【作者】 姚永红；

【导师】 武振宇；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2012， 博士

【摘要】 冷弯薄壁型钢与热轧型钢相比，具有许多优越之处，正日益广泛地应用于轻钢货架、低层住宅以及工业厂房等建筑结构之中。目前，大部分国家冷弯薄壁型钢设计规范中，都采用的是有效截面法设计构件的承载力，该方法在计算复杂截面的有效宽度时将变得异常繁琐，并且未考虑畸变屈曲的不利影响。为解决这些问题，Schafer和Pek z提出了直接强度设计方法。近年来，在冷弯薄壁型钢卷边槽形截面柱中，为提高构件局部屈曲承载力，常在腹板上设置加劲肋。此时，畸变屈曲会成为此类构件的屈曲失效模式之一。为方便水管、电线以及暖气管道在墙体中通过，常在冷弯薄壁型钢卷边槽形截面腹板中预先开设孔洞。孔洞的出现会对构件的屈曲失效模式和极限承载力产生影响。开孔试件的屈曲模式、弹性屈曲应力以及极限承载力与未开孔柱试件相比存在诸多不同之处。关于此种开孔柱构件的研究，目前大部分都是针对腹板未加劲卷边槽形截面柱。为了解开孔腹板加劲冷弯薄壁卷边槽钢柱试件的稳定性能，有必要对该类型构件开展试验和理论研究。本文通过试验、有限元、有限条以及理论分析的方法，对Q345材质开孔与未开孔腹板V形加劲冷弯薄壁卷边槽钢柱的稳定性能开展了研究工作。对两种截面形式、共计20个开孔与未开孔腹板V形加劲冷弯薄壁卷边槽钢短柱和中长柱进行了试验研究。对试件初始几何缺陷、截面尺寸以及钢材材料属性进行了详细的测量。试验中所有柱试件发生了畸变屈曲失效。在荷载下降段，中长柱除发生畸变变形外，还可以观察到绕弱轴的弯曲。孔洞不仅能改变构件的屈曲模式，还会使中长柱试件的畸变屈曲半波数发生变化。腹板上开有孔洞，加速了畸变屈曲变形的发展，导致极限荷载下降以及翼缘端部侧向变形增大。在试验过程中发现，柱试件畸变初始缺陷越大，对应的极限承载力越小，而畸变屈曲侧向变形越大。另外，对所有试验试件进行了有限元模拟，有限元分析结果与试验值吻合较好。在试验验证基础上，对Q345材质开孔与未开孔腹板V形加劲冷弯薄壁卷边槽钢柱进行了大规模有限元参数分析。通过变化柱长、加劲肋高度、腹板宽度、翼缘宽度、卷边宽度、孔洞间距以及边界条件等相关参数，研究了此类构件的稳定性能，并对比研究了相关参数变化时柱试件的极限承载力和屈曲失效模式。有限元参数分析结果是对试验数据的有效补充，为后续设计公式的建立提供了理论依据。弹性屈曲应力计算是冷弯薄壁型钢构件直接强度法应用的关键环节。按翼缘模型计算构件弹性畸变屈曲应力时需要确定腹板对翼缘的转动约束刚度。现有转动约束刚度计算公式较复杂，求解过程需要进行一次迭代。为了简化计算过程，本文提出了冷弯薄壁型钢卷边槽形截面柱翼缘转动约束刚度简化计算公式。该公式是在Lau和Hancock公式的基础上，结合我国《冷弯薄壁型钢结构技术规范》（GB50018—2002）中关于腹板和翼缘局部屈曲系数的规定而导出的，并根据Lau和Hancock公式计算结果对其进行了修正。与有限条分析值对比表明：该公式可以准确、方便地计算转动约束刚度，能够应用于冷弯薄壁型钢卷边槽形截面柱的设计计算。孔洞对开孔冷弯薄壁卷边槽钢柱试件弹性畸变屈曲应力的影响，可以通过折减全截面厚度予以考虑。本文提出的弹性局部屈曲应力和弹性畸变屈曲应力理论计算公式都与有限条或有限元分析值吻合较好。本文给出了基于直接强度法设计理念的轴压开孔与未开孔腹板V形加劲冷弯薄壁卷边槽钢柱畸变屈曲承载力设计公式，其计算值与试验结果和有限元参数分析值吻合较好。所得设计方法可以为今后设计规范的修订提供参考。有限元参数分析时，部分试件发生畸变与局部相关屈曲。本文经分析后指出，除以前学者们提出的弹性畸变屈曲应力与局部屈曲应力之比外，柱长也是影响畸变与局部相关屈曲发生的重要因素。在有限元分析结果的基础上，提出了该类型屈曲失效模式的建议设计方法，其计算值安全可靠。更多还原

【Abstract】 Cold-formed thin-walled steel is used increasingly in a wide range oflight-weight construction including steel storage rack columns, low-rise, andindustrial factory building due to its many advantages compared with hot-rolledsteel. At present, the effective section method is adopted to predict the memberbearing capacity for the design specification of cold-formed thin-walled steel inmost countries. The computation of the effective width of complex section is moredifficult and meanwhile it does not take account of the disadvantage influence of thedistortional buckling. To overcome this problem, the direct strength method wasdeveloped by Schafer and Pek z. In recent years, the cold-formed thin-walled steellipped channel section columns with an intermediate stiffener in the web are widelyused in civil engineering which can increase the local buckling bearing capacity ofthe member. In this case, the distortional buckling may be one of failure modes todecide the member capacity.In order to accommodate plumbing, electrical, and heating conduits in the walls,the holes are pre-punched in the web of lipped channel section and can alter thebuckling mode and ultimate bearing capacity of the members. The buckling modesand critical elastic buckling stress as well as ultimate bearing capacity of thespecimens with perforations are significantly different from the members withoutperforations. The majority of existing test data on cold-formed thin-walled steelcolumns with holes generally focus on the simple lipped channel sections withoutintermediate stiffener in the web. Thus, it is important to do some experiments andtheoretical investigation in order to know the stability behavior of lipped channelsection columns with holes in the stiffened web.In this dissertation, the stability behavior of cold-formed thin-walled steellipped channel section columns with and without holes in V-shaped stiffened web,which were made of Q345steel, was analyzed by experiments, finite elementmethod, finite strip method, and theoretical method.A total of20cold-formed thin-walled steel lipped channel short andintermediate length columns with and without holes in V-shaped stiffened webincluding two different cross-sections were tested. Detailed measurements of initialgeometric imperfections, cross-section dimensions, and material properties wereconducted. All of the specimens failed in distortional buckling. At post-ultimaterange, a noticeable interaction between distortional and flexural buckling bendingabout the weak axial was observed for intermediate length columns. The openings in the web result in the change of buckling modes of the members and also change thenumbers of distortional buckling half-wave of intermediate length columns.Experimentally, slotted web holes accelerated the development of distortionalbuckling deformation, which resulted in the decrease of ultimate load and increaseof lateral displacement of the flange tips. Moreover, it is found that the lagerdistortional initial imperfections of the columns would lead to the lower bearingcapacities and greater lateral deformations induced by the distortional buckling. Inaddition, all of the tested specimens are simulated by means of the finite elementmethod, and the results of the finite element accord well with that of theexperiments.On the basis of experiment verification, a comprehensive of finite elementparametric analysis were performed for Q345material cold-formed thin-walled steellipped channel columns with and without holes in V-shaped stiffened web. Thestability behavior of these specimens was studied by changing the column length,stiffener height, web width, flange width, lip width, holes distance, and boundaryconditions. The ultimate bearing capacities and failure modes were compared bychanging the above parameters. The result of finite element parametric analysis is asupplement to the experiment data that can provide a theoretical base forestablishing the design formulae.The calculation of elastic buckling stress of cold-formed thin-walled member isa key problem using direct strength method. When the elastic distortional bucklingstress of the members was calculated with flange model, it was necessary todetermine the rotational restraint provided by the web to the flange. However, thecurrent calculation formula for the rotational restraint was complicated, and oneiteration was required in the solution process. In order to simplify the calculationprocess, a simplified calculation method for the rotational restraint of cold-formedthin-walled steel lipped channel section column was proposed. Based on Lau andHancock’s formula, the proposed method was derived in combination with theregulations concerning the local buckling coefficients of the web and flange in the―Technical code of cold-formed thin-wall steel structures (GB50018-2002)‖, and itwas then modified according to the results obtained by Lau and Hancock’s formula.Compared with finite strip analytical values, it is shown that the simplified methodcan calculate the rotational restraint accurately and conveniently, and can be usedfor the calculation of cold-formed thin-walled steel lipped channel section columns.The holes influence on elastic distortional buckling stress of cold-formedthin-walled steel lipped channel columns could be approximated by modifying thewhole cross-section thickness. In this paper, closed-form prediction of elastic local buckling stress and elastic distortional buckling stress were provided and shown toagree well with finite strip method or finite element method.A suggested direct strength method to estimate distortional buckling bearingcapacity for axially compressed cold-formed thin-walled steel lipped channelcolumns with and without holes in V-shaped stiffened web had been presented, andthe values calculated by the proposed method were in good agreement with theresults of experimental and parameter analysis. The design method is very useful forcode revision in the future.In finite element parametric analysis, it was found distortional and localinteractive buckling may occur in some specimens. Previous scholars proposed thatthe ratio of elastic distortional buckling stress to local buckling stress effecteddistortional and local interactive buckling. This paper pointed out that the length ofspecimens was another important factor. Based on the finite element analysis data,the design method to consider the distortional and local interactive buckling forcold-formed thin-walled steel lipped channel columns with and without holes inV-shaped stiffened web was proposed. It is shown that the data acquired bycalculation formulae is safe and reliable.更多还原