Abstract
This paper presents the fire resistance behaviour of partially encased in concrete ultra shallow floor beams (USFB) using numerical analysis method based on material specifications of the EN1994-1-2. Investigating the behaviour of USFBs under elevated temperatures is crucial in determining their fire resistance and evaluating their overall performance in contemporary construction. Even though the manufacturing company provides fire resistances for USFBs based on EC4-1-2 procedures, their response to elevated temperature effects remains up to date neither well documented nor clearly understood. The analyses involved two different beams of span 5 m and 8 m respectively, as specified by the manufacturer. Analysis results showed that such beams, when unprotected, experience severe temperature gradients if exposed to fire, as the lower flange still remains unprotected in contrast to the concrete encased part of the cross-section. As it was anticipated, the moment capacity governs the fire resistance of the beams and the load factor highly effects the elevated temperature behaviour. In addition, the loss of the lower flange, which develops high temperatures, is not compensated by the web and consequently the moment capacity ultimately depends on the temperature of the lower flange. Results also suggest that simulated beams sustained the applied load for approximately 40 min of exposure to the standard fire.
Highlights
Various shallow floor systems have been developed recently
In spite of the fact that the fire behaviour of slim floor and slim deck systems has been investigated by various researchers [2, 5,6,7,8,9,10], systems proposed by other manufacturing companies, such as the ultra shallow floor beam (USFB) [1], have not been sufficiently studied at elevated temperatures
The methodology used in the current USFB analysis is similar to the model used in the analysis of asymmetric slim floor beams in fire presented by Maraveas et al [2]
Summary
Various shallow floor systems have been developed recently. The most commonly encountered in the industry are the ‘‘slim floor’’ and the ‘‘slim deck’’ systems. Several companies have developed their own systems, such as the ultra shallow floor beam (USFB) composite deck system [1]. The behaviour of such flooring systems when exposed to fire is generally satisfactory, because the encasing (plug) concrete acts as thermal insulation, even though the lower flange is unprotected. Due to the absence of vital information for evaluating the Eurocodes procedures for the specific system and the fact that experimental results are not available, the authors conducted a numerical simulation of such USFB systems exposed to fire For this purpose, finite element (FE) analyses with the commercial program ABAQUS were carried out. Vertical shear Horizontal shear Moment shear interaction Vierendeel bending Longitudinal shear in slab Vibration (Hz) Imposed deflection (mm)
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