Interstory Drifts from Shear Strains at Base of High-Rise Concrete Shear Walls

Shear strains may have negligible influence on maximum displacements at the top of slender shear walls, but may significantly increase interstory drift ratios at lower levels where gravity-load columns are often less flexible. A nonlinear finite-element (FE) model calibrated with experimental results confirmed that large shear strains occur in flexural tension regions of concrete walls due to vertical tension strains in the presence of diagonal cracks and in the absence of demand on the horizontal shear reinforcement. A fan of diagonal cracks will form at the base of flexurally hinging walls independent of the shear stress level. A parametric study confirmed that a principal strain angle of 75 degrees can be used to estimate shear strains from vertical tension strains. Thus interstory drift ratios due to shear strains can be estimated from the easily calculated flexural demands. A simple and safe estimate of interstory drift ratio due to shear strains is 60% of the global drift ratio. Interstory drift ratios from shear strains up to 0.8% have been measured in slender wall tests. (C) 2015 American Society of Civil Engineers.