Lu, Han, and Zhao 2010b

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Analytical Study

A finite element numerical model was developed to analyze fire response of concrete filled double skin tubular columns. The numerical model was created in order to simulate the thermal and structural responses, as seen in other experimental tests conducted in other papers. ABAQUS is used to model the columns, and was verified using fire testing results. The model utilized a sequentially-coupled thermal-stress analysis, which is needed where stress and displacements are dependent on a temperature field. Thermal analysis is performed first in order to measure the temperature distribution, and a stress/ displacement analysis is then performed with the same time measurements, where the temperature analysis are transferred to the stress/displacement analysis. Shell elements were used for the steel tubes, and solid elements were used for concrete. For the thermal analysis, heat is transferred from the fire to the exterior tubes by convection and radiation, and then conducted into the inner tubes. During the structural analysis, the columns are first loaded through endplates at an ambient temperature, and then the temperatures are read and applied based on the thermal analysis to simulate the effect of load and fire until the columns fail. The elastic properties Although in the actual situation, the steel and concrete interact together, the model recognizes the two as individual parts which deform separately. Thus, the contact interaction was taken into account using master and slave surfaces, and a coulomb friction model was used. The results from the finite element model were then compared to results from an experimental test as outlined in another paper. It is verified that the finite element model estimates the fire endurance of CFDST columns well. The parameters that influence the fire resistance are load level, capacity of inner and outer steel tubes, fire protection, effective length, perimeter of outer steel tube, and the use of steel fibre reinforced concrete. The specimens with fire protection or steel fibre reinforced concrete effectively enhanced the fire resistance in the columns, despite a thickness of only 5mm. The increase in perimeter of the outer tube increases the fire resistance.

References

Lu, H., Zhao, X-L., Han, L-H., (2011). “FE Modelling and Fire Resistance Design of Concrete Filled Double Skin Tubular Columns” Journal of Constructional Steel Research, 67 (11), November. https://doi.org/10.1016/j.jcsr.2011.04.014