Study On The Progressive Collapse Mechanism Of RC Frame Structures

With the increasing of terrorist attacks worldwide, more and more researchers start to focus on the problem of the progressive collapse of building structures. Local damage of buildings may be caused by the accident loads, such as the earthquake, explosion, fire disaster and so on. The progressive collapse of structures is defined as the spread of an initial local failure from element to element, eventually resulting in the loss of bearing capacity for main structure and the collapse of a disproportionately large part of it. The consequences would be catastrophic once the happening of progressive collapse of building structures. As a result, all kinds of extreme loads must be taken fully into consideration in order to improve the progressive collapse resistance of building structures and to ensure the safety of life and property for people.According to the dynamic experimental results of RC (reinforced concrete) members, the mechanical properties at different loading rates were studied. Based on experimental results, the tri-linear restoring force model of RC members, which took into account the loading rate effect and stiffness degradation caused by the damage of concrete, was developed. Then the failure criterion was established on the base of the failure characteristics for RC members at different loading rates.The dynamic experiment of RC members was simulated with the finite element analysis software MSC.Marc and the results were compared. Results showed that the rate-dependent model, taken account into the loading rate effect and stiffness degradation, could reflect preferably the dynamic behaviors of RC members. And a plane frame model was analyzed at different loading rates to study the effect of loading rates on the dynamic response of structures. It was shown that, with the increasing of loading rates, the strength and stiffness of members and the lateral stiffness of the whole structure model were increased. Finally, the progressive collapse process of a typical8-story RC frame at different cases was simulated numerically to study the collapse mechanism of the RC frame. The results, with and without considering the unloading stiffness degradation caused by damage, was compared to study the influence of damage. Also, the results, with and without considering the strain rate effect of strength and stiffness, was compared to study the influence of strain rate effect.