冷弯薄壁卷边槽钢屈曲承载力计算的直接强度法.pdf

湘潭大学 硕士学位论文 冷弯薄壁卷边槽钢屈曲承载力计算的直接强度法 姓名：罗洪光 申请学位级别：硕士 专业：结构工程 指导教师：马石城 20080520 摘 要摘 要 冷弯薄壁卷边槽钢普遍用于梁柱结构，随着冷弯型材材料屈服强度不断提高，冷弯 型材的厚度越来越薄，一种新的控制冷弯薄壁型钢承载力的屈曲形式-畸变屈曲逐步受 到重视畸变屈曲有别于局部屈曲和整体屈曲，对于畸变屈曲现行国家标准《冷弯 薄壁型钢结构技术规范》 （GB50018-2002） （以下简称 GB50018）还无相应计算 规定GB50018 采用传统的有效宽度法计算局部屈曲，有效宽度法在板件宽度折减计 算方面比较复杂直接强度法（Direct Strength Method）(以下简称 DSM)是一种新的冷 弯薄壁型钢设计方法，DSM 采取折减构件强度的方法，不需要确定截面的有效宽度， 只需按全截面特性进行计算DSM 能用于局部屈曲和畸变屈曲的计算弹性局部屈曲 临界应力 ol f 、弹性畸变屈曲临界应力 od f的计算是 DSM 的关键，目前,针对 ol f 、 od f较 好的计算方法是通过数值法获得其近似解，其中尤以有限条法用得最多。

利用 DSM 可 用于计算畸变屈曲的特点，解决 DSM 中 ol f 、 od f计算不便的问题，就能有效简化相关 设计工作 为此，本文先运用有限条计算程序 CUFSM 计算 ol f 、 od f然后通过 DSM 计算局 部屈曲和畸变屈曲再利用 DSM 按全截面特性计算的特点计算出卷边槽钢翼缘屈曲应 力，为与 GB50018 中的板组约束系数相区别，提出综合系数 1D k的概念，最后利用经典 的单板稳定计算公式由翼缘屈曲应力反算出 1D k 本文针对 GB50018 所附冷弯薄壁卷边槽钢截面形式，按上述步骤分别计算轴压柱 局部屈曲的 1D k和纯弯梁畸变屈曲的 1D k，在大量计算的基础上，分别拟合出冷弯薄壁卷 边槽钢轴压柱可靠支撑条件下考虑局部-整体相关屈曲影响截面翼缘综合系数 1D k计 算公式、冷弯薄壁卷边槽钢纯弯梁考虑畸变屈曲影响截面翼缘综合系数 1D k计算公 式对于前一个计算公式考虑任意整体稳定系数，进一步拟合出任意整体稳定系 数ϕ条件下的冷弯薄壁卷边槽钢轴压柱考虑局部-整体相关屈曲影响截面翼缘综合 系数 1D k计算公式 按前述计算 1D k相反的步骤， 通过拟合得到的 1D k计算公式反算出局部屈曲和畸变屈 曲承载力。

反算只利用截面几何大小和材料屈服强度，计算过程简单，相关计算结果与 试验吻合较好，达到了本文目的 本文详细分析了拟合的计算公式适用范围，并讨论了为扩大适用范围，计算公式所 需进行的改进 考虑材料抵抗系数和相关安全系数后，本文的拟合计算公式可为工程设计提供参 考本文的计算思路可作为后续工作的借鉴 关键词：关键词：直接强度法；冷弯薄壁卷边槽钢；局部屈曲；畸变屈曲；综合系数 I Abstract In recent years,the cold-formed thin-walled lipped channel steel has been applied widely in beam-column structures.The developments in the strength of the cold-formed steel make it possible to use thinner plates in building construction. As a new kind of strength-governing mode, distortional buckling is receiving more attentions. The distortional buckling is different from local buckling and global buckling.There are no specific clauses for calculating the load capacities of distortional buckling in current national specification“Technical Code for Cold-Formed Thin-Walled Steel Structures”(GB50018-202) (GB50018). GB50018 implements the traditional Effective Width Method(EWM) in calculating the load capacities of local buckling.However it’s complex in calculating the reduced width of plates by EWM.The Direct Strength Method(DSM) is a new design method of the cold-formed thin-walled steel.Since DSM is a method of calculating the reduced strength, it is unnecessary to calculate the section’s effective width and only the gross properties of the section are required.DSM can be used in the calculation of local buckling and distortional buckling.It’s critical for DSM to calculate ol f –elastic critical stress of local buckling and od f–elastic critical stress of distortional buckling.The current good method of calculating ol f and od fis numerical method which can abtain the approximative results.The Finite Strip Method is by far the most popular and general numerical method. If we overcome the difficulty of computing ol f and od f and make the most of DSM in calculating the load capacities of distortional buckling, it would make the design work simpler. In this paper,firstly the ol f and od fare calculated by finite strip analysis program CUFSM.Secondly the load capacities of local buckling and distortional buckling are figured out by DSM.Thirdly the flang’s buckling stress of lipped channel steel is worked out by DSM which only depends on the gross properties of the section.In order to differ from the coefficients of constraint action between plate components in GB50018,a new concept of the comprehensive coefficients is put forward as 1D k.Lastly the 1D k is obtained from the flang’s buckling stress by the classical single plate stability calculating formula. All the channel sections except the tested ones in this paper are taken from the appendix of GB50018.Following the above calculating steps we would obtain the local buckling coefficient 1D k of axially loaded columns and the distortional buckling coefficient 1D k of flexural beams.Based on amounts of calculations,the fitting formulae for computing 1D k are deduced.The first formula takes the effect of interaction buckling between local buckling and global buckling into account for the axially loaded cold-formed thin-walled lipped channel II columns which are supported reliably. The second formula takes the effect of distortional buckling into account for the flexural beams.Considering the overall stability coefficient,we may get the third formula from the first one and calculate 1D k under random global stability coefficient ϕ. The load capacities of local and distortional buckling can be calculated by the 1D k formula in reversed process. Owing to the only use of gross properties of the section and the yield strength, the computational process is simple.Good agreement is found between the analytical and testing results.It hits the target of this paper. It is described in detail the formulae application range. The needed improvements of the formulae are pointed out after discussions of how to extend the application range. The fitting formulae may give reference to。