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

Abstract

This paper presents the experimental results of four continuous reinforced concrete slabs with three compartments under different compartment fire scenarios. The research focuses on the quantitative relationships of the compartment fire temperatures, the temperature distribution along the thickness of the slabs, the vertical and horizontal deflections, the crack patterns and failure modes of the slabs and the corners' reaction forces. The results indicate that for a continuous floor slab, the central vertical deflection of the slab in the middle compartment is considerably affected by the vertical deflections of the slab in the two edge compartments. The boundary condition, the ratio and arrangement of the top reinforcement of the continuous slab, and the fire spreading scenarios have important effects on the failure mode of the slab in different compartments. It is evident that more severe cracking happened within the slab in the middle compartment compared to the two edge compartments. For the edge compartment, the slab may fail by large deflection and the integrity failure of the slab in the middle compartment may occur. Increasing reinforcement ratio and using the continuous reinforcement are the effective methods to prevent or delay the failure of the continuous slabs with any fire spreading scenarios.

Post-fire behaviour of continuous reinforced concrete slabs under different fire conditions

“…One reason is the longer fire duration of the present tested slabs. Another reason is that more cross shape (+) original cracks and long-span cracks appeared on the top surface of Slabs B1 to B4 due to the complex deflection trend (upward and downward deflection) of each span [27]. No doubt, this cracking pattern led to the lower structural integrity of the fire-damaged slab and thus its flexural behaviour cannot sufficiently develop.…”

“…The main reason is that there were numerous original cross cracks (+ shape) on the top surface of Span B, and fewer cross cracks appeared on the two edge spans. The original cross cracks appeared owing to the upward deflections (or negative moments) of Span B during the fire [27], and the crack spacing basically coincided with the steel spacing (200 mm) [16,41].…”

“…Thus, compared to Slab B1-PF, the structural stiffness of Slab B2-PF was larger, owing to the shorter fire duration and fewer original cross cracks (smaller fire time delay, i.e., 30 min). This observation also implies that the fire scenarios have important effects on the failure mode of the middle span in the fire-damaged slab, as they can lead to different cracks or spalling during the heating stage [27]. particularly near the interior supports.…”

“…particularly near the interior supports. The main reason for this is that higher reinforcement ratio led to more small and tiny original cracks [27], indicating that the bond between the concrete and steel was seriously compromised. In addition, owing to fewer original cracks in Span A, the flexural failure modes occurred, such as new corner and arc cracks.…”

“…In addition, about 180 min of fire duration was used in the five tests, including single-compartment, twocompartment and three-compartment fires. In fact, for many fire events, fires were observed to spread from one compartment to another compartment in the same floor or different floors [27]. Thus, the residual behaviour of the continuous slabs subjected to different compartment fires is more representative than the cases where all spans in the continuous slabs are subjected to a uniform fire.…”