Heat Transfer in Ultra-High-Performance Concrete-Filled Double-Skin Tubes Under Fire Conditions.

This paper develops an FEA modeling protocol for simulating ultra-high-performance concrete-filled double-skin tubes (CFDST) for heat transfer analysis purposes. The research presented in this paper refines the existing FE methodologies for circular, rectangular, elliptical, hexagonal, and octagonal CFDST members under fire conditions. Various modeling parameters, such as thermal properties of different materials and the thermal contact conductance at the interaction surfaces, are incorporated and controlled via an automatic algorithm for proficient modeling. It is found that the available models for calculating the thermal contact conductance at the interfaces between metal tubes and the concrete cores have a strong dependence on the cross-sectional shape. Thus, a refined model of the thermal conductance for the hexagonal and octagonal CFDST columns is proposed. Extensive experimental results (212 fire tests) are assembled from the literature to verify the proposed FE methodology. Good agreements with test results are demonstrated when predicting the temperature fields within the considered CFDST cross-sections. Consequently, extensive results from the proposed algorithm can provide an initial basis for parametric studies and for forthcoming nonlinear stress analysis simulations of CFDST columns under fire, which are primary goals in future studies. Finally, complying with the existing design codes, a new simplified analytical model based on the finite difference (FD) method is presented for predicting the temperature developments through CFDST columns. [ABSTRACT FROM AUTHOR]