Residual Strength of Composite Unprotected Steel-Deck Floor Exposed to High Temperature (Fire Flame)

Abstract

An experimental programme was conducted to find out the behaviour of composite unprotected steel beam-reinforced concrete SB-RC deck floors fabricated from three secondary steel beams welded to another two main beams topped with a reinforced concrete slab, exposed to high temperature (fire flame) of 300, 500 and 700ºC for 1 hour, then allowed to cool down by leaving them at lab condition to return to ambient temperature. The burning results show that, by exposing them to a fire flame of up to 300ºC, no serious amount of permanent deflection can result. It was also seen that the middle and lateral secondary steel beams have recovered 92 and 95% of the deflection caused by heating, respectively. While the recovered deflection of burned composite SB-RC deck floor at 500ºC was 46 and 45%, respectively. The greatest deterioration was in the exposure to 700ºC, as this leads to a higher permanent deflection of the middle and the lateral secondary steel beams, and the recovery percentage was only 11 and 18%, respectively. Then all composite SB-RC deck floors loaded till failure to determine percentage decrease in ultimate capacity. The results were compared with the behaviour of composite SB-RC deck floor without burning (reference specimen). The comparison shows that the pre-burned composite SB-RC deck floor at 300, 500 and 700ºC, gives a decrease in specimens’ stiffness compared with the unburned one, by about 17, 61 and 74% for the middle secondary steel beam, and 25, 62 and 75% for the lateral ones, respectively. Likewise, linearity behaviour of the load-deflection curve decreases and the curves become flatter as the burning temperature increased. Also, the residual ultimate strength capacity decreases as the burning temperature was increased. For the burned composite deck floors at 300, 500 and 700°C, it was 87, 64 and 38%, respectively, compared with the unburned specimen.