钢管桩在整体顶升过程中的线性屈曲分析

通过ANSYS软件利用实体单元建立整体顶升工程中钢管桩的模型,并使用弹簧单元模拟周边土层对桩的影响,同时使用接触单元模拟桩与垫块以及垫块与垫块之间的接触关系。进而完成了钢管桩整体顶升中的特征值屈曲分析,得到底部嵌固桩和非嵌固桩桩顶临界屈曲荷载随桩埋深变化的规律,以及桩顶临界屈曲荷载在整个顶升过程中随桩自由端长度变化的规律。     

开封玉皇阁整体顶升工程单桩稳定性研究

以玉皇阁整体顶升工程为背景,通过有限元分析软件ANSYS建立静压桩模型,并考虑接触非线性、几何非线性以及材料非线性等多种因素,进行了特征值屈曲分析和非线性屈曲分析,得出了上部有垫块钢管静压桩的临界荷载,对类似工程有参考价值。     

开封玉皇阁整体顶升施工中单桩稳定性分析

在文物建筑的保护中,常需要将建筑物整体顶升,采用钢管静压桩技术是近几年的一大趋势。因钢管静压桩在顶升过程中需不断在桩顶加塞垫块,故单桩稳定性问题更为突出。以开封玉皇阁整体顶升设计为例,利用有限元软件ANSYS对钢管静压桩的单桩稳定性问题进行非线性分析。分析结果表明:桩顶临界屈曲荷载随桩顶自由长度的增加而减小,钢管桩的非线性影响因子随着钢管桩直径和壁厚的增加而减小。     

下挖增层桩顶约束对基桩屈曲稳定临界荷载影响分析

以浙江饭店地下车库扩建工程为背景,假定桩顶约束不同,从而得到相应的挠曲变形函数。之后,结合Winkler弹性地基梁理论建立桩–土体系总势能方程,利用最小势能原理,导得既有建筑下挖增层改造工况下,不同桩顶约束时,桩基础的屈曲稳定临界荷载表达式。在此基础上,分析了桩顶约束对桩基础屈曲稳定临界荷载的影响。得知:随着半波数的增加,桩基础的屈曲稳定临界荷载逐渐收敛,桩顶固定收敛速度最快,铰接次之,弹性嵌固最慢;不同的桩顶约束对桩基础屈曲稳定临界荷载比影响不同,在同一开挖深度下,桩顶固定时,临界荷载比最大,弹性嵌固次之,铰接最小;随着开挖深度的增加,桩顶固定时的临界荷载比缓慢减小,而桩顶嵌固及铰接时的临界荷载比急剧降低。     

建筑物整体顶升施工中单桩稳定性分析——开封玉皇阁整体顶升设计

在文物建筑的保护中,常需要将建筑物整体顶升,采用钢管静压桩技术是近几年的一大趋势。因钢管静压桩在顶升过程中需不断在桩顶加塞垫块,故单桩稳定性问题更为突出。本文以开封玉皇阁整体顶升设计为例,利用有限元软件ANSYS对钢管静压桩的单桩稳定性问题进行非线性分析。分析结果表明:桩顶临界屈曲荷载随桩顶自由长度的增加而减小;钢管桩的非线性影响因子随着钢管桩直径和壁厚的增加而减小。     

遇真宫山门顶升施工中单桩稳定性分析

在文物建筑的保护中,常需要将建筑物整体顶升,采用钢管静压桩技术是近几年的一大趋势。因钢管静压桩在顶升过程中需不断在桩顶加塞垫块,故单桩稳定性问题更为突出。本文以武当山遇真宫山门整体顶升设计为例,利用有限元软件ANSYS对钢管静压桩的单桩稳定性问题进行特征值分析。分析结果表明:随着垫块数量的增加桩顶临界屈曲荷载逐渐减小;建议单桩自由长度不宜超过2.4m。     

嵌岩桩摩阻力数值分析法工程应用研究

以自平衡试验实际工程为背景,对嵌岩桩侧摩阻力进行数值模拟分析,提出确定嵌岩桩承载力的新方法。将嵌岩桩桩-岩摩擦假设为库仑摩擦模型,通过确定与模型相关的粘结力c、摩擦系数μ、切向接触刚度k参数,求解并绘制各级荷载作用下Q-s(荷载-桩端位移)曲线、Q-σ(荷载-指定截面应力)曲线,通过对比各参数变化对曲线形态的影响来调整模型参数,以使求解的曲线与试验实测的曲线相符合,即可认为所模拟的桩—岩模型与实际嵌岩桩相符合,最后可通过对模型施加桩顶荷载确定嵌岩桩的承载力。该应用研究表明可通过确定的粘结力c、摩擦系数μ、切向接触刚度k参数用数值模拟方法计算出同一岩层场区内不同桩径及不同嵌岩深度的嵌岩桩承载力,具有工程指导意义。     

对边弹性支承夹层玻璃板剪切屈曲分析

玻璃板与框架之间采用结构胶粘接形成的线支承连接,会因结构胶的弹性约束效应而影响玻璃板的剪切屈曲行为.本文通过有限元模拟研究了对边弹性支承夹层玻璃板在面内剪切荷载作用下的屈曲响应,分析了玻璃板长宽比、结构胶面内约束刚度、垫块几何尺寸及垫块弹性模量对夹层玻璃板剪切屈曲的影响规律.在理想简支、固支边界板件受剪屈曲临界荷载计算...     

考虑复杂地基反力分布的嵌岩灌注桩屈曲稳定分析

嵌岩灌注桩因其诸多优点在桥梁等工程领域中广泛使用,但当上覆土层软弱且桩顶自由长度较大时,桩身屈曲稳定问题应引起重视.为探讨桩侧土约束对桩身屈曲稳定的影响,假定地基反力系数呈更一般的幂分布,基于弹性地基梁理论建立桩土体系总势能方程,采用最小势能原理导得桩身屈曲临界荷载与计算长度解答,并据此讨论了地基反力系数分布模式、桩身自重及桩侧摩阻力等对桩身屈曲稳定的影响规律.这些定性的规律对嵌岩灌注桩的设计与施工具有一定的指导意义.     

接触单元在桩—土接触模拟中的应用研究

针对坐落于软岩地基上的水电站厂房地基摩擦桩加固措施,采用ANSYS中的面—面接触单元模拟桩—土之间的接触特性,并结合一中等直径灌注桩,分析桩土模型的荷载—桩顶沉降曲线、接触黏聚力—桩侧/端摩阻力和桩径—桩侧/端摩阻力变化关系,总结荷载和参数作用与影响规律,为相似工程的桩土接触数值模拟处理提供参考。     

基于ANSYS的脚手架钢管的屈曲分析

针对脚手架工程常用的钢管进行了有限元模拟,用ANSYS有限元软件模拟了该杆件在特定工况下的失稳情况,并进行了特征值理论计算、特征值屈曲计算及非线性屈曲分析,进而得出不同程度初始缺陷对杆件稳定性能的影响程度。     

三级分枝钢管树状结构有限元动力特性分析

通过对三级分枝钢管树状结构进行特征值屈曲分析、非线性屈曲分析,得出三级分枝钢管树状结构的屈曲极限荷载,对三级分枝钢管树状结构进行模态分析,得到该结构的固有频率等树状结构的动力特征,为树状结构的研究与设计提供参考。     

青岛北站撑杆式预应力钢压杆的极限承载力分析

结构的屈曲分析可分为特征值屈曲分析和非线性屈曲分析。简要阐述结构特征值屈曲分析和非线性屈曲分析的的基本理论,利用ABAQUS对青岛北站中的预应力钢压杆进行特征值屈曲分析和考虑材料非线性和几何非线性的非线性屈曲分析,对比两种分析方法所得的极限承载力的差别,同时在非线性屈曲分析中,分析在不同的初始缺陷和不同的初始预应力的条件下预应力压杆极限承载力的变化,所得结论可为同类大跨空间结构预应力压杆的设计与计算提供参考。     

考虑轴线偏差的钢顶管允许顶力计算方法

钢顶管轴向稳定性直接影响到允许顶力大小。若顶力控制不当,顶管可能发生轴向失稳破坏。顶进过程中的轴线偏差会降低轴向稳定性。为解决存在轴线偏差的钢顶管允许顶力计算问题,考虑管周土体的约束、管土摩阻力的共同作用,将钢顶管顶进过程中的轴线偏差作为初弯曲,建立并求解能量方程,获得了临界顶力荷载的解析解。结合实际工程,提出了根据容许轴线偏差量与管长共同确定初弯曲的方法,计算了不同初弯曲条件下的稳定系数与允许顶力。稳定系数与轴线偏差呈二次曲线关系,轴线偏差越大,顶管轴向稳定性越低,允许顶力越小。钢顶管施工过程中,应根据轴线偏差造成的不同初弯曲计算稳定系数与允许顶力,以控制顶管顶力,避免发生轴向屈曲。     

Iterative system buckling analysis,considering a fictitious axial force to determine effective length factors for multi-story frames

Traditional elastic buckling analysis, based on the system buckling approach, is a convenient tool for the evaluation of effective length factors of columns, in the stability design of multi-story frames. This method is superior to other analytical approaches, such as the isolated subassembly and story-based approaches, in that the inter-story and inter-column interactions are inherently taken into account. Nevertheless, use of the conventional critical load expression, in combination with results of elastic buckling analysis, may yield an excessively large effective length in members having relatively small axial forces. The present paper proposes an iterative elastic buckling analysis to determine reasonable effective length factors of columns in multi-story frames. In this paper, numerical procedures for an iterative buckling analysis using a modified geometric stiffness matrix, are described to obtain the effective length factors of the columns in multi-story frames. The axial force term in the geometric stiffness matrix is modified by adding a fictitious axial force to make the columns buckle along with the overall buckling of the frame. Iterative eigenvalue analysis is performed using the modified geometric stiffness matrix, to obtain the effective length factors of each column using the critical load expression. Example frames presented in this paper demonstrate that the proposed method not only provides excellent outcomes by amending the weakness associated with traditional elastic buckling analysis for determining the effective length factor, but is also a competitive alternative in the design of multi-story frames.     

单层肋环型椭圆穹顶网壳整体稳定性分析

大跨网壳结构具有高度的几何非线性,结构设计一般由整体稳定性控制.本文以北京某单层肋环型椭圆穹顶网壳工程为背景,利用非线性有限元计算方法,对其整体稳定性进行了线性特征值屈曲、弹性屈曲以及弹塑性屈曲三方面的分析,并求得了它们的极限荷载.同时,还考察了钢材的屈服强度以及初始缺陷对极限荷载的影响,并将数值计算结果与拟壳法所得的设计临界荷载进行了比较,得出的结论对实际工程具有一定参考价值.     

Sensitivity analysis of critical forces of trusses with side bracing

The present research is devoted to the study of out-of-plane buckling of trusses with elastic side bracing. In this paper, a sensitivity analysis of critical buckling loads of a truss due to bracing stiffness is carried out. A method based on the sensitivity analysis for the determination of the threshold bracing stiffness condition for full bracing of a truss is proposed. The influence lines of the unit change of the bracing stiffness on the buckling load, for different initial bracing stiffness, are investigated. The approximations of an exact relation between the buckling load and bracing stiffness are found. The buckling length related to the side-support distance as a function of bracing stiffness is also determined. It is shown that the buckling length of truss chords with elastic side supports is larger than that assumed in design codes.     

New method of inelastic buckling analysis for steel frames

In general, the concept of bifurcation stability cannot be used to evaluate the critical load of typical steel frames that have geometric imperfections and primary bending moment due to transverse loads. These cases require a plastic zone or plastic hinge analysis based on the concept of limit-load stability instead. However, such analyses require large computation times and complicated theories that are unsuitable for practical designs. The present paper proposes a new method of inelastic buckling analysis in order to determine the critical load of steel frames. This inelastic analysis is based on the concept of modified bifurcation stability using a tangent modulus approach and the column strength curve. Criteria for an iterative eigenvalue analysis are proposed in order to consider the primary bending moment as well as the axial force by using the interaction equation for beam-column members. The validity and applicability of the proposed inelastic buckling analysis were evaluated alongside elastic buckling analysis and refined plastic hinge analysis. Simple columns with geometric imperfections and a four-story plane frame were analyzed as benchmark problems. The results show that the proposed inelastic buckling analysis suitably evaluates the critical load and failure modes of steel frames, and can be a good alternative for the evaluation of critical load in the design of steel frames.     

Creep induced contact and stress evolution in thin-walled pipe liners

Finite element simulations of the contact conditions and stresses which evolve as a thin walled polymeric pipe liner deforms under uniform pressure are presented. The support received by a liner from its host pipe is seen to be a function of the thickness of the liner, with thinner liners receiving more support. The nature of this support is described in terms of contact forces and areas. The stress evolution is quantified by decomposing the stress at the critical point into flexural and compressive components. Ratios of flexural stress to compressive stress greater than two indicate the dominance of flexural stresses and suggest that flexural properties may be most appropriate when designing liners to resist buckling. Likewise, stress ratios less than two suggest that compressive properties may be most appropriate. Flexural to compressive stress ratios are seen to increase with increasing host pipe ovality, gap between the liner and host pipe, longitudinal imperfections, and applied pressure.