Experimental and Theoretical Study on Catenary Mechanism of Steel Frame Beam Subject to Fire

Two fire tests were carried out on planar steel sub-frames to study the catenary mechanism of steel frame beams exposed to fire. The temperature distribution of steel frame structure and catenary mechanism of steel frame beam under different fire protection conditions were studied by experiments. According to axial forces and deformations of frame beams in fire, the formation and development of catenary mechanism were illustrated. A analysis method, which could calculate the internal force and deflection of steel frame beams exposed to fire, was proposed based on the matrix analysis method and plastic hinge theory. This method could consider the degradation of mechanical properties of rotation constraints at high temperatures. The method was validated against fire test data, and the influence of different initial constraint conditions on the catenary mechanism of steel frame beams exposed to fire was analyzed using this proposed method. It is shown that the initial axial constraint stiffness has a significant effect on the axial force and deformation of the steel frame beam at elevated temperatures, while the initial flexural strength and rotational stiffness of the joint mainly affect the position and sequence of plastic hinge formations of steel frame beam at elevated temperature.