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Fire Performance of Steel Tubular Columns Filled with Normal Strength Concrete



The main goal of this paper is to predict the fire resistance rating (FRR) of composite concrete filled tubular (CFT) columns without external fire protection. In order to do that, the response of axially and eccentrically loaded columns to mechanical load in fire conditions is investigated. This study is based on data from 41 available full scale tests of columns filled with siliceous aggregate normal strength plain concrete, tested in the last 25 years by various researchers [1-6]. Analyses are carried out taken into account different parameters for which results are given, including different stress-strain relationships for concrete combined with two yield criterions, namely linear and hyperbolic Drucker-Prager. Different formulations of thermal expansion are investigated. Regarding properties influencing temperatures inside the cross-section, influence of formulations of specific heat of concrete and thermal gap conductance between steel tube and concrete core are investigated. Sensitivity study concerning mesh size as well as imperfections shape and magnitude is carried out. Recommendations regarding model application range are given based on evaluation of the results, which are plotted or showed against independent variables such as relative slenderness, utilization ratio or boundary conditions. Mean ratio of calculated fire resistance time to time of fire resistance measured during experimental test is presented. For the proposed model and for set of 41 tested specimens the ratio is around 1.0, with a standard deviation around 0.3 for all specimens, while standard deviation does not exceed 0.2 for pinned-fixed and fixed-fixed columns in most cases. Selected results are presented in detail.

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