Shear strength of squat reinforced concrete walls subjected to earthquake loading — trends and models

This paper reports research aimed at better understanding the seismic behavior of squat reinforced concrete walls, as well as developing design recommendations. Observations on the seismic shear strength of squat RC walls are presented and discussed. Emphasis is given to the failure mode characterized by inclined web cracking due to diagonal tension. Available design and behavioral shear strength models are compared against experimental data obtained from previous research programs. From studying trends of behavior, a design model for calculating shear strength is proposed and calibrated with experimental results. This model assumes that shear strength is calculated by adding a concrete contribution to the shear resisted by the wall web reinforcement. The methodology follows a simplified strut-and-tie model which is dependent upon the maximum inclined crack width. Shear strength is a function of the moment-to-shear ratio, vertical load, and the percentages of vertical and horizontal reinforcement. Also, the strength model depends on the extent of reinforcement (horizontal and vertical) that has reached plastic strains at a given drift angle. This fact is significantly different from the usual code assumption in which all web reinforcement is assumed to yield at strength. The proposed model is suited for performance-based design because strength is a function of drift angle. The shear strength model leads to a better estimation of wall seismic shear resistance than any other model used in codes and in the literature; for the wall database used, measured-to-calculated strength ratios were very close to 1.0 with the smallest coefficient of variation.