Effect of Rotational Base Stiffness on the Behavior of Load-Bearing Masonry Walls

Slender load-bearing masonry walls are typically used in low-rise commercial and industrial settings, where they are an efficient system to resist out-of-plane forces and gravity loads. Masonry walls are usually built upon concrete footings, with their first course mortared upon the concrete surface, and their reinforcement is spliced to dowels cast into the foundation. Despite the inherent rotational stiffness of this type of connection, when the walls are slender (height-to-thickness ratio $>30$) North American masonry codes direct the designer to assume a pinned condition at the base, neglecting the rotational stiffness provided by the foundation. This is because of the valid concern that the damage at the base under cyclic loading degrades the connection rapidly, turning it effectively into a hinge for structural purposes. Due to the scarcity of experimental studies on this topic, the objectives of this study are to (1) quantify the reactive rotational stiffness at the support for typical foundations used in masonry construction, (2) assess the increase in load-bearing capacity provided by the base stiffness during cyclic load, (3) investigate the base damage, and (4) determine the effect of the foundation stiffness on critical aspects of the structural response of the walls, such as stiffness, ultimate capacity, energy dissipation, and failure modes. To accomplish this, four moderately slender load-bearing masonry block walls were built with different degrees of base stiffness and tested under a combination of gravity and nonreversed cyclic lateral loads. Results from the tests showed an increase in load-bearing capacity and decreased deflections with increased rotational base stiffness. The walls achieved their ultimate loading capacity with little to no degradation at the base during the experiment. The moment capacity of the walls obtained during the tests exceeded that predicted by the design provisions. These results suggest that accounting for the additional strength provided by the base may be important for the design of other elements connected to the walls. It also highlights the need for additional cyclic testing on masonry walls with higher slenderness, accounting for the presence of a rotational stiffness at the base.