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Numerical analysis of masonry-infilled reinforced concrete frames subjected to seismic loads and experimental evaluation of retrofit techniques


Masonry-infilled reinforced concrete (RC) frames constitute a significant part of the building inventory in earthquake-prone regions around the world. The development of accurate analysis tools and of retrofit techniques is important for enhancing the seismic safety of older construction of this type. Most of the existing analytical approaches have either adopted simplified models with limited predictive capabilities or been restricted to the monotonic loading regime. Additionally, many of the retrofit methods used in practice have not been experimentally validated. The present study aimed to establish and use refined computational tools for the reliable and robust analysis of masonry-infilled RC frames with and without retrofit, and to experimentally validate recently developed retrofit schemes. Constitutive models have been developed to allow the analysis of infilled frames. An existing smeared-crack model has been enhanced to accurately describe diffuse cracking and crushing in concrete and masonry under cyclic loading. Furthermore, a novel cohesive interface model has been formulated to describe strongly localized cracks in the concrete columns and the behavior of the mortar joints. The model can account for various aspects of the cyclic behavior, such as the cyclic normal unloading/reloading response, the frictional sliding and geometric dilatation and the irreversible crushing under large compressive stresses. A major challenge was the formulation of a robust stress update algorithm, which is also presented. The models are validated with experimental tests at the material and at the structural level. The analyses demonstrate the capability of the models to accurately capture the response of infilled frames. The results of large-scale, shake-table tests on a masonry-infilled RC frame are also presented. The purpose of the tests was to evaluate two retrofit methods for infills, using overlays of Engineered Cementitious Composite material (ECC) and of Glass Fiber Reinforced Polymer (GFRP). The material properties, specimen configuration, input ground motions and experimental observations are described in detail. Both retrofit techniques improved the performance of the specimen. A series of nonlinear analyses has been conducted to provide further insight on the behavior of the retrofitted specimen. Dynamic analyses have been conducted for infilled RC frames subjected to a collection of eight ground motions, scaled to match a target intensity level. The results of the analyses indicate that the addition of an ECC overlay can significantly improve the performance of an infilled frame

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