Citation

Haksever A, Ehm C. Fire Safety J. 1987; 12(2): 109-119.

Copyright

(Copyright © 1987, Elsevier Publishing)

DOI

unavailable

PMID

unavailable

Abstract

The fire resistance of slab structures in case of fire was calculated with the aid of a computer program. The calculation program uses the yield line theory and verifies constitutive equations determined with experimental data.The basis of calculations using the yield line theory is the proof of the equilibrium between internal work done along the prescribed yield lines and the external work induced by the lateral and the restraining loads. The fire resistance is attained when the load-bearing capacity of the slab member is identical with the acting total loads. Owing to the fact that the reinforcement steels and concrete show a considerable deformation capability when they are subjected to elevated temperatures of over 400 [deg]C and that, at the same time, the bond between concrete and steel is severely affected, the technical yield line theory is very suitable for the calculation of the fire resistance of slabs under fire action.The basic data for the constitutive equations were experimentally determined with the help of test equipment especially developed for investigations into the high temperature behaviour of concrete under uniaxial and biaxial compressive stresses. With the test data an analytical formulation of the ultimate strength envelopes and of stress-strain relations was done, which was used for the verification of the calculation program.The satisfactory agreement between the experimental and the calculation results confirms the efficiency of the yield line theory for determining the fire resistance of slabs. The investigations on two-way slabs with the usual thickness show that the slenderness ratio has only a small influence on the fire resistance. This influence becomes negligibly smaller as the side ratio increases, because the bearing system reduces to a one-way slab condition while the fire resistance decreases. Calculations on one-way slabs with all-round free support showed that a fire resistance of 90 min can, in most cases, be attained simply when the axial distance of the reinforcement is increased or an increase in the amount of necessary reinforcement is made.