Experimental study on the fire behaviour of reinforced concrete slabs under combined uni-axial in-plane and out-of-plane loads

Abstract

In this paper four large scale fire tests on the reinforced concrete slabs, under combined uni-axial in-plane and out-of-plane loading conditions with vertical restraint at four corners of the slabs, are presented. The research focuses on the quantitative relationship between horizontal restrained force and deformations, cracking patterns and spalling of the slabs in fire. Also the vertical restraint forces at the four corners of the slabs were measured in the tests. Comparisons of the results indicate that the compressive uni-axial in-plane loads have a considerable effect on the number and directions of cracks on the top of the concrete slabs in fire. The uni-axial in-plane restrained slabs have larger mid-span deflections and lower deflection recovery ratios than the slabs without in-plane loading. In addition, the test results indicate that increasing reinforcement ratio can effectively prevent the integrity failure of the restrained slabs. The research generates valuable test data which can be used to validate the numerical models developed by fellow researchers in the field of structural fire engineering.

Experimental investigation on the fire resistance of cast‐in‐situ hollow core concrete slabs constructed using filler boxes and an assembly box system

“…After that, the mid‐span deflection of each slab increased almost linearly the end of the test. This observation is similar to those of the conventional simply‐supported slabs, that is, when the average furnace temperatures exceed 600 °C, their mid‐span deflection ratio would suddenly increase. This is mainly due to the increasing temperature gradient (thermal bowing) and the decreased material properties …”

“…Clearly, the mid‐span deflections of these tests did not reach the normal furnace‐test limit of span/30 even when they undergo a long heating period of approximately 5 hours. In contrast, a review of literature shows that the mid‐deflections of conventional simply‐supported slabs often exceed the limit of span/30 or span/20, if they undergo the similar heating period. Hence, in term of the structural stiffness and strength, the present tested slabs had good performance compared to what could be expected from the behavior of conventional concrete slabs, although they have higher temperature gradient, steel temperatures and serious spalling.…”

“…In recent years, a number of experimental studies have been conducted to investigate the fire behavior of reinforced concrete slabs, and it is acknowledged that reinforced concrete floor slabs play a key role in enhancing the fire resistance of the building. However, as noted in the following literature review, most of the tests considered conventional concrete slabs.…”

“…Zhu conducted six fire tests of full‐scale two‐way RC slabs, which included slabs with two edges being clamped, slabs with two edges being simply supported, two‐way RC slabs, and flat‐plate floors slabs. Wang et al conducted nine large‐scale fire tests on the reinforced concrete slabs under axial in‐plane and out‐of‐plane loading conditions with vertical restraint at four corners of the slabs. In addition, a series of fire tests on a full‐scale eight‐story steel‐framed building were conducted in 1996 .…”

Fire Behavior of Continuous Assembled Monolithic Hollow‐Ribbed Slabs

“…As a new structure, the AMH slabs have no rational failure criterion under fire yet; the fire failure criterion of conventional reinforced slabs has to be adopted to discuss their fire resistance. Obviously, the load bearing function of the AMH slabs was maintained during the fire exposure time; and almost all the displacements of panels A and B were upwards, which are in opposite directions compared with those of the isolated AMH slab under fire, thus the inplane constraints have a considerable effect on the fire behavior of the AMH slab [24]. e test phenomenon indicated most soleplates of congruent boxes have been burned through since 40 min after ignition; as fire continued, the increasing number of cracks occurred at the top surfaces around panels A-F.…”