残余应力对局部轴压焊接圆柱壳承载力的影响

焊接钢圆柱薄壳广泛应用于钢筒仓和钢油罐结构中,屈曲通常是该结构的设计控制条件,圆柱薄壳的屈曲在大多数荷载工况下对焊接几何缺陷十分敏感.现有研究标明,焊接残余应力可少量提高均匀轴压圆柱壳的稳定承载力,但对于局部轴压荷载下圆柱薄壳中残余应力的效应,相关的研究很少.采用施加收缩应变法,建立了分别考虑焊接几何缺陷以及考虑或不考虑焊接残余应力焊接圆柱薄壳的数值分析模型,研究了含有周向焊缝、竖向焊缝以及砌砖式焊缝(patterned welds)的局部轴压焊接圆柱壳屈曲行为,通过比较考虑/不考虑残余应力圆柱薄壳的计算结果,得到残余应力对局部轴压圆柱壳承载力的影响.     

轴压圆柱薄壳的屈曲分析

通过对大量的试验数据进行数理统计分析,提出了计算轴心受压圆柱壳屈曲应力的经验公式,该式表明在其他因素相同的情况下,屈曲应力与壳体厚度t1.5成正比,而经典理论则认为屈曲应力与厚度t成正比.通过圆柱壳在自重作用下的屈曲试验和有限元分析,验证了该经验公式的正确性.非线性有限元全过程分析显示,圆柱壳在其荷载位移全过程曲线上存在一个近似水平的后屈曲承载力"平台"(Plateau),与之相应的是在壳壁上形成了一个局部"凹陷"(Dimple),而试验得到的平均屈曲应力约等于平台对应的后屈曲应力.由此发现,试验或经验公式所得到的实际上是圆柱壳的后屈曲应力,而并非其初始屈曲应力.承受局部轴向压力的圆柱壳,在压力作用点附近亦形成一个与后屈曲承载力平台对应的局部凹陷.同上述凹陷一样,这类凹陷需要一个近似常量的压力来维持其不稳定的后屈曲平衡.给出了该作用力的计算公式,且它与t2.5成正比,从而亦间接证明了后屈曲应力或经验公式确定的应力与t1.5成正比的关系.对以往试验现象作出了合理解释,提出的两个计算屈曲应力和局部屈曲荷载的公式具有理论意义和实用价值.     

冷弯薄壁卷边H型钢受弯构件局部屈曲分析

采用有限条软件CUFSM对200种不同截面几何参数的冷弯薄壁卷边H型钢在荷载作用下的局部屈曲应力进行计算,并利用构件的屈曲应力分析了不同的卷边宽厚比、截面宽高比、腹板高厚比、翼缘宽厚比对冷弯薄壁卷边H型钢局部屈曲性能的影响。在此基础上,提出了适用于求解冷弯薄壁卷边H型钢在荷载作用下局部屈曲应力的简化计算式,并将简化公式计算的结果与有限条法计算的结果进行对比,表明所提出的简化计算式具有很好的适用性和精确性。     

中德欧规范关于圆柱壳轴向稳定承载力比较

圆柱壳在轴向荷载作用下容易发生局部屈曲,其局部稳定是设计关注的重点。选取不同半径、厚度、长度、边界条件的圆柱壳,根据中国、德国、欧洲规范的相关规定,分别计算圆柱壳的轴向稳定承载力,分析总结它们之间的差异,并对现行中国规范提出合理化建议,供设计人员参考。     

《钢结构设计规范》(GB50017—2002)焊接工字梁腹板的局部稳定和考虑屈曲后强度的计算

与现行《钢结构设计规范》(GBJ17—88)相比,新修订的《钢结构设计规范》(GB50017—2002)对焊接工字梁腹板屈曲临界应力和局部稳定的计算作了较大的改动,增加了梁腹板考虑屈曲后强度设计的相关条文。对弯矩、剪力和局部压力单独作用下的腹板屈曲临界应力作了修正,考虑了板件的几何缺陷和材料非弹性性能,对于直接承受动力荷载的吊车梁及类似构件或不考虑腹板屈曲后强度的焊接工字梁,要求按规定配置加劲肋,并验算腹板的局部稳定性,计算局部稳定的相关公式随着临界应力的修正也作了相应的调整;建议承受静力荷载和间接承受动力荷载的焊接工字梁宜考虑腹板屈曲后强度,按考虑腹板屈曲后强度来计算梁的的抗剪和抗弯承载力,而不再验算腹板的局部稳定。本文详细介绍了规范条文修改的理论依据,比较了新旧设计方法的差异,并通过设计实例说明了新设计方法的优越性。     

中外规范关于圆柱壳环向稳定承载力比较

圆柱壳在风荷载或负压作用下容易发生局部屈曲,其局部稳定是设计关注的重点。选取不同半径、厚度、长度、边界条件的圆柱壳,根据中国、德国、欧洲规范的相关规定,分别计算圆柱壳的环向稳定承载力,分析不同规范计算值之间的差异,从而为类似工程提供参考。     

规范EN1993-1-5的延伸:受压圆柱弯曲板特征值分析

对简支圆柱弯曲板的弹性屈曲性能进行数值分析,板件纵向边缘无约束和加载边缘约束,研究曲率、长宽比及荷载类型(由纯压缩至全平面弯曲)的影响。随后,考虑曲率的影响,对EN 1993-1-5给出的计算方法进行延伸,以用于内置板材的临界应力计算。基于数值模拟结果所提出的建议方法,能够安全、准确地估算出弹性临界应力(最小值)。     

圆柱壳中无粘结预应力筋的等效荷载计算方法

利用圆柱壳的弹性薄壳小挠度理论公式推导出圆柱壳中无粘结预应力筋的等效荷载计算方法,并应用有限元软件ANSYS对结果进行了对比验证。同时也指出,预应力筋应该用来平衡外加荷载而不是直接用来平衡环向力。     

轴心受压开口薄壁构件弹塑性屈曲荷载的统一计算方法

通过分析构件截面上应变与轴向力间的关系，以构件轴向应变为基本参数，提出了轴心受压开口薄壁构件的弹塑性屈曲荷载统一计算方法，给出了轴压构件的弯曲屈曲、扭转屈曲、弯扭屈曲等屈曲荷载的弦截法迭代格式，可应用于H形、T形、L形、十形截面等不同开口形式的轴压构件屈曲荷载计算，并可考虑具有残余应力的弹塑性本构关系。该方法以无残余应力的弹性屈曲荷载对应的轴向应变作为初始值，根据不同屈曲形式对应的非线性方程计算弦截区间点的函数值，进行弦截法迭代计算，得到弹塑性构件的临界轴向应变，进而获得屈曲荷载等信息。该方法采用的弦截法收敛速度快、计算量小、无需嵌套循环，可有效解决两端铰接轴心受压开口薄壁构件的弹塑性屈曲快速计算问题，便于工程应用。     

轴压功能梯度材料圆柱壳的弹、塑性屈曲分析

功能梯度材料板壳弹性屈曲领域研究已取得许多卓有成效的成果,而弹塑性、塑性屈曲问题的研究却鲜有报道。针对功能梯度材料圆柱壳的弹、塑性屈曲问题,采用有限元软件ABAQUS开展了数值模拟与分析。分析中采用叠层模型,定义材料沿厚度方向的梯度特性,计入材料的物理非线性和前屈曲几何非线性的影响。计算得到弹、塑性功能梯度材料圆柱壳的屈曲临界荷载和变形模式,给出了壳体从弹塑性屈曲到塑性屈曲的转化过程,并对屈曲类型对应的区域进行划分,研究了壳体厚度、组分参数对屈曲临界状态的影响。     

Buckling of cracked cylindrical thin shells under combined internal pressure and axial compression

Linear eigenvalue analysis of cracked cylindrical shells under combined internal pressure and axial compression is carried out to study the effect of crack type, size and orientation on the buckling behavior of cylindrical thin shells. Two types of crack are considered; through crack and thumbnail crack. Our calculations indicate that depending on the crack type, length, orientation and the internal pressure, local buckling may precede the global buckling of the cylindrical shell. The internal pressure, in general, increases the buckling load associated with the global buckling mode of the cylindrical shells. In contrast, the effect of internal pressure on buckling loads associated with the local buckling modes of the cylindrical shell depends mainly on the crack orientation. For cylindrical shells with relatively long axial crack, buckling loads associated with local buckling modes of the cylindrical shell reduce drastically on increasing the shell internal pressure. In contrast, the internal pressure has the stabilizing effect against the local buckling for circumferentially cracked cylindrical shells. A critical crack length for each crack orientation and loading condition is defined as the shortest crack causing the local buckling to precede the global buckling of the cylindrical shell. Some insight into the effect of internal pressure on this critical crack length is provided.     

Stability of circular cylindrical steel shells under combined loading

Circular cylindrical shells made of steel are used in a large variety of civil engineering structures, e.g. in off-shore platforms, chimneys, silos, tanks, pipelines, bridge arches or wind turbine towers. They are often subjected to combined loading inducing membrane compressive and/or shear stress states which endanger the local structural stability (shell buckling). A comprehensive experimental and numerical investigation of cylindrical shells under combined loading has been performed which yielded a deeper insight into the real buckling behaviour under combined loading . Beyond that, it provided rules how to simulate numerically the realistic buckling behaviour by means of substitute geometric imperfections. A comparison with existing design codes for interactive shell buckling reveals significant shortcomings. A proposal for improved design rules is put forward.     

网格圆柱扁壳的稳定性

本文用将网格壳转化为连续壳的方法建立了网格圆柱扁亮屋盖的稳定平衡微分方程,所得的方程是属于异性圆柱扁壳的方程,并用方法求得简支边界条件的网格圆柱扁壳的临界荷载计算公式。     

叉筒网壳子结构圆柱面交叉立体桁架系巨型网格结构的稳定性研究

本文针对子结构为单层叉筒网壳的圆柱面交叉立体桁架系巨型网格结构,分析了结构的构成、形体参数、支承方式等;建立了几何非线性力学模型,编制了相应的稳定分析程序;针对本结构的特点,着重研究了结构的稳定性能、失稳形式(局部失稳与整体失稳),以参数分析的形式研究了结构局部失稳与整体失稳的关系,找出了不同跨度结构在整体与局部失稳临界状态某些参数的取值规律,并给出了整体与局部失稳状态的分界曲线,可为该结构形式的工程应用提供参考。     

双曲冷却塔下部子午线形对结构性能的影响

在不影响冷却塔冷却性能的前提下,对双曲冷却塔塔筒下部半径和下支柱斜率进行微调,并分析了其对结构动力特性、承载性能及稳定性的影响。研究表明,塔筒下部子午线形对结构的线性特征值屈曲分析结果影响甚微,下支柱斜率等于或略小于塔筒下缘斜率可以有效提高结构基频,提高其抗风性能。塔筒下部区域斜率的突然下降或持续快速下降均会使附近环向膜应力及环向位移发生突变,也因此可能使局部稳定无法满足要求。所以,在设计中应保证塔筒下部区域的子午向斜率与上部斜率一致缓慢下降,使应力分布连续平缓,同时又可在不增加壁厚的情况下满足局部稳定要求。     

On the buckling of cylindrical shells with through cracks under axial load

Presence of cracks or similar imperfections can considerably reduce the buckling load of a shell structure. In this paper, the buckling of cylindrical shells with through cracks has been studied. A general finite element model has been proposed, verified and applied to some novel cracked shell buckling problems for which documented results are not available. A special purpose program has been developed for generating finite elements models of cylindrical shells with cracks of varying length and orientation. The buckling behavior of cracked cylinders in tension and compression has been studied. The results of the analysis are presented in parametric form when it seems to be appropriate. Sensitivity of the buckling load to the crack length and orientation has also been investigated.     

Parametric study on buckling behaviour of dented short carbon steel cylindrical shell subjected to uniform axial compression

Generally, thin cylindrical shells are susceptible for geometrical imperfections like non-circularity, non-cylindricity, dents, swellings, etc. All these geometrical imperfections decrease the static buckling strength of thin cylindrical shells, but in this paper only effect of a dent on strength of a short (Lc/Rc∼1, Rc/t=117, 175, 280) cylindrical shell is considered for analysis. The dent is modeled on the FE surface of perfect cylindrical shell for different angles of inclination and sizes at half the height of cylindrical shell. The cylindrical shells with a dent are analyzed using non-linear static buckling analysis. From the results it is found that in case of shorter dents, size and angle of inclination of dents do not have much effect on static buckling strength of thin cylindrical shells, whereas in the case of long dents, size and angle of inclination of dents have significant effect. But both short and long dents reduce the static buckling strength drastically. It is also found that the reduction in buckling strength of thin cylindrical shell with a dent of same size and orientation increases with increase in shell thickness.     

强冰雪灾害下大型薄壁圆柱钢壳结构稳定性研究

2008年我国南方地区发生强冰雪灾害,造成不少钢结构破坏。在化工、电力等工程中有很多作为整个系统关键设备的大型薄壁圆柱钢壳结构,柱壳内通常需设置一些横梁支承工艺设备,壳体既受到由上部壳体、顶盖和设备自重等荷载形成的沿环向均匀分布的整体轴向压力,又受到横梁支座传递来的局部轴向压力。在这些荷载作用下结构已经积累了一定的内力和变形,一旦再遭受强冰雪灾害,面积较大的顶盖和相连的其他管道上会快速积聚较大的雪荷载,导致结构发生失稳破坏。根据结构施工和使用过程,考虑加载路径的影响,先施加整体均布轴向压力,再施加局部轴向压力,然后施加模拟强积雪荷载的均布轴向压力,对112个带焊缝初始缺陷的薄壁圆柱壳结构进行了非线性稳定性数值分析。研究表明:随着初始整体荷载水平提高,柱壳承受积雪荷载的能力下降;随着缺陷幅值的增大,柱壳承受积雪荷载的稳定承载力与整体均布轴压下的稳定设计承载力的比值增大,其后屈曲承载能力也提高。柱壳下部储有浆液时;壳体承受积雪荷载的能力有小幅提高。根据大量计算结果,提出了考虑加载历史的遭受强冰雪荷载的圆柱壳稳定性设计建议。     

Static buckling analysis of thin cylindrical shell with centrally located dent under uniform lateral pressure

One of the common failure modes of thin cylindrical shell subjected to external pressure is buckling. The buckling pressure of these shell structures are dominantly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the critical buckling pressure of thin cylindrical shells with a centrally located dent is studied using non-linear static finite-element analysis of ANSYS under external pressure with simply supported boundary conditions at the top and bottom edges of the thin cylindrical shell.