Class 4 stainless steel I beams subjected to fire

Structural elements composed of Class 4 sections are common in stainless steel buildings structures. These thin walled profiles are more susceptible to the occurrence of local buckling. Additionally, in beams the lateral-torsional buckling is also a common failure mode. These instability phenomena are intensified at high temperatures. This work has the main objective of presenting a numerical study on the fire behavior of beams with Class 4 stainless steel sections when subjected to pure bending and high temperatures. The influence of several parameters, as geometrical imperfections and residual stresses, on the ultimate load will be evaluated and comparisons between the numerical results and the Eurocode 3 rules will also be made.     

Der Einfluss von Imperfektionen in dünnwandigen geschweißten Rechteckquerschnitten unter Druckbeanspruchung

On imperfections in thin‐walled welded rectangular hollow section compressive members. This contribution presents the results of a research project analysing some aspects of stability failure of thin‐walled RHS compression members that are likely to exhibit combined global and local buckling. In particular the influence of various imperfections, namely residual stresses due to weld‐ing and local as well as global geometrical defects, on the load‐carrying capacity is subject to detailed experimental and numerical investigations. The insight into the structural behaviour leads to recommendations for standardized imperfections that should be used in the context of the numerical modelling of class‐4 square and rectangular hollow section members subjected to compression.     

Interactive instabilities of thin‐walled laminated composite pultrusion box columns

The problem of interactive buckling and post‐buckling of intermediate length thin‐walled columns built of laminated plate elements subjected to compressive load has been proposed and solved analytically. Pultrusion columns have wide‐range applications in high‐rise building due to their low weight and high load carrying capacity. Classic stability theory and laminate theory were implemented to prove the existence of mixed‐mode buckling in thin‐walled pultrusion columns. Interactive stability modes can result in lower loading capacity of most compressive members and affects their post‐buckling behaviour in major proportions. Interactive buckling load analysis has been performed by means of a simplified theoretical model and verified by means of numerical analysis. The calculations were carried out for commonly used square section thin‐walled composite columns dimensions. The post‐buckling performance of selected sections has been investigated and an optimum layup configuration criterion for each section has been extracted according to pre‐ and post‐critical behaviour. Copyright © 2010 John Wiley & Sons, Ltd.     

Geometrische Ersatzimperfektionen für Tragfähigkeitsnachweise zum Biegeknicken von Druckstäben

Member imperfections for verifications against lateral buckling of compression members. The main focus of the article is on investigations about the lateral buckling of compression members made of hot‐rolled I‐profiles. First of all the general load‐carrying behaviour is clarified. Afterwards necessary member imperfections are determined in case of pure normal force or combined bending stress. The results are compared to the values of the actual design codes. For members with pure compression force and buckling about the strong axis new member imperfections are specified. By these values up to 12% higher ultimate loads as up to now can be utilized.     

Beulbemessung diskret gelagerter dünnwandiger kreiszylindrischer Stahlsilokonstruktionen nach EN 1993‐1‐6

Buckling design of discretely supported thin‐walled steel silo structures according to EN 1993‐1‐6. This paper deals with the exemplary application of alternative buckling design procedures, as introduced by the new European Standard on buckling of steel shells, to a practical thin‐walled steel silo structure. First the general features of these design procedures as well as relevant issues of structural modelling are outlined. Then the outcomes of the different buckling design procedures are compared to each other and critically evaluated.     

夹芯板弯曲屈曲分析的有限条-棱方法

用有限条 -棱方法对冷弯薄壁型钢压型表面泡沫夹芯板进行了弯曲屈曲分析 ,得到了夹芯板受压面层屈曲时的临界应力、屈曲荷载及屈曲半波长 ,并与试验结果进行对比 ,理论值与试验值吻合较好     

十字加劲钢板剪力墙的抗剪极限承载力

我国《高层民用建筑钢结构技术规程》规定了钢板墙剪切弹性屈曲不先于剪切屈服,其明显的不足是没有利用板的屈曲后强度,同时弹性屈曲也不能作为结构在弹塑性阶段的设计指标。本文应用板的大挠度弹塑性有限元方法对十字加劲方形钢板剪力墙的屈曲后性能和极限承载力进行了系统的研究,并在大量数值分析的基础上,提出了以板的平均剪切应变相应的剪应力作为钢板剪力墙承载能力的极限状态,以达到利用薄板屈曲后强度的目的,进而提出了钢板剪力墙承载力的设计简化计算公式及钢板墙侧柱刚度阈值的计算公式,供设计参考。数值计算结果表明,影响钢板墙抗剪性能主要有三个参数:板高厚比、肋板刚度比和边柱刚度。     

受压波纹板组局部相关屈曲特性研究

拱型波纹钢屋盖结构是一种典型的冷弯薄壁结构,其波纹截面板组的宽厚比远远超过有关规范宽厚比限值的上限要求,结构的极限承载能力既取决于其整体稳定承载能力也取决于其局部相关屈曲承载能力。本文根据拱型波纹钢屋盖结构的成型特点和受力特性,建立了波纹槽形截面板组局部相关屈曲分析的有限元模型,对不同宽厚比的受压波纹槽形截面板组的局部相关屈曲特性进行了理论计算,并与同形状同尺寸平板槽形截面板组的屈曲特性进行了比较分析。研究结果表明,如同平板板组一样,波纹板组也可能发生局部相关屈曲,但其板组屈曲半波长要受制于小波纹的几何尺寸,即屈曲半波应位于波形构造的波节点之间或波峰、波谷之间,而平板槽形截面板组的屈曲波长则可以自由调节,这点与平板板组的屈曲特性存在明显的差异。并且波纹的存在对板组屈曲性能有显著提高。理论研究与相应的试验研究符合很好。     

Berechnung von gekrümmten Stäben mit Kreishohlprofil unter Berücksichtigung der Querschnittsverformung

Analysis of tube‐bars with initial curvature including deformation of cross‐section. Curved bars under bending show a nonlinear distribution of stresses with peak at internal side of the section. Bernoulli‐hypothesis is still valid but Naviers bending theory can no more be applied. Additionally the effect of deformation of the thin‐walled tube‐section must be taken into account. This effect is unfavourable for stresses and deformations if the bending moment increases the curvature of the bar. This paper gives formulae for calculation of internal forces, stresses and deformations considering both mentioned effects; examples show the application. Finally the principle of virtual work is formulated and demonstrated at a two‐hinged arch.     

冷弯开口薄壁帽型截面受压钢构件压弯承载力的研究

对冷弯开口薄壁帽型截面受压构件的压弯极限承载力进行了分析研究,主要考虑构件长细比、荷载偏心距和构件初弯曲对压弯极限承载力的影响。利用MATLAB7.0.1和ANSYS10.0计算得到受压构件基于截面边缘纤维屈服准则的临界荷载和弹性弯扭屈曲荷载,进而利用ANSYS10.0对受压构件的弹塑性极限荷载进行了计算。通过对三种不同的计算方法得到的极限荷载进行比较,分析了冷弯开口薄壁帽型截面受压构件压弯极限承载力的计算方法。结论中评价了单轴对称截面压弯构件的设计公式。研究表明,该设计公式具有一定的安全储备,满足设计要求。     

矩形开口对吸收塔结构非线性屈曲特性影响分析

为了分析矩形开口参数对于吸收塔结构稳定性的影响规律,以一实际在建吸收塔结构为研究背景,基于参数化模型的正交试验,采用有限元软件ANSYS对比分析了不同开口参数下吸收塔柱壳结构的非线性屈曲特性。结果表明:开口角度对于结构的影响较其他参数大,开口角度小于90°时,结构的非线性屈曲极限荷载下降趋势较为明显,超过120°后,降幅趋于缓和,壁厚25 mm工况下,90°开口时结构的非线性屈曲极限荷载较0°开口时下降91%,120°开口时较0°开口时下降95.2%;结构的非线性屈曲极限荷载随着矩形开口高度的增加而逐渐减小,但开口位置对于结构稳定性的影响在整个过程中近似呈线性变化。     

Ermittlung der Grenztragfähigkeit von Mehrschraubenverbindungen bei Normalkraft‐Biegemoment‐Interaktion

Determination of the ultimate bearing capacity of multi‐bolt connections with normal force – bending moment – interaction. This paper will present a general design method for single or multi‐bolt connections of beams with arbitrary thin‐walled cross sections, suitable for application in computer programs. The design method is based on the classical strain iteration algorithm for the determination of the stress distribution in cross sections. In this case, the ultimate capacity of bolted connections will be obtained using an iterative numerical determination of the elastic‐plastic stress distribution in the connection elements. The numerical method will be derived in two steps – the first step is the numerical determination of the stress distribution in the connection for a given combination of internal forces and the next step is the determination of the ultimate bearing capacity of the connection. Furthermore, an analytical design method for a multi‐bolt tube connection will be derived. Finally, results of numerical and analytical calculations will be compared with corresponding test results.     

边缘加劲板件有效宽厚比设计方法中的板组效应研究

本文根据能量原理,建立了边缘加劲板件的弹性屈曲理论和卷边槽形截面薄壁构件的板组相关屈曲理论。通过屈曲理论分析,得到了非均匀受压边缘加劲板件的屈曲系数及其反映板组效应的约束系数,并将其引入新修订的《冷弯薄壁型钢结构技术规范》(GB50018)的有效宽厚比设计方法中。本文介绍了50根冷弯薄壁型钢受压构件试验,并按修订后的规范方法进行了试件承载力计算,计算值与试验值比较,偏于安全。将考虑板组效应的有效宽厚比设计方法与国内外现行规范设计方法相比较,具有优越性。     

Untersuchungen zur Längssteifigkeit von Stahlstützen mit kastenförmigem Querschnitt

Experimental tests and theoretical analyses of longitudinal stiffness of closed cross‐sections steel columns. In structures made of thin‐walled elements it is of great importance to establish how the compressed elements change their stiffness while loading increases. Nonuniform change of longitudinal stiffness induces change of force and stress redistribution. More ductile elements take less loading and more stiff, tensed, ones are being overloaded. Columns with closed cross‐sections, box cross‐sections and hollow circular cross‐sections need to be distinguished from steel elements with longitudinal stiffness decreasing while loading increases. Shortening of column working in elastic‐plastic phase comes from material compression, cross‐section walls buckling and increased displacement of column as a whole. Imperfections that depend on fabrication process of cross‐section have a great influence on stiffness variation of an element. It can be designated, among other factors, from the equilibrium paths of tested elements. Those equilibrium paths, up to the limit point, were obtained by applying incremental method of numerical integration of equilibrium equations assuming initial displacements and residual stresses of column's walls and initial displacements of column's axes. Some numerical analyses were calculated using FEA software LUSAS. All theoretical analyses were verified by experimental tests carried out by the authors with full scale elements: box cross‐section columns – length 5280 mm, cold‐formed welded cross‐section columns – length 2000 mm. The research results and analyses by others were also used.     

冷弯薄壁型钢构件的直接强度设计法

受压或受弯的冷弯薄壁卷边槽钢有板件局部屈曲，截面畸变屈曲和整体弯曲屈曲或弯扭屈曲三种模式。本文着重介绍板件的相关屈曲和计算截面畸变屈曲应力的方法并阐述了三种屈曲模式之间的相关关系。指出用传统的有效截面设计法计算受压和受弯冷弯薄壁卷边槽钢承载力的弊端，较详细地说明了用构件全截面计算的直接强度设计法。     

Elephant's foot buckling in pressurised cylindrical shells

Metal cylindrical bins, silos and tanks are thin shell structures subject to internal pressure from stored materials together with axial compression from the frictional drag of stored materials on the walls and horizontal loads. The governing failure mode is frequently buckling under axial compression. The internal pressure exerted by the stored fluids or solids can significantly enhance the buckling strength, but high internal pressures lead to severe local bending near the base. Local yielding then precipitates an early elastic‐plastic buckling failure. This failure mode, commonly known as “elephant's foot buckling”, has received relatively little attention to date and until recently was often ignored in tank and silo design. This problem is an unusual buckling condition, because it involves very high tensile stresses in one direction, coupled with rather small compressive stresses in the orthogonal direction. Thus, although it is a buckling failure involving considerable plasticity, it occurs at low buckling stresses and under conditions that appear to be classically “slender”. The normal concatenation of “slender” with “elastic” in buckling formulations does not apply at all here. This paper describes alternative approaches to the formulation of design rules for the elastic‐plastic instability and collapse of axially‐loaded internally‐pressurised thin cylindrical shells adjacent to the base support. The differences between the different approaches arise from different conceptual models for the manner in which an elastic‐plastic slender structure instability should be treated.     

薄壁钢梁中的横向正应力及其对强度和稳定性的影响

对工字形钢梁在横向分布和集中荷载作用下 ,各板件内的横向正应力进行了分析和比较 ,指出了在支座截面和跨中集中荷载作用截面 ,有时必须考虑这个横向正应力的影响。还对横向正应力对钢梁整体稳定性的影响采用板件稳定理论的方法进行了研究 ,并发现它对单轴对称截面的钢梁 ,在横向荷载作用下的稳定性有很大的影响。提出的钢梁稳定理论的新的表述 ,证实了传统的稳定理论 ,并且与采用ANSYS板壳单元进行的稳定性分析结果一致     

Evaluation of the compression strength of profiled metal sheet faces of sandwich panels

An important design criterion of metal sheet faced lightweight sandwich panels is the compression strength of the face layer. Failure mode of a thin profiled face is characterized by local buckling of the flanges and the web of the profile, by column-type buckling of the entire profile and by yielding of the most stressed flange. Calculation models based on analytical studies have been developed to determine the critical buckling stresses. The evaluation of the compressive resistance at the ultimate limit state is a more difficult task. The paper studies the applicability of the design expressions given in Eurocode 3 to the evaluation of compressive resistance of face profiles.     

Von der Bauteilfügung zu leichten Tragwerken: Trocken gefügte Flächenelemente aus UHPFRC

Light‐Weight Structures made of thin walled, dry jointed surface elements made of UHPFRC With the development of novel jointed, thin walled and thus light components the resource‐efficient use of ultra‐high performance fiber‐reinforced fine grained concrete in structures can be realized. The manufacturing of modular and efficient UHPFRC components is achieved by the digital workflow as a result of digital design, calculation and CNC‐controlled manufacturing technology. By linking lightweight concrete components with new, high‐precision non standardized joints, such components can be connected material and force flow compatible with each other. The results with dry jointed T‐beams show the manufacturability and the potential of the dry jointing system on a large scale. When checking the load capacity of thin‐walled construction elements, the influence of fiber reinforcement must be especially considered.     

Remarks to the Direct Strength Method

The effects of local plate buckling on the load carrying capacity of thin walled members are usually accounted for by the established method of effective widths. As a consequence, the current design concepts of such members are often complicated. Part of these complications arise from the need to determine effective properties of members. Therefore Schafer and Peköz developed the Direct Strength Method as an alternative to current practice. A strength curve for the entire member is used similarly to the strength curve for the effective width of an element.The Direct Strength Method is here compared to the approaches of effective width, reduced stress and effective thickness. A more profound understanding of the method's conception can be gained on this basis. As a result, the Direct Strength Method assumes the plastic reserve of the section shape to influence the cross-section capacity of locally buckled members. This assumption is checked by our own tests on thin-walled I-sections. A proposal to extend the Direct Strength Method to the interaction between axial force and bending is presented in a second step. Here, the limitations of the method will become clear. Particularly, the Direct Strength Method may lead to an overestimation of the ultimate load, if a shift of the effective centroid causes an additional bending moment. For the time being, the Direct Strength Method can therefore not be a general design concept and further investigations are necessary.