Effect of Openings on Structural Performance of Unreinforced Masonry Infilled Frames


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Title: Effect of Openings on Structural Performance of Unreinforced Masonry Infilled Frames

Author(s): G. Al-Chaar, G. E. Lamb, and M. A. Issa

Publication: Special Publication

Volume: 211


Appears on pages(s): 247-262

Keywords: cyclic loading; multibay; multistory; openings; reinforced concrete; seismic; stiffness; strength; unreinforced masonry

Date: 2/1/2003

Door or window openngs in masonry infill panels can reduce the lateral strength and stiffness on infill-frame systems. In an effort to study these effects, a series of tests were conducted on half-scale test structures consisting each of three stories and three bays. Infill panels of the control structure were solid with no openings while panels of the second structue were perforated with window and door openings of varying size and location. The test structures were designed to replicate typical building practice of the early 1950's with little or no seismic detailing of frame reinforcement. The test structures were subjected to cyclic in-plane lateral forces to study their strength and deformation capacity under seismic excitation. The cyclic loading was chosen to apply displacemet demands on the structures, representative of those that are expected to occur during strong earthquake motions. Test results discussed in this paper are presented in terms of observed changes in strength, stiffness and deformation capacity of both test structures. Damage patterns and propagation of cracks in the concrete frame and masonry infill during loading are illustrated and discussed in terms of measured histories of force and deflection. Experimental results supported by analytical studies are used to estimate overall reductions in strent, deformation capacity and stiffness due to the presence of openings in the panels.