Realistic modelling of Concrete Filled Tubular (CFT) columns in fire

Concrete filled tubular (CFT) columns are widely used all over the world, due to their significant advantages in construction speed and high fire resistance. This paper employs the commercial finite element analysis package ANSYS to model the behaviour of isolated CFT columns in fire. The finite element model is validated by comparing the simulation results with 34 fire test results of various CFT columns with different boundary conditions and under different loading. A numerical parametric study is then performed to investigate the sensitivity of simulation results to different assumptions introduced in the finite element model. The results of these numerical studies show that whether or not including slip between the steel tube and concrete core in the numerical model has little influence on the calculated column fire resistance time. However, including slip gives better prediction of column deflection behaviour. Introducing an air gap between the steel tube and the concrete core can improve the accuracy of predictions for both structural temperatures and structural performance. Using different tension strength or tangent stiffness of concrete has minor effect on the calculated column fire resistance. Different amounts of column initial deflection have some influence on column fire resistance times. Nevertheless, the influence is relatively small so that it is acceptable to use a maximum initial deflection of L/1000 as commonly assumed by other researchers. © 2007 Taylor & Francis Group.