【作者】 吕学涛；

【导师】 张素梅； 杨华；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2010， 博士

【摘要】 方钢管混凝土柱充分利用了钢材和混凝土的材料特性,具有抗弯性能好、施工方便、抗火性能好等优点,在国内外高层与超高层建筑中得到广泛应用。因钢管外露,方钢管混凝土柱的抗火性能与设计是其在工程实践中的关键问题之一。现有研究和现行规范及规程多假设其四面均匀受火,而实际火灾中方钢管混凝土柱也可能承受非均匀火灾作用,如单面火灾、两面火灾以及三面火灾作用等。背火面的形成,不同程度地降低了方钢管混凝土柱的整体温度,亦使材料的损伤程度较四面均匀受火情况有所减轻;受火方式的改变,使方钢管混凝土柱产生温度变形和附加偏心距,使非均匀受火的方钢管混凝土柱的受力机理和抗火性能与四面受火情况有较大差异。为此,进行了单面、相对两面及三面受火的方钢管混凝土柱的耐火极限和抗火性能的试验研究与理论分析,具体包括以下四部分:(1)三面、单面受火的方钢管混凝土柱抗火性能试验研究进行了4根三面受火和2根单面受火的方钢管混凝土柱足尺明火抗火性能试验,主要参数包括荷载比、荷载偏心距和受火方式。获得了两种火灾方式作用下的方钢管混凝土柱的变形全过程及破坏模式,实测了截面特征点温度、轴向变形、柱中侧向变形以及耐火极限等热学和力学参数。(2)方钢管混凝土柱截面温度分布及参数分析基于构成方钢管混凝土柱的钢材、混凝土以及防火保护层的热工性能模型,利用ANSYS有限元分析软件,建立了可考虑界面热阻的方钢管混凝土柱在单面、相对两面、三面及四面火灾作用下的截面温度场分析模型,并用现有试验结果进行了模型验证。分析了上述火灾作用下方钢管混凝土柱截面的典型温度场及分布规律,研究了升温时间、含钢率、截面边长以及防火保护层厚度对不同火灾作用下方钢管混凝土柱截面温度分布的影响规律。(3)方钢管混凝土柱耐火极限与抗火性能理论分析收集整理了钢材和混凝土在高温下的热膨胀系数、强度、弹性模量以及应力-应变关系模型,确定了适合本文的材料热力学参数。利用Fortran90编制了基于恒载升温作用路径的方钢管混凝土柱在单面、相对两面、三面以及四面火灾作用下的耐火极限与抗火性能理论分析程序。利用本文进行的三面、单面火灾试验结果以及其他研究者的相关试验数据,验证了提出的理论分析模型。在此基础上,研究了不同受火条件下方钢管混凝土柱轴向变形-时间关系曲线与侧向变形-时间关系曲线,分析了不同受火方式对方钢管混凝土柱抗火性能的作用机理和影响规律。(4)非均匀受火的方钢管混凝土柱耐火极限参数分析与抗火设计进行了单面、相对两面、三面以及四面火灾作用下方钢管混凝土柱耐火极限的参数分析,分析了荷载比、截面边长、长细比、荷载偏心率、钢材和混凝土强度、含钢率以及保护层厚度的影响规律。在工程常用范围内,提出了单面、相对两面和三面火灾作用下方钢管混凝土柱的剩余承载力简化计算公式,并提供了满足不同防火等级的方钢管混凝土柱所需的厚涂型防火防护层厚度设计建议。更多还原

【Abstract】 By combining the mechanical advantages of steel and concrete materials, concrete filled square hollow steel (SHS) columns have been gaining their popularity in high-rise buildings recently due to the excellent moment bearing capacity, convenience in construction, and high fire resistance. In concrete-filled SHS applications, the fire resistance design is one of the crucial issues as the steel tubes are exposed when the structures are against fire. However, most current codes and researches focus on the situation when columns are under four-side fire, and can not be adopted to predict the bearing capacity of SHS columns under three-side, opposite-two-side or single-side fire which also occur in real applications. Concrete-filled SHS columns under the other three conditions may have lower overall temperature and less severe damage in materials than those under four-side fire. The absence of exposing to fire in some sides may also cause additional lateral temperature deformation and increase the bending moment on columns, making the static behaviour of such columns different from those ones under four-side fire. In this contest, experimental and theoretical studies were carried out to investigate the fire resistant behaviour and the ultimate capacity of concrete-filled SHS columns under high temperatures, including the following four main parts.(1) Experimental study on the fire resistant behaviour of concrete-filled SHS columns under three-side and single-side fire.Six full-scale SHS columns subjected to sustained loading with different loading levels or loading eccentricities were tested to collapse, among which four were under three-side fire and the other two were under single-side fire, to investigate the deformation-loading curves and the failure mode of the columns. The measurement includes both thermal and mechanical parameters, like the temperatures at the representative points along the cross-section, the axial deformation, the lateral deflection at the mid-hight of the column, and the ultimate fire resistance capacity, et al.(2) Cross-sectional temperature distribution of concrete-filled SHS columns and parametric analysisBased on the thermal properties of material components like steel, concrete and fire coating, finite element models were built by ANSYS to investigate the typical temperature field and temperature distribution along the cross-section of concrete-filled SHS columns under three-side, opposite-two-side and single side fires with the consideration of the contact thermal resistance. The models were verified by test results from papers published to date. Parameteric analysis was then conducted to discuss the influence of the exposure time, the area of steel over concrete, the dimension of cross-sections, and the thickness of fire coats on the temperature distribution along the cross-section of concrete-filled SHS columns.(3) Theoretical analysis on the fire resistant behaviour of concrete-filled SHS columns at high temperaturesTheoretical analysis were conducted using Fortran 90, considering the path of constant loading under elevating temperatures, to investigate the fire resistance of concrete-filled SHS columns under three-side, opposite-two-side and single side fires with the material thermal-mechanical parameters determined according to the collected studies on the thermal expanding coefficients, the strength, the elastic modulus and the stress-strain relationship for steel and concrete under high temperatures. Using the test results in this thesis and those from published papers as benchmark, the analysis method was proved to be reliable to predict the fire resistant behaviour of concrete-filled SHS columns. The axial deformation versus time curves and the mid-height deflection versus time relations were investigated for the concrete-filled SHS columns under single-side, opposite-two-side, and three-side fires, respectively, to clarify the mechanism of the columns under different fire conditions and the influence of the different fire boundary conditions.(4) Parameteric analysis on the fire resistance of concrete-filled SHS columns under non-uniform fires and practical designParameteric analysis was carried out to investigate the influence of the loading level, the cross-sectional dimension, the slenderness ratio, the loading eccentricity, the steel and concrete strength, the ratio of steel area over concrete and the thickness of the fire coats on the fire resistant capacity of concrete-filled SHS columns under single-side, opposite-two-side and three-side side fires. Based on the analysis results, equations were brought up to predict the residual strength of concrete-filled SHS columns with parameters whithin the range of real concrete-filled SHS applications when subjected to single-side, opposite-two-side and three-side side fires. Designing recommendations for the thichness of spray insulation were suggested for concrete-filled SHS columns under different fire resistant levels.更多还原