Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

Abstract

To better understand the fire behaviour of in-plane restrained reinforced concrete slabs, this paper presents six fire tests on two-way spanning concrete slabs under compressive bi-axial in-plane and flexural outof-plane loads. The data presented include furnace temperatures, temperature distributions, vertical and horizontal deflections, restraint forces, crack patterns, and characterisation of spalling of the six slabs during both heating and cooling phases. Comparison of the results indicates that bi-axial in-plane loads may have a negative effect on the vertical and horizontal deflection trends of the restrained slabs in fire. In addition, snap though behaviour and subsequent severe reversals of deflection trends were observed for the first time in concrete slabs with sustained bi-axial in-plane restraint during heating and cooling stages. Fire behaviour of the restrained slabs were considerably different from those of the simply supported slabs, and thus the effect of uniaxial or bi-axial in-plane restraints on the failure mode should be considered to establish reasonable failure criteria for these slabs. In addition, it is suggested that the corners of the in-plane restrained slabs should be reinforced by arranging the whole span top steels along two directions since the corners easily fracture with large diagonal cracks during fire tests.

Behaviour of continuous reinforced concrete floor slabs subjected to different compartment fires

“…[7][8] with no horizontal restraint were free to move horizontally, and thus the arch action or compressive membrane action cannot be reasonably considered during the fire tests. In recent years, Wang et al [9,10] conducted a series of full-scale fire tests on the reinforced concrete slabs which included five square slabs and four rectangular slabs under combined uniaxial in-plane and out-of-plane loading, along with vertical restraints at the four corners of the slabs. The test results indicate that the fire behaviour of the restrained slabs is dependent on the restraint type, restraint level and slab aspect ratio.…”

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

“…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.…”

“…For each test, sand bags (each weighing 50 kg) were placed on the slab to simulate the live loads, and the applied loads were equivalent to a uniformly distributed load of 2.0 kN/m 2 , which is recommended in the reference …”

“…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 .…”