New Algorithm for Calculating Heat Transfer in Cavities of Hollow Core Concrete Slabs Exposed to Fires

摘要

In this paper, an algorithm based on the network, method suggested by Oppenheim for calculating the radiative heat flow in a cavity of hollow core concrete slabs exposed to fires is presented. It is assumed that the pressure in a cavity keeps atmospheric pressure during a fire, and the lost heat from the air due to expansion and immediate moving away from a cavity is neglected. The heat in a cavity is transfer via both heat conduction in air and thermal radiation among boundaries, and special regard is paid to modeling heat transfer by radiation. The effective radiative heat flow system of equations is derived and expressed in matrix form. The system of equations features a symmetric coefficient matrix and can be solved using LDLT factorization. Node radiative thermal loads are calculated from effective radiative heat flows at edges of elements located on internal cavities. The nonlinear finite element program TF1ELD written by first author has employed the new algorithm. Temperature distribution in a hollow core concrete slab exposed to ISO 834 fire is calculated using TF1ELD, and numerical results demonstrate that the new algorithm is very effective and is useful for further study of structural behavior of hollow core concrete slabs in fires.