GFRP管夹层灌浆修复锈蚀圆钢管T形节点受压性能研究

为研究GFRP管夹层灌浆修复锈蚀钢管节点的受压性能,改变支主管直径比、锈蚀率及修复构造,完成8个T形圆钢管节点的支管轴向受压静力加载试验。通过对主管加速锈蚀及GFRP管夹层进行灌浆修复,实测各钢管节点的破坏模式、荷载-变形曲线和荷载-应变曲线,分析节点受压承载力和初始刚度。结果表明：质量损失10%的主管锈蚀会使T形圆钢管节点受压承载力下降近20%,但未改变节点的失效模式;主管GFRP管夹层灌浆修复使锈蚀T形圆钢管节点的受压承载力提高100%左右,且较未锈蚀对比T形圆钢管节点可提高约70%;GFRP外管的约束作用是提升节点受压性能的关键,采用无约束作用的PVC外管会使灌浆层过早开裂并剥离,修复效果一般;主管焊接连接键可以增强钢管与灌浆夹层之间的锚固,其对PVC管夹层灌浆修复锈蚀节点的提升作用更明显,但对有GFRP约束修复T形圆钢管节点的贡献很小。建立并验证了各类T形圆钢管节点的有限元模型,揭示未修复节点主管塑性化变形失效机制,以及GFRP管夹层灌浆的约束作用对于锈蚀节点受压性能的提升机理。     

长沙贺龙体育场钢屋盖圆管相贯节点足尺试验研究

本文对长沙贺龙体育场钢屋盖结构中的6个圆钢管相贯节点进行了足尺试验研究,观察到试件节点的破坏主要分三种:受拉支管与主管的连接焊缝断裂破坏;受压支管靠近主管的端部的局部屈曲破坏;受压支管端部局部屈曲与受拉支管焊缝断裂的联合破坏。主管壁上的等效应力分布和发展很不均匀,而且复杂。由于本次节点试件存在主管强、支管弱的特点,节点破坏不属于规范规定的主管过度塑性变形的破坏形式,不能按现行规范公式计算。运用有限元求解相贯节点的极限承载力是一种有效的方法。试验证明,长沙贺龙体育场的钢屋盖设计是安全、经济、可靠的。     

主管灌混凝土平面X形圆钢管节点受压承载力试验研究

对6个不同截面几何参数主管中灌混凝土的平面X形圆钢管节点在支管轴向压力作用下的承载性能进行单调加载试验研究。描述了X形圆钢管混凝土节点破坏现象,给出了支管轴力-整体位移曲线、支管轴力-主管管壁变形曲线以及节点区域折算应变分布曲线,并将支主管外径比β、主管径厚比γ和支主管壁厚比τ对节点承载力和抗压刚度的影响进行分析。结果表明：节点初始抗压刚度随着β、γ的增大而提高,而τ对初始抗压刚度影响很小;所有节点试件主管测点都未进入塑性,均为支管根部冠点首先进入塑性,且直到破坏时折算应变一直保持最大;主管灌混凝土使钢管节点承载力明显提高。有限元计算结果与试验结果吻合较好。     

支管灌混凝土平面X形圆钢管节点轴压性能试验研究

为研究支管灌混凝土X形圆钢管节点的轴压性能,对6个不同截面几何参数的支管灌混凝土X形圆钢管节点进行了单调加载试验。介绍了节点试验方案,揭示了节点破坏模式,给出了加载点荷载 端位移曲线、支管轴力-主管壁变形曲线以及节点区域折算应变分布曲线,并将支主管外径比β、主管径厚比γ和支主管壁厚比τ对节点轴压承载力和弹性轴压刚度的影响进行了分析。试验研究结果表明：节点试件均表现出较好延性;所有试件的主管壁最大竖向变形位移都大于0.03倍主管直径,在判定该类圆钢管节点轴压承载力时应该采用极限变形准则;节点轴压承载力与弹性轴压刚度都随着β和τ的增加以及γ的减小而提高;所有试件的支管根部测点都未进入塑性且主管都是鞍点和冠点之间的中间测点首先进入塑性;在试验参数条件下,支管灌混凝土对X形圆钢管节点轴压承载力提高不明显,甚至会降低其轴压承载力。目前GB 50017-2003《钢结构设计规范》公式不能较好地计算支管灌混凝土X形圆钢管节点轴压承载力。     

平面X形圆钢管混凝土节点平面外受弯性能试验研究

为了解平面X形圆钢管混凝土节点的平面外受弯性能,分别对4个主管填混凝土和4个支管填混凝土的平面X形圆钢管节点进行支管平面外弯矩作用下的试验研究。考察了支管、主管分别填混凝土2种情况下节点的破坏模式和应力分布,并分析了钢管内混凝土对节点平面外抗弯刚度及承载力的影响。试验中支管填混凝土节点出现了主管塑性、支管局部屈曲和支管受拉侧焊缝或热影响区管壁开裂的破坏模式,主管填混凝土节点则发生了支管局部屈曲及支管受拉侧焊缝开裂破坏。主管填混凝土节点与支管填混凝土节点相比,由于主管内填混凝土对于主管管壁的局部变形起到明显的约束作用,明显提高了主管的径向刚度,增大了节点的平面外抗弯刚度。实测节点承载力与欧洲规范计算的空钢管节点理论承载力比较表明,主管内填混凝土能极大提高节点平面外受弯承载力,最大可提高132%;支管内填混凝土可使节点平面外受弯承载力最大提高60%。     

Experimental investigation and design of round ended elliptical steel tubular T-joints under axial compression

圆端形椭圆钢管是一种融合圆形和矩形截面特征优势的构件，其圆端部分可以提供良好约束，矩形部分可实现快捷连接，在桁架结构中有着良好的应用前景，然而目前尚缺乏有关圆端形椭圆钢管相贯节点的受力性能研究。为此，通过对13根圆端形椭圆钢管T形相贯节点开展轴压性能试验，研究相贯类型、主支管径比、主支管夹角和是否填充混凝土等对其破坏模式、承载力、初始刚度和延性等力学性能的影响，明确圆端形椭圆钢管T形相贯节点在支管受压作用下相较圆形或矩形钢管相贯节点的承载特征差异，揭示相贯节点的受力机理，提出圆端形椭圆钢管相贯节点的轴压承载力计算式。研究结果表明，圆端形椭圆钢管T形相贯节点表现出良好的轴压性能；支管与主管圆弧段连接的相贯节点轴压承载力分别为圆形或矩形钢管相贯节点的1.07~1.66倍，具有明显的承载优势；主管填充混凝土可使圆端形椭圆钢管T形相贯节点的轴压承载力和初始刚度分别提高75.5%~103.4%和11.9%~60.6%；通过试验结果验证，提出的轴压承载力计算式可较准确地评估圆端形椭圆钢管T形相贯节点的轴压承载力。     

Behaviour of Concrete-Filled Double-Skin Circular Hollow Section Cross Joints Under Axial Compression

This paper presents an experimental investigation on concrete-filled double-skin circular hollow section (CHS) cross joints under axial compression. A total of twenty-two right-angled CHS cross joints with different brace to chord diameter ratio (β), inner tube to outer tube thickness ratio of chord (ω) and hollow ratio of chord (χ) were tested, in which eighteen concrete-filled double-skin CHS cross joints were studied for different shapes of inner tube of chord, two traditional empty CHS cross joints and two traditional concrete-filled CHS cross joints were tested for comparison. The joint strengths, failure modes, load-deformation curves and strain distribution curves of all specimens are reported. The effects of brace to chord diameter ratio (β), inner tube to outer tube thickness ratio of chord (ω), hollow ratio of chord (χ), shape of inner tube of chord and concrete strength on the behaviour of concrete-filled double-skin CHS cross joints under axial compression were evaluated. It is shown from the comparison that the ultimate load and initial stiffness of CHS cross joints are significantly enhanced by strengthening the chord member with inner tube and concrete infill. Furthermore, the ultimate strengths are increased with the increase of the β ratio, whereas the ultimate strengths are decreased with the increase of the χ ratio for all types of concrete-filled double-skin CHS cross joints. On the other hand, the ultimate strengths are enhanced with the increase of the ω ratio and concrete strength for all types of concrete-filled double-skin CHS cross joints, but the enhancement is insignificant. The corresponding finite element analysis was also performed and calibrated against the test results. The design equations are proposed based on the test and finite element analysis results for concrete-filled double-skin CHS cross joints, which are verified to be more accurate.     

圆端形椭圆钢管T形相贯节点轴压性能试验研究与承载力计算

圆端形椭圆钢管是一种融合圆形和矩形截面特征优势的构件,其圆端部分可以提供良好约束,矩形部分可实现快捷连接,在桁架结构中有着良好的应用前景,然而目前尚缺乏有关圆端形椭圆钢管相贯节点的受力性能研究。为此,通过对13根圆端形椭圆钢管T形相贯节点开展轴压性能试验,研究相贯类型、主支管径比、主支管夹角和是否填充混凝土等对其破坏模式、承载力、初始刚度和延性等力学性能的影响,明确圆端形椭圆钢管T形相贯节点在支管受压作用下相较圆形或矩形钢管相贯节点的承载特征差异,揭示相贯节点的受力机理,提出圆端形椭圆钢管相贯节点的轴压承载力计算式。研究结果表明,圆端形椭圆钢管T形相贯节点表现出良好的轴压性能;支管与主管圆弧段连接的相贯节点轴压承载力分别为圆形或矩形钢管相贯节点的1.07～1.66倍,具有明显的承载优势;主管填充混凝土可使圆端形椭圆钢管T形相贯节点的轴压承载力和初始刚度分别提高75.5%～103.4%和11.9%～60.6%;通过试验结果验证,提出的轴压承载力计算式可较准确地评估圆端形椭圆钢管T形相贯节点的轴压承载力。     

Plastic mechanism analysis of welded thin-walled T-joints made up of circular braces and square chords under in-plane bending

Welded thin-walled T-joints made up of circular hollow section (CHS) braces and square hollow section (SHS) chords were tested under static in-plane bending load. The hollow sections are cold-formed and have thicknesses less than 4 mm. The CHS-SHS T-joints are used in building the undercarriages and structural supports of equipment and structural systems used in the road transport and agricultural industries. Failure in the CHS-SHS T-joints was observed to occur as a result of chord-face yielding. Chord cracking was also observed after large deformations, resulting in a peak load being attained in these joints. There is no design formula in the existing CIDECT design guides, IIW static recommendation and Eurocode 3 for CHS-SHS T-joints under in-plane bending. In this paper, load versus chord flange indentation graphs, for the CHS-SHS T-joints are used to determine the deformation limit that defines the ultimate strength of the joints. The deformed shape of the chord observed from experimental tests is used to create a yield line model. The weld size and the rounded corners of the SHS chord are considered in the model. A formula is derived, for the ultimate strength of the CHS brace and SHS chord vierendeel connections based on a plastic mechanism analysis using yield line theory. There is a reasonably good agreement between the ultimate strength predicted using this formula and that determined experimentally.     

T形钢管混凝土插板连接节点受弯性能研究

采用精细化有限元分析方法对T形钢管混凝土插拔连接节点的平面内受弯性能进行了研究.首先通过与试验结果进行对比,验证了精细化有限元模型的正确性和准确性.在此基础上研究了主管壁厚、支管壁厚、主管形式和混凝土强度对节点破坏模式和承载力的影响.结果表明,钢管混凝土插板连接节点的破坏模式和钢管插板连接节点不同,为主管冲剪破坏和支管...     

Tests of concrete-filled stainless steel tubular T-joints

This paper describes a test program on a wide range of concrete-filled cold-formed stainless steel tubular T-joints fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. A total of 27 tests was performed. The chord member of the test specimen was filled with concrete along its full length. Both high strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens filled with nominal concrete cylinder strength of 30 MPa were tested. The axial compression force was applied to the top end of the brace member, which was welded to the center of the chord member. Local buckling failure of brace member was the main failure mode observed during the tests. Hence, the axial compression force was then applied by means of a steel bearing plate to avoid failure of brace member. The failure modes of chord face failure and chord side wall failure as well as crushing of the concrete infill were observed. All the tests were performed by supporting the chord member of the specimen along its entire length to apply the pure concentrated force without any bending moment. The test results were also compared with design rules for carbon steel tubular structures, which is the only existing design guideline for concrete-filled tubular joints. It is shown that the design strengths predicted by the current design rules are quite conservative for the test specimens. It is also recommended that the contribution of stainless steel tubes should be included in the design rules since it has significant effects on the ultimate bearing capacity of concrete-filled stainless steel tubular T-joints.     

Experimental and numerical study on fire resistance of circular tubular T-joints

This paper focuses on experimental investigation and preliminary numerical parametric study on fire resistance of CHS T-joints under axial compression. In experimental test, three CHS T-joints subjected to axial load are heated in accordance with predefined heating curves in electric heating furnace. The failure mode of the specimens at elevated temperature is found from experimental observation to be plastic failure of chord face around the brace/chord intersection. The experimental phenomena and displacement–temperature curves show that the T-joints fail suddenly after temperature exceeds certain value. Additionally, the temperature–time and displacement–temperature curves of specimens obtained from experimental measurements are used to verify the accuracy of finite element models presented in this study. In preliminary numerical parametric study, the finite element models are built using finite element software ABAQUS. Sequentially coupled thermal–stress analysis is used to conduct numerical simulation. The comparison between experimental and numerical results shows that the proposed finite element models can simulate the fire test successfully and are reliable to carry out a preliminary numerical parametric study to investigate the influence of several principal dimensionless parameters on fire resistance of CHS T-joint, such as α, β, γ, and loading ratio n. For the CHS T-joints with different values of β and n, the reaction force caused by constraint at chord ends is also studied. It has been found that the behavior of CHS T-joint at elevated temperature is significantly affected by the geometrical parameters and loading ratio n. Additionally, the reaction force cannot be neglected if the chord ends are fully constrained.     

Experimental investigation of cold-formed stainless steel tubular T-joints

This paper describes a test program on a wide range of cold-formed stainless steel welded tubular T-joints fabricated from square and rectangular hollow section brace and chord members. A total of 22 tests was performed. High strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens were tested. The tests were performed by supporting the chord member of the specimen along its entire length with the pure concentrated force applied to the chord face by the brace member. The ratio of brace width to chord width (β) of the specimens varied from 0.5 to 1.0 so that failure modes of chord face failure and chord side wall failure were observed. The test results were compared with the design procedures in the Australian/New Zealand Standard for stainless steel structures, CIDECT and Eurocode design rules for carbon steel structures. It is shown that the design strengths predicted by the current design specifications are conservative for the test specimens calculated using the 0.1%, 0.2%, 0.5% and 1.0% proof stresses as the yield stresses. The 0.2% proof stress is comparatively more reasonable to predict the design strengths of stainless steel welded tubular T-joints for both ultimate limit state and serviceability limit state. In this study, it is shown that the ultimate limit state controls rather than the serviceability limit state for most of the test specimens.     

Numerical investigation on stress concentration factors of square bird-beak SHS T-joints subject to axial forces

This paper presents a numerical study on stress concentration square bird-beak square hollow section (SHS) welded joints. Both conventional and square bird-beak SHS joints considered have T-shapes and are simply supported at their chord ends. Refined finite element models are developed to obtain the strain/stress concentration factors (SNCFs/SCFs) of square bird-beak joints with various dimensions. The FE models are validated by comparing with the experimental data. The SNCF differences among considered hot spots are analyzed for the identification of critical locations. The influences of three major non-dimensional parameters, i.e., brace/chord width ratio β, chord wall slenderness ratio 2γ, and brace/chord wall thickness ratio τ, on the stress concentration factors (SCFs) of square bird-beak T-joints are revealed on the basis of numerous parametric studies. Comparisons of joint types are finally made. The results indicate that, in case of identical non-dimensional parameters, square bird-beak SHS T-joints provide SCFs smaller than conventional SHS T-joints in most occasions, especially when β is small; and SCFs of square bird-beak T-joints are expected to be lower than CHS T-joints with small β and large 2γ and τ.     

覆板加强的方钢管T形节点轴向滞回性能试验研究

为研究采用覆板加强的冷弯方钢管T形节点的轴向滞回性能,对2组支管与主管的截面宽度比β分别为0.4和0.8的方钢管直接焊接节点和采用覆板加强的方钢管T形节点进行了轴向往复加载试验。详细介绍了试验节点的设计、试验过程及破坏形态,并对节点试件的滞回曲线、骨架曲线、耗能和延性等性能进行了分析。试验中,试验节点经历了主管屈服、初始开裂、裂纹闭合、裂缝扩展、裂缝贯通五个主要阶段,但各试件的开裂位置并不相同。加强覆板阻止了裂缝向主管管壁发展,有效避免了主管管壁的撕裂破坏,使开裂后支管的受压荷载继续上升,因而节点开裂后受拉能力较未加强节点的好。支管与主管截面宽度比越小,试件的耗能能力和延性越好。但覆板加强处理降低了试件的耗能能力,且支管与主管宽度比越小其耗能能力的降低越明显。受拉裂缝会降低试件的延性,故轴拉循环的延性较对应的轴压循环的差。在β=0.8时,覆板加强对试件的抗震延性有所改善,但β=0.4时加强节点试件的位移延性系数低于未加强节点。覆板加强节点在支管轴向往复荷载作用下的拉压不均衡问题应引起重视。     

Square hollow section (SHS) T-joints with concrete-filled chords subjected to in-plane fatigue loading in the brace

In recent years, there has been an increased use of concrete-filled composite tubular joints in bridge construction. The reliability of these joints under fatigue therefore need to be investigated to avoid any catastrophic failures. In this paper, hollow section T-joints made up of square hollow section (SHS) chords and braces are investigated. The chords of the SHS–SHS T-joints were concrete-filled thereby forming welded composite tubular T-joints. The SHS–SHS T-joints with concrete-filled chords were strain gauged and tested under static loading to determine stress concentration factors (SCFs) at hot spot locations, where cracks are likely to propagate. Fatigue tests of the welded composite joints were also carried out under cyclic in-plane bending in the brace to obtain stress range vs. number of cycles (S–N) data. The maximum stress concentration factor (SCF) at hot spot locations in a welded composite tubular T-joint was found to be generally lower than the maximum SCF in an empty (or called unfilled) hollow section SHS–SHS T-joint. Fatigue failure in welded composite tubular T-joints occurred through the initiation and propagation of cracks at weld toes in either the chord or brace member, with the majority of tests exhibiting the first visual crack at weld toes in the chord. The welded composite tubular T-joints were found to have better fatigue strength compared to the empty hollow section SHS–SHS T-joints. Design rules are recommended for the SHS–SHS T-joints with concrete-filled chords through analysis of fatigue test data using the hot spot stress method.     

主管内填混凝土矩形和圆形钢管桁架受弯性能对比试验研究

为研究主管内填混凝土对矩形和圆形钢管桁架结构受弯性能的影响及两者区别,进行了矩形和圆形钢管桁架空管、仅受压主管内填混凝土和拉压主管均内填混凝土三种类型桁架的对比试验研究。试验结果表明:矩形截面桁架均发生节点失效,空管桁架为受压主管侧壁鼓曲破坏,仅受压主管内填混凝土和拉压主管均内填混凝土桁架发生受拉主管顶板的冲剪破坏;圆形截面空管桁架和仅受压主管内填混凝土桁架发生空管节点处的主管侧壁鼓曲破坏,拉压主管均内填混凝土桁架为受拉支管受拉断裂破坏。主管内填混凝土有助于提高主管轴向刚度,提高节点强度和刚度及整体承载力,节点承载力按规范计算结果偏于安全,桁架整体变形计算需考虑节点变形的影响。两种截面空管桁架的承载力及变形差异不明显,主管内填混凝土后,圆形截面桁架的整体和节点承载力比相应矩形截面桁架承载力要高,变形能力更好,且节点变形比例更小。     

震后火灾下内置单环加强T形圆管节点受火性能分析

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