单角钢螺栓连接节点板受压性能及极限承载力研究

通过某特高压输电线路塔架结构中典型的单角钢螺栓连接节点的足尺试验,对节点板的受压性能、破坏形式及极限承载力进行了研究。利用有限元程序ANSYS建立合理的有限元模型模拟节点板的受力性能,并与试验结果进行了对比分析。将试验及有限元模拟结果与现行国内外钢结构规范关于节点板受压承载力计算公式的计算值进行了比较,验证了现行规范公式对于该类单角钢连接节点板受压承载能力计算的适用性。     

输电塔钢管-插板连接节点板承载力研究

输电工程中输电塔架节点通常采用节点板连接的方式,其受力情况非常复杂。通过对5组输电塔架典型节点的足尺试验和有限元分析,考察节点板的受力性能和破坏模式,并利用多参数有限元分析不同破坏模式下宽厚比、无支长度以及节点板构造等主要参数对节点板承载力的影响,提出有(无)加强环板的节点板承载力计算方法,并与试验和有限元所得的结果进行比较。结果表明:基于插板连接的节点板建议计算方法合理有效,具有较好的适用性。     

输电铁塔十字组合角钢主材与斜材连接方法试验研究

通过输电铁塔的塔架试验,对十字组合角钢主材与塔身正侧面斜材的两种连接形式进行了试验研究,对组合角钢主材应变进行测量,在此基础上对十字组合角钢轴力、稳定承载力及主材受力不均匀性进行了分析,结果表明:在相同的外荷载作用下,传统连接形式的塔架加载至设计荷载110%时,主材发生失稳破坏,新型连接形式的塔架加载至设计荷载的115%时,主材发生失稳破坏;新型连接形式的十字组合角钢两肢的受力均匀性优于传统连接形式的十字组合角钢;考虑填板布置形式的十字组合角钢稳定承载力计算方法与试验结果吻合较好,计算方法合理。     

输电铁塔单双角钢变换节点试验研究与承载力计算方法

主要针对架空输电线路铁塔设计中常用的单双角钢变换节点进行承载力研究,建立其力学模型,对节点强度和稳定性进行理论分析,提出节点水平连接板板厚的计算方法,给出节点荷载传递系数。对不同板厚的单双角钢变换节点进行足尺试验和有限元分析,并将试验结果与有限元结果进行对比分析,二者吻合较好,验证了单双角钢变换节点的荷载传递机理,同时验证了水平连接板设计计算方法的可行性。     

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。     

全装配式外套筒-加强式外伸端板组件梁柱连接节点抗弯承载力研究

提出全装配式外套筒-加强式外伸端板组件梁柱新型连接节点,通过理论分析、试验研究和有限元分析,确定了节点受力计算模型,推导出节点抗弯承载力理论计算式,并与有限元模拟值和试验结果进行比较,三者吻合较好,证明其具有合理性和良好的适用性。所提出的节点抗弯承载力计算方法可为该类节点的设计和计算提供理论工具。试验研究与有限元分析还表明,装配式外套筒-加强式外伸端板组件梁柱连接节点的屈服机制为:外套筒和柱壁内凹受压屈曲、外伸端板压屈、节点屈服;梁柱连接节点具有良好的耗能能力,增大外套筒厚度,节点屈服荷载增加,耗能能力提高。     

输电钢管塔空间KK型管板连接节点极限承载力

空间KK型管板连接节点作为输电钢管塔中最主要的节点型式,其安全性是整个塔架结构安全的重要保证。相比较于平面K型节点,在考虑实际结构中节点空间效应后的KK型节点的受力性能更为复杂。在平面K型管板节点的试验研究基础上,对两类空间KK型管板节点展开参数化分析,重点讨论了节点几何尺寸参数和主管轴压应力比等因素对节点极限承载力的影响变化规律。结合大量有限元参数分析所得计算结果,并综合考虑各种因素对节点极限承载力的影响,提出了空间KK型管板连接节点在主管管壁局部屈曲破坏模式下的极限承载力建议计算方法。     

顶底角钢自复位钢框架M-θ_r关系的研究

提出一种得到顶底角钢自复位节点M-θr关系的实用计算方法。基于对连接破坏机构的研究,通过组件法推导出自复位节点各个阶段的承载力,采用基于Eurocode 3和Kishi-Chen函数模型拟合得到连接的弯矩-转角关系,并对各个阶段提出设计应注意的问题。对文中方法计算结果与有限元分析结果、已有试验结果进行比较,结果吻合良好,从而验证文中方法的有效性。在有限元分析中,节点表现出较好的自复位性能,同时转动中心附近的柱腹板应力集中明显,需合理设计加劲肋和加强板,保证板件的局部稳定。     

钢管十字插板连接承载力试验研究及有限元分析

为了研究广东某新建220 kV输电钢管塔交叉斜材连接所采用的十字插板连接形式的受力性能,选用连接处8组足尺连接节点进行承载力试验,连接件形式分别采用普通条形板、角钢、弯折板;结合试验结果,运用ANSYS软件对试件进行非线性有限元分析及参数分析,给出了连接件面积与钢管面积比值、钢管开槽长度与钢管管径比值的临界解。结果表明:该输电塔交叉斜材钢管管径配合下的十字插板连接安全可靠但不够经济,在轴压作用下采用近似等面积的角钢和弯折板连接件形式对节点承载力无影响;连接件面积与钢管面积比值大于临界解时,钢管发生弹塑性失稳破坏,小于临界解时,十字插板连接位置发生破坏。     

超大承载力端板连接节点有限元分析和设计方法

超大承载力端板连接节点能够提供比普通构造的端板连接节点和大承载力端板连接节点更大的抗弯承载力,可以应用于大跨或重载钢结构中。由于超大承载力端板连接节点的螺栓拉力分布不均匀、端板受力状态复杂,现有的端板连接节点设计方法不能直接应用。此文建立超大承载力端板连接节点的有限元模型,通过已有试验验证模型的可靠性|利用有限元模型分析单调荷载下超大承载力端板连接节点的受力性能,提出弯矩作用下受拉区端板的屈服线模型和受拉区螺栓承担拉力的分布模型。在所提模型的基础上基于我国规范提出超大承载力端板连接节点的抗弯承载力设计方法。比较所提设计方法得到的节点抗弯承载力设计值与有限元得到的屈服承载力,在我国规范规定的高强度螺栓受拉极限状态条件下所提方法得到的设计结果偏于安全。     

Compressive behavior of central gusset plate connections for a buckling-restrained braced frame

Buckling-restrained braced frames (BRBFs) are used as lateral-load resisting systems in seismic design. The braces in BRBFs are connected to beams and columns by gusset plate connections, and can yield in both tension and compression instead of buckling. Although tests of buckling-restrained braces (BRBs) have demonstrated their ability to withstand significant inelastic axial deformation, large-scale BRBF tests have exhibited central gusset plate buckling before BRBs develop the ultimate compressive strength. To extend and better understand the experimental work, this paper presents an analytical study of the compressive behavior for BRBF central gusset plate connections using the finite element computer program ABAQUS. A model of a previously tested BRBF is conducted to predict experimental buckling load of the central gusset plate and verify the accuracy of a simple model of a central gusset plate connection including a beam and part of the BRB. The out-of-plane deformation of the central gusset plate resembles the buckled shape of a gusset plate with low bending rigidity provided by the BRB end. The experimental buckling load of the central gusset plate cannot be predicted based on the AISC-LRFD approach with an effective column length factor of 1.2. Therefore, a parametric study on the compressive strength of BRBF central gusset plate connections is conducted with various gusset plate dimensions and free-edge stiffeners. An inelastic plate buckling equation together with coefficient charts is proposed to predict ultimate load. For gusset plates with sufficient free-edge stiffener rigidity, the yield load can be developed and increased to the post-yield strength level. A required free-edge stiffener size is also recommended for BRBF central gusset plates to develop compressive yield load.     

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.     

Evolutionary structural optimization of steel gusset plates

Evolutionary structural optimization is applied to determine the optimum shape of steel gusset plates subjected to axial forces. A number of different gusset plates used in various types of connections is considered for this purpose. The evolutionary structural optimization approach is employed to find the optimum shapes of a gusset plate used in these connections. The first example considers a gusset plate having two holes which are utilized in the connection of double angle carrying a tensile force. Within this example the effect of certain parameters in the evolutionary structural optimization process such as material removal ratio, mesh size and modeling of holes on the final shape is investigated. The gusset plates having three, four and five holes are also designed for optimal shape. Furthermore design examples include two rows of multiple holes as well as staggered holes and connections with multiple members. The final shapes obtained in the single member bolted connections are generally similar to those used in practice. However, they are lighter. Those shapes obtained for the multiple member connections and welded double angle connections are unpredictable. Although the shapes obtained in all the examples are lighter than the ones used in practice, they might be more expensive to produce. It is shown that the evolutionary structural optimization method has a potential in determining the optimum shape of gusset plates.     

Study on failure modes of steel truss bridge gusset plates related to tension and shear block failure

Tension and shear block failure is a limit state which occurs in the connection of tension steel members. The failure mechanism is a combination of tensile failure on one plane and shear failure on the perpendicular plane. The design strength equations for the tension and shear block failure are described in the well known design codes. However, they provide inconsistent levels of safety when they are used in different types of connections. In this paper, the authors survey the design strength equations in the various codes. Then, the pertinent strength equations for the gusset plates of steel truss bridges are selected. Moreover, the authors propose a pair of strength equations for compression and shear block failure for gusset plates subjected to compressive force. And to examine the applicability of proposed equations and to investigate the mechanical behavior of compression gusset plates, parametric analyses on the various thicknesses of gusset plates were conducted.     

低屈服点钢扣板连接的试验研究

同心支撑框架被广泛用于钢结构房屋的抗震设计中。在地震激励下,同心支撑框架的支撑会承受循环拉压荷载。由于支撑的屈曲,其抗压强度通常低于抗拉强度,这可能会降低支撑框架的抗震性能。该文对采用弱扣板强支撑的设计理念进行了验证。扣板选用低屈服点钢(LYP),从而使设计的扣板在支撑屈曲前发生屈服。低屈服点钢的屈服强度很低,但其延性很好。通过一系列试验验证循环荷载作用下低屈服点钢扣板的性能。研究发现,在低屈服点钢扣板上增加槽型约束(STR)可以大大提高其抗震性能。在拉压荷载作用下,有槽型约束的低屈服点钢扣板可以提供类似大小的强度。扣板的耗能能力同样得到提高。基于此研究成果,给出低屈服点钢扣板的一些设计建议。     

Vortex-induced vibration tests of circular cylinders connected with typical joints in transmission towers

Vortex-induced vibration (VIV) tests on full-scale cylinders are undertaken to study the vibration performance of steel tubes connected with typical joints in transmission towers, including [-shaped gusset plate connection, U-shaped gusset plate connection, cross-gusset connection and the flange. Due to the asymmetric flexural stiffness for the cross section of the [-shaped or U-shaped gusset plate, VIV is only generated about the minor axis. The paper presents the relationship between the slenderness ratio and the occurrence wind speed of VIV about the minor axis. Moreover, it has been shown that VIV can occur not only in laminar flows, but also in turbulent flows, and the amplitude decreases as the turbulence intensity rises. The amplitude is affected by the wind attack angle, and drops as the wind attack angle decreases. It is revealed that for the cylinders connected with [-shaped gusset plates with the slenderness ratio of 100∼200, the value of Strouhal number ranges from 0.20 to 0.21and the reduced velocity from 5.0 to 5.5.     

Experimental study of low yield point steel gusset plate connections

Concentrically braced frames have been used widely in the seismic-resistant design of steel building structures. During earthquake excitation, the braces of the concentrically braced frame are subjected to recursive tensile and compressive forces. The compressive strength of the brace is usually less than its tensile strength because of the buckling of the brace, and this may degenerate the seismic resistance capacity of the braced frame. In this reported research, an alternative design concept that adopts the weak gusset plate-strong brace is examined. The gusset plate is designed to yield prior to the buckling of the brace. Low yield point (LYP) steel is selected for the gusset plate. The LYP steel possesses low yield strength and high elongation capacity. A series of experimental studies was carried out to examine the LYP steel gusset plates under cyclic loads. It is found that adding slot-type restrainers (STR) to the LYP steel gusset plate greatly enhances the seismic resistance of the gusset plate. The proposed LYP steel gusset plate with an STR is able to provide similar strengths under tensile and compressive loads. The energy dissipation capacity of the gusset plate is also increased substantially. Based on this study, suggestions are made for the design of LYP gusset plates.     

Prediction of the tensile capacity of cold formed angles experiencing shear lag

The present study deals with the shear lag phenomenon in cold formed angles under tension, which are connected on one leg. A new expression for shear lag factor which represents the net section reduction coefficient has been suggested in the present paper. The proposed expression based on the regression analysis of 108 experimental results reported in the literature is validated by experiments involving net section failure in angles under tension. Totally 18 experiments were carried out on single angles fastened with bolts to the gusset plates under tension loaded upto net section rupture mode of failure. The experimental test parameters considered are number of bolts, pitch and shear lag distances and ratio of connected leg length to unconnected leg length. The tensile capacities are evaluated by various specifications such as AS/NZS:4600:2005, NAS:2001, AISC:2005, BS:5950-Part5:1998, IS:800-2007 and the proposed equation. A comparative study of tensile capacities predicted based on various codes and the experiment results is presented in this paper. For the tested range of specimens, both NAS:2001 and AISC:2005 standards over-predicted the capacities for all the specimens. The IS:800-2007 and AS/NZS 4600:2005 predictions are good for the specimens with three bolted connections and unconservative in the case of specimen with two bolts. Both BS:5950-Part-5:1998 and the proposed equation for IS:801 predict good estimate of the tensile capacity of cold formed angle members. The proposed equation for cold formed steel tension members, which is in the same format of IS:800 (2007) (Indian code for Hot rolled steel design), has been demonstrated to be good.     

Ultimate strength of gusset plate connections with fillet welds

Braced frames are commonly used as lateral-load resisting systems in seismic design. The braces are connected to the beams and columns by gusset plate connections. Fillet welds are commonly used to connect the gusset plates to the beams and columns. And the fracture of the interface welds were observed in the past research and earthquakes. This paper focused on the ultimate strength of interface weld connection between gusset plate and frame elements when the brace is in tension. Pilot experimental study was conducted with four specimens and proved that the evaluation recommended by AIJ works well. A verified finite element analysis model was developed to conduct a parametric study. The studied parameters are the brace angle, gusset plate size, and eccentricity of brace. From the parameter study, it is confirmed that the tensile brace axial force is primarily transferred to the interface weld within an extension Whitmore region, which is named as the effective region in the AIJ evaluation. And the extension Whitmore region is affected by the gusset plate geometrical constraint. A revised extension Whitmore region is suggested by considering the aforementioned parameters. The AIJ evaluation using the revised extension Whitmore region is also compared with the UFM, and showed better evaluation for the rectangular shape gusset plate.     

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.