Analytical model for non-ductile moment frames with masonry infill walls and retrofit method using friction dampers

Abstract

Most columns in non-ductile reinforced concrete (RC) do not satisfy the reinforcement details demanded by current seismic design codes. Such columns exhibit brittle shear failure before or after yielding of longitudinal reinforcements caused by significant pinching and cyclic deterioration in their strength and stiffness. In order to prevent the collapse of non-ductile RC buildings, it is necessary to identify the accurate seismic performance of those buildings, and to retrofit them with the most appropriate method. In this dissertation, numerical model that can accurately and efficiently simulate the cyclic behavior of non-ductile RC columns considering pinching and cyclic deterioration is proposed. Modeling parameters are calibrated to the test results of 40 RC columns with shear failure. Forward stepwise regression analyses are conducted to propose the empirical equations of the modeling parameters. It is shown that the Pinching4 model with the proposed empirical equations accurately simulates the cyclic behavior of shear-critical columns including pinching and cyclic deterioration in strength and stiffness. In addition to the proposed RC column models, masonry infill wall model is also proposed to understand the contribution of partial- and full-height infill walls to the RC frames. For this purpose, three RC frame specimens were tested under quasi-static cyclic loading. Numerical model parameters for the masonry infill walls were calibrated to match the observed cyclic curves of the tested frames. Three gravity load designed three-story frame models are considered (bare-, partially infilled- and fully infilled-frames). Numerical analyses were conducted for the frame models. By adopting the proposed component models for non-ductile RC frames, a method for the design of friction damping systems is proposed. The proposed retrofit method mainly targets the low- to mid-rise regular reinforced concrete (RC) buildings. The proposed method is verified using a six-story RC building designed considering only gravity loads. This dissertation includes important contributions to (1) modeling method for columns in non-ductile RC buildings through the development of efficient concentrated plasticity model; (2) modeling method for partial- and full-height infill walls based on the experimental results and numerical parametric assessment; (3) simple and non-iterative friction damper design method that can improve the seismic performance of non-ductile RC buildings.