method has been confirmed from a series of reinforced concrete shearwall experiments. Comparison between flexural deflections determined from a test series, and theoretically determined values, shows that the proposed method can provide an accurate prediction of both flexural deflections and flexural stiffness reduction of shearwalls subjected to loadings in greater than 50% ultimate lateral load. The experimentally determined shear deflections of these walls indicate that, with a vertical load on the shearwall of a value up to 0.2 f_c′ of the linear shear deformations will respond in a linear behavior up to 65% of the ultimate lateral load, which can be satisfactorily predicted by the linear theory.