ABSTRACT
Concrete filled tubular (CFT) columns are widely used all over the world, due to their significant advantages in construction speed and high fire resistance. Columns are critical members of a structure. Because of various interactions between a column and its adjacent members in a complete structure, the loads and boundary conditions of the column change under fire conditions. Such variations should be evaluated to enable proper design of the column as part of a frame structure. This paper presents the results of a series of numerical studies on the behaviour of rotationally restrained CFT columns exposed to the standard fire condition. The numerical simulations are conducted using a general finite element analysis package ANSYS. The finite element model is first validated by comparing with the results of a series of full-scale fire tests on rotationally restrained CFT column assemblies conducted at the University of Manchester. The test assembly consisted of a CFT column jointed by a pair of short beams from two sides using extended end plate connections. The column was loaded axially and the applied loads on the beams varied to give different amounts of initial bending moment in the column. By comparing the failure times of the column assemblies to the isolated columns under different bending moments, it was conclude that the design column bending moment may be taken as that arising from the unbalanced beam load acting on the surfaces of the steel tube. Another objective of the numerical simulations is to investigate the effect of rotational restraint on column effective length, which confirmed the recommendation in EN 1994–1-2. In addition, the numerical simulations confirm that the slip between the steel tube and the concrete core has no significant influence on the failure time of CFT columns.
