SEISMIC PERFORMANCE ASSESSMENT OF ALL-MASONRY INFILLED FRAMES USING FINITE ELEMENT STUDY

Abstract

This research study presents the seismic performance assessment of a newly proposed masonry infilled frame system, referred to as all-masonry infilled frames, under in-plane seismic loading conditions. Unlike conventional masonry infilled frames where reinforced concrete or steel is often used as the bounding frame material, the bounding frame of all-masonry infilled frames is made of masonry units. A literature review revealed that there are limited systematic studies on seismic behaviour and performance evaluation of masonry infilled frames in general. There are no design provisions available in the North American masonry design standards addressing the seismic design of masonry infilled frames. This study was motivated to fill the research gap in seismic behaviour and performance evaluation of masonry infilled frames. A numerical study using finite element modeling and supplemented by experimental testing was the main strategy adopted in the study. The physical specimens were tested to 1) experimentally evaluate the behaviour and strength of all-masonry infilled frames under loading conditions that can be achieved with the laboratory capabilities; and 2) provide results for validation of the finite element model. The numerical study began with the development of a finite element macro-model capable of incorporating properties of masonry infilled frames using OpenSees. The model was verified under both monotonic pushover and quasi-static cyclic analyses. Subsequently, the model was used in a finite element study to conduct the seismic performance assessment of all-masonry infilled frames covering a range of design parameters. The experimental results showed that all-masonry infilled frames exhibited similar behaviour in terms of stiffness and strength as their infilled RC frame counterparts. However, differences in terms of ultimate failure mode were observed. While the infill corner crushing was the predominant failure mode for the infilled RC frames, diagonal cracking extending into the boundary columns was the governing failure for all-masonry infilled frames. The post-ultimate behaviour of all-masonry infilled frames was sustained with higher displacement ductility than their infilled RC frame counterparts. The developed model showed that its novelty from existing models was its consideration of infill shear behaviour. While diagonal struts were used to represent the compressive behaviour of the infill, the shear behaviour of mortar joints was captured by a shear spring, configured in a serial manner with the struts. The compressive constitutive law assigned to the struts and the shear behaviour assigned to the shear spring were defined based on material properties observed in the auxiliary tests on masonry prisms. The verification showed that the proposed multi-strut-spring model simulated the in-plane response adequately for both static and cyclic loading conditions. The seismic performance assessment of all-masonry infilled frames was conducted using Incremental Dynamic Analysis (IDA) technique. Eight all-masonry infilled frame archetypes with different design parameters were analysed under 22 pairs of strong ground motion records. The seismic performance of all archetypes was presented in terms of IDA curves, pushover curves, and fragility curves for three levels of performance limit states. Seismic response modification factors were also determined for all archetypes. The results showed that the all-masonry infilled frames attained a seismic modification factor, R, comparable to the SFRS category of moderately ductile to ductile masonry shear walls as defined in the Canadian masonry design standard CSA S304-14.