Research On Progressive Collapse Mechanisms Of RC Frames With Infill Walls

Progressive collapse of structures refers to the phenomenon that the collapse of structures disproportionate to the original damage. The original damages are usually triggered by the abnormal loads, design flaws and malevolent events. A series of progressive collapse accidents raised much attentions on this topic, and many experimental and numerical studies on progressive collapse mechanisms of structures have been performed in recent decades. At the present time, progressive collapse studies have been focused on the analyses of the collapse resisting mechanisms of frames, and behaviors of beams, slabs, beam-column joints and steel braces in progressive collapse scenario, and so on. However, study on the role of infill walls played the in the progressive collapse process is limited. In view of these, laboratory experiments and numerical analyses are presented in this dissertation to systematically study effects of infill walls on the progressive collapse mechanisms of RC frame. Four parts are included in this dissertation as follows:(1) A four-bay, two-story bare frame specimen was constructed, and was tested by performing quasi-static loading on the center column using displacement control. The applied load and displacements, cracks development, reinforcement fracture process and reinforcement strains at critical points of the bare frame specimen during the progressive collapse process were observed. Not only the beneficial role compressive arch action played in resisting progressive collapse of frames was analyzed, but also the adverse compressive arch action was discussed.(2) A frame with solid infill walls specimen and a frame with perforated infill walls specimen were constructed, respectively. The reinforcement details, section dimensions and loading approach, and so on are the same with those of the bare frame specimen, except that solid infill walls and perforated infill walls were constructed in the second story of the frames, respectively. The applied load and displacement, cracks development, reinforcement fracture process and reinforcement strains at critical points were observed, and the failure mechanisms of the frame with solid infill walls specimen and the frame with perforated infill walls specimen were discussed. Effects of solid infill walls and perforated infill walls on progressive collapse performance of RC frames were analyzed, by comparing the experimental results of the frame with solid infill walls specimen, the frame with perforated infill walls specimen with those observed from the experiment of the bare frame specimen.(3) Finite element models of the bare frame specimen, the frame with solid infill walls specimen and the frame with perforated infill walls specimen were constructed. The equivalent struts models represented the solid infill walls and perforated infill walls in progressive collapse scenario were discussed, respectively. The finite element modes were validated by comparing with the numerical resu lts and experimental results. The internal forces in the finite element models of the three frame specimens were studied. Parametric analyses of the frame with solid infill walls specimen and the frame with perforated infill walls specimen were conducted to study effects of infill walls strength, reinforcement diameters and frame members dimensions on numerical results of the frame with solid infill walls specimen, and to study effects of infill walls strength and opening dimensions on the numerical results of the frame with perforated infill walls specimen.(4) Nonlinear dynamic analyses were performed on three types of prototype structures in details, including four-bay by eight-story planer bare frame, frame with solid infill walls and frame with perforated infill walls, to study their deformation and internal forces under first story-center column, first story-penultimate column, and first story-external column removal scenarios. The results of three frames from nonlinear dynamic analyses were compared. Effects of bay numbers and story numbers on the responses of three types of frames under column removal scenarios were analyzed.