Comparison of residual stress in relaxed and non-relaxed weldments of steel plates

In this study, two methods, X-ray diffraction (nondestructive) and hole-drilling (destructive) are applied to measure the residual stress of gas metal arc welded steel plate. Both non-relaxed and relaxed (local heating, furnace annealing and bead blasting) weldments are examined to understand the residual stress distributions before and after elimination of residual stresses. Results show that the heat affected zone of gas metal arc welding method is about 10 mm from the weld centerline. The local heating method is very effective in reducing the residual stress caused by the cold work of the original steel plate. The furnace annealing method reduces the residual stress to compressive but not uniformly distributed. The detrimental fluctuation of residual stress is successfully reduced and uniformly relaxed to be beneficially compressive in the bead blasting. Most importantly, X-ray diffraction shows more precise and better handling than hole-drilling method in terms of data error.     

Ultimate strength of dented steel plates under edge shear loads

The aims of this paper are to investigate the ultimate shear strength reduction characteristics of steel plates due to local impacts, and also to develop the ultimate shear strength design formulae of dented steel plates. The ANSYS nonlinear finite element code is used to investigate the effects of shape, size (depth, diameter), and location of the denting on the ultimate strength behavior of simply supported steel plates under edge shear loads. A closed-form expression for predicting the ultimate shear strength of dented steel plates is derived by the regression analysis based on the computed results. The results and insights developed from the present study will be very useful for damage tolerant design of steel plated structures with local denting.     

Influence of friction stir welding residual stresses on the compressive strength of aluminium alloy plates

The mechanical behaviour of welded structures can be significantly affected by the effects of the employed joining process. The main goal of this work is to assess the influence of the longitudinal residual stresses on the overall compressive performance of aluminium friction stir welded plates. Longitudinal residual stress distribution was measured by means of the contour method and introduced as initial condition into a finite element model of the compressed assembly. Also, the sensitivity of the plates to the magnitude of the initial geometrical imperfections was analysed. It can be inferred that both factors influence the plate's mechanical behaviour.     

Effects of welding residual stress on compressive behavior and ultimate strength of corroded plate

This study examined the effects of welding residual stress on the compressive behavior and the ultimate strength of the corroded plate. First, welding residual stress was obtained by the thermal elastic-plastic analysis. Then, the change of welding residual stress and the deflection due to the volume loss was investigated by using a newly developed program based on FEM. Finally, the effects of welding residual stress on the compressive behavior and the ultimate strength of the corroded plate were investigated by the elastic-plastic large deformation analysis. As results, the beginning point of the reduction of the initial stiffness with welding residual stress was earlier than that without welding residual stress. Such effect was observed significantly in the case that the volume was lost in the region which has compressive residual stress. Furthermore, the ultimate strength of the corroded plate was reduced by welding residual stress regardless of the plate length, the corroded regions and the reduction of the thickness. The effect of welding residual stress on the ultimate strength became small with the decrease of the thickness.     

论钢结构焊接残余应力控制与消残方法

结合施工实践,分析了钢结构焊接残余应力的成因及危害,鉴于此提出了焊接残余应力的控制目标和措施,并总结了消除构件残余应力的方法,从而提高钢结构的整体承载力、增强结构的安全性。     

Identification of factor determining strength under compressive loads of steel members corrected by heating/pressing

By using cruciform columns, factors dominating behavior under compressive loads of steel structural members, whose locally buckled part was corrected by heating/pressing, have been elucidated. They were geometric residual imperfection resulted from incomplete correction and increase of yield stress due to large plastic deformation caused by local buckling and its correction process. For soundness diagnosis of the corrected member, the importance of these factors was investigated based on the results of the numerical simulation. Although the increase of yield stress did not affect the ultimate strength, that changed the deformation mode of the member after the ultimate situation. As the result, it was elucidated that the increase of yield stress was not important in the soundness diagnosis. The residual imperfection affected the buckling and ultimate strength of the corrected member. Rather the size of the region than the absolute value in the out-of-plane direction of the residual imperfection should be controlled as small as possible for ensuring the soundness of the corrected member.     

T型钢节点焊接残余应力及变形研究

运用有限元方法分析研究了T型节点焊接的残余应力与变形,重点阐述了该T型焊接变形的类型、残余应力分布规律及控制焊接变形的措施,供类似工程参考。     

A semi-analytical method for the elastic-plastic large deflection analysis of welded steel or aluminum plating under combined in-plane and lateral pressure loads

The aim of the present paper is to develop a semi-analytical method which can quickly and accurately compute the elastic–plastic large deflection response of welded steel or aluminum plating under a combination of biaxial compression/tension, biaxial in-plane bending, edge shear and lateral pressure loads, until the ultimate limit state is reached. The post-weld initial imperfections (i.e. initial deflection and residual stresses) are included in the method as parameters of influence. It is assumed that the plating is simply supported at all (four) edges which are kept straight. A unique feature of the developed method is that geometric nonlinearity associated with large deflection response of plating under combined loads is treated by analytically solving the nonlinear governing differential equations of the elastic large deflection plate theory, while material nonlinearity due to plasticity is dealt with implicitly by a numerical procedure. This approach reduces the magnitude of numerical computations, resulting in a saving of modeling effort and computing time. As another contribution, this paper investigates and discusses the ultimate strength characteristics of plating, by varying the plate properties and load combinations, based on elastic–plastic large deflection analysis using the developed method.     

拉压性能不同钢箱梁的纯弯曲弹塑性分析

将材料本构关系简化成拉压屈服极限不同的理想弹塑性模型,对纯弯曲作用下的钢箱梁弹塑性全过程进行了分析,得到了依赖于拉压比γ的弹性、塑性极限弯矩以及弯矩与曲率之间的关系,所得到的公式经过一定的几何参数变化,同样适用于形、槽形、矩形等钢梁的弹塑性分析,当γ=1时所得结果退化为拉压性能相同的弹性极限弯矩与塑性极限弯矩。     

钢结构焊接变形的预防和处理方法探讨

介绍了钢结构构件由于焊接产生的变形问题，结合长期施工经验，从立柱底板、H型钢焊制等方面提出一些钢结构焊接变形的预防和矫正措施，以提高钢结构构件的加工质量。     

焊接钢梁残余应力有限元分析

采用通用有限元软件ANSYS模拟分析焊接工字梁的焊接过程,对焊接残余应力场进行数值模拟并进行有限元分析,从而得到焊接钢梁残余应力的大小及分布规律,以便设计人员在进行相关焊缝设计时对残余应力的大小进行估算,为工程实践应用提供一定的指导。     

Ultimate strength of perforated steel plates under combined biaxial compression and edge shear loads

The present paper is a sequel to the author's papers [Paik JK, Ultimate strength of perforated steel plates under edge shear loading. Thin-Walled Structures 2007; 45: 301–6, Paik JK Ultimate strength of perforated steel plates under axial compressive loading along short edges. Ships Offshore Struct, 2007; 2(3): (in press)]. In contrast to the previous papers with the focus on edge shear or uniaxial compressive loads, the aim of the present study is to investigate the ultimate strength characteristics of perforated steel plates under combined biaxial compression and edge shear loads, which is a typical action pattern of steel plates arising from cargo weight and water pressure together with hull girder motions in ships and ship-shaped offshore structures. The plates are considered to be simply supported along all (four) edges, keeping them straight. The cutout is circular and located at the center of the plate. A series of ANSYS nonlinear finite element analyses (FEA) are undertaken with varying the plate dimension (thickness). Based on the FEA results obtained, closed-form empirical formulae of the ultimate strength interaction relationships of perforated plates between combined loads, which can be useful for first-cut estimations of the ultimate strength in reliability analyses or code calibrations, are derived.     

扁平钢箱梁U肋焊接残余应力数值模拟分析

已建成的扁平钢箱梁桥在运营过程中发现一些与结构、构造和制造相关的病害,并且随着服役时间的增长越来越突出。其原因是扁平钢箱梁结构采用薄板组焊而成,因此,扁平钢箱梁在未受力之前,便已存在着由于焊接所产生的应力场和变形场,导致扁平钢箱梁普遍出现裂纹等病害。运用热结构耦合法对扁平钢箱梁U肋与桥面板交接处焊接的温度场和应力场进行数值模拟计算分析,并得到焊接残余应力的分布规律,为进一步分析结构病害与加固设计提供依据。     

Buckling analysis of stiffened plates subjected to non-uniform biaxial compressive loads using conventional and super finite elements

This paper presents the buckling analysis of stiffened plates, using both conventional and super finite element methods. Mindlin plate and Timoshenko beam theories are utilized so as to formulate the plate and stiffeners, respectively. The arbitrary oriented stiffeners can be positioned anywhere within the plate element and are not limited to be placed on nodal lines. Therefore, any configuration of plate and stiffeners can be modeled. Furthermore, extensive boundary conditions as well as general in-plane loading conditions can be considered using the proposed method. As the applied in-plane loads are not uniform, the buckling load is evaluated in two steps. First, the elasticity problem is solved to determine the stress distribution in prebuckling stage. Applying the principle of minimum potential energy, based on derived stress distribution, yields to the buckling equation of stiffened plates. Numerical examples are proposed to study the accuracy and efficiency of the developed super elements. Effects of various combinations of biaxial loads along with different boundary conditions on buckling characteristics of stiffened panels are also investigated.     

焊接残余应力对网架负荷加固的影响分析

负荷条件下对网架结构进行加固时,焊接残余应力对网架结构的内力、变形有较大影响。本文结合某网架负荷加固工程,通过运用ANSYS有限元软件对焊接杆件施加等效温度荷载的方式,模拟网架负荷加固杆件焊接时的热胀冷缩。通过相应的应力、变形分析,得出焊接残余应力对网架结构负荷加固的影响。     

复杂动载作用下钢纤维混凝土材料参数特征分析

采用常三轴动力试验仪对不同钢纤维含量、不同围压、应变速率为10-3/s作用下混凝土的主要参数进行试验与分析,结果表明:①随着围压的增大,各种不同钢纤维含量的混凝土峰值应力显著提高;②同一种围压条件下,基体强度等级愈高峰值应力的增加幅度也愈高,峰值应力随钢纤维含量的变化不大;③围压对峰值应变的影响较大,随围压的增大,峰值应变明显增大;在有围压的条件下峰值应变随钢纤维含量的增加而提高得不多;④钢纤维含量对割线模量有一定的影响,对基体强度较低的混凝土的影响要比强度等级高的混凝土显著;围压对钢纤维混凝土割线模量也有一定影响,随围压的增加,钢纤维混凝土的割线模量表现为先增加后减小,但增加和减小的程度都不大;围压的变化对基体强度较高的混凝土割线模量影响不大,对基体强度较低的混凝土基本呈下降趋势;⑤混凝土的泊松比离散性较大,钢纤维含量和围压对泊松比的影响不是很大,主要集中在0.11～0.20之间;⑥在三轴动荷载的情况下,钢纤维的掺入对混凝土的压缩韧度指数ηc5基本上没有影响;但韧度指数ηc10随钢纤维含量的增加有显著提高,变形不大时作用不明显,当变形较大时,钢纤维提高韧性的作用得以充分体现;钢纤维的增韧效果在基体强度较低的...     

Master formula for evaluating vibration frequencies of structural members under compressive loads

In this article, the prediction of free vibration characteristics of various initially compressively loaded structural members is given in the form of a master formula. These structural members are optimised for the strength criteria and are subjected to high initial compressive loads (or stresses). These initial compressive loads have to be considered when the free vibration characteristics are evaluated. The standard method is to solve the differential equation considering the term corresponding to these loads. Though this is possible for simple structural members, it is often difficult while dealing with complex structural members with complicated effects. Under these circumstances, the popular approximate continuum and numerical methods like the Rayleigh–Ritz and finite element methods are used to obtain reliable and accurate solutions to the initially loaded free vibration characteristics of these structural members. However, these approximate methods are also having their inherent difficulties. To avoid this, a simple but accurate formula is developed, which is very useful for the design engineers while dealing with structural members used in missiles and rockets. The use of master formula for the first mode and also higher modes of vibration has been shown for typical structural members.     

焊接残余应力的产生及其消除方法

在分析残余应力产生原理的基础上,介绍了焊接残余应力的概念,并探讨了焊接残余应力产生的原因及其影响因素,提出了消除焊接残余应力的方法,指出研究和测量构件中残余应力对生产和科学试验具有重要意义。     

Strength assessment of steel plates subjected to compressive load and dent deformation

This work presents an assessment of the ultimate compressive strength of damaged steel plates with a local dent. Extensive non-linear finite element analyses are performed, where three groups of analyses are considered. In the first group, the effect of the dent orientation (longitudinal and transverse) is studied for three plate thicknesses. For the second group, the direction of the dent depth (upward and downward) with respect to the global initial imperfection is explored. In the third group, the variation of the dent size for several plate thicknesses and its influence on ultimate compressive strength is investigated. The post-collapse behaviours are discussed and the inflection plate slenderness with and without dent is observed, at which the behaviour of the plate changed. A certain dent breadth to the plate breadth ratio is established, revealing the different plate response. Based on the performed analyses, a generalised expression of the ultimate strength reduction factor due to dent is developed.     

Minimum principles and initial stress method in elastic-plastic analysis

A finite-step elastic-plastic constitutive model is formulated by means of a minimum principle for the continuum. Then a standard finite-element approach is adopted in order to obtain the corresponding minimum principle for the element constitutive law. Analogously the structural response is described by a pair of dual nonlinear programming (NLP) convex problems. Existence of a solution is discussed. An algorithm of the initial stress type is formulated stepwise in order to review critically features and limits relevant to such an approach.