Response spectrum of a reinforced concrete frame structure under various column removal scenarios

Abstract

In a frame structure, sudden removal of a load-bearing member (e.g., a column) causes structural vibrations, often leading to a partial or total progressive collapse. Since the term ”sudden column removal” is imprecise, it is worth evaluating how the rate of column removal influences the maximum displacement and how this response refers to the one produced by the static column removal. Both linear and nonlinear, inelastic modeling of the reinforced concrete members are considered using the OpenSees finite element framework. The numerical simulations consist of a gradual increase in column removal time from near zero to asymptotically approaching the static response. Due to the asymmetry of the analyzed frame building, three column removal scenarios are investigated. It is observed that the impact of column removal rate depends on the ability of the remaining structure to withstand the lack of column and the natural period of the mode shape corresponding to the downward motion of the model without the column. Also, the column removal durations producing 95% of the maximum response are identified and their ratios to the respective natural periods are given. These investigations can be helpful when planning numerical simulations and physical experiments. Finally, a novel simplified single degree of freedom system with support removal is proposed and its response spectrum is developed. This simplified model helps to understand more complex multi-degree of freedom systems.