初始缺陷对矩形钢管混凝土柱壁板屈曲后强度的影响

为了研究焊接残余应力和几何初始缺陷对矩形钢管混凝土柱壁板屈曲后强度的影响,采用有限元软件ABAQUS进行参数分析,参数包括壁板的屈服强度、宽厚比、几何初始缺陷取值大小、是否施加几何初始缺陷和焊接残余应力,并考虑两者耦合作用,给出考虑焊接残余应力和几何初始缺陷后的矩形钢管混凝土柱壁板有效宽度计算公式,并与试验数据进行比较。结果表明:建立的有限元模型能较好地模拟壁板的局部屈曲和屈曲后行为,焊接残余应力和几何初始缺陷都会降低壁板屈曲后强度,且焊接残余应力的影响较大; 不同强度等级的钢材都需要考虑焊接残余应力和几何初始缺陷的影响,对于屈服强度大于460 MPa的高强钢材,当宽厚比大于65时,可以忽略几何初始缺陷的影响; 给出的有效宽度计算公式可以较为准确且偏保守地预测矩形钢管混凝土柱壁板屈曲后强度。     

对预装体外钢筋的钢-混凝土组合梁弹塑性屈曲的数值分析

连续组合梁的极限承载力由侧向畸变屈曲、局部屈曲,或者由两者的相互作用决定,这一点与纯钢梁的扭转屈曲破坏模式完全不同。利用有限元模型对负弯矩区的组合梁进行了弹塑性有限元分析,其中考虑了初始几何缺陷和残余应力,最终发现有限元分析结果与试验结果吻合良好。另外,对负弯矩区的预装体外钢筋的组合梁进行了参数研究。分析了影响组合梁承载能力和屈曲弯矩抗力的因子,如初始几何缺陷、钢梁的残余应力、力比值、预应力范围、负力矩钢筋、板、翼缘和梁的宽厚比。利用有限元法对负弯矩作用下的25组共200根具有不同截面参数、初始几何缺陷、残余应力和不同力比值的组合梁进行了分析。将计算出的屈曲弯矩率与改进宽厚比的曲线与中国规范中钢柱设计曲线进行了对比。结果证实:对于改进了的宽厚比值,本文依据中国规范的设计曲线推导出来的设计方法可以用于对组合梁屈曲强度的评估。     

门式钢管脚手架稳定承载力的有限元分析

为了对新型门式钢管脚手架的承载性能有充分的认识,保证其安全性,提出较准确的有限元分析模型以供参考。本文在对由两种新型门架(MF0817、MF1017)组成的三步六跨门式钢管脚手架承载性能进行试验研究并将其简化为平面框架进行稳定计算的基础上,应用有限元分析软件ANSYS对3组脚手架试验方案进行数值模拟计算,包括特征值屈曲分析以及考虑构件的初始缺陷和结构的几何非线性的极限承载力分析,并将有限元分析结果与试验结果及解析解进行对比。分析结果表明,构件的初始缺陷对脚手架的稳定承载力影响较大,有限元分析结果与试验研究结果吻合较好,本文所建的有限元模型能较真实地反映结构实际受力情况。     

门式钢管脚手架稳定承载力的有限元分析

为了对新型门式钢管脚手架的承载性能有充分的认识,保证其安全性,提出较准确的有限元分析模型以供参考.本文在对由两种新型门架（MF0817、MF1017）组成的三步六跨门式钢管脚手架承载性能进行试验研究并将其简化为平面框架进行稳定计算的基础上,应用有限元分析软件ANSYS对3组脚手架试验方案进行数值模拟计算,包括特征值屈曲分析以及考虑构件的初始缺陷和结构的几何非线性的极限承载力分析,并将有限元分析结果与试验结果及解析解进行对比.分析结果表明,构件的初始缺陷对脚手架的稳定承载力影响较大,有限元分析结果与试验研究结果吻合较好,本文所建的有限元模型能较真实地反映结构实际受力情况.     

轴压下薄壁圆柱形壳屈曲试验承载力的准确可靠预测方法

论述了一种能可靠并准确预测偏心荷载下薄壁圆柱形壳屈曲试验的方法。详细描述了试验装置和试件,包括用配套的设备测量试件表面的几何缺陷。为了精确地预测屈曲试验的荷载,根据不同的复杂度建立了不同的有限元模型模拟试验装置,并研究了初始几何缺陷、荷载偏心、沿柱圆周方向的荷载偏心位置和影响边界条件的不同试验装置对屈曲承载力的影响。解释了具有简单刚性支座的有限元模型会过高估计屈曲试验承载力的原因。尽管这些模型均考虑了初始几何缺陷和荷载偏心的影响。作为对比,计算了考虑实际支座条件有限元模型的结果。在有限元模型中,用弹性实体单元模拟固定装置,用面—面接触单元模拟试件与支座间的接触面,计算出的屈曲承载力与试验有着平均约-1.59%的偏离。沿有缺陷薄壁圆柱形柱圆周方向的荷载偏心位置对屈曲承载力有显著影响。     

薄壁异形铝合金轴压构件畸变屈曲性能试验研究

进行了6个薄壁异形截面铝合金短柱轴压作用下畸变屈曲性能的试验研究。采用LVDT测量了试件的局部几何初始缺陷,得到了该类构件局部几何初始缺陷的形状和幅值。进行了4组铝合金试样的拉伸试验,得到了6063-T5铝合金的本构关系。在薄壁异形截面铝合金短柱的轴压试验中,记录了各构件的轴向位移、板件平面外位移、应变和荷载等数据,分析了畸变屈曲对试件极限承载力、变形和应变发展等的影响。建立了薄壁异形截面铝合金轴压构件的有限元模型,并将有限元模拟得到的构件承载力、破坏模态、应变发展以及变形情况等结果与试验结果进行了对比,验证了该有限元模型的准确性。     

460MPa级高强度钢材工字形截面轴心受压柱局部稳定有限元分析和设计方法研究

为研究标准屈服强度为460 MPa的高强度钢材工字形截面轴心受压柱的局部稳定受力性能,采用通用有限元软件ANSYS建立有限元模型,考虑残余应力和局部初始几何缺陷的影响,与已有的460 MPa高强度钢材工字形截面轴心受压柱试验进行对比分析,验证了有限元建模方法的正确性。利用经过验证的有限元模型,针对460 MPa高强度钢材工字形截面轴心受压柱的局部屈曲性能进行有限元参数分析,并将已有试验结果、有限元参数分析结果,与中国、美国和欧洲钢结构设计规范中的设计曲线进行对比,提出新的设计公式。结果表明:钢板厚度、钢板长宽比、局部初始几何缺陷幅值和残余压应力值对构件翼缘极限承载力的影响很小,但对翼缘局部屈曲承载力有较大影响;所提出的建议设计计算公式相对于中国、美国和欧洲钢结构设计规范中的设计计算方法,更加适用于460 MPa工字形截面轴心受压柱极限应力和局部屈曲应力的设计计算。     

平面门式刚架静力屈曲的仿真分析

应用ANSYS有限元程序,对柱脚铰接的平面门式刚架进行了静力屈曲分析。在仿真分析中,主要考虑荷载分布和初始几何缺陷的大小对刚架临界屈曲荷载的影响。分析结果表明:刚架的临界屈曲荷载和荷载的分布有关;初始几何缺陷对刚架临界屈曲荷载的影响随着刚架高跨比的变化而不同。     

大跨度多弧形钢拱结构的受力性能试验与分析研究

以西安建筑科技大学体育训练馆46.5米跨多弧形钢拱网格结构为工程背景,采用重力加载方式,对该大跨钢拱结构进行了现场原位试验。综合考虑结构的跨度、变截面形式、初始几何缺陷、荷载布置和多种荷载工况,采用有限元ANSYS软件建立了整体有限元模型,分别进行了该结构的特征值屈曲分析和几何非线性分析,找出了结构的屈曲模态,考察了不同初始缺陷对结构影响的敏感程度。根据试验数据与理论分析结果的比较,分析了该结构的受力机理,破坏形态和薄弱位置。结果表明,钢拱网格的结构形式均能很好满足结构跨度、负荷宽度、屋面荷载以及抗震性能等方面的要求,结构整体稳定性较好,初始几何缺陷对该类结构稳定承载力影响显著。研究成果为进一步评价该类结构可靠性及合理性提供有力的依据。     

屈曲约束支撑极限承载力研究方法探讨

屈曲约束支撑极限承载力的研究方法目前集中在试验和理论分析方面,这些技术都是基于对实际结构进行大量的假设和简化,但简化和假设很难完全符合实际,特别是对于支撑的约束条件以及初始缺陷等会影响结构极限承载力的因素。提出用有限元技术来研究初始几何缺陷对屈曲约束支撑极限承载力的影响,以其与试验和理论相佐证。     

Stochastic imperfection modelling in shell buckling studies

One possible avenue that may improve design against buckling is to recognise and account for the random nature of initial geometric imperfections introduced by manufacturing. This paper presents the application of a probabilistic methodology to the design and analysis of cylindrical shells under axial compression. Results from two cases are presented and compared: the first involves stringer-stiffened steel cylinders failing elastoplastically, whereas the second examines unstiffened composite cylinders buckling elastically. In both cases, the method is underpinned by statistical analysis of imperfections measured on nominally identical specimens. Nonlinear FE analysis is used for strength assessment and the results of the statistical analysis are introduced in the imperfection modelling. It is demonstrated that the method has advantages over code design based on ‘lower bound’ curves, in terms of the calculated buckling loads but also in offering a systematic and rational way by which randomness in imperfections can be assessed.     

Assessment of the ultimate strength of narrow stiffened panel test specimens

The ultimate strength of five narrow stiffened panels tested with two stiffeners under axial compression until collapse and beyond is determined by finite element analysis, and is compared with experimental results. Models with two half bays plus one full bays in the longitudinal direction are used in the finite element analysis. The material properties used in the finite element analysis have been evaluated by tensile tests. The initial geometrical imperfections also affect significantly the collapse behavior of the stiffened panels. Hence, the initial imperfections of the stiffened plates were measured before the experiment. The results of the FE analysis with measured and with equivalent initial imperfections are compared and conclusions are derived about the possible bias of the results when the initial imperfections are not measured.     

Form of circumferential weld-induced imperfections for tapered-wall cylindrical shell structures

Initial geometric imperfections have a great effect on the buckling strength of thin-walled cylindrical shells under axial compression, and the circumferential weld-induced imperfection is usually the most deleterious imperfection form. Two axisymmetric imperfection forms proposed by Rotter and Teng have widely been employed in the buckling analysis of cylindrical shells. However, the applicability of the two forms for tapered-wall cylinders needs further study, since they are derived from the elastic bending theory for long thin-walled cylinders with a constant wall thickness. This paper presents a modified form of circumferential imperfection for tapered-wall cylinders. Finite element analyses are carried out by employing the trapezoidal strain field approach to model the welding process, and the obtained circumferential depression shapes are used to evaluate the availability of the modified imperfection form. It is shown that the modified imperfection form is reasonable for any wall thickness ratio between two adjacent strakes, and the most suitable shape function, which is very close to the FE results, can be obtained by giving suitable values of the roundness in the modified form.     

有多条轴对称焊接凹陷的钢圆柱薄壳在内压力和轴压力共同作用下的强度

钢筒仓中圆柱薄壳承受内压力和轴压力共同作用:在轴压和低内压作用下,壳可发生弹性失稳;在轴压和高内压作用下,壳可发生塑性破坏.内压轴压共同作用下的圆柱薄壳对几何缺陷比较敏感:单条轴对称焊接凹陷可使壳的承载力降低;而多条轴对称凹陷由于相邻凹陷的相互作用,可使壳的强度进一步降低;对于小间距的凹陷,这种相互作用更为明显.本文首次对有多条小间距轴对称凹陷轴压圆柱薄壳的整体结构在不同水平内压作用下的强度进行了有限元分析,并将计算结果与欧洲规范EC3的设计曲线进行比较,对EC3的设计曲线提出了修改意见,从而达到安全设计的目的.     

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.     

Flexural strength of tubular flange girders

A tubular flange girder is an I-shaped steel girder with either rectangular or round tubes as flanges. A tubular flange girder has a much larger torsional stiffness than a conventional I-shaped plate girder of similar weight, which results in a much larger lateral-torsional buckling strength. Finite element (FE) models of tubular flange girders with hollow tubes (HTFGs) are developed in this paper, considering material inelasticity, instability, initial geometric imperfections, and residual stresses. A parametric study is performed using the FE models to study the effects of stiffeners, geometric imperfections, residual stresses, cross section dimensions, and bending moment distribution on the lateral-torsional buckling flexural strength of HTFGs. These analytical results are used to evaluate formulas for determining the flexural strength of HTFGs.     

Effects of imperfections of the buckling response of composite shells

The results of an experimental and analytical study of the effects of initial imperfections on the buckling response and failure of unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells are presented. The shells considered in the study have six different shell-wall laminates two different shell-radius-to-thickness ratios. The shell-wall laminates include four different orthotropic laminates and two different quasi-isotropic laminates. The shell-radius-to-thickness ratios includes shell-radius-to-thickness ratios equal to 100 and 200. The numerical results include the effects of traditional and nontraditional initial imperfections and selected shell parameter uncertainties. The traditional imperfections include the geometric shell-wall mid-surface imperfections that are commonly discussed in the literature on thin shell buckling. The nontraditional imperfections include shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. The cylinder parameter uncertainties considered include uncertainties in geometric imperfection measurements, lamina fiber volume fraction, fiber and matrix properties, boundary conditions, and applied end load distribution. Results that include the effects of these traditional and nontraditional imperfections and uncertainties on the nonlinear response characteristics, buckling loads and failure of the shells are presented. The analysis procedure includes a nonlinear static analysis that predicts the stable response characteristics of the shells, and a nonlinear transient analysis that predicts the unstable response characteristics. In addition, a common failure analysis is used to predict material failures in the shells.     

Reliable and accurate prediction of the experimental buckling of thin-walled cylindrical shell under an axial load

Reliable and accurate method of the experimental buckling prediction of thin-walled cylindrical shell under an eccentric load is presented. The experimental arrangement and specimens are discussed in detail, including the measurement of the geometric imperfections of the specimen's surface using a coordinate measuring machine. Different FE models, in terms of complexity, are used to simulate the experiment arrangement in an attempt to get a good agreement with the experimental buckling loads and study the effect of measured initial geometric imperfections, load eccentricity, load eccentricity position along the shell's circumferential direction and different experimental arrangement that influence the boundary conditions. It has been demonstrated that FE models with simplified rigid support conditions overestimate the prediction of the experimental buckling load even though these models included the effects of the measured initial geometric imperfections and load eccentricity. By contrast, FE models with realistically modeled support conditions achieved the best result. The average deviation −1.59% from the experimental buckling loads was achieved using the FE model simulating the mounting devices as elastic bodies and with surface-to-surface contact interaction behavior on the support. The presented work also demonstrated the strong influence of the eccentric load position along the imperfect shell's circumferential direction on the buckling of the thin-walled shell.     

Experimental and Numerical Study on Buckling Behavior of a Rigidly Stiffened Plate with Tee Ribs

In the bridge structures, stiffened plates are usually designed as rigidly stiffened when the orthotropic steel box girder is used as the main load-bearing structure. Therefore, the buckling mode of stiffened plates is plate buckling which occurs in subpanel supported by stiffeners. The orthotropic steel box girder is used as the main girder for Egongyan Rail Special Bridge, which is a self-anchored suspension bridge. Plates of the steel girder are rigidly stiffened with unequal spacing open ribs, and the most slender stiffened plate is the mid web stiffened with Tee ribs. In order to ensure the safety of the bridge, the buckling behavior of the web and orthotropic steel box girder under axial compression, including ultimate strength, post-buckling behavior and failure modes, should be clearly investigated by experimental and numerical methods. The design, loading and testing methods of the 1:4 scale model of the orthotropic steel box girder are introduced in detail firstly. The orthotropic steel box girder and the stiffened web finite element (FE) models are validated by the test results, and the effects of residual stress and the magnitude of geometric imperfections are discussed roughly. Based on the validated web FE model, a detailed parametric study is performed to systematically investigate the effects of residual stress and geometric imperfections on buckling behavior of the web. The effect of shapes of geometric imperfections discussed is highlighted. Through tracing stress states, the failure modes of stiffened plate are in agreement with the experimental phenomenon to some extent. Results show that shapes of geometric imperfections have significantly influenced post-buckling behavior and failure modes of the web, but slightly affected the ultimate strength. It is advised that residual stress and geometric imperfections should be controlled to make full use of excellent performance of steel materials.     

Ultimate strength of stiffened plates with a square opening under axial and out-of-plane loads

The high strength to weight ratio and high stiffness to weight ratio of stiffened plates find wide application in aircraft structures, ship structures, offshore oil platforms and lock gates. The strength and stability of stiffened plates is highly influenced by openings and initial imperfections. The main objective is to study the behaviour of stiffened steel plates with openings up to collapse and to trace the post-peak behaviour under axial and out-of-plane loads. Four stiffened steel plates with a square opening were fabricated for testing. Angle sections were used as stiffeners. Imperfections in the plate, stiffener and overall imperfection of the whole panel were measured. All fabricated panels were tested to failure. A finite element (FE) model was developed for the analysis of stiffened plates with initial imperfections and validated with the test results. Parametric studies were conducted using the developed FE model, and interaction curves and equations were developed for the design of stiffened plates with initial imperfections and openings. The interactive effect for stiffened panels with a square opening was found to be linear, with proportional reduction of the ultimate axial load carrying capacity due to the constant out-of-plane load.