Response of Full-Scale Slender Masonry Walls with Conventional and NSM Steel Reinforcement Subjected to Axial and Out-of-Plane Loads

The response of four slender reinforced masonry walls to combined axial and out-of-plane loading is presented herein. The testing series compares the response of walls with conventionally embedded steel reinforcing bars to those with near-surface-mounted (NSM) steel reinforcement. Each wall was constructed from 190 mm wide hollow concrete masonry units to a length of 1,200 mm and a height of 7,800 mm, with a gross reinforcement ratio of 0.26%. Each wall was simply supported and loaded cyclically in the out-of-plane direction within the elastic response range (up to 90% of the nominal yield strain of the reinforcing bars) with the applied axial loading ranging from 0 to 250 kN. The moment resistance of each wall increased with increasing applied axial load; however, the out-of-plane load resistance of the conventionally reinforced walls decreased due to secondary moment effects. The stiffer walls with NSM reinforcement exhibited increasing out-of-plane load resistance due to the increasing moment resistance and to the lower displacement of the system which reduced secondary moment effects. The final loading cycle of each wall displaced the walls to at least twice the yield displacement while maintaining an imposed axial load of 60 kN (for both conventionally reinforced walls and one of the walls with NSM reinforcement) or 120 kN (for one of the walls with NSM reinforcement). Comparing the response of the walls in their final loading cycles, the conventionally reinforced and NSM reinforced walls had similar maximum moment resistance; however, the average out-of-plane load resistance at the yield point of the walls with NSM reinforcement was 180% of the conventionally reinforced walls. This experimental series represents the first full-scale tests of very slender concrete block masonry walls reinforced with NSM steel bars.