Nonductile behavior of reinforced concrete frames with masonry infill panels subjected to in-plane loading

Lessons learned from earthquakes in the last fifty years have spurred changes in building seismic code requirements. As these requirements became more stringent, structural evaluation of old structures became necessary to determine their seismic vulnerability.; This study addressed a popular type of building in high seismic zone that have lateral load-resisting systems constructed from reinforced concrete (R/C) frames with masonry infill panels. The R/C frames in old structures do not have the ductile detailing required for modern construction in high and medium seismic zones. Masonry infill panels were also not recognized as integral structural members and were exempt from old and current building code specifications. It is obvious that the masonry infill panels in a structural frame, not only add significant strength and stiffness, but also influence the dynamic behavior of the entire building.; An experimental program was carried out to evaluate this structural system. Five single-story half-scale laboratory models with different numbers of bays were constructed. The five models represent: a single-bay bare frame, single-bay with CMU infill, single-bay with brick infill, double-bay with CMU infill, and triple-bay with brick infill. These models were fully instrumented and tested under lateral in-plane loading to failure. Prior to cracking, the infill redistributes the stresses in the frame resulting in more displacement and stresses in the windward column than that of the others. After cracking, diagonal struts were developed in the infill, resulting in increasing the overall strength of the infilled frame.; Non-linear finite element analyses were carried out on the experimental models. Load-deflection curves for FEA reasonably predicted experimental behavior of specimens in terms of deflection. Ultimate failure load corresponding to each specimen was predicted with accuracy.; Finally, a new idealized analytical model was proposed to determine the capacity evaluation of this structural system. This model characterizes the strength and stiffness behavior of multi-bay frames with infilled masonry. Post-yield behavior, residual strength, and the effects of bay multiplicity on structural behavior were also presented.