The Effect of Support Conditions on the Fire Resistance of a Reinforced Concrete Beam

This report examines the behaviour of reinforced concrete beams with rectangular crosssection exposed to fire from the bottom and the sides. The study was performed with 2D finite element analysis using SAFIR. The effect of various support conditions was studied during the exposure to a four-hour ISO-fire for single-span beams with pinned and rotationally restrained supports, allowing for varying levels of horizontal restraint in both cases. The results showed that the provision of horizontal restraint was beneficial to the fire resistance of the beams in both cases. The provision of rotational restraint greatly improved the behaviour of the beams compared to the pinned supported case. The effect of continuity was investigated with beams spanning over two and three bays subjected to a four-hour ISO-fire. Within this analysis the effect of different lengths of the top reinforcing bars at the supports was investigated. Compared to the single span beam, the continuous beams resisted the fire exposure for a longer period of time. The different lengths of the reinforcing bars did not greatly increase the fire resistance of the beams. The influence of the full process of fire development was analysed with one, two and three-bay beams without horizontal restraint. These beams were exposed to the ISO-fire for 30, 60 and 90 minutes followed by a decay phase. The analysed beams showed good behaviour. Failure only occurred when the decay phase started close to the failure time reached during the full ISO-fire.

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