【作者】 刘兵；

【导师】 王振清；

【作者基本信息】 哈尔滨工程大学 ， 固体力学， 2013， 博士

【摘要】 在火灾高温的作用下，结构钢的性能会发生严重劣化，钢结构建筑及其构件将发生复杂的内力重分布现象，结构和构件的变形也会显著加剧，从而造成结构整体的承载性能大大削弱，危及结构的安全，严重时会导致结构发生整体倒塌或破坏。因此建立合理的钢结构构件的抗火研究分析方法，特别是通过系统的理论研究，分析其在各种温度条件下的受力状态变化，具有重要的理论意义和工程应用价值。本文在前人的工作基础上，对火灾高温作用下纯弯钢梁的弯扭屈曲受力状态做了进一步的研究，主要研究工作如下：1.考虑高温对结构钢材料性能的影响，分析了高温下（20°C≤T≤300°C）纯弯钢梁的弹性弯扭屈曲变化，给出了两端简支纯弯钢梁、两端固支纯弯钢梁、悬臂纯弯钢梁在高温下临界屈曲弯矩的计算表达式，并考虑了受弯钢梁屈曲前变形对弯扭屈曲临界弯矩的影响。2.推导了高温下（20°C≤T≤300°C）横向均布荷载作用下、横向集中荷载作用下的受弯钢梁临界屈曲弯矩和临界弯矩系数的计算表达式以及变截面受弯钢梁临界屈曲弯矩的计算表达式。3.通过算例分析了钢梁临界屈曲弯矩的变化，由算例分析可知：钢梁截面形式和荷载位置作用点位置的不同，对钢梁在高温下的弹性临界屈曲弯矩的差别也很大，但随着温度的提高，临界屈曲弯矩的下降趋势一致，下降的幅度也比较类似。4.根据弹塑性理论，对火灾高温作用下简支钢梁在弹塑性阶段的弯扭屈曲和临界屈曲弯矩进行了分析，给出了弹塑性阶段临界屈曲弯矩的计算表达式，通过算例分析了钢梁弹塑性阶段临界屈曲弯矩随温度的变化，并利用Ansys有限元软件模拟了钢梁在火灾燃烧不同时刻的竖向变形。5.在考虑高温对结构材料性能的影响基础上，对高温下含裂纹简支梁的振动频率变化问题展开分析，建立了含裂纹简支梁在高温下的自由振动频率方程，通过算例对含裂纹简支钢梁和含裂纹简支铝合金梁在高温下的自由振动进行了模拟运算，分析了其振动基频随温度的变化规律，给出了高温下含裂纹简支梁的自振频率与材料弹性模量的变化关系表达式。由分析可知：温度的升高导致了结构材料弹性模量的不断下降，而材料弹性模量的下降又使得梁自振频率随之不断降低，而且在梁中裂纹的相对深度越大，随着温度的不断升高，梁自振频率的下降幅度也越大，而裂纹位置离支座位置越近，对高温下梁自振频率的变化影响就越小。更多还原

【Abstract】 The material properties of the steel degenerate with temperature increased. Internal forceredistribution and obvious deformation will be appeared in the steel structure. The integralload capacity weakens sharply. Even totally collapse or damage will be happened due to a fire.So it is important to build a reasonable fire resisting method. It is meaningful to analysis theinternal force variation against temperature, especially through theoretical analysis.The flexural torsional buckling of steel beams in high temperature is discussed in thispaper. The aspects that were studied in this research are as follows:1. The elastic flexural torsional buckling of steel beams are analysised in hightemperature ranging from20℃to300℃considering the influence of high temperature onmaterial properties. The critical buckling moment equations of simply supported, fixed endedand cantilever beams considering the deformation before buckling are also provided.2. The buckling critical moment and the corresponding coefficient equations of beamswith constant and varying cross-sections under transverse uniform or concentrated loads aredriven in high temperature ranging from20℃to300℃.3. The critical buckling moments of steel beams against temperature are analysisedthrough an example. It is can be known from the example that influence of the section formand load point on elastic buckling critical moment in high temperature are observably. Thedowntrend and magnitude of the critical buckling moment against temperature of the twoinfluencing factors are analogously.4. The flexural torsional and critical buckling moments of simplely supported steelbeams against temperature are analysised based on elastic-plastic theory. The elastic-plasticcritical buckling moment equations are provided. The elastic-plastic critical bucklingmoments of steel beams against temperature are analysised through an example. The verticaldeformations of steel beam at different fire burning moments are simulated by ANSYS.5. The vibration frequencies of simply supported beam with cracks is analysisedconsidering the influence of temperature on material properties. The free vibration frequencyequation of simply supported beam with cracks in high temperature is provided. The vibration frequency variations of a simply supported steel beam and a aluminum alloy beam withcracks against temperature are obtained through numerical simulation. A series of conclusioncan be obtained. Material Young’s modulus decrease with temperature increased, the decreaseof material elasticity modulus will result in the decrease of natural frequency. Deeper crackbring more significant drop of natural frequency against temperature, the influence of crackon natural frequency is small when the crack is near the support. The relational expression ofnatural frequency and Young’s modulus of the simply supported beam is also obtained.更多还原