Imperfection sensitivity of plate girder webs subjected to patch loading

This paper is aimed at studying the influence of initial geometric imperfections on the postbuckling behavior of longitudinally stiffened plate girder webs subjected to patch loading. A sensitivity analysis is conducted herein using two approaches (deterministic and probabilistic) in order to investigate the effect of varying imperfection shape and amplitude on both, the postbuckling response and ultimate strength of plate girders under patch loading. This sensitivity analysis is performed by means of nonlinear finite element analysis. At first, the initial shape imperfections are modeled using the buckling mode shapes resulting from an eigenvalue buckling analysis. Thereafter, the amplitude of the buckling shapes for the various modes is varied, and then introduced in the nonlinear analysis. The results show the influence of these modes and amplitudes on the resistance to patch loading.     

Ultimate strength of longitudinally stiffened I-girder webs subjected to combined patch loading and bending

A numerical study is performed to investigate the ultimate strength of I-girder webs subjected to the combined action of patch loading and bending moment. The study was conducted by means of nonlinear finite element analysis. Initial geometrical imperfections, plastic material behaviour and large deflection effects were considered in the model. The finite element model was validated against experimental results taken from the literature. A parametric study was carried out in order to investigate the influence of the magnitude of the bending moment and the relative location of the stiffener on the ultimate strength to patch loading. Furthermore, diagrams showing the interaction between the aforementioned parameters are presented.     

Buckling of cylindrical open-topped steel tanks under wind load

Vertical cylindrical welded steel tanks are typical thin-walled structures which are very susceptible to buckling under wind load. This paper investigates the buckling behavior of open-topped steel tanks under wind load by finite element simulation. The analyses cover six common practical tanks with volumes of 2×10³ m³ to 100×10³ m³ and height-to-diameter ratios H/D<1. The linear elastic bifurcation analyses are first carried out to examine the general buckling behavior of tanks under wind load, together with comparison to that of tanks under uniform pressure and windward positive pressure (only loaded by positive wind pressure in the windward region). The results show that for larger tanks in practical engineering, the stability carrying capacity of wind load is relatively lower. It is also indicated that the buckling behavior of tanks under wind load is governed by the windward positive pressure while wind pressure in other region of tank essentially has no influence on the buckling performance. The geometrically nonlinear analyses are then conducted to investigate the more realistic buckling behavior of tanks under wind load. It is found that the buckling behaviors of perfect tanks and imperfect tanks are much different. The weld induced imperfection only has little influence on the wind buckling behavior while the classical buckling mode imperfection has significant influence, leading to a considerable reduction of wind buckling resistance. The influences of thickness reduction of cylindrical wall, liquid stored in the tank and wind girder on the buckling behavior are also examined. It shows that the thickness reduction of cylindrical wall considerably reduces the wind buckling resistance while sufficient liquid stored in the tank and wind girder significantly increase the wind buckling resistance.     

Influence of longitudinal stiffeners on elastic stability of girder webs

In this paper, linear buckling analyses of plates with longitudinal stiffeners having various shapes and positions and subjected to axial force, in-plane bending and shear are developed. The aim is to give some new practical insights about the shape and optimum position of longitudinal stiffener in webs when axial force, bending moment and shear act. By means of a comprehensive numerical investigation, some practical issues for buckling phenomena in stiffened plates, taking into account (a) dimensions and shape (square and rectangular) of the plate, (b) dimensions and shape of the stiffener (with open and closed cross-sections), (c) location of the stiffener, and (d) load configuration (uniform compression, pure bending, combinations of axial compression and bending, and shear) are developed.     

Patch loading and improved measures of incremental launching of steel box girder

Yandangshan Bridge is a tied-arch bridge of double-line railway with a (90 + 90) m continuous steel box girder and passes over a very busy highway in China. The incremental launching of the steel box girder of this bridge is a challenge for bridge builders, mainly because of the patch loading caused by large self-weight, large camber, unsymmetrical and flexible temporary transverse beams. Due to on-site working conditions, many commonly used measures cannot be taken for the launching of this bridge. The launching process is simulated using finite element method. The results have shown that significant local stress concentration would occur in the web plate and bottom plate of the girder if no improved measures are applied. The influencing factors of the stress concentration are studied. Four measures to reduce the local stress of the girder are presented and put into practice: to add two slide shoes on every pier; weld six short launching noses at the diaphragm of leading end of the box girder; pre-lift the 6 slide shoes on one temporary pier at different positions to eliminate part of the deflection of the temporary transverse beams, and use special adjustable slide shoes in one span. The whole launching process has been monitored and the measured stress and deformation coincide with the results of finite element analysis. Good effects have been obtained by applying the four improved measures. The incremental launching of the steel box girder of Yandangshan Bridge has been successful.     

Steel plate girder webs under combined patch loading,bending and shear

During bridge erection employing the incremental launching method, plate girders are subjected to a combined loading situation. Due to the support reaction, the thin webs are withstanding concentrated loads, and due to the self weight of the launching nose and the span between the piers the web is also under the action of bending and shear force. This paper is aimed at investigating the nonlinear behavior of unstiffened girder webs subjected to combined loading (concentrated loading, bending and shear) by using the finite element method. Firstly, the numerical models are validated against experimental results taken from the literature. Secondly, each individual resistance is calculated in order to normalize the applied loads. Thereafter, a parametric analysis is conducted looking at the interaction between the three types of loading, and a combined failure mode is identified. Finally, the results shows limits in the resistance when all three loads are applied.     

Patch loading resistance of girders with corrugated webs

The corrugated steel plate is a widely used structural element in many fields of application because of its favourable properties and has been applied since the 1920s. For the last 20 years it has been increasingly used in the web of steel and composite bridges. When such a bridge is incrementally launched, buckling of the thin steel web may occur. In this paper, a numerical model is developed on the basis of previous experiments. Numerical investigations are made for the determination of the patch loading resistance, and the geometric parameters which influence the patch loading resistance and the structural behaviour are determined and analysed. Existing design formulas from the literature are summarised from the point of view of bridges, and enhanced according to the numerical results and the existing and additional experiments.     

带初始缺陷的平面钢框架的敏感性分析

给出一个门式刚架承载力的敏感性和统计性分析。阐述了包括2个单层受压柱系统的典型稳定性问题,这个系统的要素相互影响,并且结合随机的不完善性,将影响承载力。采用Sobol敏感性分析法研究相互影响的因素。Sobol敏感性分析法应用于区别主要输入的随机缺陷和它们的高阶互动效应对承载力的影响。根据试验结果,考虑了大部分缺陷。采用拉丁超立方抽样方法,实现了对初始缺陷的模拟。几何非线性解决方案提供了数值解。采用梁单元对框架实现网格划分。平面钢框架的柱分别考虑采用2种边界条件。分析了承载力设计值与柱长度系数之间的关系。     

A simplified analytical procedure for assessing the worst patch load location on circular steel silos with corrugated walls

Silos are widely used in the food and chemical industries for the storage of granular materials. The calculation of their wall dimensions is complicated since the interaction between the stored material and that from which the silo is made is complex, a consequence of their very different mechanical behaviours. The loads exerted on the silo walls by stored materials must be taken into account in silo design, and the means for calculating them is contemplated in Eurocode EN 1991-4. The complexity of the phenomena that occur within silos often leads to the appearance of unexpected and asymmetrically distributed pressures. This is taken into account in the above Eurocode via the concept of the patch load, which is asymmetric and can be exerted at any point on the silo wall. A finite element model has been developed in order to check that the stress resultants derived from the patch load on steel silos with corrugated walls may be predicted by using the well-known expressions of shell theory. Then, a simplified analytical procedure has been developed for predicting the worst location of patch loads for all metal silos, but with special application to corrugated steel silos in Action Assessment Class 3. It has been found that significant differences may be found for most cases with the worst location for the patch load defined in Eurocode for welded silos in Action Assessment Class 2. On the other hand, the values obtained for the maximum meridional membrane stress resultant do not significantly differ, except for high slenderness values in intermediate slenderness silos.     

Eccentrically patch-loaded steel I-girders: The influence of patch load length on the ultimate strength

The ultimate strength of steel I-girders is reduced when the loads are applied at an eccentricity relative to the center of the section, compared with the centric case, for which the loads are applied in the plane of the web. Current expressions for the strength reduction coefficient for eccentrically patch-loaded steel I-girders do not account for the length of the patch loading. In this paper, the effect of patch load length is investigated using a substantially larger data set than was available in the past. The length of the patch load is found to have a significant influence on the strength reduction coefficient for small ratios of flange thickness to web thickness, t_f/t_w.     

Non-linear analysis of perforated steel plates subjected to localised symmetrical load

Although the literature contains a number of studies which have been developed to describe the non-linear behaviour of ordinary plates, few works are available on perforated plates, and studies on non-linear behaviour of perforated plates under localised symmetrical load are not studied in depth. The aim of this paper is to provide some insights into the elasto-plastic behaviour of plate girder web panels with circular holes under localised symmetrical load.Numerical analyses of square and rectangular perforated plates with centred and eccentric holes were developed. Results provide new insights into post-critical mechanisms in perforated plates subjected to localised loads when the length of the symmetrical compressive load, hole diameter and steel yield limit vary. An increase in the critical slenderness of the plate (a value at which transition from elastic to plastic collapse occurs) and a corresponding reduction in the elastic critical load occur when the dimensions of the hole increase. A further increase in the critical slenderness occurs when the length of the localised load is reduced. High-performance steel may be subject to buckling with a lower possibility of post-critical mechanisms: a reduction in critical slenderness occurs when the steel grade increases. Lastly, numerical analyses of slender and thick perforated plates were developed and their results compared.     

折线形腹板钢梁的局部承压性能有限元分析

折线形腹板钢梁是将传统钢梁中的平腹板用折线形钢板来代替,是波纹腹板钢梁的一种。该钢梁具有较高的承载力及良好的经济优势。目前,在国内外仅对梯形腹板钢梁的局部承压性能有少量研究。本文作者采用有限元方法对折线形腹板钢梁局部承压性能进行研究,了解其在实际试验中可能发生的破坏模式和各因素对其局部承压力性能的影响,并为今后试验作准备。     

单箱三室波形钢腹板悬臂梁扭转与畸变分析及试验研究

为研究单箱三室波形钢腹板箱梁悬臂状态下的扭转与畸变性能,以乌曼斯基第二理论和箱梁理论为基础,考虑了波形钢腹板的褶皱效应对箱梁纵向刚度的影响,推导了单箱三室波形钢腹板悬臂梁扭转与畸变微分方程,并采用初参数法及弹性地基梁比拟法求解了约束扭转和畸变产生的翘曲正应力和剪应力计算式。通过1片单箱三室波形钢腹板双悬臂梁进行了偏载和对称加载试验,验证了扭转与畸变翘曲应力计算公式的正确性。最后,利用推导的理论模型,分析了梁高、箱室宽度及波形钢腹板厚度等参数对偏载作用下单箱三室波形钢腹板组合箱梁截面翘曲应力的影响。研究结果表明:提出的理论计算公式可用于准确计算单箱三室波形钢腹板悬臂梁扭转与畸变效应;悬臂梁翘曲正应力主要由畸变变形引起,而约束扭转主要产生翘曲剪应力,且悬臂梁扭转和畸变产生的翘曲正应力值和剪应力值与弯曲正应力和剪应力的比值较大,因此,单箱三室波形钢腹板悬臂状态下扭转和畸变产生的翘曲正应力和剪应力不可忽略;梁高和箱室宽度对单箱三室波形钢腹板的翘曲应力影响较为显著,波形钢腹板厚度对其几乎没影响。     

波形钢腹板组合槽型梁静载试验与有效预应力分析

波形钢腹板组合槽型梁是一种新型下承式开口薄壁桥梁结构,对4片按照1/4相似比进行设计的试验梁进行两点对称加载和有限元分析,研究两组试验梁在对称荷载作用下的荷载位移关系、截面应变分布、裂缝发展规律和破坏形态等,分析张拉预应力和释放预弯力后试验梁底板混凝土的有效预压应力。研究表明：竖向荷载作用下试验梁符合平截面变形规律,应忽略波形钢腹板对抗弯刚度的贡献和底板混凝土对抗弯承载力的抵抗作用;试验梁混凝土受压区受限于上翼缘板,其应变分布为梯形而非常规的三角形分布;下承式槽型截面的中性轴偏低,波形钢腹板预弯钢梁反弹能够有效地对混凝土施加预压应力;采用波形钢腹板能有效提高槽型梁的预应力施加效率,文中建议的波形钢腹板组合梁预应力等效荷载法,能准确计算此类结构的混凝土有效预压应力;两组试验梁由于配筋量的不同分别发生塑性和脆性弯曲破坏;波形钢腹板组合槽型梁的自重轻、抗弯刚度较大、具有较好的延性和抗裂性能。     

Behaviour of concrete-filled steel columns under the seismic loading

This paper describes results of a dynamic analysis on partially concrete-filled steel columns, which are used for piers of the motorway viaduct. As a seismic loading the ground motion measured in the main shock and one of the post shocks of Chuetsu earthquake in 2004 are used. These two shocks have different vibration patterns and therefore the influence of the vibration pattern of the seismic load can be investigated. Through the analysis it is found that the main shock, which has smaller ground acceleration than the post shock, causes a larger displacement of the column because the frequency component of the main shock is similar to the natural frequency of the column.     

Strength of I-girders with Delta stiffeners subjected to eccentric patch loading

In this paper the effects of Delta stiffeners on strength and behavior of I-girders subjected to eccentric patch loading has been investigated. To achieve the objectives extensive computer work has been carried out using the finite element method. The beams considered here had different geometry and stiffeners arrangement. The reliability of the numerical models and results are confirmed by comparison with experimental results which show good agreement. Furthermore, the results indicate that numerical models can be used to analysis different I-girders with different stiffeners. The results also show that Delta stiffeners are more efficient than other stiffeners, especially in the case of eccentric patch loading; also the capacity of critical patch loading of I-girders increases by about 95 percent compared to the other stiffened girder.     

波形钢腹板PC组合箱梁在玉春桥中的应用研究

针对一座波形钢腹板PC组合箱梁桥——玉春车行天桥,对其波形钢腹板和抗剪连接键的设计与构造进行了介绍,并对波形钢腹板和抗剪连接键的受力性能进行了计算分析,计算结果表明,在正常使用极限状态下,钢板的剪应力满足规范要求,且不会在钢板剪切屈服之前发生局部屈曲、整体屈曲或合成屈曲的破坏形式;剪力连接键的抗剪承载能力满足使用要求且具有较大的安全裕度。