钢节点板的渐进结构优化设计

渐进结构优化法被用于确定轴力作用下钢节点板的最优形状。采用一系列不同的节点板应用在不同类型的连接中,然后采用渐进结构优化法来寻找在这些连接中最佳形状的节点板。第一个例子假定节点板具有两个孔,可以用于带张力的双角钢连接,分析了某些参数如材料去除率、网格尺寸和带孔模型的最终形状。带3、4、5个孔的节点板同时也被设计为最佳形状。此外,设计模型包括两排多孔、错排多孔连接。最后,在单个螺栓连接中优化确定的形状与目前实际使用的非常相似,然而其重量更轻。那些为多重连接和焊接双角连接的形状目前还不可预测。这表明渐进结构优化法在确定节点板最佳形状方面还有研究的潜力。     

Bolted steel slip-critical connections with fillers: I. Performance

This paper reports the results of sixteen experiments of bolted slip-critical connections with fillers. Fifteen of the connections used oversized holes and one connection used standard holes. Such connections with oversized holes are commonly fabricated for use with structures such as long-span trusses, since the use of oversized holes allows erection in-place rather than first assessing fit-up on the ground. Filler plates are used to connect members of different depths or widths. The sixteen experiments reported herein highlight the behavior of bolted steel connections with oversized holes in which fillers are included and are undeveloped, partially developed, or fully developed. Both single-ply and multi-ply fillers are investigated, as are welded developed fillers, and specimens fabricated using either turn-of-the-nut or tension control bolts to pretension the connection. The results augmented with previous literature document the slip and shear strengths of these connections, propose formulas for assessing these strengths for the different conditions investigated, and provide recommendations for design of these types of connections.     

Bolted steel slip-critical connections with fillers: II. Behavior

Research has been conducted to better understand the effect of fillers in bolted steel connections. In a companion paper, the results of sixteen experiments on bolted steel slip-critical connections with fillers are presented along with proposed design recommendations. In this paper, detailed behavior of the specimens is documented through an examination of deformation and strain response. Additionally, mechanisms are proposed that clarify key aspects of the behavior of bolted connections with fillers, including prediction of slip and shear strengths. A stochastic analysis, using order statistics, is employed to quantify the detrimental effects of multiple possible slip surfaces on expected slip strength. The use of multiple plies and the effects of developing the filler plate are investigated with respect both to the experimental results and the proposed behavioral mechanisms. The results indicate that the use of multiple plies exacerbates the detrimental effects on slip strength and, to a lesser extent, on shear strength. Furthermore, filler development reduces and in many cases eliminates the reduction in slip and shear strengths.     

既有桥梁粘钢加固受力特性分析

本文在既有桥梁粘钢加固的基础上,通过有限元数值分析计算,比较了粘钢加固前后在自重和汽车荷载作用下的挠度和纵向应力变化,并进行了正截面抗弯承载能力验算,评价了既有桥梁粘钢加固改造的效果。结果表明粘钢加固后钢板能够有效地参与受力,主梁受压区截面高度增大,承载力增大,受力更加合理;加固后正截面抗弯极限承载力有所提高;桥梁的整体性和刚度均有显著改善。     

Local buckling of steel plates in concrete-filled thin-walled steel tubular beam-columns

The availability of high strength steels and concrete leads to the use of thin steel plates in concrete-filled steel tubular beam-columns. However, the use of thin steel plates in composite beam-columns gives a rise to local buckling that would appreciably reduce the strength and ductility performance of the members. This paper studies the critical local and post-local buckling behavior of steel plates in concrete-filled thin-walled steel tubular beam-columns by using the finite element analysis method. Geometric and material nonlinear analyses are performed to investigate the critical local and post-local buckling strengths of steel plates under compression and in-plane bending. Initial geometric imperfections and residual stresses presented in steel plates, material yielding and strain hardening are taken into account in the nonlinear analysis. Based on the results obtained from the nonlinear finite element analyses, a set of design formulas are proposed for determining the critical local buckling and ultimate strengths of steel plates in concrete-filled steel tubular beam-columns. In addition, effective width formulas are developed for the ultimate strength design of clamped steel plates under non-uniform compression. The accuracy of the proposed design formulas is established by comparisons with available solutions. The proposed design formulas can be used directly in the design of composite beam-columns and adopted in the advanced analysis of concrete-filled thin-walled steel tubular beam-columns to account for local buckling effects.     

Behavior of thin gusset plates in compression

The use of cold-formed steel members for roof and floor truss applications is gaining widespread acceptance in the United States. However, there is little technical information regarding the behavior and design of thin gusset plates in compression. Thus, a study was initiated at the University of Missouri-Rolla aimed at investigating the behavior of thin steel gusset plates in compression. Key parameters that were considered in the experimental study were the thickness of the gusset plate, the width and length of the gusset plates, the fastener location, and the fastener pattern. Both a plate model and a column model were investigated for computing the strength of a thin plate in compression. Based on the findings of this study, design recommendations are proposed.     

不锈钢节点板连接件数值分析

尽管不锈钢和碳素钢的力学性能有本质区别,然而,现行规范规定不锈钢连接设计时仍基本遵循碳素钢的设计准则,仅在此基础上稍作修改。对于常见的角钢单肢与加固板连接的情况,EN1993-1-4以及SCI/欧盟不锈钢设计手册对不锈钢的设计规定,直接采用了EN1993-1-8对碳素钢净截面承载力的设计规定,且未作任何修改。对单肢与加固板采用单排螺栓连接的L型不锈钢的净截面承载力进行了研究。建立奥氏体不锈钢的数值模型,并利用现有的试验结果对其进行了验证。这些模型随后用于进行参数研究。最后,基于研究结果对L型不锈钢净截面承载力的设计方程进行了修正,并通过统计分析验证了该方程可靠性。     

Instability of steel gusset plates in compression

As a result of the structural failure of the I-35W Bridge in Minneapolis in 2007, the Federal Highway Administration (FHWA) issued guidelines for the load rating of gusset plates and recommended that the capacity of these plates on non-redundant steel truss bridges be verified. The purpose of this study is to examine the buckling behaviour of steel gusset plates in greater detail, accounting for parameters that were not explicitly included in the guidelines, such as initial deformations of the gusset plate, stiffness of the framing members, load distribution from the framing members to the plate and load eccentricity. For this purpose, a finite-element model of a gusset plate was developed and verified against experimental measurements. Results show that, for in-plane compressive loads with no moment and no eccentricity, the FHWA guidelines for load rating are conservative and safe for initial out-of-plane deformations up to one plate thickness.     

Parametric finite element study on slotted rectangular and square HSS tension connections

A parametric finite element analysis study was carried out on slotted rectangular and square hollow structural section (HSS) tension connections without welding at the end of the gusset plate for different weld length ratio, slot orientation, weld size and level of HSS corner strength compared to its flat segment. Finite element models for the parametric study were developed and validated against test results of the connection with the tube slotted. The modified weld length ratio was found to be a better parameter than the modified eccentricity ratio in characterizing the net section efficiency of a slotted HSS tension member when the weld length is short. Improvements to provisions in CSA-S16-01 and ANSI/AISC-360-05 for slotted tubular tension connections were proposed based on results of the study.     

结构钢V形缺口板断裂试验

对25个结构钢V形缺口板试件进行断裂试验。试验表明:裂纹起始于受三轴强约束的V形缺口厚度心部,随后沿厚度方向扩展,裂纹贯通后迅速沿宽度发展,宏观裂纹大致垂直于载荷方向,单缺口试件断裂延性略高于双缺口试件,薄板断裂延性明显高于厚板。断口呈暗灰色,断口大量韧窝显示出明显的剪切断裂痕迹,断裂类型为正断和剪断混合型断裂,显示了断裂的定性规律。从整体上看,试验数据离散性较小,为研究结构钢断裂机理及抗断理论提供了可靠的试验依据。     

Buckling optimization of variable thickness prismatic folded plates

This paper deals with the structural shape optimization of prismatic folded plates under buckling load consideration. Buckling loads are determined using linear, quadratic and cubic, variable thickness, C(0) continuity, Mindlin-Reissner finite strips. The whole structural optimization process is carried out by integrating finite strip analysis, cubic spline shape and thickness definition, semi analytical sensitivity analysis and mathematical programming algorithm. The objective is either the maximization of the critical buckling load or minimization of the cross-section of the prismatic folded plate with constraints on the volume and buckling loads. Several examples are included to illustrate various features of the optimization algorithm, including plates and stiffened panels.     

Parametric analysis of steel bolted end plate connections using finite element modeling

This paper presents and discusses results of parametric analyses on the behavior of bolted extended end plate connections using Finite Element (FE) modeling tools. The analyses were calibrated to experimental results that are also briefly reviewed in this paper. The analytical models took into account material nonlinearities, geometrical discontinuities and large displacements. Comparisons between numerical and experimental data for moment-rotation curves, displacements of the end plate, and forces on bolts showed satisfactory agreement. Phenomenological T-stub failure models were also used for calculations of the flexural strength for the end plate. These models clearly support the numerical results and show how the interaction between the end plate and the bolts changes the connections’ behavior. The results presented herein show that failures associated with either formation of yield lines in the plate (Mode 1) or bolt tension failure (Mode 3) are well-defined, while failures due to combinations of these mechanisms (Mode 2) represent levels of interaction between the end plate and bolts that are difficult to predict accurately. These results also indicate that the T-stub analogy has limitations in representing the yield lines at the end plate, leading to limitations both in accounting for prying action and in predicting values for strength and stiffness of the connection.     

FE model of beam-to-column extended end-plate joints

The rotational behaviour of steel end-plate connections can be studied using the finite element method for the following three reasons: 1) such models are inexpensive and robust; 2) they allow the understanding of local effects which are difficult to measure accurately physically; and 3) they can be used to generate extensive parametric studies. This paper presents a full three-dimensional ANSYS finite element model of steel beam to column bolted extended end-plate joints for use to obtain their behaviour. The model includes: contact and sliding between different elements; bolt pre-tension; and geometric and material non-linearity.The model was calibrated and validated with experimental results found in the literature and with the model proposed by Eurocode 3. The results from the finite element analysis were verified by comparing the obtained moment-rotation curve of the joint. The procedure for determining the moment-rotation curve using finite element analysis is also given, together with a brief explanation of how the design moment resistance and the initial rotational stiffness of the joint are obtained.     

Numerical investigation of net section failure in stainless steel bolted connections

Despite fundamental differences in the mechanical behaviour of stainless steel and carbon steel, design provisions for stainless steel connections in current standards essentially follow the rules for carbon steel with some limited modifications. For the case of net section capacity, the design rules from EN 1993-1-3 for cold-formed carbon steel have been adopted for stainless steel connections in EN 1993-1-4 and the SCI/Euro Inox Design Manual without any modification. In this paper, an investigation into the behaviour of stainless steel connections failing by net section rupture has been conducted. Numerical models for austenitic and ferritic stainless steel have been developed and validated against existing test results. The validated models were subsequently used to perform parametric studies to investigate the main parameters affecting the net section rupture of bolted connections; these include edge distance e₂ and bolt configuration. By studying the stress distribution along the net section for different edge distances and bolt arrangements, it was found that the ductility of stainless steel is sufficient to ensure extensive redistribution of stresses prior to fracture. Hence, a revised design equation (based on that given in EN 1993-1-3) for net section capacity of stainless steel connections has been proposed and its reliability demonstrated by means of statistical analysis.     

影响栓接双角钢节点抗火性能的临界因素

双角钢节点经常用于钢框架结构中,当火灾发生时,这些节点在结构构件间的荷载传递上起着至关重要的作用。对火灾下螺栓连接双角钢节点的响应还缺乏了解。采用有限元程序ANSYS,对栓接双角钢节点的抗火性能进行数值研究。分析中,考虑了材料和几何非线性,钢材的高温特性和非线性接触交互作用。通过与其他文献的试验结果进行对比,对该模型进行验证,并通过参数研究量化临界因素对螺栓双角节点的影响。结果表明:螺栓孔的大小、边距、热梯度和梁腹板的细长度对栓接双角钢节点的抗火性能影响很大。     

Performance-based seismic design of steel frames using ant colony optimization

In this paper, a performance-based optimal seismic design of frame structures is presented using the ant colony optimization (ACO) method. This discrete metaheuristic algorithm leads to a significant improvement in consistency and computational efficiency compared to other evolutionary methods. A nonlinear analysis is utilized to arrive at the structural response at various seismic performance levels, employing a simple computer-based method for push-over analysis which accounts for first-order elastic and second-order geometric stiffness properties. Two examples are presented to illustrate the capabilities of ACO in designing lightweight frames, satisfying multiple performance levels of seismic design constraints for steel moment frame buildings, and a comparison is made with a standard genetic algorithm (GA) implementation to show the superiority of ACO for the discussed optimization problem.     

Finite element modeling of bolted connections in thin-walled stainless steel plates under static shear

The recently performed experimental study indicates that the current Japanese steel design standards (AIJ) cannot be used to predict accurately the ultimate behavior of bolted connections loaded in static shear, which are fabricated from thin-walled (cold-formed) SUS304 austenite stainless steel plates and thus, modified formula for calculating the ultimate strength to account for the mechanical properties of stainless steel and thin-walled steel plates were proposed. In this study, based on the existing test data for calibration and parametric study, finite element (FE) model with three-dimensional solid elements using ABAQUS program is established to investigate the structural behavior of bolted shear connections with thin-walled stainless steel plate. Non-linear material and non-geometric analysis is carried out in order to predict the load–displacement curves of bolted connections. Curling, i.e., out of plane deformation of the ends of connection plates which occurred in test specimens was also observed in FE model without geometric imperfection, the effect of curling on the ultimate strength was examined quantitatively and the failure criteria which is suitable to predict failure modes of bolted connections was proposed. In addition, results of the FE analysis are compared with previous experimental results, failure modes and ultimate strengths predicted by recommended procedures of FE showed a good correlation with those of experimental results and numerical approach was found to provide estimates with reasonable accuracy.     

Bearing failure in stainless steel bolted connections

Although the mechanical behaviour of stainless steel and carbon steel differs significantly, design provisions for stainless steel connections in current standards are essentially based on the rules for carbon steel. For bolted connections, the design resistances in EN 1993-1-4 and the SCI/Euro Inox Design Manual for Structural Stainless Steel are based on those in EN 1993-1-8 and EN 1993-1-3 with only some minor modifications. In this paper, an investigation into the bearing behaviour of stainless steel connections between both thick and thin plates has been conducted. Numerical models for previously tested specimens in austenitic and ferritic stainless steel have been developed and validated. The validated models were then used to perform parametric studies to investigate the key variables affecting the bearing failure of bolted connections; these include edge distance e₂, end distance e₁ and plate thickness t. The investigation showed the deformation behaviour of stainless steel connections to be somewhat different from that of carbon steel connections, with stainless steel exhibiting pronounced strain hardening. However, the locations of fracture initiation obtained from the numerical models matched those observed during experimental studies of both carbon steel and stainless steel connections and this feature has been used as the basis for defining a consistent, strength based criterion of failure. The results of the parametric studies have been utilised as the basis for design provisions for bearing failure in stainless steel bolted connections that cover both the ultimate and the serviceability limit states and which are both more economic and more straightforward than the present EC3 provisions.     

Optimization of steel floor systems using particle swarm optimization

Particle swarm optimization (PSO) is used for the design of composite and non-composite steel floor systems. The design problem is the minimization of the mass or the cost of a steel floor configuration subject to constraints related to the Canadian S16 design standard. The PSO algorithm was applied to three different steel floor bays. Outputs returned are the girder and beams sizes, steel deck profile, concrete slab thickness, number of interior beams and the number of steel studs needed per beam. Results show the PSO can consistently find the optimum floor configuration by minimizing the total mass or cost while satisfying all design criteria.     

Parametric finite element study of slotted end connections to circular hollow sections

The influence that the shear lag phenomenon may have on the strength of tubular connections has been addressed in design provisions with variable efficiency factors that affect the tube net area. However, an experimental program carried out on gusset plate connections to the ends of circular hollow section (CHS) members has indicated that these provisions may be overly conservative. As part of the experimental program, a total of eight specimens was tested under quasi-static tension and compression loading considering three connection types frequently used in practice. Moreover, results of a parametric analysis undertaken based on finite element models of these connections (where the responses were verified with the test results) showed considerable differences between the calculated connection strength and the predicted capacity by design provisions. In the finite element analysis, a nonlinear time step analysis was performed considering nonlinear material properties and 8-noded solid elements were used throughout the modeling. The gradual propagation of cracks in the material was emulated by definition of a maximum equivalent strain as the failure criterion with the activation of a “death feature” of the elements. The influence of parameters such as: the weld length (L_w), a proposal to use the eccentricity reduced by half the flange-plate thickness and the tube diameter-to-thickness (D/t) ratio have been studied. The analysis results have shown that a gradual transition between several failure modes takes place as the weld length increases. Also, the likelihood of developing the full efficiency of the tube net cross-sectional area, if a minimum ratio of L_w/w=1.0 is used, is illustrated.