Influence of cold bending on the resistance of wide flange members

Cold rolling is used for bending straight members with hot rolled wide-flange sections to create arches. Extensive studies have shown that the influence of residual stresses due to hot rolling on the resistance of wide-flange steel sections is nonnegligible. On the contrary, the residual stress pattern due to roller bending has been only recently identified. Its effects on the elasto-plastic behavior of curved members have not been studied sufficiently. In this paper, an in-depth study of the influence of such residual stresses is performed. Considering the residual stress pattern due to cold bending, interaction diagrams and buckling curves for cold bent steel arches are developed. The results are quantified and compared with those for hot-rolled and stress free members. This allows designers to appreciate the available margins of safety when using standard interaction equations and buckling curves for cold bent members. Furthermore, the results suggest the necessity for the development of buckling curves for cold bent members including initial imperfections.     

钢拱的平面外稳定性分析

给出了钢拱在一般荷载作用下的压弯相关公式,并通过对荷载条件、圆心角、不同截面放置方式等影响参数进行分析,验证了相关公式的安全性和适用性.     

圆管截面两铰圆弧纯压拱的平面外稳定性及设计方法

拱的平面外稳定极限承载力设计一直没有成熟的设计方法及规范指导。通过分析两铰圆管截面圆弧钢拱的平面外弹性屈曲性能,指出Timoshenko未考虑翘曲的经典解与有限元分析结果吻合很好。在弹塑性平面外稳定性分析的基础上,借鉴单轴对称截面轴心受压构件的弯扭屈曲设计方法,提出以面外屈曲荷载对应的正则化长细比为参数进行面外稳定性设计的方法。借鉴我国GB 50017—2003《钢结构设计规范》中柱子曲线的表达式,建立纯压两铰圆管截面圆弧拱稳定承载力的实用计算公式及设计曲线。     

基于有限元法的L形轴压钢柱屈曲分析

利用有限元法对L形截面钢异型柱轴心受压构件,在考虑非弹性和初始缺陷的基础上,进行了特征值屈曲分析和非线性屈曲分析,并将分析结果与规范柱子曲线进行了比较,从而证明了利用有限元法对实际L形截面钢异型柱进行分析是有效的。     

Proposed residual stress model for roller bent steel wide flange sections

The manufacturing process of structural wide flange steel sections introduces residual stresses in the material. These stresses due to hot-rolling or welding influence the inelastic buckling response of structural steel members and need to be taken into account in the design. Based on experimental data standardized residual stress models have been proposed for inclusion in inelastic buckling analyses. By incorporating these residual stress models their effect on the resistance of beams and columns can be obtained. Residual stress models for roller bent steel sections are currently not available. Roller bent wide flange sections are manufactured by curving straight members at ambient temperature. This manufacturing technique, which is also known as roller bending, stresses the material beyond its yield stress, thereby overriding the initial residual stresses prior to bending and generating an entirely new pattern. This paper proposes a residual stress model for roller bent wide flange sections, based on earlier conducted numerical investigations which were validated by experimental research performed at Eindhoven University of Technology. The proposed residual stress model can serve as an initial state of a roller bent steel section in fully non-linear finite element analyses to accurately predict its influence on the inelastic buckling response.     

变截面H型钢柱相关屈曲性能研究

采用板壳单元离散变截面H型钢柱,并同时考虑构件整体与局部初始缺陷、残余应力、材料屈服、几何非线性等因素的影响。根据数值分析的结果,重点研究了腹板宽厚比、腹板楔率、翼缘宽厚比、长细比等参数对板件局部屈曲与构件整体稳定的影响,总结了压力作用下变截面H型钢柱局部屈曲、整体屈曲和相关屈曲的发展过程以及影响因素。     

侧向支撑对腹板开洞钢拱平面外弹性屈曲的影响分析

腹板开洞钢拱通过设置侧向支撑可以阻止钢拱发生平面外弯扭屈曲,支撑刚度的大小会对钢拱屈曲临界荷载产生影响.采用有限元方法分析了不同荷载、拱脚条件、支撑类型和位置对钢拱平面外屈曲稳定的影响.研究表明：在刚性支撑情况下,钢拱屈曲临界荷载随支撑刚度增大而增大,铰支钢拱屈曲半波随支撑数量的增加而增加,当支撑数量为n时,会出现n＋1个屈曲半波.两种支撑类型共同工作时,在侧向刚度支撑足够的情况下,扭转支撑对钢拱平面外屈曲临界荷载的影响有限.当侧向支撑刚度达到临界支撑刚度时,其屈曲临界荷载不再随支撑刚度的增大而增大.     

Finite element simulations of residual stresses in roller bent wide flange sections

Curved structural wide flange steel sections are frequently used in buildings or bridges. These sections are usually curved at ambient temperatures with a roller bending machine. This process alters the residual stress distribution, which may affect the elasto-plastic buckling behavior of arches. This paper presents a numerical modeling technique to estimate residual stresses in curved wide flange sections manufactured by the pyramid roller bending process. The technique incorporates material non-linearity, geometrical non-linearity and contact modeling. Numerically obtained residual stresses are compared to experimental results and good agreement was found for the top flange. Only moderate agreement was observed for the web but very good coherence was realized for the bottom flange. It is concluded that a finite element analysis can be used to estimate residual stresses in roller bent wide flange sections.     

Out-of-plane strength design of spatially trussed arches with a rectangular lattice section

Although several studies of the out-of-plane strength and design of steel arches with a solid web section have been reported, little research of the out-of-plane strength and design of spatially trussed arches has been reported in the open literature or design codes. In deference to the steel arch with a solid web section, the shear deformations play important parts in the out-of-plane inelastic buckling behavior of spatially trussed arches. In addition, global out-of-plane inelastic buckling of a spatially trussed arch is associated with local buckling of its components such as chord and diagonal web tubes and hence local component buckling influences the out-of-plane strength of the arch. This paper investigates the out-of-plane inelastic strength and design of spatially trussed circular arches with a rectangular lattice section under general loading using a three-dimensional nonlinear inelastic numerical approach. Methods for the out-of-plane inelastic strength and design of spatially trussed arches under uniform compression or under uniform bending are developed, based on which interaction equations for the design of spatially trussed steel arches under general loading against their out-plane failure are proposed. These interaction equations provide good lower bounds for the out-of-plane strength of spatially trussed arches.     

高强度钢材轴心受压钢柱整体稳定性能的缺陷影响研究

为研究高强度钢材轴心受压构件的整体稳定受力性能,了解构件的几何初始缺陷和截面残余应力对其屈曲强度和失稳变形的影响,以及与普通强度钢材轴压杆相比高强度钢材柱的整体稳定性能对缺陷敏感性的变化,采用有限元方法进行数值模拟计算,通过变换几何初始缺陷系数、残余应力数值大小和钢材强度等参数,对计算结果进行对比分析。研究结果表明,随着钢材强度的提高,高强度钢材轴压杆的整体屈曲强度对初始缺陷的敏感性明显降低,特别是对残余应力分布的敏感性;此外,初始缺陷的影响还与构件的长细比有直接关系。研究工作进一步揭示了高强度钢材轴压柱整体稳定性能的特点和优势。     

Buckling of cylindrical shells under transverse shear

This work concerns with experimental studies on buckling of thin-walled circular cylindrical shells under transverse shear. The buckling loads are also obtained from finite element models, empirical formulae and codes and are compared. Experiments are conducted on 12 models made of stainless steel by rolling and longitudinal seam welding. In situ initial geometric imperfection surveys are carried out. The tests are conducted with and without axial constraint at the point diametrically opposite the loading. Theoretical analyses are carried out using ABAQUS finite element code. Two finite element models considered are: (i) geometry with real imperfection (FES-I) and (ii) critical mode imperfect geometry (FES-II). In the former, the imperfections are imposed at all nodes and in the latter, the imperfection is imposed by renormalizing the eigen mode, using the maximum measured imperfection. General nonlinear option is employed in both the cases for estimating the buckling load. Galletly and Blachut’s expressions, design guidelines of Japan for LMFBR main vessel expressions (empirical formulae), ASME and aerospace structural design codes are used for comparing with experimental loads.The comparisons of experimental, numerical and analytical buckling loads reveal the following. The numerical results are always higher than the experimental values; the percentage difference depends on the wall thickness. FES-II predicts somewhat a lower load than that of the FES-I. The Japanese guidelines predict the lowest load, which is conservative. Experimental loads are lower than that predicted by both ASME and aerospace structural design codes.     

A numerical imperfection sensitivity study of cold-formed thin-walled tubular steel columns at uniform elevated temperatures

A numerical study is carried out on cold-formed rectangular hollow section columns to evaluate the sensitivity of column failure strength to initial imperfections, stress–strain relationships and to assess the existing design methods. It is shown that the magnitude of initial local buckling imperfection has a significant effect on the ultimate strength of short columns where failure is predominantly local buckling. Its effect on long columns is relatively small. Similarly the magnitude of initial global imperfection has more influence on the ultimate strength of a long column, whose failure is governed by global buckling, than on short columns, where local buckling controls. The shape of the stress–strain relationship of cold-formed steel will have noticeable effect on the column failure load. Current design methods, for high temperatures in ENV1993-1-2 and for ambient temperature in ENV1993-1-3, can provide a valid basis of calculation but modification will be necessary, depending on the exact model of stress–strain relationship of cold-formed steel at elevated temperatures.     

460MPa高强钢柱整体屈曲性能:试验研究及设计方法

受压柱的整体屈曲性能是钢结构研究的重要课题之一,尤其是近几年来应用越来越多的高强钢。对460MPa高强受压构件的整体屈曲性能进行试验研究。对包括焊接箱形截面和I形截面的12根钢柱进行试验。测量构件的残余应力、初弯曲和加载偏心率等初始缺陷。结合试验结果研究其屈曲变形和屈曲承载力。建立有限元模型,并与当前及以往研究中考虑初始缺陷的试验数据进行对比。采用经过验证的模型对大量不同截面尺寸和不同长度的柱的屈曲承载力进行估算,并将计算结果与其他钢结构规范的设计值进行对比。结果表明:460MPa高强钢柱,其无量纲屈曲强度与普通强度钢柱相比明显提高,并给出了相应的柱曲线和设计公式。     

复合型高性能钢材轴压构件整体稳定性能研究

为提升现代钢结构工程的综合抗灾能力,集高强度、高延性、耐蚀性和耐火性为一体的新一代复合型高性能钢材已经出现。该文针对该类钢材焊接工字形截面轴压构件的整体稳定性能,设计并完成6个长柱稳定试验,研究构件的稳定承载力和失稳破坏形式,并将试验结果与我国《钢结构设计标准》(GB 50017—2017)的柱子曲线进行对比,给出建议的曲线选型;同时,建立有限元模型并验证其准确性和可靠性;进一步通过大量算例分析初始缺陷、残余应力、材料强度和本构模型等对轴压构件整体稳定性能的影响;最后,基于参数分析算例结果,拟合复合型高性能钢材轴压构件新的柱子曲线公式,提出整体稳定设计方法。研究成果对促进该类钢材的工程应用具有重要意义。     

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.     

960 MPa高强度钢材轴压构件整体稳定性能试验研究

为研究960 MPa高强度钢材轴压构件的整体稳定性能,对6个焊接工字形和等边箱形截面试件进行了静力试验研究,测量了试件的几何初弯曲、荷载初偏心以及截面残余应力分布等初始缺陷,分析了试件的失稳破坏形态,得到了整体稳定承载力,并与规范设计曲线进行了对比分析。利用试验结果验证了有限元分析模型,并进行参数分析。研究结果表明：试件的破坏模态均为整体弯曲失稳,除两个几何初始缺陷过大的试件外,其他试件的整体稳定系数试验值均明显高于规范设计值;参数分析结果表明,960 MPa钢材焊接截面轴压构件的整体稳定系数较普通钢材显著提高,建议采用GB 50017-2003中的a类柱子曲线设计此类轴压构件,同时拟合了960 MPa高强度钢材的柱子曲线公式。     

Interaction of buckling modes in castellated steel beams

This paper investigates the behaviour of normal and high strength castellated steel beams under combined lateral torsional and distortional buckling modes. An efficient nonlinear 3D finite element model has been developed for the analysis of the beams. The initial geometric imperfection and material nonlinearities were carefully considered in the analysis. The nonlinear finite element model was verified against tests on castellated beams having different lengths and different cross-sections. Failure loads and interaction of buckling modes as well as load-lateral deflection curves of castellated steel beams were investigated in this study. An extensive parametric study was carried out using the finite element model to study the effects of the change in cross-section geometries, beam length and steel strength on the strength and buckling behaviour of castellated steel beams. The parametric study has shown that the presence of web distortional buckling causes a considerable decrease in the failure load of slender castellated steel beams. It is also shown that the use of high strength steel offers a considerable increase in the failure loads of less slender castellated steel beams. The failure loads predicted from the finite element model were compared with that predicted from Australian Standards for steel beams under lateral torsional buckling. It is shown that the Specification predictions are generally conservative for normal strength castellated steel beams failing by lateral torsional buckling, unconservative for castellated steel beams failing by web distortional buckling and quite conservative for high strength castellated steel beams failing by lateral torsional buckling.     

焊接不锈钢工字形截面受弯构件整体稳定与设计方法

总结了作者在清华大学完成的一批焊接不锈钢梁在弯矩荷载作用下的整体稳定性能试验,试验以试件的长细比为主要变化参数,对8根工字形截面梁进行了研究.试验的材料是奥氏体型316冷轧板,材料应力-应变关系通过拉伸试验获得;同时采用有限元软件ANSYS建立包含初始缺陷的有限元模型,对试件的极限承载力和荷载-变形关系进行分析,并与试验结果进行了对比,以证明有限元分析的合理性和适用性,为进一步研究奠定基础.同时,还将试验结果与欧洲规范和作者的建议设计方法进行了对比.分析结果表明:通过合理建模的有限元分析结果与试验结果吻合良好,有限元分析能够合理的模拟焊接不锈钢梁的整体稳定性能,作者所建议的设计方法的计算结果与欧洲规范相近,能够应用于工程设计并保证足够安全.     

Experimental and numerical study on the stability capacity of Q690 high-strength circular steel tubes under axial compression

This paper presents experimental investigation on the local and overall buckling capacity of Q690 high-strength circular steel tubes under axial compression. Coupon tests are undertaken to obtain the Young’s modulus, Poisson’s ratio, tensile yield stress and ultimate tensile strength of Q690 steel material. Forty-two specimens under axial compression are tested to evaluate the buckling behavior and the failure mode. Test results indicate that most of the existing design standards are conservative for the design of Q690 steel tubes. The distribution model of residual stress is measured by cutting ring method. Then, a finite element model based on modified column deflection curve method (CDC) is built to assess the effects of initial imperfection and residual stress on the stability capacity of the steel tubes. Finally, design methods and recommendations are provided for estimating the stability capacity of high-strength circular steel tubes.     

不同面外约束下带缝钢板剪力墙的抗剪性能研究

采用有限元软件ABAQUS,考虑几何非线性和面外初始缺陷的影响,对比分析钢筋混凝土板约束、刚性板约束以及无面外约束的带缝钢板剪力墙在水平荷载作用下的刚度、抗剪承载力、延性和耗能能力,并研究面外约束对带缝钢板的应力分布和面外屈曲的影响。结果表明:钢筋混凝土板可以抑制带缝钢板的弹性屈曲,降低带缝钢板的拉力带效应,提高带缝钢板剪力墙的延性、抗剪承载力和耗能能力。为了使钢筋混凝土板能更好地约束带缝钢板的面外屈曲,建议在剪力墙的小变形阶段,混凝土板不参与抗剪。