Temperature prediction of concrete-filled rectangular hollow sections in fire using Green's function method

An efficient numerical approach using the Green's function solutions of transient heat conduction for predictions of thermal response inside a concrete-filled rectangular hollow section subjected to fire is proposed in this paper. Thermal properties of construction materials are assumed to be isotropic and homogeneous. The Green's function approach adopts different series expansions for small and large time solutions, therefore the desirable convergence properties can be achieved at any range of time by using the time partitioning strategy. A useful analytical relation in terms of step Green's functions is derived in this paper to incorporate the multidimensional effect, in particular, for Neumann (prescribed flux) boundary conditions. A modified lumped capacitance method, together with an "orthogonal flux" concept, are employed to deal with spatially varying heat flux at the steel-concrete interface, where Duhamel's theorem is applied in piecewise manner along the interface to incorporate the fire boundary conditions. No spatial discretization is required in the numerical algorithms based on the Green's function approach.