具有空心圆形截面圆钢拱的平面内非线性分析

分析研究了具有空心圆形截面圆钢拱的平面内非线性性能。提出了一些设计参数,如边界条件,矢跨比和夹角对强度的影响。此外,还讨论了其他一些因素,如几何和材料非线性,初始缺陷的影响。文中提供了分析拱非线性性能的预测标准和计算其非线性屈曲荷载的公式。分析发现:初始缺陷对强度的影响主要取决于拱的柔度和缺陷尺度,当拱圈深度越大,这种相关性就越小。几何非线性的影响,主要取决于拱的深度和柔度。短粗的拱较之长细拱受到矢跨比的影响要小一些。边界条件的影响极大程度上取决于浅拱的程度和柔度。细长拱较之短粗拱其强度退化更快。     

Design of circular steel arches with hollow circular cross-sections according to EC3

Design of either pin-ended or fixed circular steel arches with hollow circular cross-sections subjected to a uniformly distributed vertical load along the horizontal projection of the entire arch with the aid of the EC3 provisions is discussed. Appropriate modification factors are proposed that should be included in EC3 interaction equations, to improve their accuracy for the design of such arches.     

实腹圆弧钢拱的平面内稳定极限承载力设计理论及方法

拱的平面内稳定极限承载力设计一直没有成熟的规范指导。本文用有限壳单元模型先分析了工形截面两铰圆弧钢拱的平面内弹性屈曲性能,与拱的经典屈曲理论作了对比,指出了必须同时考虑长细比和矢跨比对屈曲荷载的影响。然后分析了两铰圆弧钢拱受静水压力和其它荷载作用下的弹塑性屈曲性能,指出了典型破坏机理为拱两侧1/4跨附近形成塑性铰导致结构失效。利用拱的弹性屈曲荷载定义了拱的正则化长细比,用Perry-Robertson公式的形式,建立了拱的稳定系数与正则化长细比的关系,提出了受静水压力的两铰圆弧钢拱的平面内稳定极限承载力设计方法,并用轴力和弯矩的两项相关公式提出了受其它荷载作用下的平面内稳定极限承载力设计方法。     

In-plane strength of concrete-filled steel tubular circular arches

More than 400 concrete-filled steel tubular (CFST) arch bridges have been constructed worldwide so far. However, design codes or guidance for the in-plane strength design of CFST arches are yet to be developed. In current design practice, the philosophy for the in-plane strength design of reinforced and prestressed concrete arches is widely adopted for CFST arches. For this, the CFST arches are considered under central or eccentric axial compression and are treated similarly to CFST columns, and the classical buckling load of CFST columns is used as the reference elastic buckling load of CFST arches. However, under transverse loading, the in-plane elastic buckling behaviour of CFST arches, particularly shallow CFST arches, is very different from that of CFST columns under axial compression. In addition, different from CFST columns under central or eccentric axial compression, CFST arches are subjected to significant nonlinear bending actions and transverse deformations prior to buckling and these will influence the strength of CFST arches greatly. Therefore, it is doubtful if the current method for in-plane strength design of CFST arches can provide correct strength predictions. In this paper, a method for the in-plane strength design of CFST circular arches, which is consistent with the current major design codes for steel structures, is developed by considering both geometric and material nonlinearities. A design equation for the in-plane strength capacity of CFST arches under uniform compression, and a lower-bound design equation for the in-plane strength check of CFST arches under combined actions of bending and compression are proposed.     

Thermoelastic flexural–torsional buckling of steel arches

This paper presents the lateral buckling behaviour of steel arch members with a doubly symmetric I-shape cross-section subjected to a linear gradient temperature field over the cross-section. The steel arch is subjected to an in-plane linear temperature gradient field whilst it experiences expansion along its length due to the in-plane temperature gradient producing an in-plane curvature. As the steel arch continues to be subjected to increasing temperature differential and increasing average temperature, the bending moments and axial compressive forces in the steel arch increase and upon reaching a critical value, the steel arch bifurcates from its primary equilibrium position and fails in lateral–torsional buckling mode. A novel non-discretisation mechanical-based methodology developed recently is used to model the behaviour of the steel arch prior to buckling, whilst the classical buckling theory is used to determine the critical temperature which causes flexural–torsional buckling. The proposed methodology allows for the critical temperature gradient and critical average temperature to be ascertained using an iterative method. Using a comprehensive parametric study, the variations of the thermal gradient and the critical average temperature to various parameters are then investigated. The model proposed here provides a closed-form solution for which it forms a platform which can be used for structural steel arch design and evaluation in the development of codified approaches to fire design on a performance based design.     

腹板开洞钢拱的平面内稳定极限承载力设计理论及方法

腹板开洞钢拱组合了拱和开洞构件的特性,目前在轻轨列车站篷及航站楼等的钢结构中有广泛应用。本文首先用有限壳单元分析了以工形截面腹板开洞圆弧钢拱为代表的拱的平面内弹性屈曲性能,考察了腹板孔洞的几何参数和拱本身的几何参数对屈曲荷载的影响;按照整体屈曲荷载的等效原则,把腹板开洞拱等效为由两个T形截面和缀板组成的格构式构件,并给出了格构式构件的等效截面尺寸。然后研究了各参数下的腹板开洞钢拱的弹塑性屈曲性能,定量考察了孔洞对稳定极限承载力的削弱作用,提出了腹板开洞钢拱特有的单边塑性铰的破坏机理。利用已经建立的拱的稳定系数与拱的正则化长细比的关系,根据等效构件的换算长细比,提出了受静水压力及其它荷载分布形式的腹板开洞拱的平面内稳定极限承载力设计方法。     

GDQR求解变截面圆拱的屈曲问题

给出了两端不可压缩变截面拱的屈曲方程，用广义微分求积法则(GDQR)分析了不变截面拱的屈曲问题后，又将该方法引伸到另外三种变截面圆拱的屈曲问题，求出了在三类边界条件下第一类和第二类稳定性的屈曲荷载．求解过程中，使用了Lagrange和Chebyshev两种权系数矩阵，并作比较．结果表明，用GDQR求解不变截面或变截面屈曲问题时，方法简单，易于理解且精度高．使用这两种权系数，求解Chebyshev权系数时要用到符号编程，比较耗时，但是该方法相对Lagrange法收敛性要好．     

Seismic behavior of steel plate shear walls with centrally placed circular perforations

The behavior of unstiffened thin steel plate shear walls with circular perforations placed at the center of the infill plates is examined. A shear strength equation is developed for perforated steel plate shear wall with circular perforation at the center. A series of single storey perforated steel plate shear walls with different aspect ratios and different perforation diameters were analyzed to assess the proposed shear strength equation. A comparison between the nonlinear pushover analysis and the proposed equation shows excellent agreement. The proposed shear strength equation is applied for design of boundary columns of one 4-storey and one 6-storey perforated steel plate shear walls. The predicted design forces in the boundary columns for the selected perforated shear walls are compared to the forces obtained from nonlinear seismic analysis. The proposed equation gives very good predictions for the design forces in the boundary columns.     

工形截面钢拱考虑腹板局部屈曲的承载力设计方法研究

把工形截面钢拱的腹板做高做薄是提高其承载力的有效方法之一。该文采用大挠度弹塑性壳单元模型,研究焊接工形截面两铰圆弧钢拱在允许腹板局部屈曲条件下的平面内稳定承载力及其设计方法,其中考虑钢拱几何初始缺陷和残余应力的影响。首先,对钢拱在均匀轴压力作用下的承载力和破坏机理进行有限元数值分析和参数研究,考察拱截面腹板高厚比、钢拱几何长细比、截面翼缘腹板板厚比和翼缘宽厚比对钢拱稳定系数的影响。在设定的钢拱翼缘宽厚比范围内,基于大量的钢拱承载力数值分析结果,提炼出腹板高厚比和翼缘腹板板厚比组合效应的等效正则化腹板高厚比,进而获得钢拱稳定系数与等效正则化腹板高厚比以及钢拱正则化长细比之间关系的计算公式。其次,研究压弯组合作用下钢拱腹板高厚比变化对钢拱整体稳定承载力的影响,揭示钢拱压弯组合作用下的破坏机理及稳定承载力。最后通过对大量钢拱算例进行不同压弯组合工况下的极限承载力分析,提出了钢拱在一般荷载或组合荷载作用下承载力设计的计算公式。     

Non-linear in-plane stability analysis of FG circular shallow arches under uniform radial pressure

In this paper, non-linear stability behavior of functionally graded (FG) circular shallow arches subjected to a uniform radial pressure is investigated by an analytical method. For this purpose, the classical single layer assumption is used to approximate the displacement field through the arch. Donnell׳s non-linear model for shallow shells is employed to derive the strain–displacement relations. The material properties vary smoothly through the thickness of the arch according to a power-law distribution. The governing equilibrium equations and the complete set of boundary conditions are extracted employing the principle of virtual displacements and variational calculus. Because of considerable pre-buckling deformations of shallow arches, the stability analysis is accomplished considering the pre-buckling deformations. The non-linear equilibrium paths are presented for two symmetric types of boundary conditions. Results show the influences of properties dispersion, geometrical characteristics, and boundary conditions on the stability behavior of the FG circular shallow arches. Also, the results of the paper are compared with the known data in literature.     

Buckling of monosymmetric arches under point loads

A finite element procedure is described for analysing the flexural-torsional buckling of arches of monosymmetric cross-section. First an inplane analysis is performed to obtain the distributions of axial force and bending moment in the arch. These are then substituted into the buckling equation for monosymmetric arches, and the resulting eigenvalue problem is solved numerically. Higher order quintic shape functions are used to describe the element displacement fields. The effects of the distances from the arch shear centre axis of point and uniformly distributed loads are also included in the analysis.

Flexural-torsional buckling tests on circular aluminium arches of monosymmetric I-section are also described. The test results for arches subjected to central concentrated point loads are compared with the finite element theory.     

Time-dependent in-plane behaviour and buckling of concrete-filled steel tubular arches

This paper presents a theoretical analysis for the time-dependent behaviour and buckling of concrete-filled steel tubular (CFST) circular arches due to shrinkage and creep of the concrete core under a sustained uniform radial load. The algebraically tractable age-adjusted effective modulus method is used to model the time-dependent behaviour of the concrete core, based on which the differential equations of equilibrium for the time-dependent analysis of CFST arches are derived and analytical solutions for the long-term displacements, stresses and internal forces of CFST arches under the sustained load are obtained. It is shown that the visco-elastic effects of creep and shrinkage of the concrete core have significant long-term effects on the in-plane structural behaviour of CFST arches. The long-term radial and axial displacements, as well as the bending moment, increase substantially with time. For a CFST arch with a low area ratio of the steel tube to the concrete core, the long-term deformations may be excessive and affect the serviceability of the CFST arch. The increases of the long-term stresses in the steel tube with time are significant, while the long-term stresses in the concrete core decrease with time and may change from compressive to tensile if the time is sufficiently long. It is demonstrated that the time-dependent change of the equilibrium configuration of the CFST arch can lead to a buckling configuration being attained in the time domain under a sustained load, which is lower than the buckling loads of the CFST arch under short-term loading. The solution for the possible prebuckling structural life for time-dependent creep buckling of deep CFST arches is derived and can be used to determine the effects of various parameters on the creep buckling of a CFST arch.     

Non-linear plastic analysis of steel arches under lateral buckling

Curved graphs are proposed that relate the shape of the box cross-section of an arch to the real ultimate lateral strength for various values of length, support conditions and of height of the cross-section.The real ultimate lateral strength of a series of arches is determined and the results obtained are then compared to those provided by Sakimoto and Komatsu [1].Elastic–plastic steel material and geometric non-linearity hypotheses, residual stresses, and initial lateral deflection are all taken into consideration with respect to the real ultimate lateral strength.     

基于突变理论的扁拱跳跃屈曲分析

分析了扁拱在静载荷或动载荷作用下发生跳跃屈曲的原因。采用尖点突变理论建立悬链线形拱的跳跃屈曲模型，推导临界荷载公式，并采用Matlab工具计算及Ansys验算模型理论正确性，最后对上述两种方法所得值进行比较。     

Experimental study of low-yield-point steel plate shear wall under in-plane load

This paper describes the study of the low-yield-point (LYP) steel plate shear walls under in-plane load. In the LYP steel plate shear wall system, LYP steel was selected for the steel plate wall while the boundary frame was constructed by the high strength structural steel. A series of experimental studies examined the inelastic shear buckling behavior of the LYP steel plate wall under monotonic in-plane load. The effects of width-to-thickness ratio on the shear buckling of LYP steel plates were examined. The stiffness, strength, deformation, and energy dissipation characteristics were investigated by performing cyclic loading tests on the multistorey LYP steel plate shear walls. Excellent deformation and energy dissipation capacity were obtained for all specimens tested. The LYP steel plate shear wall system is able to exceed 5% of storey drift angle under lateral force.     

Behavior of thin-walled circular hollow section tubes subjected to bending

Thin-walled steel circular hollow sections (CHSs) are widely used in wind turbine towers. The tower tubes are mainly subjected to bending. There have been a few experimental studies on the bending behavior of thin-walled CHS steel tubes. This paper describes a series of bending tests to examine the influence of section slenderness on the inelastic and elastic bending properties of thin-walled CHS. In addition, the influence of stiffeners welded in the steel tube is considered. Sixteen bending tests were performed up to failure on different sizes of CHS with diameter-to-thickness ratio (D/t) varying from 75 to 300. The experimental results showed that the specimens with small diameter-to-thickness ratios failed by extensive plastification on the central part of the tube. With the increase of diameter-to-thickness ratio, the local buckling phenomena became more pronounced. The stiffeners in the steel tubes increased the load carrying capacity and improved the ductility of the specimens. The experimental results were compared with current design guidelines on thin-walled steel members in AISC-LRFD, AS4100 and European Specification. It was found that the test results agreed well with the results based on AS4100 design code.     

Nonlinear thermomechanical post-buckling of circular FGM plate with geometric imperfection

Nonlinear thermomechanical post-buckling of an imperfect functionally graded material (FGM) circular plate, subjected to both mechanical load and transversely non-uniform temperature rise, is presented. The material properties of FGM plates are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Based on von Kármán's plate theory, equilibrium equations governing a large axi-symmetric deformation of the FGM circular plate under thermomechanical loads are derived. In the analysis, the geometric imperfections of the plate are taken into account. By using a shooting method the nonlinear ordinary differential equations with immovably clamped boundary conditions are solved numerically. Responses for the nonlinear thermomechanical post-buckling responses of the FGM plate are obtained. Numerical examples are presented that relate to the performances of perfect and imperfect, homogenous and graded plates. Characteristic curves of the post-buckling deformation of the imperfect FGM circular plate varying with thermal loads, imperfection parameters and volume fraction index are plotted. And then effects of the load parameters, materials constitution, and the geometric imperfection of the plate on the deformation are discussed in detail.     

In-plane buckling behavior of slender parabolic concrete-filled steel tubular arches with fixed ends

现有规范采用“等效梁柱法”计算长细比不超过80的钢管混凝土拱的平面内稳定承载力,而实际工程中有近20%拱桥拱肋长细比超过上述限值,即大长细比钢管混凝土拱。因此,利用ABAQUS建立了有限元分析模型,在基于现有试验数据验证模型可靠性的基础上,对大长细比抛物线形钢管混凝土无铰拱在竖向均布荷载作用下的平面内稳定性能进行了分析,研究了长细比、矢跨比、含钢率、混凝土强度和钢材强度对拱肋平面内稳定承载力的影响;基于参数分析结果,对现有平面内整体稳定系数公式进行修正,提出了大长细比抛物线形钢管混凝土拱平面内稳定承载力设计公式。结果表明：拱肋稳定承载力随长细比增大显著降低,随矢跨比和含钢率增加近似线性提高。其中,矢跨比对大长细比拱肋影响更为显著,而含钢率对采用高强钢的拱肋影响更大;所提出的设计公式计算结果与有限元分析结果吻合良好,有限元分析结果与公式预测结果比值的均值为1.02~1.08,标准差为0.039~0.051,变异系数为3.74%~4.72%。     

Thin circular hollow section-to-plate T-joints: Stress concentration factors and fatigue failure under in-plane bending

Welded thin-walled (t<4 mm) tube-to-plate T-joints made up of cold-formed circular hollow sections welded onto a plate to form a moment resistant connection are used in the road transport and agricultural industry to manufacture equipment and other structural systems. Fatigue design of these joints is not available in current standards. An understanding of the stress concentrations and failure in these connections is therefore necessary as a step towards understanding the fatigue behaviour of these connections. Stress concentration factors (SCFs) of welded thin-walled (t<4 mm) circular hollow section (CHS)-to-plate T-joints are determined at different locations along the weld toes on the tubular brace. The distribution of SCFs along the weld toes shows that the highest SCF occurs at the weld toes in the circular brace at the 0° line. The ratio of the end of test fatigue life (N4) to the through-thickness fatigue life (N3) in the thin CHS-plate T-joints is found to fall within the range of N4/N3 found in previous research of both thick and thin-walled joints. Surface crack growth monitoring is used to obtain an approximation of the length of surface crack at the point of occurrence of a through-thickness crack. The relationship between surface crack length and the occurrence of a through-thickness crack is important in that it can be used as a measure of the criticality of a surface crack during structural health monitoring of equipment or structures.     

Effect of flattening circular hollow sections in truss and dome structures

Circular hollow steel sections are normally specified in truss and dome structures to take advantage of their efficiency in compression and the ease in which they can be curved to match the various radii of different domes. However, it is not easy to connect these members together or to other members. In order to connect them together or to other members the ends are sometimes squashed or flattened. Although the process of flattening does not reduce the area of the section, it does reduce the flexural stiffness of the section. The aim of this paper is to study the behaviour of circular hollow members with flattened edges, in compression. Variables in the tests include the diameter, thickness and length of the sections, and number of bolts in the connection. Two failure modes were observed and these are overall flexural buckling (OFB) of the member and excessive deformation of the transition zone (DTZ). The results from these tests are compared with the flexural compressive resistance formula in the South African steel code (SANS10162-1) and the European steel code (EN 1993-1-1), with a view of determining a simple formula for designing such members.