UC San Diego

Unreinforced masonry panels are often used as interior or exterior partitions in reinforced concrete frames. How infills affect the seismic performance of an RC building is an intricate issue since their exact role in the seismic load resistance is not yet clearly understood due to the interaction with the bounding frame. Assessing this role presents a challenge for structural engineers due to the variety and complexity of observed failure mechanisms and the lack of reliable methods able to capture these mechanisms. Furthermore, there is a lack of experimental data from large-scale dynamic tests of multi-story, multi- bay infilled frames to validate the analytical tools. This dissertation addresses this intricate issue with extensive analytical and experimental studies. The testing program involved quasistatic tests of small and large-scale specimens with and without openings and shake-table tests of a large-scale, three-story, two-bay, RC frame. This frame, which had a non-ductile design and was infilled with unreinforced masonry panels with openings, was the largest structure of this type tested on a shake table. The design of the specimens, the testing procedures, and the obtained results are discussed in this dissertation as they enhanced the understanding of the structural behavior. The experimental data has been used to validate the proposed analytical tools. These include a nonlinear finite element methodology and a simplified assessment tool for the engineering practice. The finite element modeling methodology combines the smeared and discrete crack approaches to capture the shear and flexural failure of RC members, crushing and splitting of brick units and the mixed-mode fracture of mortar joints. A systematic approach has been developed to calibrate the material parameters, and the comparison with the experimental results indicates it can successfully capture the nonlinear behavior of the physical specimens. The validated models have been used in parametric studies to identify the critical material parameters and assess the influence of design parameters and variations of the geometrical configurations to the structural response. The parametric studies and experimental findings have been used to develop a simplified method for the structural assessment of infilled frames. The proposed approach can estimate the structural performance, including the stiffness and strength and can be used for the construction of simple strut models for an entire structure