Effects of RC ties on seismic performance improvement of confined masonry walls under combined in-plane, out-of-plane, and vertical loads

Abstract

This study aimed at understanding the role of vertical RC ties in the seismic performance improvement of confined masonry walls under combined in-plane, out-of-plane, and vertical loads through nonlinear static analysis. For this purpose, finite element models were developed using simplified micro modelling method which were verified against the experimental results. Then, parametric studies were carried out to evaluate the response sensitivity of the masonry walls to the interaction of in-plane, out-of-plane, and vertical seismic demands. Two sets of wall models were considered; one without RC vertical ties (URM) and the other with these structural members (CM). Two ratios of height-to-length for the walls and five levels of vertical loads (representing resultant forces from dead, live, and vertical ground motion component loads) were considered. The loading was applied according to two protocols; (1) applying vertical loads prior to the application of in-plane displacement, and (2) applying out-of-plane uniform pressure after employing three different levels of vertical loads and then two different levels of in-plane displacements. It was found out that the in-plane strength of CM walls, in the worst case, changed –22% and 0% under 1 g of upward and downward vertical ground motion acceleration, respectively with respect to the wall under gravity loads only; whereas, this change for the corresponding URM walls is −100% and + 43%, respectively. The sensitivity of out-of-plane strength of CM walls to prior in-plane and vertical ground motion acceleration in the worst case was also found marginal; with −17% to −1% change under 1 g of upward and downward vertical ground motion acceleration, respectively. The change for the corresponding URM walls was −100% and −27%, respectively.