Influence of reinforcement arrangement in flexural fire behavior of hollow core slabs
Abstract This paper describes standard scale fire tests conducted on four precast prestressed hollow core slabs configurations under flexure. The influence of the reinforcement arrangement was investigated using two test parameters: the average axis distance (from 30.1 to 46.7 mm), and the type of reinforcement (5 mm diameter wires and 9.5 mm diameter strands). An ISO 834 standard fire was applied maintaining the load level in a four-point test arrangement constant. The results presented different failure mechanisms, types of cracks, spalling patterns, and fire resistance ratings and it was shown that wires displayed optimal behavior as opposed to strands. A comparison was carried out with the current verification methods provided in Eurocode 2 part 1–2, and showed that verification methods tend to overestimate the calculation of fire resistance when both wire and strands are moved away from the exposed surface.
Full-scale fire tests on hollowcore floors
The results from two large-scale fire tests on a hollowcore floor plate, supported on protected steelwork, are presented in this paper. The two tests were identical except for the connection details between the units and supporting steel beams, with Test 2 having a more robust detail to tie the units and beam together. The floor was purposely subjected to a very severe fire created by specifying unrealistically small ventilation openings, compared to modern office construction. The hollowcore floor plate performed very well supporting the full applied static load for the duration of the tests. A beneficial load path mechanism created by lateral thermal restraint to the floor units was highlighted, which has not previously been considered. The tests showed that the small-scale standard fire tests, used to assess fire resistance periods, can be very unrealistic and ignores the beneficial effects of whole building behaviour. The test results presented reinforce the experience gained from real fires that hollowcore floor slabs have good overall inherent fire resistance.
Shear resistance of prestressed hollow core floors exposed to fire
Prestressed hollow core units are now the most widely used type of precast flooring. This success is largely due to the highly efficient design and production methods, flexibility in use, surface finish and structural efficiency. Fire tests conducted during recent years in some laboratories resulted in premature shear failure. Similar types of failure were not stated in other laboratories and never at real fires. The reason lies in the faulty test set-up, neglecting completely the influence of connections and surrounding structure on the fire resistance of hollow core slabs. This paper provides a detailed analysis of the effect of fire on prestressed hollow core floors, explains the phenomenon of induced thermal stresses in the webs of the units and the principle of the interlocking effect to realise sufficient shear capacity at fire. Four full-scale fire tests were carried out at the Technical Universities of Liege and Gent in Belgium, to investigate the influence of parameters governing the shear capaci...