STUDY OF SEISMIC BEHAVIOUR OF MASONRY INFILLED RC FRAMES

Abstract

This thesis was motivated to investigate the seismic behaviour and seismic performance of concrete masonry infilled reinforced concrete (RC) frame systems. In this case, the masonry infills are constructed in tight contact with the frame and thus considered as “participating” infills in load sharing. The study aimed to provide a numerical framework for assessing the seismic performance of such structures as a Seismic Force Resisting System. The study contains three distinctive components. First, the study developed and validated a meso-finite element model using OpenSees software to analyze masonry infilled RC frames . The model was used in a reliability study where the failure probability of infill walls was calculated with spatially varying random fields of masonry compressive strength and under seismic loads of varying return periods. An algorithm was developed to estimate the resistance factor specified in the Canadian masonry design standard CSA S304-14 for masonry infills. Results suggested that the S304-14 resistance factor is conservative and a value of 0.65 was proposed. A relationship was established between the required resistance factor and the desired reliability index for six Canadian cities for the reliability aspect of design of masonry infills. The second component involved the development of a macro-model capable of representing the behaviour of masonry infilled frames under cyclic loading with much improved efficiency. Using compression struts in combination with a shear spring configurated in a serial manner, the model considered the infill compression, infill shear and frame failures as potential failure modes. The effect of infill openings was also considered by incorporating the concept of strut width reduction factors in the model. The validation of the model against the test results showed that the proposed model simulated the in-plane response adequately for both static and cyclic loading conditions and for infills with and without openings. The final component involved a seismic performance assessment study of masonry infilled RC frames using the Incremental Dynamic Analysis technique. Seven masonry infilled frame archetypes with varying design parameters were analyzed under 30 pairs of strong ground motion records. Seismic performance was presented through IDA curves. The fragility curves were presented and discussed for distinct performance limit states, including immediate occupancy (IO), life safety (LS), and collapse prevention (CP). The results showed that infills enhance the seismic performance of the frame structure. However, using the CSA S304-14 infill design provisions overestimates this effect. A specific provision needs to be developed for the design of masonry infilled frames under seismic loading.