Fire Resistance of Composite Beams with Composite Slabs under Hinge Constraints

Abstract

To study the fire resistance of monolithic composite beams and separated composite beams with composite slabs under hinge constraints, constant-load temperature rise tests were conducted on a full-scale two-span continuous beam. The test phenomena, temperature distribution, displacement changes, and failure modes of the composite beam were studied during the entire process of the fire. The results showed that the cracking of the seams between the precast slabs of the separated composite slabs led to an increase in the burned area of the composite slabs and an increase in the temperature of the composite beams. No obvious cracking was observed at the postpouring seams of the monolithic composite slabs, the integrity and fire resistance of which were better. After the temperature stopped increasing, the steel beam cooled faster than the concrete composite slabs. The deformation recovery of the steel beam was restricted by the composite slabs, which were subject to the joint action of the constraining force generated by the deformation recovery of the steel beam and the external load, resulting in longitudinal cracks along the medial axis of the top of the slabs. The deformation recovery ratios of the two types of composite beams with composite slabs under hinged conditions after the temperature stopped increasing were similar. The calculation method of the axial force and horizontal displacement of the composite beam with composite slabs under the hinge constraint at the beam end in the fire was established, and the calculation results were in good agreement with the test results, with good calculation accuracy.