Experimental and analytical investigation of masonry infill and confined masonry wall assemblies

Abstract

Masonry has the benefit of strength and ease of construction but lacks the ability to resist lateral forces due to its brittle nature. However, with the addition of concrete confining frames to plain masonry walls, additional strength and ductility can be attained. Two such confinement systems include masonry infill and confined masonry walls. Currently, masonry infill assemblies are the most common form of lateral force resisting systems in countries where access to more traditional concrete and steel materials is limited. However, recent studies have stated that confined masonry provides improved performance because of the bond between the concrete and brick. This thesis presents an investigation of the behavior of both types of concrete confinement methods and identifies advantages of each system with regards to strength, ductility, and performance during strong ground motion events. To accomplish this objective, 1/3-scale specimens were constructed and tested in direct shear to determine the load-displacement response for both masonry infill and confined masonry walls and compared with results of each type of concrete confinement technique as compared to a plain masonry specimen. The masonry infill wall strength was 35% larger and deflected ten times more than the plain masonry wall at peak load. The confined masonry showed 80% more strength capacity; however, only deflected 2.5 times more than the plain masonry wall at peak load. The test results were incorporated into analytical models that approximated the load displacement response observed during the tests. The models were used to perform a nonlinear push-over analysis on a reduced scale 5-story building damaged by the Nepal earthquake. The first story walls of the confined masonry model failed at a base shear that was 27% larger than the masonry infill model. First story drifts were 64% larger in the masonry infill model. This supports the general observation that each wall has merit in a specific design scenario. Masonry infill walls may be preferred in for designs where energy dissipation may be critical. On the strength side, confined masonry walls may be preferred where strength is preferred over ductility.