局部火灾下正放四角锥网架结构中杆件的约束效应研究

发布时间：2018-05-10 06:21

本文选题：局部火灾 + 正放四角锥网架　；参考：《南京工业大学》2015年硕士论文

【摘要】：网架结构是大跨度建筑结构常用形式之一,其建筑火灾时有发生。关于影响网架结构抗火性能的关键参数已有了系统研究,但对于局部火灾下网架结构的失效机理还未有细致深入的研究。局部火灾下,网架结构中低温部分的杆件对高温部分杆件的热膨胀有约束作用,产生了附加温度应力,而受约束杆件高温下屈曲后仍具有一定的承载力。本文分析杆件间约束效应的目的是为了定量得出杆件的轴向约束刚度,具体研究工作与成果如下。(1)基于非经典板理论,本文将网架上、下弦杆系分别连续化,并分别以上、下弦杆层为研究对象,建立了平面应变基本微分方程,求解得到上、下弦杆层的平面应变。考虑简支位移边界条件,由上、下弦杆层的几何方程,求得上、下弦杆层在常温下的面内位移解析解。网架结构在常温下的挠度拟夹层板法中已经给出。(2)在恒载升温条件下,弹性模量将随温度的升高而减小,同时上、下弦杆层及腹杆层将产生热膨胀。针对这种高温下的结构响应,对常温下网架结构面内位移和挠度解析解中的弹性模量进行修正,并线性叠加高温下的热膨胀量,得到网架结构在均匀升温历程中,网架结构瞬态面内位移和挠度解析解。(3)局部火灾下的网架结构,其升温边界条件为非均匀温度场。在非均匀温度场中,任取上、下弦杆层的面内微元,假定微元内温度均匀分布,利用均匀温度场下网架结构面内位移和挠度解析解,求得该微元的面内位移和挠度,以微元到火源中心轴的距离为积分区间,积分可得非均匀升温历程中网架结构瞬态面内位移和挠度解析解。(4)将杆件节点几何坐标代入非均匀温度场中网架结构面内位移和挠度解析解,可得节点面内位移和挠度。在局部火灾下网架结构的节点位移变化是由弹性模量的衰减、热膨胀和杆件间约束共同作用造成的。其中,节点位移公式仅考虑了弹性模量的衰减、热膨胀引起的位移变化；数值分析方法所得到的节点位移则考虑了弹性模量的衰减、热膨胀和杆件间约束的综合作用。节点位移数值解与解析解之差即为杆件因约束产生的轴向变形△S,再由数值分析得到的因约束效应产生的杆件附加温度轴力△N,即可得到杆件产生单位轴向约束变形所需的轴力ΔN/ΔS,定义为轴向约束刚度ks。上述分析得到的局部火灾下网架结构杆件轴向约束刚度的求解方法,为杆件的屈曲后承载力校核提供了关键技术,为网架结构受火失效机理的进一步研究提供了理论基础。
[Abstract]:Space-truss structure is one of the common forms of long-span building structure, and its building fires occur from time to time. The key parameters affecting the fire resistance of space truss structures have been systematically studied, but the failure mechanism of the space truss structures under local fire has not been studied in detail and thoroughly. Under the local fire, the low temperature part of the truss structure has the constraint on the thermal expansion of the high temperature part of the bar, resulting in additional temperature stress, but the restrained member still has a certain bearing capacity after buckling at high temperature. In this paper, the purpose of analyzing the constraint effect between bars is to obtain quantitatively the axial constraint stiffness of the members. The concrete research work and results are as follows: 1) based on the theory of non-classical plate, the upper and lower chord systems are respectively continuous and above, respectively. The basic differential equation of plane strain is established and the plane strain of upper and lower chords is obtained. Considering the boundary condition of simply supported displacement, from the geometric equations of upper and lower chords, the analytical solutions of in-plane displacement of upper and lower chords at normal temperature are obtained. It has been given in the deflection pseudo-sandwich plate method at room temperature that the elastic modulus will decrease with the increase of temperature under the condition of heating under dead load, and at the same time, the lower chord layer and the web layer will produce thermal expansion. In view of the structural response at this high temperature, the elastic modulus in the analytical solution of in-plane displacement and deflection of the grid structure is modified at room temperature, and the thermal expansion of the grid structure is linearly superposed at high temperature, and the uniform heating process of the grid structure is obtained. The analytical solution of transient in-plane displacement and deflection of grid structure. 3) the temperature rise boundary condition of the grid structure under local fire is non-uniform temperature field. In the non-uniform temperature field, the in-plane micro-element of the upper and lower chord layer is taken, and the in-plane displacement and deflection of the micro-element are obtained by using the analytical solution of the in-plane displacement and deflection of the grid structure under the uniform temperature field, assuming the uniform distribution of the temperature in the micro-element. Taking the distance from the differential element to the central axis of the fire source as the integral interval, The analytical solution of the transient in-plane displacement and deflection of the grid structure during the non-uniform heating up process can be obtained by integrating the geometric coordinates of the bar node into the analytical solution of the in-plane displacement and deflection of the grid structure in the non-uniform temperature field, and the in-plane displacement and deflection of the node can be obtained. The joint displacement of grid structure under local fire is caused by the attenuation of elastic modulus, thermal expansion and constraint between members. The joint displacement formula only takes into account the attenuation of elastic modulus and the change of displacement caused by thermal expansion, while the node displacement obtained by numerical analysis takes into account the attenuation of elastic modulus, the comprehensive effect of thermal expansion and the constraint between members. The difference between the numerical solution of node displacement and the analytical solution is the axial deformation S caused by the constraint of the member, and the additional temperature axial force N caused by the constraint effect is obtained from the numerical analysis, and the unit axial constraint of the member can be obtained. The axial force 螖 N / 螖 S required for deformation is defined as the axial constraint stiffness KS. The method to solve the axial constraint stiffness of the truss members under local fire provides a key technique for checking the post-buckling bearing capacity of the truss, and provides a theoretical basis for the further study of the fire failure mechanism of the latticed structures.
【学位授予单位】：南京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU356

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