Summary
A description is given of an experimental and theoretical investigation into the stresses induced in steel and concrete in reinforced concrete slabs subjected to high temperatures and thermal gradients.
It is shown that the observed stresses in the steel are dependent on time and previous temperature cycling of the slabs. Initially, the stresses in the steel were in close agreement with the values derived from the elastic analysis but as shrinkage and creep increased, with time and temperature, large losses of tensile stress were measured until, in several cases, the steel developed compression even while the thermal gradients were considerable. The main cause of the loss of tensile stress in the steel was attributed to the increased rate of concrete shrinkage at temperatures near or above 100°C, with secondary effects due to creep and reduction in the expansion coefficient.
Design recommendations are made which enable the final equilibrium stresses to be determined within fairly wide limits and it is shown that the final steel stresses are likely to bear little relation to the stresses calculated from an elastic analysis alone.
