【作者】 何子奇；

【导师】 周绪红；

【作者基本信息】 兰州大学 ， 工程力学， 2014， 博士

【摘要】 本文对冷弯薄壁型钢轴压构件畸变屈曲、畸变与局部相关屈曲的力学机理和设计理论进行了研究,主要包括轴压构件畸变屈曲的试验研究、理论分析和设计理论,轴压构件畸变与局部相关屈曲的试验研究、理论分析和设计理论。以上述系统研究为基础,对冷弯薄壁轴压构件已有的设计理论进行深入研究后提出了失稳系数法设计理论。进行了9个腹板加劲窄翼缘卷边槽形截面和9个腹板及翼缘均加劲宽翼缘卷边槽形截面的轴压构件畸变屈曲性能试验研究,试验主要参数为构件长度。分析了试件的破坏模式,分析了试件的荷载-应变关系曲线、荷载-畸变位移关系曲线、荷载-轴向压缩位移曲线,分析了试件长度、板件加劲、宽窄翼缘、初始缺陷对轴压构件畸变屈曲性能的影响。建立了薄壁轴压构件的有限元分析模型,对试件进行了模拟分析,基于有限元模型进行了冷弯薄壁型钢轴压构件参数化分析。以试验研究和有限元分析为基础,对畸变屈曲的变形模式、板件边缘加劲和中间加劲作用进行了理论分析,揭示了畸变屈曲模式的失稳力学机理,解释了畸变屈曲后极限承载力较局部屈曲为低的根本原因,分析了构件尺寸、初始缺陷和边界条件对构件极限承载力的影响。对国内外弹性畸变屈曲临界应力分析的数值计算方法和简化模型计算方法进行了归纳总结。深入研究了目前国际上广泛使用的两个畸变屈曲极限承载力设计公式,这两条计算曲线均为悉尼大学Hancock基于相同试验结果提出,分别作为直接强度法和有效宽度法畸变屈曲极限承载力计算公式,被北美规范、澳洲规范和中国规程所使用。但是,为中国规程和澳洲规范所采用的有效宽度法畸变屈曲极限承载力计算公式与直接强度法计算公式存在较大误差,而且计算曲线较短。本文基于试验和Hancock等人畸变屈曲试验结果,提出了一条新的畸变屈曲极限承载力计算公式,解决了不同规范计算误差较大的问题,并延伸了计算曲线长度。基于试验结果,对直接强度法畸变屈曲计算公式的非弹性段进行了修正。进行了9个腹板加劲卷边较小槽形截面和9个腹板加劲卷边较大槽形截面的轴压构件畸变屈曲与局部屈曲相互作用性能试验研究,试验主要参数为构件长度。分析了试件的破坏模式,分析了试件的荷载-应变关系曲线、荷载-畸变位移关系曲线、荷载-轴向压缩位移曲线,分析了试件长度、板件加劲、大小卷边、初始缺陷对轴压构件畸变与局部相关屈曲性能的影响,研究了畸变-局部相关屈曲和局部-畸变相关屈曲两类不同的失稳力学行为。建立了薄壁轴压构件的有限元分析模型,对试件进行了模拟分析,基于有限元模型进行了冷弯薄壁型钢轴压构件参数化分析。以试验研究和有限元分析为基础,对畸变与局部相关屈曲的耦合变形模式、板件边缘加劲和中间加劲作用进行了理论分析,揭示了畸变与局部相关屈曲模式的失稳力学机理,解释了畸变与局部相关屈曲极限承载力较畸变屈曲和局部屈曲为低的根本原因,分析了构件尺寸、初始缺陷和边界条件对构件极限承载力的影响。深入研究了直接强度法畸变与局部相关屈曲极限承载力的NLD和NDL两个计算公式,提出了与我国规范相协调的有效宽度法畸变与局部相关屈曲极限承载力的ELD和EDL两个计算公式,并采用本文和国内外试验结果对这4个公式进行了计算准确性分析。提出了畸变屈曲、畸变与局部相关屈曲的设计理论,提出了检查识别畸变屈曲和畸变-局部相关屈曲、检查识别局部屈曲和局部-畸变相关屈曲的判定准则,给出了相应的判定公式,采用本文和国内外试验结果对该判定准则进行了计算准确性分析。深入研究了冷弯薄壁型钢轴压构件极限承载力计算的有效宽度法、直接强度法和折减强度法,提出了冷弯薄壁型钢轴压构件承载力计算的失稳系数法。提出了单个板件以及构件的失稳系数概念,推导了失稳系数计算公式,给出了局部、畸变、整体及其之间相关屈曲的失稳系数公式,给出了局部、畸变、整体3种基本屈曲模式的失稳系数表。提出了失稳模式判定理论,对构件可能发生的屈曲行为及其相关屈曲模式进行判定识别,给出了失稳系数法计算步骤。采用本文和国内外试验结果对失稳系数法进行了计算准确性分析。本文的主要创新点如下：(1)通过试验研究、有限元参数分析、理论分析相结合的方法,深入研究了畸变屈曲性能,揭示了畸变屈曲模式的失稳力学机理,阐明了畸变屈曲后极限承载力较局部屈曲为低的根本原因。提出了与中国规范有效宽度法相协调一致的畸变屈曲极限承载力计算公式。(2)通过试验研究、有限元参数分析、理论分析相结合的方法,深入研究了畸变与局部相关屈曲性能,揭示了畸变与局部相关屈曲模式的失稳力学机理,阐明了畸变与局部相关屈曲后极限承载力较畸变屈曲和局部屈曲为低的根本原因,明确了畸变-局部相关屈曲和局部-畸变相关屈曲的不同力学行为。(3)提出了与中国规范有效宽度法相协调一致的畸变与局部相关屈曲极限承载力计算公式ELD和EDL。首次提出了检查识别畸变屈曲和畸变-局部相关屈曲、检查识别局部屈曲和局部-畸变相关屈曲的判定准则,并给出了物理意义明确的判定公式。(4)首次提出了冷弯薄壁型钢轴压构件局部屈曲、畸变屈曲、整体屈曲及其之间相关屈曲的极限承载力统一设计理论—失稳系数法。采用本文提出的失稳模式判定理论以及局部、畸变和整体屈曲共3套基本失稳系数表,确定构件的屈曲模式后通过查表得到相应的失稳系数,该失稳系数与钢材屈服承载力相乘即为构件失稳行为的极限承载力。失稳系数法能统一考虑3种基本屈曲模式及其相关屈曲模式的极限承载力,并且以简单的失稳系数进行计算。更多还原

【Abstract】 Instability mechanism and design theory of the distortional buckling, and the interaction buckling of distortional and local modes of cold-formed thin-walled steel columns under axial compression have been studied in the thesis, including experimental study, theoretical analysis and design theory of the distortional buckling, and the interaction buckling of distortional and local modes of columns. Based on these systematic studies, and a research on the existing design methods for cold-formed thin-walled steel columns, a novel design theory is proposed, namely instability coefficient method.An experimental research was conducted to investigate the distortional buckling behavior and failure modes of cold-formed thin-walled steel columns under concentrically load. Nine web-stiffened lipped channel sections with narrow flanges and nine web-stiffened and flange-stiffened lipped channel sections with wide-flange were tested. The effect of the columns length, plates with intermediate stiffener, web to flange ratio, initial geometrical imperfections were studied. Axial compressive load vs. strains curves, axial compressive load vs. distortional displacement curves and axial compressive load vs. axial shortening curves were experimentally measured and analyzed. A three-dimensional finite element analytical model of cold-formed thin-walled steel columns was developed by using ABAQUS software to analyze those specimens. A parametric analysis employing the FEA model for cold-formed steel columns was performed. Theoretical analysis for the deformation modes and the performance of plate-stiffened of cold-formed thin-walled steel columns undergoing distortional buckling was conducted on the basis of the experimental results and the finite element analysis results. Instability mechanism of distortional buckling mode is revealed by the studies. The main cause that the post-buckling strength of the distortional buckling mode is compared lower with the local buckling mode is explained. The influence of geometries, initial imperfections and boundary conditions to the ultimate load-carrying capacity of steel columns are researched.Numerical methods and simplified analysis models for the elastic distortional buckling analysis were summarized. The source, evolution and performance of the formulas and test data for the two strength design curves developed by Hancock are studied, for predicting the load-carrying capacity in the distortional mode. A proposed strength design curve based on available test data and Hancock’s strength design curves are then compared with the current design methods, the Direct Strength Method and the Effective Width Method, which are incorporated in the "North American specification for the design of cold-formed steel structural members"(AISI-NAS:2007),"cold-formed steel structures"(AS/NAS4600:2005), and the Chinese "Technical specification for low-rise cold-formed thin-walled steel buildings"(JGJ227-2011). The results indicate that the current design standards adopted the two strength design curves for the DSM and EWM, but they have some differences at the partial extent. A novel formula is proposed for dealing with this problem. The range of applicability of the proposed strength equation is extended from that in AS/NZS4600and is shown to be more accurate than AS/NZS4600when compared with that in the NAS S100. Based on the recent test results, the strength design curve of distortional mode in inelastic buckling range in the DSM is modified.An experimental research was conducted to investigate the interaction of distortional and local buckling behavior and failure modes of cold-formed thin-walled steel columns under concentrically load. Nine web-stiffened lipped channel sections with smaller edge stiffeners and nine web-stiffened lipped channel sections with larger edge stiffeners were tested. The effect of the columns length, plates with intermediate stiffener, the size of edge stiffeners, initial geometrical imperfections were studied. Axial compressive load vs. strains curves, axial compressive load vs. distortional displacement curves and axial compressive load vs. axial shortening curves were experimentally measured and analyzed. The local-distortional and distortional-local interaction modes, which are dissimilar structural behavior, were analyzed. A three-dimensional finite element analytical model of cold-formed thin-walled steel columns was developed by using ABAQUS software to analyze those specimens. A parametric analysis employing the FEA model for cold-formed steel columns was performed. Theoretical analysis for the coupled deformation modes and the performance of plate-stiffened of cold-formed thin-walled steel columns experiencing the interaction of distortional and local buckling was conducted on the basis of the experimental results and the finite element analysis results. Instability mechanism of the interaction of distortional and local mode is revealed by the studies. The main cause that the post-buckling strength of the interaction of distortional and local modes is compared lower with the distortional and/or local buckling mode is explained. The influence of geometries, initial imperfections and boundary conditions to the ultimate load-carrying capacity of steel columns undergoing the interaction behavior are researched.The two design formulae NLD and NDL of load-carrying capacity in the direct strength method for the interaction of distortional and local buckling are studied in depth. The two design formulae ELD and EDL of load-carrying capacity for the interaction of distortional and local buckling, which is in harmony with the effective width method, are proposed. The four design formulae are then compared with the experimental results undergoing the interaction of distortional and local buckling in this work and collecting from the literature. Design theory concerning the load-carrying capacity of the distortional and the interaction between distortional and local modes is developed. A criterion for identifying the buckling mode between distortional and distortional-local, and between local and local-distortional is established. According to the criterion, two formulae to check the buckling modes are presented. The two formulae are then compared with the experimental results experiencing the interaction between distortional and local buckling in this work and collecting from the literature. An accuracy of determination concerning the criterion is analyzed.The Effective Width Method, Direct Strength Method and Strength-reduction Method for calculation of the load-carrying capacity of cold-formed thin-walled steel columns under axial compression are studied in depth. A novel design theory, Instability Coefficient Method, is then developed. A conception of instability coefficient for an element and member is put forward. A general formula for calculation the load-carrying capacity of cold-formed steel columns is presented. Several instability coefficients concerning the local, distortional, Euler buckling and interaction buckling between them are derived. Three Tables of the local, distortional and Euler buckling are given according to the corresponding instability coefficients. A theory checking buckling mode and failure mode, which can identify if the pure buckling mode or mixed mode will be occurred for a given column, is presented. A calculation process of the Instability Coefficient Method is also given. The calculated results on the basis of the Instability Coefficient Method are then compared with the experimental results in this work and collecting from the literature. An accuracy of determination concerning the method is analyzed.The following is a summary of the main creative points of this thesis.1. Through the experimental research, finite element parametric analysis and theoretical analysis, the mechanical performance of the distortional buckling is studied systematically and in-depth. The instability mechanism of the distortional buckling mode is revealed. The root causes, which the post-buckling strength of the distortional mode is lower than the local mode, are clarified. A proposed EWM design formula for predicting the load-carrying capacity in the distortional mode is presented.2. Through the experimental research, finite element parametric analysis and theoretical analysis, the mechanical performance of the interaction of distortional and local buckling mode is studied systematically and in-depth. The instability mechanism of the interaction of distortional and local buckling mode is revealed. The root causes, which the post-buckling strength of the interaction of distortional and local buckling mode is lower than the distortional and/or local mode, are clarified. The experimental clearly evidence of the occurrence of the local-distortional and distortional-local interaction modes, which are dissimilar structural behavior, is provided and analyzed.3. The two design formulae ELD and EDL of load-carrying capacity of cold-formed thin-walled steel columns experiencing the interaction of distortional and local modes are developed in the shape of effective width method. A criterion for identifying the buckling mode between distortional and distortional-local, and between local and local-distortional is established for the first time. According to the criterion, two formulae to check the buckling and failure modes are also presented with clear physical meaning.4. A unified design theory, Instability Coefficient Method, is presented for the first time for predicting the load-carrying capacity of cold-formed thin-walled steel columns. The method deals with the local, distortional, Euler buckling and the interaction buckling between them at the same time. The three tables of the local, distortional and Euler buckling are given according to the corresponding instability coefficients. A theory checking buckling mode and failure mode, which can identify if the pure buckling mode or mixed mode will be occurred for a given column, is presented. Based on these available conditions, the load-carrying capacity of a given column will be determined by the instability coefficient multiplying yielding carrying capacity of steel.更多还原