Abstract
Concrete filled steel tubular (CFST) columns have a high probability to resist high temperatures compared to steel structures, whose evaluation after a fire is limited by the resulting deformation. A better understanding of the behaviour of CFST columns after a fire, affected by the maximum temperature achieved by the concrete infill, is required to properly estimate their residual strength and stiffness in order to adopt a reasonable strategy with minimum post-fire repair. In this paper, a fiber beam model for the simulation of the post-fire response of slender concrete-filled steel tubular (CFST) columns is presented. First, the model is validated against experimental results and subsequently it is employed to analyse the post-fire response of circular CFST columns. The variation of the residual strength with the load level for realistic fire resistance times is numerically studied. Actually, in a building, the columns support load even while a fire is being extinguished, so it is important to take into account this loading condition when predicting the post-fire behaviour. Therefore, in this research, the complete analysis comprises three stages: heating, cooling and post-fire under sustained load conditions. The model considers realistic features typical from the fire response of CFST columns, such as the existence of a gap conductance at the steel-concrete interface or the sliding and separation between the steel tube and the concrete.
Highlights
Composite columns have a high probability to resist a fire compared to steel structures, whose evaluation after a fire is straightforward and limited by the resulting deformation
Concrete-filled steel tubular (CFST) columns need a more detailed assessment since the concrete infill is deeply affected by the maximum temperature achieved during the fire
A better understanding of the behaviour of concrete-filled steel tubular (CFST) columns after fire is required to develop innovative techniques to estimate their residual strength and stiffness since it will allow adopting a reasonable strategy with minimum post-fire repair
Summary
Composite columns have a high probability to resist a fire compared to steel structures, whose evaluation after a fire is straightforward and limited by the resulting deformation. Some investigations on stub CFST specimens can be found which have served to assess the post-fire residual capacity of these composite columns. With regard to numerical models, it must be highlighted that the work of Yang et al [8] who presented a FEM program for the entire fire exposure process under loaded conditions and the material properties developed by Han et al [1] for stub columns were applied. A fiber beam model for the postfire response of CFST columns is presented, which considers realistic features and is programed to reproduce the entire fire exposure process under constant load. The model is validated against experimental results and employed to carry out an analysis of the change in the residual strength with the load ratio for realistic fire resistance times
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