Dynamic shear amplification of reinforced concrete coupled walls

Dynamic shear amplification has been commonly studied in cantilever reinforced concrete wall systems, how-ever, coupling beams or slabs can generate axial loads that can modify the response. A parametric study is carried out that covers 432 nonlinear time-history analyses (72 models with 6 records) of 2 coupled walls with different length, including variations in the amount of boundary element steel ratio (1%, 3% and 5%), amount of slab steel ratio (0.0%, 0.3% and 0.6% - 0.0% is defined for connected walls without coupling), building height (25 m, 50 m and 75 m), and wall length (2 m, 4 m and 6 m). The walls are represented with nonlinear fiber models; while the coupling slabs are elastic within the length with a rigid-perfectly plastic model at both element ends. The shear amplification values depend on the coupling level, with the highest amplification values being observed for connected (not coupled) systems. The high values for connected walls are due to the rapid plas-tification of the wall because of the low structural redundancy. The mean shear amplification values are 1.45, 1.10 and 1.35 for coupling slabs with reinforcing steel ratio of 0.0%, 0.3% and 0.6%, respectively. The proposed expression for the dynamic shear amplification also depends on the response modification factor of the walls, a parameter directly related to nonlinearity sources. On the other hand, an expression used by many codes that depends on the number of floors does not necessarily represent the amplification that occurs in tall buildings with moderate coupling, since the plastification at the base in such cases is difficult to achieve given their large elastic displacement capacity, as well as, cases that incorporate a minimum base shear criterion, that reduce the nonlinearity incursions.