焊接薄壁箱形构件在国家体育场中的应用研究

研究了在焊接箱型截面构件内部合理设置横向和纵向加劲肋的方法,分析了设置纵向加劲肋对提高构件承载力的影响,并通过非线性有限元法对薄壁箱形构件的抗震性能进行了分析。     

Improving strength and ductility of continuous composite plate girder bridges

The ultimate load carrying capacity of continuous composite plate girder bridges is usually limited by the local buckling failure of steel girders at interior supports. This paper presents a simple reinforcement method which changes the failure mechanism of the continuous girder from local buckling to formation of plastic hinges at the interior supports and mid-span. Such a change in failure mechanism greatly improves the strength and ductility of the superstructure. In this method the compressive portion of the web near the interior support is braced against local buckling by bolting pairs of stiff bracing elements on opposite sides of the web. The bracing elements prevent local buckling failure of the support section and create a section which can rotate inelastically at plastic moment allowing the second hinge to form at mid-span. The bracing elements may be plates or longitudinal stiffeners which should be designed to remain elastic while the section undergoes plastic deformation. The behavior of plate girders which are reinforced by such bracing elements is studied using nonlinear finite element analyses.     

新型冷弯箱形组合截面受弯构件力学性能研究

冷弯薄壁双轴对称箱形截面具有形心、弯心重合的特点,与单轴对称开口截面相比具有抗弯、扭刚度大的优点。基于箱形截面的以上特点,应用冷弯∑形构件两两电弧点焊连接,形成两种新型箱形组合截面——翼缘对焊箱形组合截面和翼缘叠焊箱形组合截面。采用非线性有限元的分析方法,通过对两种新型截面与相同参数的单肢∑形构件的细致比较分析,以及单一参数变化条件下新型截面构件的屈曲模式、变形过程、弯矩-曲率关系等方面的分析,全面研究两种新型截面受弯构件的静力学性能。研究表明:两种新型截面构件与其单肢∑形构件相比,具有抗弯承载力明显提高,构件不会出现畸变屈曲、局部变形小等性能优势,可以深入研究并合理推广使用。     

Buckling measurement and numerical analysis of M-type ribs stiffened composite panel

A combination of methods of strategy which combines optical measurements and numerical calculations was developed to study the buckling behavior and failure modes of composite panel with M-type stiffeners under compression. Utilizing the non-contact optical means for non-destructive testing, the full-field buckling deflections/evolution and compressive failure of the panel surface were systematically collected for mechanical analysis. Based on continuum mechanics modeling, the buckling and post-buckling behaviors of the composite panel were predicted and compared with the buckling shapes that are obtained from experiments. The numerical simulation methods and experimental test technique in the work provides a useful tool to study the compressive buckling behaviors of composite panel with M-type stiffeners.     

Nonlinear analysis of concrete-filled thin-walled steel box columns with local buckling effects

Local buckling of steel plates reduces the ultimate loads of concrete-filled thin-walled steel box columns under axial compression. The effects of local buckling have not been considered in advanced analysis methods that lead to the overestimates of the ultimate loads of composite columns and frames. This paper presents a nonlinear fiber element analysis method for predicting the ultimate strengths and behavior of short concrete-filled thin-walled steel box columns with local buckling effects. The fiber element method considers nonlinear constitutive models for confined concrete and structural steel. Effective width formulas for steel plates with geometric imperfections and residual stresses are incorporated in the fiber element analysis program to account for local buckling effects. The progressive local and post-local buckling is simulated by gradually redistributing the normal stresses within the steel plates. Two performance indices are proposed for evaluating the section and ductility performance of concrete-filled steel box columns. The computational technique developed is used to investigate the effects of the width-to-thickness ratios and concrete compressive strengths on the ultimate strength and ductility of concrete-filled steel box columns. It is demonstrated that the nonlinear fiber element method developed predicts well the ultimate loads and behavior of concrete-filled thin-walled steel box columns and can be implemented in advanced analysis programs for the nonlinear analysis of composite frames.     

板件中间加劲的复杂卷边槽钢轴压构件弹性畸变屈曲应力的实用计算法

为了研究板件中间加劲的复杂卷边槽钢轴压构件畸变屈曲临界应力的简便计算方法,应用有限条分析软件CUFSM对冷弯薄壁板件中间加劲的复杂卷边槽钢以及腹板中间V型加劲的复杂卷边槽钢共90个轴压构件进行数值模拟,分析各参数对构件弹性畸变屈曲临界应力的影响。经拟合分析,得出针对板件中间加劲的复杂卷边槽钢、腹板中间V型加劲的复杂卷边槽钢轴压构件的弹性畸变屈曲临界应力的简化计算公式,并验证该公式的有效性。     

球头加劲铝合金轴压构件的局部稳定设计方法分析

工程中常采用对铝合金截面设置球头加劲肋的方法来提高受压构件的稳定性能,为了研究球头的设置对局部稳定承载力的影响,对包含球头的8个方管、10个十字形和13个工字形截面轴压柱模型进行了数值模拟,将得到的承载力与我国GB 50429—2007《铝合金结构设计规范》、欧洲规范EN 1999-1-1和美国铝合金设计手册中对含加劲肋的受压构件局部稳定承载力预测值进行比较,研究了各规范中设计方法的精度。结果表明,我国规范对于十字形截面构件的预测误差有随板件宽厚比增大而增大的趋势,对方管截面和工字形截面构件预测精度较高,误差在10%以内,由于存在一些构件预测偏于不安全的情况,建议采用我国规范方法计算中间加劲板件的稳定承载力时,引入一定的安全系数。设置球头加劲肋后,构件局部稳定承载力相比未设加劲肋的可提高10%～43%,因此可将板件制作得更薄,提高利用效率。     

不同截面形式高强冷弯薄壁槽钢构件受弯承载力试验研究

对36个屈服强度为550 MPa的高强冷弯薄壁槽钢受弯试件进行静力试验研究,考虑了加劲形式和卷边形式对试件受弯性能的影响,其中加劲形式分为无加劲、翼缘中间V形加劲和翼缘及腹板中间V形加劲3种,卷边形式分为直卷边、斜卷边和复杂卷边3种。试验结果表明：加劲形式和卷边形式是影响试件受弯承载力和屈曲模式的重要因素;与无加劲形式相比,采用板件中间V形加劲有效减小了板件宽厚比,试件受弯承载力提高了30%~70%;同种加劲形式下,短（直、斜）卷边试件受弯承载力提高幅度最大,复杂卷边试件提高幅度次之,长（直、斜）卷边试件提高幅度最小;试验过程中试件发生了局部屈曲、畸变屈曲与局部和畸变相关屈曲。对试验进行了有限元模拟,模拟结果与试验结果吻合较好。     

带肋冷弯薄壁方钢管混凝土柱滞回性能研究

对3根带肋冷弯薄壁方钢管混凝土柱进行滞回试验,主要参数为轴压比。试验结果表明：纵向加劲肋有效延缓了钢管壁局部屈曲的发生;其滞回曲线饱满,具有良好的耗能能力;随着轴压比的增大,柱承载力略有增大,而延性、耗能能力则明显减小;当横向位移大于6倍的屈服位移时,大轴压比的刚度退化速度最快。建立了该类试件的有限元模型,对比可得有限元模拟结果与试验结果吻合较好。基于有限元模型对该类构件开展机理分析和参数分析。结果表明：在带肋冷弯薄壁方钢管的约束下,核心混凝土的强度得到了较大提高;钢管局部屈曲发生在峰值荷载后,局部屈曲只发生在纵向加劲肋和钢管角部间;材料强度、轴压比、钢管宽厚比和长细比等参数对该类构件的承载力有较大影响;混凝土强度、轴压比和长细比对荷载-位移骨架曲线形状有较大影响。基于参数分析建议了该类构件的简化滞回模型,简化计算结果和有限元计算结果吻合较好。     

国家体育场桁架柱内柱多腹杆焊接节点性能研究

对国家体育场钢结构桁架柱的节点进行了比例为1∶5的缩尺模型试验研究和有限元分析。该节点为主桁架梁与桁架柱的连接节点,由1根菱形内柱与11根箱形截面腹杆形成的复杂空间管节点,并且节点内布置了许多加劲肋。论文介绍了节点的试验方法,描述了整个加载过程中节点行为和最后的破坏模式。从节点受力性质、构造、几何尺寸等角度,讨论了节点的破坏机理。研究表明节点的薄弱环节出现在受压腹杆,发生局部屈曲。弦杆内设置加劲肋是防止弦杆板件塑性破坏和局部屈曲的有效构造措施。论文提出了实际结构中该节点设计和制作时应采取的措施。     

Buckling behavior improvement of steel plate shear wall systems

To improve buckling stability and to prevent early elastic buckling of infill plates, vertical and horizontal plate stiffeners are designed for steel plate shear wall (SPSW) systems. Furthermore, effective design of stiffeners for SPSW systems results in improved structural behavior, such as increase of stiffness, capacity and energy absorption. In this paper, the effect of stiffeners is studied on SPSW structural behavior and consequently a rational method is proposed to determine the minimum required moment of inertia for stiffeners resulting in local buckling mode of the infill plate. The proposed requirement is then compared to results obtained from tests previously conducted, as well as those gained from finite element (FE) analyses performed for this study. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

960 MPa高强度钢材轴心受压构件局部稳定试验研究

针对960 MPa高强度钢材轴心受压构件的局部稳定性能,对4个箱形截面试件和4个工字形截面试件进行了轴心受压试验。分析了试件的局部稳定性能,并将试验结果与我国、美国和欧洲钢结构设计规范的相应设计计算结果进行了对比分析,研究各国规范对960 MPa高强度钢材轴心受压构件局部稳定性能设计计算的适用性。研究结果表明：当构件的板件宽厚比相同时,960 MPa高强度钢材构件的局部屈曲后强度要大于460 MPa高强度钢材构件,960 MPa高强度钢材构件应考虑钢材的屈曲后强度;我国现行钢结构设计规范中关于轴心受压构件局部屈曲应力的计算结果不适用于960 MPa高强度钢材构件;在试验钢材板件宽厚比范围内,960 MPa高强度钢材构件的局部屈曲承载力,采用美国规范和欧洲规范的设计计算结果较为准确。     

国家体育场焊接方管桁架单K节点试验研究

为考察构造复杂的国家体育场焊接方管桁架单K节点的受力性能和承载力,进行了两个典型节点的1∶3缩尺比例的模型试验和有限元分析。试验结果表明,节点强于杆件,节点的极限承载力都能达到设计荷载水平的2倍以上,且节点区范围内的板件未观察到局部失稳或断裂现象。有限元分析能较好地模拟试验现象。试验结果和有限元分析结果证明,节点区的板件局部加厚和内置加劲肋等加强措施是有效的。     

高强度钢材箱形截面轴心受压短柱局部稳定试验研究

针对高强度钢材焊接箱形截面柱的局部稳定受力性能,对4个Q460钢材等边箱形短柱进行轴心受压试验。根据试验结果分析试件的局部屈曲应力、极限应力随板件宽厚比的变化规律,并将试件的局部屈曲应力、极限应力与我国、美国、欧洲钢结构设计规范以及陈绍蕃建议的相应设计方法和计算公式进行对比分析。结果表明,钢板的宽厚比越大,试件截面的利用率越低,局部屈曲后强度越富余;我国钢结构设计规范中对于试件的局部屈曲应力的计算公式不适用于等边箱形短柱;对于等边箱形短柱的极限应力,美国、欧洲钢结构设计规范和陈绍蕃建议的设计方法的计算结果较为接近,且均略高于试验结果,这3种设计方法都是可行的。进一步修改已有的计算公式,以适用于计算Q460高强度钢材等边箱形短柱的局部屈曲应力;建议采用陈绍蕃建议的设计方法,并进一步修改欧洲钢结构设计规范的计算公式,以适用于计算Q460高强度钢材等边箱形短柱的极限应力。     

腹板开孔复杂卷边槽钢双肢拼合构件轴压性能试验研究

通过12根腹板开孔复杂卷边槽钢和Σ形复杂卷边槽钢双肢拼合工字形简支轴压构件的轴压试验，研究了构件承载能力、失稳模式和拼合作用。采用有限元软件ANSYS对试验进行了模拟，验证了分析模型准确性。并通过有限元变参数分析研究了孔高、孔宽和孔间距对拼合构件承载力的影响。结果表明：复杂卷边槽钢截面双肢拼合开孔构件的腹板多波失稳现象明显，屈曲发生时两腹板间的相互支撑作用较强；Σ形复杂卷边槽钢截面双肢拼合开孔构件能有效地控制腹板局部屈曲的发生并显著提高短柱、中长柱的承载力；设置腹板加劲肋有助于提高孔洞周围板件变形的约束作用，同时也减弱了两单肢腹板间的相互支撑作用；相同条件下，Σ形复杂卷边槽钢截面双肢拼合开孔构件的轴压承载效率与复杂卷边槽钢截面双肢拼合开孔构件相比，短柱提高了32%，中长柱提高了10%，长柱提高了2%；非加劲截面构件在不同长度下，孔高为腹板高度1/2(69 mm)时构件的稳定承载力较孔高为25 mm时下降约7%；而孔宽、孔间距对上述两类截面构件稳定承载力影响不大；此外，采用直接强度法预测非加劲截面双肢拼合构件的承载力结果偏于保守，而对加劲截面双肢拼合构件则略显不安全。     

反复荷载作用下L形钢管混凝土柱滞回性能研究

本文介绍了7根L形钢管混凝土柱试件在承受常轴力和水平荷载作用下的试验研究.试验中考虑了不同的轴压比、内部有无加劲和加载方式对试件抗震性能的影响.试验结果表明.内部加劲能够明显地延缓柱子钢板的屈服,而且柱子的耗能能力和延性也有较好的改善.最后通过编写计算程序,对L形钢管混凝土柱的荷载-变形进行了全过程分析.考察了常用的方钢管混凝土柱的钢材和混凝土的本构关系对L形钢管混凝土柱纤维模型数值分析的适用性,计算得到的弯矩一轴力一曲率关系和荷载一位移关系与试验结果吻合较好.     

Monotonic and cyclic behavior of concrete-filled steel-tube beam-columns considering local buckling effect

A mathematical model is developed to evaluate the monotonic and cyclic behavior of concrete-filled steel tube (CFST) beam-columns with rectangular cross section. The model includes the reduction in the steel compressive strength due the local buckling effect. The degradations in unloading and reloading stiffness of steel tube due to local buckling are also included. The model is based on fiber element method in which uniaxial stress–strain material laws are used for cross section components. The results obtained from the mathematical model were compared with experimental results for columns under monotonic as well as cyclic loads. It is observed that the proposed model predicts well the columns and beams nonlinear behavior compared with the experimental results.     

Test description of steel X‐bracing system using low‐grade steel and internal oblique transverse stiffeners

A sample of steel X‐braced frame was studied using laboratory tests by which system behaviour and its failure modes were driven. The braces were designed based on the idea of using low‐grade steel in lateral load resisting system. Therefore, stocky braces were used. A rigid central core at intersection point of braces was considered. Oblique transverse stiffeners were provided inside the braces' cross‐section for more lateral stiffness and reduction of system yield displacement. Intervals between stiffeners were determined to create guided local buckling before global buckling of braces and thus dissipate energy by accordion behaviour. The hysteresis and energy absorption diagrams were presented. The system ductility has also been calculated. The obtained results represent uniform and stable energy absorption and reasonable system ductility by using low‐grade steel, rigid central core and oblique transverse stiffeners. Copyright © 2010 John Wiley & Sons, Ltd.     

A study into optimization of stiffeners in plates subjected to shear loading

A great deal of attention has been focused on plates subjected to shear loading over the past decades. One main fact in design of such elements, which fall in the category of thin-walled structures, is their buckling behavior. Plate girders and recently shear walls are being widely used by structural engineers, as well as ship and aircraft designers. The role of stiffeners is proved to be vital in design of such structures to minimize their weight and cost.In this work, by using ANSYS finite element method of analysis, some 1200 plates are analyzed in order to study the role of stiffeners and to come up with some limits for an optimized design procedure. This eigenvalue method of analysis is first validated with the theoretical calculations and known cases for a wide range of typical panel geometries.The results show that the number of panels produced by intermediate transverse stiffeners should not be less than the value of plate's aspect ratio. In other words, the transverse stiffeners should divide the length of the plate to portions equal or less than its width.It is also shown that the optimum geometric properties of the stiffeners correspond to the point when the buckling shape of a plate changes from the overall mode to local mode. Furthermore, all stiffened plates, with a similar aspect ratio and number of stiffeners, have a specific value of EI_s/aD, for which the critical shear stress is optimal. In addition, some expressions to predict these properties are presented.