火灾下受约束蜂窝梁悬链线效应理论研究

发布时间：2018-03-07 23:36

本文选题：受约束蜂窝梁　切入点：不均匀温度分布　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：火灾下受约束钢梁的悬链线效应是指:随着温度的升高,由于钢梁的热膨胀变形受到约束,钢梁内产生轴力;随着温度的进一步升高,钢梁发生大挠度变形,梁内轴力由压力转变为拉力并继续承担外荷载的现象。考虑受约束钢梁的悬链线效应可有效发挥结构潜能,显著提高构件的临界温度。但目前对钢梁悬链线效应的研究集中于数值研究,且多是基于均匀温度假设,尚没有成熟的理论分析方法。本文首先采用经验证的有限元模型分析了火灾下受约束钢梁悬链线效应受力机理。结果表明,火灾下钢梁经历三个阶段:压弯阶段、屈曲后阶段及悬链线阶段,钢梁受力机制由梁受弯承载机制转变为悬链线拉力承载机制;截面不均匀温度分布引起的热弯效应增大了钢梁的挠度;与实腹梁相比,蜂窝梁腹板所起的作用很小,可以忽略。其次研究了不同参数对火灾下受约束钢梁悬链线效应的影响,考虑的参数有温度梯度、荷载比、轴向约束刚度比、跨高比、开孔率、孔间腹板宽度及孔偏心。结果表明,荷载比、轴向约束刚度比及跨高比对火灾下受约束蜂窝钢梁的悬链线效应有较大影响,小荷载比及大跨高比蜂窝梁更适宜考虑悬链线效应;而开孔率、孔间腹板宽度及孔偏心对火灾下蜂窝梁的受力性能影响十分有限。最后基于平衡方程、本构方程及几何方程提出了一种适用于火灾下受约束蜂窝钢梁悬链线效应的简化分析方法。考虑了蜂窝梁孔洞上下方腹板对轴力的贡献及进入悬链线阶段时孔洞上方截面由压应力转变为拉应力的应力路径影响。将简化分析方法计算结果与有限元分析结果进行比较,从梁内约束轴力、跨中挠度及特征温度三个方面评估了该方法的准确性。结果表明,本文提出的简化分析方法预测的结果与有限分析得到的结果吻合良好,并可用于分析火灾后期受约束蜂窝钢梁的受力性能。当不考虑蜂窝梁腹板对轴力的贡献时,该方法预测的轴力偏小;当不考虑升温过程中截面由压应力转变为拉应力的应力路径影响时,该方法在悬链线阶段预测得到的挠度偏大。
[Abstract]:The catenary effect of restrained steel beam under fire is that with the increase of temperature, the thermal expansion deformation of steel beam is restrained, and the axial force is produced in the steel beam, and with the further increase of temperature, the large deflection of steel beam occurs. Considering the catenary effect of restrained steel beam, the potential of the structure can be effectively realized by changing the axial force from the pressure to the tensile force and continuing to bear the external load. But the research on catenary effect of steel beam is focused on numerical research, and most of them are based on the assumption of uniform temperature. There is no mature theoretical analysis method. Firstly, the finite element model is used to analyze the mechanism of catenary effect of restrained steel beam under fire. The results show that the steel beam under fire goes through three stages: compression and bending stage. In post-buckling stage and catenary stage, the stress mechanism of steel beam changed from flexural loading mechanism to catenary tension bearing mechanism, the thermal bending effect caused by non-uniform temperature distribution of section increased the deflection of steel beam. The influence of different parameters on catenary effect of restrained steel beam under fire is studied. The parameters include temperature gradient, load ratio, axial restraint stiffness ratio, span height ratio, open hole ratio, etc. The results show that load ratio, axial restrained stiffness ratio and span height ratio have great influence on catenary effect of restrained honeycomb steel beam under fire, and small load ratio and long span height are more suitable to consider catenary effect than honeycomb beam. However, the effect of opening ratio, web width and eccentricity of holes on the behavior of honeycomb beams under fire is very limited. Finally, based on the equilibrium equation, A simplified analysis method for catenary effect of restrained honeycomb steel beams under fire is proposed by constitutive equation and geometric equation. The contribution of upper and lower webs of honeycomb beams to axial force and the hole at catenary stage are considered. The influence of the stress path of the upper section from compressive stress to tensile stress is obtained. The calculated results of simplified analysis method are compared with the results of finite element analysis. The accuracy of the proposed method is evaluated from three aspects: confined axial force, mid-span deflection and characteristic temperature. The results show that the predicted results of the simplified analysis method proposed in this paper are in good agreement with the results obtained from the finite analysis. It can be used to analyze the behavior of confined honeycomb steel beams in the later stage of fire. When the contribution of web to the axial force is not considered, the axial force predicted by this method is small. When the influence of the stress path from compressive stress to tensile stress is not taken into account in the heating process, the deflection predicted by this method in catenary phase is larger than that in the catenary stage.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU391;TU352.5

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