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处于整体结构中的构件受到相邻结构构件的约束作用,其火灾中的反应与单个构件具有明显差异。采用约束框架模拟整体结构为组合梁提供约束作用,通过2个组合梁试件研究简支组合梁和连续组合梁的火灾反应。试验表明,在整个火灾过程中,组合梁轴力、挠度及其抵抗弯距相互影响和转化,共同抵抗外荷载作用。在火灾初始阶段,组合梁轴力为压力,削弱了组合梁抗火能力;在火灾中后期,组合梁轴力发展为拉力,挠度可达跨度的1/15,产生的悬链线效应有效提高了组合梁极限抗火能力。简支组合梁和连续组合梁均发生了下翼缘屈曲,下翼缘屈曲是组合梁轴力由压力向拉力的转折点。依据功能原理建立了组合梁下翼缘屈曲的屈服线模型和计算方法,计算结果与试验结果吻合良好。
Components in a unitary structure are constrained by adjacent structural components, and their response to a fire is significantly different from a single component. The restraint frame was used to simulate the whole structure to provide the restraint for the composite beam. The fire response of simply supported composite beam and continuous composite beam was studied by two composite beam specimens. Experiments show that during the whole fire process, the combined beam axial force, deflection and its resistance to bending affect each other and transform to jointly resist the external load. In the early stage of fire, the axial force of the composite beam is the pressure, which weakens the fire resistance of the composite beam. In the late stage of the fire, the axial force of the composite beam develops into a tensile force, the deflection can reach 1/15 of the span, resulting in a catenary effect effectively improving the combination Beam limit fire resistance. The buckling of the lower flange occurs for the simply supported composite beam and the continuous composite beam, and the buckling of the lower flange is the turning point of the composite beam’s axial force from the pressure to the tension. According to the functional principle, the yield curve model and calculation method of the flange buckling under the composite beam are established. The calculated results are in good agreement with the experimental results.