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Study on fire resistance time of hybrid reinforced concrete beams

This paper studies the fire resistance time of hybrid reinforced concrete beams. A method of calculating the strength reduction coefficient of the longitudinal reinforcement of the hybrid reinforced concrete beams is proposed. Then, an allowable flexural reduction coefficient is suggested for the fire endurance of hybrid reinforced concrete beams. Based on the section properties of the hybrid reinforced concrete beams and the allowable flexural reduction coefficient, a method of calculating the fire resistance time that considers the ratio of the longitudinal reinforcement and the thickness of the concrete cover is described. This method uses mechanical properties of the materials at high temperatures proposed by scholars from various countries and analytic calculations of the temperature profiles in the rectangular beams. Fire resistance tests of six hybrid reinforced concrete beams were carried out. The temperatures measured from the test and the calculated temperatures are well fitted. The calculated fire resistance times and those obtained from a test are similar. Finally, the fire resistance time of the hybrid reinforced concrete beams is calculated under different conditions to provide two samples. The influence of the thickness of the concrete cover and the ratio of the longitudinal reinforcement on hybrid reinforced concrete beams is studied.