纯压圆弧形钢管桁架拱平面内稳定性能及设计方法

目前针对钢管桁架拱平面内稳定性能及承载力的研究较少,缺少相应的设计方法。提出了钢管桁架拱截面剪切刚度表达式,考虑剪切变形的影响推导了纯压两铰圆弧桁架拱屈曲荷载的简化计算公式以及换算长细比表达式。基于有限元方法,全面分析了截面高宽比、矢跨比、腹杆夹角及腹杆截面尺寸等不同参数对平面桁架拱和空间桁架拱弹性屈曲性能的影响,结果表明采用简化公式与有限元分析结果吻合良好。借鉴实腹拱和格构柱的稳定设计方法,采用大挠度弹塑性有限元法系统研究了平面及空间纯压桁架拱的相关稳定承载力,发现节间弦杆长细比与桁架拱整体长细比的比值是衡量局部稳定对整体稳定影响的关键参数,在此基础上提炼出纯压桁架拱的相关作用影响系数,并拟合得到了纯压桁架拱的稳定设计曲线,从而为一般荷载作用下压弯桁架拱的稳定承载力的设计奠定了基础。     

平面钢管桁架拱平面外稳定试验研究与有限元分析

对2个跨度为10 m的圆弧形平面圆钢管桁架拱模型进行全跨均布荷载作用下的静力试验研究,分析了平面钢管桁架拱的平面外稳定承载力。引入平面外转动弹簧单元、水平位移弹簧单元,建立弹簧-杆系有限元模型,对试验模型进行非线性有限元分析。试验和有限元分析结果表明：下弦杆无平面外支撑的平面钢管桁架拱,在极限状态时,受压上、下弦杆发生侧向弯曲失稳,并引起整体平面外弯曲失稳破坏;圆钢管相贯节点的平面外转动刚度对试验模型的平面外稳定承载力影响显著。弹簧-杆系有限元分析结果与试验结果较为吻合,可为同类型结构的平面外稳定分析、设计提供参考。     

我国拱形钢结构设计理论研究现状与展望

结合我国JGJ/T 249-2011《拱形钢结构技术规程》的颁布,对拱形钢结构设计、计算及施工中的关键问题如受力性能、结构选型、稳定性能及加工制作等方面进行了阐述。研究表明：与梁柱等直构件相比,拱形钢结构的设计理论、特别是稳定设计方法更为复杂,其受力和工作机理受拱轴线形式、跨度、矢跨比、拱脚边界条件、截面形式、荷载形式及组合、面外支撑条件等诸多因素影响。拱形钢结构平面内失稳对荷载和变形的非对称初始缺陷较为敏感,对于钢管桁架拱必须考虑弦杆局部失稳对整体稳定承载力的削弱作用;平面外弯扭失稳时,变形及受力复杂,其稳定承载力受拱脚、荷载条件及支撑布置影响显著;初步建立平面内稳定设计方法并在规程中予以体现,包括实腹式截面拱（含腹板开孔钢拱）、钢管桁架拱以及钢管混凝土拱等结构形式;平面外稳定性及面外支撑设计是拱形钢结构设计理论的重要组成部分,在规程中还有待进一步补充和完善。     

焊接工字形截面抛物线拱平面内稳定性试验研究

进行了全跨竖向均布荷载和半跨竖向均布荷载作用下焊接工字形截面两铰抛物线钢拱平面内稳定承载力试验研究。通过试验揭示了抛物线钢拱平面内的失稳破坏机理,全跨竖向均布荷载作用下抛物线钢拱发生不完全反对称的平面内失稳破坏,半跨竖向均布荷载作用下抛物线钢拱发生反对称的平面内失稳破坏;半跨竖向均布荷载作用下抛物线钢拱的稳定承载能力低于全跨竖向均布荷载作用下的稳定承载能力;试验结果与有限元法分析结果进行了对比,二者吻合良好,有限元法研究钢拱的平面内稳定具有很高的精度;试验结果验证了工字形截面抛物线钢拱平面内稳定性设计方法安全可靠,可供设计使用。     

钢管桁架拱的稳定性能及应用

首先介绍桁架拱的组成特点、力学特性及工程应用,探讨拱的弹性和非弹性失稳特点及分类.结合桁架拱弹性屈曲模型、荷载作用类型及初始挠度沿轴线的分布形式,指出了桁架拱几种可能的破坏和失稳形式.在钢管桁架拱形结构失稳模态分析的基础上,利用非线性有限元分析方法,对立体管桁架拱进行了面内整体稳定承载力分析,从结构的荷载-位移全过程曲线考察了桁架拱稳定性能的基本规律,从中找到控制桁架拱设计的主要失稳形式.最后,结合南通体育会展中心拱支网壳结构的整体稳定性能进行研究,指出现阶段对桁架拱稳定性分析的基本方法和步骤.     

某采光顶及幕墙支承结构设计

对某工程入口采光顶及幕墙支承结构的设计进行了深入探讨.由于建筑造型的要求,该采光顶张弦桁架与一般张弦桁架有很大区别,为了保证桁架的整体稳定,需要在上弦杆设置面外撑杆、竖腹杆与上弦杆刚接且要求竖腹杆截面的面外抗弯刚度大于面内刚度.此外,由于入口幕墙风荷载主要由采光顶边梁来承担,且该梁跨度达到36m,采用箱型宽扁梁截面可以满足其强度和变形要求.最后,由于下弦杆张拉力较大且竖腹杆与上弦杆刚接,必须设计合理的张拉施工方案,以保证结构安全.     

Warren型平面钢管桁架受压弦杆的面外稳定承载力

受压弦杆面外失稳是Warren型平面钢管桁架面外失稳的主要形式,其受力状态可以简化为支撑弹簧压杆。确定腹杆提供的支撑弹簧刚度是计算压杆面外稳定承载力的必要条件。考虑节点面外转动刚度的影响,推导了腹杆对弦杆支撑弹簧刚度计算公式。对4~15跨的支撑弹簧压杆建立了相应的标准化屈曲计算模型,进行有限元屈曲分析,得到不同跨数压杆的弹簧刚度与面外稳定承载力的数值关系表,通过计算支撑弹簧刚度可以方便地查表得到不同跨数Warren型平面钢管桁架受压弦杆的面外稳定承载力。通过数值算例比较,查表法简便可行,可以在实际工程设计中参考应用。     

全装配式桁架檩条力学性能试验研究

针对螺栓连接装配式桁架檩条的力学性能,进行了7组不同工况的足尺静力加载试验,研究压力及风吸力作用下结构的荷载-位移、荷载-应变等变化规律,分析各部件的工作机理及破坏形式。结果表明:装配式桁架檩条的试验破坏模式与理论破坏模式基本一致,但其试验承载能力明显高于理论值,且构件挠度试验值也远大于理论值;压力荷载作用下弦杆和腹杆螺栓连接节点强度不足是导致试件破坏的主要原因,而风吸力作用下试件的主要破坏原因是下弦杆的局部受压承载力不足。建议实际设计中,对螺栓连接节点进行改进以增加其刚度或对檩条整体刚度进行适当折减,并适当增大端腹杆截面,提高其承载能力。     

空间KK形圆管搭接节点静力性能试验研究与有限元分析

以上海旗忠网球中心为工程背景,对平面内外均搭接的空间KK形圆管节点（空间KK-Ov形节点）的静力性能进行了静力单调加载的试验研究和有限元非线性分析。详细介绍了节点试验方案,分析了搭接节点的受力性能、破坏模式、荷载-位移曲线及应变变化规律。在此基础上,建立了非线性有限元分析模型,对节点试验进行了数值模拟,计算结果与试验结果吻合良好。试验结果和有限元分析表明：空间KK-Ov形节点在发生承载力破坏时,常伴随有受拉腹杆与弦杆连接焊缝的开裂;四根腹杆交错搭接的构造,使得空间KK-Ov形节点具有明显区别于间隙节点破坏时管壁局部变形的特征,两受压腹杆之间的弦杆管壁在腹杆压力作用凹陷与腹杆局部屈曲是该类节点的主要破坏模式;平面外两腹杆搭接率ζ_t对节点承载力有一定影响,随平面外两腹杆搭接率的增大（即ζ_t绝对值变大）,节点承载力将会减小。现行规范公式用于计算空间KK-Ov形节点承载力,既未考虑单K平面内搭接的影响,亦未考虑空间参数变化的影响,计算结果较试验结果偏于保守。     

竖向荷载和水平荷载共同作用下钢管拱平面内稳定承载力设计研究

采用二阶弹塑性有限单元法对竖向荷载和水平荷载共同作用下的圆形截面两铰抛物线钢管拱的平面内稳定承载力进行研究。考虑材料非线性、残余应力、初始几何缺陷、矢跨比和长细比等因素对钢管拱平面内力稳定承载力的影响。结果表明：残余应力对其竖向承载力影响很小;初始几何缺陷会显著降低中等长细比钢管拱的承载力;矢跨比和长细比是影响钢管拱承载力的重要因素,但拱的竖向承载力并不随矢跨比和长细比的均匀变化而变化。研究竖向荷载和水平荷载共同作用下两铰抛物线钢管拱达到平面内极限状态时的N-M相关关系,并拟合两铰压弯抛物线钢拱承载力N-M相关关系统一表达式。提出了竖向荷载为全跨均布和半跨均布荷载,同时考虑水平方向荷载作用的两铰抛物线钢拱平面内整体稳定承载力设计建议,可供相关设计问题参考应用。     

Out-of-plane elastic buckling load and strength design of space truss arch with a rectangular section

The out-of-plane stability of the two-hinged space truss circular arch with a rectangular section is theoretically and numerically investigated in this paper. Firstly, the flexural stiffness and torsional stiffness of space truss arches are deduced. The calculation formula of out-of-plane elastic buckling loads of the space truss arch is derived based on the classical solution of out-of-plane flexural-torsional buckling loads of the solid web arch. However, since the classical solution cannot be used for the calculation of the arch with a small rise-span ratio, the formula for out-of-plane elastic buckling loads of space truss arches subjected to end bending moments is modified. Numerical research of the out-of-plane stability of space truss arches under different load cases shows that the theoretical formula proposed in this paper has good accuracy. Secondly, the design formulas to predict the out-of-plane elastoplastic stability strength of space truss arches subjected to the end bending moment and radial uniform load are presented through introducing a normalized slenderness ratio. By assuming that all components of space truss circular arches bear only axial force, the design formulas to prevent the local buckling of chord and transverse tubes are deduced. Finally, the bearing capacity design equations of space truss arches are proposed under vertical uniform load.     

Experimental study on local buckling of axially compressed steel stub columns at elevated temperatures

There are few design provisions in codes and standards on local buckling of steel columns under fire conditions. To examine the local stability of steel stub columns at elevated temperatures, 12 stub columns were tested under simultaneous application of load and fire conditions. The test variables included Grade (type) of steel, buckling resistance, temperature and load levels. During fire tests, cross sectional temperatures, axial displacement, buckling deflection, and local buckling failure modes of flange and web of stub columns were recorded at various temperatures. Data from the tests is utilized to evaluate buckling resistance of flange and web both at room and elevated temperatures by applying the ultimate strain method and curve inflexion point method. Results from fire tests are utilized to validate a finite element model developed for tracing local buckling of steel columns at elevated temperatures. Results from fire tests and finite element analysis show that failure mode of columns at room and elevated temperatures follow similar pattern but the load bearing capacity of Q460 steel columns degrade much more rapidly under fire conditions than that of Q235 steel columns. Further, Eurocode 3 provisions for local buckling produce non-conservative results in certain situations.     

Recent research advances on the ECBL approach. Part II: interactive buckling of perforated sections

Perforated cold-formed steel sections are often used in civil engineering as structural members for residential buildings and storage racks construction. In the case of buildings the perforations are provided to permit piping and bridging, while for rack systems they allow for simple connections between members. The load bearing capacity of these sections are influenced not only by the local buckling, global buckling and interaction between these two, but also by the reduction of cross-sectional properties due to perforations. Because of the wide variety in the size and configuration of perforations, it is impossible to provide a practical design procedure to calculate the ultimate strength of such a type of sections. The main objective of this paper is to calibrate an effective design width formula for the perforated sections and, using the ECBL approach, to evaluate an equivalent α imperfection factor for European buckling curves, in order to adapt them for sections with different perforation patterns.     

U形肋加劲板局部稳定性试验研究

U形肋加劲板是构成钢箱梁顶板、底板的主要板件,U形肋腹板与被加劲板局部失稳是其两种主要失稳破坏模式。为研究U形肋加劲板的局部稳定性能,分别设计并制作了U形肋腹板与被加劲板壁板两组局部稳定试件,并考虑U形肋腹板宽厚比、被加劲板宽厚比以及U形肋翼缘与腹板间弯曲半径变化。通过轴压试验得到了U形肋加劲板的局部失稳破坏模式、稳定承载力、应力-位移曲线以及局部稳定折减系数。试验研究表明：随着局部板件宽厚比的增大,试件由强度破坏转变为失稳破坏,且失稳破坏特征表现得越明显。当板件宽厚比不小于22.5时,宽厚比较大的板件先于其他板件失稳。U形肋腹板与翼缘之间弯曲半径增大时,U形肋腹板宽度及宽厚比变大,导致U形肋腹板稳定承载力降低。将试验结果与公路钢桥规范中的稳定系数曲线对比发现,对于钢桥规范中的稳定曲线,采用钢材屈服强度计算得到的板件稳定承载力明显小于试验值,而采用抗拉强度计算得到的板件稳定承载力接近试验值,说明采用钢桥规范计算U形肋加劲板稳定承载力,其安全系数和钢材的抗拉强度与屈服强度比值相当。     

In-plane stability and shear deformation analysis of the H-beam hollow arch

H-shaped circular arc is a relatively novel type of open-web steel arch, and currently, no reports have been published concerning its in-plane stability. In this paper, the elastic and elastic–plastic in-plane stability of the H-shaped hollow circular arch is studied by theoretical deduction combined with numerical simulation. First, the overall shear rigidity of the H-shaped circular arch is calculated, and the elastic buckling load formula of the arch is proposed and verified considering double shear deformation under full-span radial and uniform loading. The overall elastic buckling load deduced in this paper is reasonable according to the finite element analysis. The results indicate that the influence of shear deformation on the overall elastic buckling load of the arch decreases with the increase of the span length. The arch-bearing capacity is the largest when the rise-span ratio is 0.25. Second, the restriction conditions necessary for avoiding local buckling of the chordal web before integral buckling of the H-shaped steel hollow circular arch are analyzed. Finally, the elastic–plastic failure mechanism of the H-shaped arch under full-span radial and uniform loading is examined, and the formula for determining the ultimate bearing capacity that is achievable before failure under full-span radial and uniform loading is proposed. ANSYS analysis shows that under the radial uniform loading, the chordal bars will yield near 1/4L and 3/4L, and ultimately, the structural failure of the lower chord occurs in the vicinity of 1/4L. The formulas presented in this paper agree well with the results obtained from the finite element analysis and can be used as a reference for engineering applications.     

Design rules for web crippling of CFRP strengthened aluminium rectangular hollow sections

Web crippling failure (web buckling and web yielding) is critical for thin-walled members when subjected to concentrated load. Carbon fibre reinforced polymer (CFRP) is attracting increasing research interest as a strengthening material for metallic structural members. Improved web crippling capacity of aluminium rectangular hollow sections has been achieved with CFRP being attached to the exterior and/or interior of the webs from a series of tests conducted by the authors. This paper focuses on developing design rules for predicting the nominal crippling strength of CFRP strengthened sharp-corner aluminium tubular sections: rectangular hollow section (RHS) and square hollow section (SHS), under end bearing load. The existing design rules for bare sections without CFRP strengthening are firstly reviewed and assessed, including design rules for both cold-formed steel structural members (Australian/New Zealand standard (AS 4100-1998) and North American Specification) and aluminium structures (Australian/New Zealand standard (AS 1664-1997) and American aluminium design manual). They are modified to take account of the improved capacity due to CFRP strengthening. The proposed design rules are calibrated against test results.     

蜂窝梁滞回性能研究

为了研究地震作用下蜂窝梁滞回性能、局部稳定性以及局部屈曲对蜂窝梁滞回性能的影响规律,采用试验研究与理论分析相结合的方法对蜂窝梁滞回性能进行研究。设计4根不同腹板高厚比的正六边形孔蜂窝简支梁试件,在简支梁中央施加低周往复荷载进行拟静力试验。通过试验得到不同腹板高厚比正六边形孔蜂窝梁的滞回曲线、骨架曲线、刚度退化曲线,计算相应的延性系数及耗能系数,分析其破坏过程和破坏形态,研究蜂窝梁的滞回性能和破坏机理。结果表明:腹板高厚比较大的正六边形蜂窝梁主要破坏方式为孔间腹板局部屈曲,屈曲会导致试件变形急剧增加,滞回性能迅速变差,造成试件承载力下降而破坏;腹板高厚比越大,腹板越容易发生局部屈曲变形,因此,在实际工程中蜂窝梁应该严格限制腹板高厚比。     

腹板开洞钢拱的平面内稳定极限承载力设计理论及方法

腹板开洞钢拱组合了拱和开洞构件的特性,目前在轻轨列车站篷及航站楼等的钢结构中有广泛应用。本文首先用有限壳单元分析了以工形截面腹板开洞圆弧钢拱为代表的拱的平面内弹性屈曲性能,考察了腹板孔洞的几何参数和拱本身的几何参数对屈曲荷载的影响;按照整体屈曲荷载的等效原则,把腹板开洞拱等效为由两个T形截面和缀板组成的格构式构件,并给出了格构式构件的等效截面尺寸。然后研究了各参数下的腹板开洞钢拱的弹塑性屈曲性能,定量考察了孔洞对稳定极限承载力的削弱作用,提出了腹板开洞钢拱特有的单边塑性铰的破坏机理。利用已经建立的拱的稳定系数与拱的正则化长细比的关系,根据等效构件的换算长细比,提出了受静水压力及其它荷载分布形式的腹板开洞拱的平面内稳定极限承载力设计方法。