脚手架系统几何缺陷及节点刚度研究

介绍了脚手架系统几何缺陷的现场测量结果,包括柱子、框架的几何缺陷及荷载偏心。在浇筑混凝土前,测量现场脚手架系统的实际初始几何缺陷和荷载偏心。对随机抽取的构件进行试验,研究节点刚度,获得绕水平轴及竖轴的转角。对节点构造(双向、三向及四向节点)、弯曲轴、荷载方向进行试验。对数据进行统计分析,使其能应用于脚手架系统模拟和概率评估中。     

Structural modelling of support scaffold systems

In this paper, accurate three-dimensional advanced analysis models are developed to capture the behaviour of support scaffold systems, as observed in full-scale subassembly tests consisting of three-by-three bay scaffold systems with various combinations of lift height, number of lifts and jack extension. The paper proposes methods for modelling spigot joints, semi-rigid upright-to-beam connections and base plate eccentricities. Material nonlinearity is taken into account in the models based on the Ramberg-Osgood expression fitted to available experimental data. Actual initial geometric imperfections including member out-of-straightness and storey out-of-plumb are also incorporated in the models. The ultimate loads from the nonlinear analyses were calibrated against failure loads and load-deflection responses obtained from full-scale subassembly tests. The numerical results show very good agreement with tests, indicating that it is possible to accurately predict the behaviour and strength of complex support scaffold systems using material and geometric nonlinear analysis. The paper highlights the main difficulties in the numerical modelling of support scaffold systems, and describes mechanical models for implementing base plate, U-head and spigot joints in the analysis.     

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.     

Tests and finite element analysis of pin-ended channel columns with inclined simple edge stiffeners

This paper presents an experimental investigation and a finite element analysis on cold-formed channels with inclined simple edge stiffeners compressed between pinned ends. Compression tests of pin-ended channel columns with inclined simple edge stiffeners have not been performed till now. A total of 36 channel specimens including three different cross sections with different edge stiffener inclined angles and column lengths were tested. Detailed measurements of initial geometric imperfections and material properties of the specimens were also conducted before the above tests. Failure modes include local buckling, distortional buckling, flexural buckling and interaction among these buckling modes were observed in tests. The results indicate that inclined angle and loading position significantly affect the ultimate load-carrying capacity and failure mode of specimens. Moreover, a non-linear finite element model was developed and verified against tests. Geometric and material non-linearities were included in the model. Results from the finite element analysis agree well with experimentally ultimate loads and failure modes. However, it should be improved on prediction for certain displacement.     

On the modelling of different types of imperfections in silo shells

The assessment of imperfections is most important for determining the load-bearing capacity of a thin-walled shell structure. Different ways of modelling imperfections are discussed in this paper and steel silo shells are used as an application. Buckling tests were performed on different types of model shell - standard quality and high quality with reduced heat input during welding. For the numerical studies two different approaches were used as well: an axisymmetric approach with substitute geometric imperfections and an FEM approach, where the nodal coordinates were derived from surveying the specimen. It was found that there is considerable gain in the buckling strength due to the presence of the granular solid. The larger the initial imperfections in the shell the greater the gain in strength compared to the empty cylinder. The modelling of the uneveness of the edges with uneven dead loading is also discussed.     

Numerical modelling of steel plate girders at normal and elevated temperatures

The main goal of this study is to increase the knowledge on the behaviour of steel plate girders subjected to shear buckling at both normal and elevated temperatures. Hence, numerical models were duly validated with experimental tests from the literature. Experimental tests on steel plate girders with different configurations were numerically reproduced, showing a good agreement between numerical and experimental results. Afterwards, applying the validated numerical models, sensitivity analyses on the influence of initial imperfections were performed. Different values for the maximum amplitude of geometric imperfections were considered and residual stresses were also taken into account. Finally, the effect of the end supports configuration was also studied aiming to understand the strength enhancement given by the rigid end support at normal temperature and evaluating if that strength enhancement is maintained in case of fire.     

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.     

Accurate modeling of joint effects in lattice transmission towers

Lattice Transmission towers are vital components of overhead transmission lines which play an important role in the operation of electrical power systems. Accurate prediction of the structural capacity of lattice towers under different failure modes is very important for accurate assessment of the reliability of transmission lines and power grids, and for design of efficient failure containment measures. Traditionally, lattice towers are analyzed as ideal trusses or frame-truss systems without explicitly considering loading eccentricities and slippage effects in bolted joints. Such effects are always observed in full-scale tower tests and introduce great differences in the ultimate bearing capacity and failure modes obtained from classical linear analysis models. In this paper experimental results available from full-scale prototype tests of a single-circuit 110 kV and a single-circuit 220 kV lattice transmission towers subjected to different load cases are presented and compared with those obtained from four series of numerical models that include joint eccentricity effects and different joint slippage models. The numerical simulation results confirm that joint slippage dramatically increases the deformation of the lattice towers, while its influence on load-bearing capacity will vary in different load cases according to the magnitude of vertical loading and the tower failure mode. Results from the pushover nonlinear static analysis of the towers considering both joint slippage and eccentricity are found in agreement with the experimental results. This type of analysis can be used to model joint effects in lattice towers.     

Shear resistance of longitudinally stiffened panels—Part 1: Tests and numerical analysis of imperfections

This paper deals with the results of four full-scale tests, numerical simulation of tests and initial geometric imperfection analysis for longitudinally stiffened panels in shear. The tests examine the influence of varying position and bending stiffness of one trapezoidal longitudinal stiffener on the panel shear resistance and its buckling behaviour. The stiffeners were designed such as to obtain both global and local buckling shapes. Numerical simulations (FEA), based on the test girder geometry, the measured initial geometric imperfections and elastic-plastic material characteristic from the tensile tests, demonstrate a very good agreement with the tests. The initial geometric imperfection study on different verified numerical models shows a limited sensitivity of the panel shear capacity to any kind of imperfection shape variation with amplitude at the allowable fabrication tolerances. Finally, the paper offers some ideas for modelling geometric imperfections with regard to the design or research demands.     

Axially compressed cylindrical shells with local settlement

The design of cylindrical metal silos and tanks is often controlled by considerations of buckling under axial compression. Whilst the effects of geometric imperfections on the buckling strength have been extensively explored, few studies have explored the effects of defects in the boundary conditions and the effects of residual stresses have received even less attention.This paper investigates the initiation and development of imperfections caused by local differential settlement at the supported base and their effect on the elastic buckling of a thin cylindrical shell under axial compression. The shells were treated as initially perfect with perfect support, but developing geometric imperfections and residual stresses as a consequence of local displacement at the supported edge and with residual stresses consistent with the induced geometric imperfections.The results raise interesting questions concerning the criteria of failure and appropriate tolerance measurements for constructed cylindrical shells.     

上海南站无柱雨棚铸钢节点试验研究

上海南站无柱雨棚铸钢节点由于其汇交杆件多,理论分析无法考虑节点制作过程中的各种缺陷。为了深入了解该节点的受力性能并确保结构在设计荷载下的安全性,根据设计要求对该铸钢节点进行了三组单向拉伸试验,并进行了精细有限元分析。通过试验与有限元分析结果的比较,验证有限元分析的正确性,并由此通过理论计算推断铸钢节点的应力状况,为设计提供数据依据。     

扣件式脚手架用钢管稳定系数研究

当前,在计算脚手架用钢管稳定承载力时,轴心受压构件稳定系数大多仍沿用GB 50018—2002《冷弯薄壁型钢结构技术规范》的取值。资料表明,脚手架与GB 50018—2002计算中考虑的缺陷和截面存在差异。通过分析国内外相关规范中稳定系数φ取值,依照规范中综合缺陷数学模式,考虑48×3.5钢管的截面特性和实际几何缺陷,提出稳定系数φ修订意见。根据试验所测得结构稳定承载力,对初始弯曲和稳定系数φ的取值进行研究,并给出建议值。     

Dynamic buckling of fiber composite shells under impulsive axial compression

The paper deals with dynamic buckling due to impulsive loading of thin-walled carbon fiber reinforced plastics (CFRP) shell structures under axial compression. The approach adopted is based on the equations of motion, which are numerically solved using a finite element code (ABAQUS/Explicit) and using numerical models validated by experimental static buckling tests. To study the influence of the load duration, the time history of impulsive loading is varied and the corresponding dynamic buckling loads are related to the quasi-static buckling loads. To analyse the sensitivity to geometric imperfections, the initial geometric imperfections, measured experimentally on the internal surface of real shells, are introduced in the numerical models. It is shown numerically that the initial geometric imperfections as well as the duration of the loading period have a great influence on the dynamic buckling of the shells. For short time duration, the dynamic buckling loads are larger than the static ones. By increasing the load duration, the dynamic buckling loads decrease quickly and get significantly smaller than the static loads. Since the common practice is to assume that dynamic bucking loads are higher than the static ones, which means that static design is safe, careful design is recommended. Indeed, taking the static buckling load as the design point for dynamic problems might be misleading.     

支撑系统的模拟

对具有不同升降高度、升降机数量和杰克延性的3+3支撑系统的足尺试验进行数值模拟,分析支撑系统性能。介绍了模拟栓接节点、半刚性梁连接及底板偏心的方法。基于Ramberg-Osgood方程,考虑材料非线性,并考虑了轴线不直、表面与轴线不垂直等初始几何缺陷。通过足尺试验得到的破坏荷载和荷载-位移曲线,对非线性分析得到的极限荷载进行修正。数值结果与试验很吻合,表明采用几何非线性和材料非线性分析能很好地研究支撑系统的性能和极限承载力。分析了支撑系统模拟中的一些难题,建立了底板、U型头、栓接节点的力学模型。     

FEA on bearing behavior of cuplok scaffold based on tri-linear semi-rigid joint model

利用三折线半刚性节点模型,结合碗扣式脚手架竖向承载力足尺试验,对碗扣式脚手架的竖向失稳问题进行了有限元模拟、结果对比和性能分析。模拟中重点考虑碗扣节点的材料非线性和构件的初始几何非线性。结果表明,三折线半刚性节点模型精度可靠,适用于碗扣式脚手架的精细化数值模拟。此外,对影响碗扣式脚手架受力性能的因素进行了研究,包括底端边界条件、碗扣式半刚性节点初始刚度和伸长段长度。研究发现：以上因素对碗扣式脚手架受力性能有不同程度影响,中间立杆离地对承载力影响较大,承载力随碗扣节点初始刚度增大而增大并呈现三段式变化,承载力随伸长段长度增大而减小并呈现两段变化。     

Structural response of stainless steel oval hollow section compression members

Cold-formed stainless steel oval hollow sections (OHS) offer the combined aesthetic appeal of circular hollow sections and stainless steel, together with the structural efficiency associated with cross-sections of differing geometric properties about their two principal axes. To date, no structural design guidance exists for these cross-sections, principally due to their relatively recent introduction and a lack of fundamental structural test data. This paper examines the structural response of stainless steel OHS compression members and presents design recommendations. A series of laboratory tests was carried out to generate fundamental structural performance data. Tensile coupon tests were initially performed to establish the basic material stress–strain characteristics of the sections. These were followed by stub column tests to determine the average compressive response of the cross-sections and flexural buckling tests to obtain ultimate load carrying capacity data for use in the determination of a suitable buckling curve for stainless steel OHS. Measurements of the geometric properties of the test specimens including initial imperfections were carried out. The full load–displacement responses of the specimens were recorded and have been presented herein. A finite element (FE) modelling programme was performed in parallel with the experimental study. Once the FE models had been validated against the test results, parametric studies were carried out to further investigate the influence of individual key parameters, including the aspect ratio and local slenderness of the cross-sections as well as the member slenderness. Based on the obtained experimental and numerical results, a class 3 limit for stainless steel OHS in compression and a suitable buckling curve for OHS columns have been proposed.     

Numerical Modelling of the Influence of Joint Typologies on the 3D Behaviour of a Steel Sub-Frame Under a Natural Fire

In order to address the complex loading condition of steel joints in fire, and based on the experimental fire tests on steel frames with different joint typologies, performed at the University of Coimbra (Santiago et al. 2008), a detailed three-dimensional model was developed and calibrated to simulate the behaviour of welded and bolted end plate beam-to-column joints. The structural frame is modeled combining 3D shell, solid and joint elements, thereby taking into account the effect of the local failure modes, and the realistic behaviour of the frame exposed to a natural fire. The numerical model accounts for the initial geometrical imperfections, non-linear temperature gradient, geometrical and material nonlinearity and temperature dependent material properties. The results show the performance of each individual structural joint component under heating and cooling conditions and identify the main dependencies of the geometrical and mechanical variables of the components on the joint behaviour. The global behaviour of the frame and the joint failure modes are compared and discussed with the experimental observations.     

反对称Pratt桁架中斜腹杆受压大偏心N形圆钢管节点静力性能试验研究

对反对称Pratt桁架中的斜腹杆受压大偏心N形圆钢管节点的静力性能进行了单调加载试验研究。实施了4个负向大偏心、4个正向大偏心和1个无偏心斜腹杆受压N形圆钢管节点静力试验。介绍了节点试验方案,考察了斜腹杆受压大偏心圆钢管节点破坏现象,给出了加载点荷载-端位移曲线、腹杆轴力-管壁变形曲线以及折算应变分布曲线,并分析了偏心率对节点承载力、刚度和延性的影响。研究结果表明：该节点可以作为理想铰接节点考虑;随着节点偏心率从 -1.30增大到0,节点承载力逐渐提高,当偏心率为0时达到最大;节点转变成正偏心,偏心率增大到0.50时,随着偏心率增大,试件承载力逐渐减小;之后随着偏心率继续增大,承载力又有略微增大;虽然两种规范（GB 50017-2003《钢结构设计规范》、欧洲Eurocode 3）计算均值与试验值比较接近,且GB 50017-2003计算均值更接近试验值,但两种规范计算承载力的变化趋势均与试验结果不符。     

Global buckling and the interaction of initial imperfections of columns subjected to conservative loading

This paper deals with the problem of global instability of slender systems with imperfections. The inaccuracies in the systems are modelled assuming an initial curvature and the introduction of the eccentricity of an external load. Systems loaded by Euler’s load or by a force directed towards the positive pole are considered. The problem is formulated on the basis of an energetic method. Analysis of the global imperfections is carried out. The results of analytical, numerical and experimental research concerning the mutual relations between the introduced imperfections and their influence on the system behaviour are presented.     

输电塔单变双角钢过渡节点试验研究与计算方法

选取3个单变双角钢过渡节点作为研究对象,制作8个过渡节点模型,将其中6个足尺试验模型分别在受拉和受压工况下进行弹性加载试验,2个缩尺试验模型分别在受拉和受压工况下进行破坏加载试验,结合有限元模拟,分析单变双角钢过渡节点的力学特性和受力情况。数值模拟了弹性和破坏加载工况下单变双角钢过渡节点关键部位的应变变化和应力分布,并与加载试验进行对比。考虑上、下靴板之间的偏心距对单变双角钢过渡节点水平板上水平应力不均匀分布的影响,基于有限元模拟和加载试验,对现有的不同单变双角钢过渡节点水平板厚度计算方法进行比较与评估,通过与水平板设计厚度进行对比,分析不同计算方法的优化效果和安全裕度。结果表明:上、下靴板与水平板连接焊缝的偏心距是影响水平板受力的主要因素,水平板上对应上、下靴板的十字交汇处水平应力最大,并向四周扩散且逐渐减小; 有限元模拟结果与试验结果吻合良好,研究结果可为单双角钢过渡节点的结构设计提供指导。