Investigation of the Linear and Non-Linear Dynamic Behavior of Existing Reinforced Concrete Buildings through Tests and Simulations
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This dissertation presents a comprehensive experimental and numerical investigation of the linear and nonlinear dynamic response of Reinforced Concrete (RC) buildings to dynamic loads. To this end, two actual RC buildings were tested using eccentric-mass shakers. The first test structure, located in Utica, NY, was a ten-story RC building deteriorated due to the severe winters in the area. The second building had a two-story infilled RC frame, located in El Centro, CA, and was damaged by major earthquakes. The vibration tests aimed at understanding the system-level dynamic behavior of buildings with and without damage. The effect of the excitation direction, amplitude, and frequency on the linear and nonlinear structural response is also investigated. To achieve these goals, a number of infill panels were sequentially removed from both structures, and shaker excitations with varying characteristics were performed at each removal stage. The recorded data were also used to assess the accuracy and sensitivity of system identification methods often used to estimate the dynamic properties of structures. A time- and a frequency-domain method are employed to estimate the dynamic properties of the buildings and recommendations for the selection of the reference channels are provided based on the results of a parametric study. The test data from the two-story building indicate that the structure exhibited significant nonlinearity during the forced-vibrations due to the opening of cracks in the frame and the infill. Due to the nonlinearity, the resonant frequencies dropped drastically while the deformation of the structure was a combination of the mode shapes identified using the ambient-vibration data. The contribution of each mode changed depending on the excitation frequency, direction, and amplitude.The numerical studies focus on developing tools that can efficiently, yet accurately, simulate the important features of the building response. This includes the decision regarding the structural and non-structural components that need to be included in a numerical model, as well as the hysteretic rules governing the nonlinear behavior of infilled frames. The validated building models are employed to assess the accuracy of building-code provisions related to the estimation of the fundamental period and eccentricity. Moreover, a nonlinear material law, which accounts for the evolution of strength and stiffness of infills, is proposed and implemented. The material law is validated with laboratory tests, as well as data from the building in El Centro. In fact, the model of the two-story building simulates the damaged condition of the building, and the response of the building to the dynamic tests with good accuracy.