Ermüdungsprobleme dünnwandiger kaltgeformter Bauteile

Fatigue behaviour of thin‐walled coldformed steel profiles. Current design concepts for thin‐walled structural members take local buckling into account in determining the ultimate capacity. Local buckling may be accompanied by large deformations, which entail secondary bending stresses. Such secondary stresses can be neglected in usual design, but there are no information available regarding their influence on fatigue design. For the investigation of that problem fatigue tests were carried out with thin‐walled cold‐formed U‐channels exposed to pure bending. Following the systematically numerical investigations it will be proposed to limit the cyclic load by 60% of the ultimate load in order to avoid fatigue damage of thin‐walled cold‐formed profiles.     

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.     

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.     

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.     

Dünnwandige,mikrobewehrte Betonbauteile unter Querkraftbeanspruchung

Shear strength of thin‐walled, micro‐reinforced concrete members Within the second funding period of the DFG Priority Programme 1542 ”Concrete Light“ investigations on the load‐bearing behavior of ”Ultra‐lightweight, Thin‐walled Tubular Concrete Members“ are carried out at the IBMB, division of concrete construction of the TU Braunschweig. Due to the currently insufficient amount of investigations dealing with the shear strength of micro‐reinforced concrete (ferrocement) members, fundamental studies had to be performed. These include experimental and theoretical investigations on the shear strength of profiled, thin‐walled concrete beams with micro‐reinforced webs. The performed tests showed the improved cracking behavior and failure notice of micro‐reinforced specimens, when compared to conventionally reinforced specimens. Furthermore, the conservative and thus secure estimation of the shear strength of micro‐reinforced beams using the design approaches provided by EC2+NA or ACI 318 is proven.     

Formänderungsgrößenverfahren mittig gedrückter dünnwandiger Stäbe mit einfach‐ und doppeltsymmetrischen offenen Querschnitten

Deformation method for centrically compressed thin‐walled bars with mono‐ and bisymmetrical open cross‐sections. In correspondence with the classic deformation method of warping torsion for thin‐walled bars [1], that method has been moved into the field of column stability. For the single cross‐sectional symmetry, the general solution of the fundamental system of equations has been found and its particular shapes for three basic kinds of column support presented. Thereby, the formulas or the boundary simplified for analysis of the bimoments have been settled. These relations have been simplified for the double cross‐sectional symmetry. An analysis of a bisymmetrical cross‐section has lead to the determination of the necessary boundary forces for the three kinds of column support considered. It has been shown that all the relations for torsion are similar to those for bending. A proposal for the calculations of the critical loads of torsional buckling in continuous columns has been formulated and a relevant numerical example given. The paper calls special attention to the related merits of Professor Kurt Klöppel , a graduate of the former Technischen Hochschule Danzig. Actually, already 100 years have passed since the foundation of TH Danzig. It is also the predecessor of the contemporary Politechnika Gdańska, with which the author is being connected since 1949.     

Parabolschalen aus Hochleistungsbeton als Solarkollektoren

Parabolic shells made from high‐performance concrete for solar collectors Parabolic troughs for concentrating solar power plants are mainly built as spatial steel frameworks which support curved mirror elements pointwise. Today, significant cost savings can merely be expected from cheaper construction material as shown by a first prototype made from concrete [1]. Alternative concepts inspired by commercially established collector modules with an aperture width of about 6 m as well as large scale collector modules with an aperture width of up to 10 m have been developed within the priority program SPP 1542 „Concrete light” funded by the German Research Foundation (DFG) in cooperation of the Technical University of Kaiserslautern and the Ruhr‐University Bochum. These concepts also differ with respect to support conditions and cross‐sectional shapes. They include single‐walled solid shells with additional bracings according to the flux of forces or employ void formers and associated effective values for bending and axial stiffness. Of course, both fulfill the strict requirements set on lightweight and material efficient structures. Most relevant actions on the parabolic shells result from self‐weight, wind loads and torsional moments due to the driving system, which are considered locally and globally to capture their influence on the shell's design.     

Verbesserte Tragfähigkeit von dünnwandigen Tragwerken durch Hybridbauweise und Flächenstrukturierung

Improved load‐carrying capacity of thin‐walled structures via hybrid and non‐smooth wall constructions. This contribution deals with modified wall constructions of thin‐walled structures which aim to improve their load‐carrying capacity and imperfection‐sensitivity without a corresponding increase in total weight.     

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.     

Thin‐walled steel trussed rafters

The Danish Building Research Institute has helped to develop a trussed rafter from thin‐walled steel members with bolted joints, with particular application to the construction of simpler and cheaper glasshouses for commercial horticulture. The project concentrated on a rafter with a 20‐metre span able to carry installation loads, but extended also to the design of thin‐walled columns, purlins and rails. A patented joint enables a single bolt to connect two web members and the top or bottom chord.     

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.     

On the behavior of thin walled composite beams with stochastic properties under matrix cracking damage

Thin walled composite beam structures are prone to damage which results in change in the performance of these structures. The change in the performance due to damage may get confused with the variation in the performance due uncertainties in the properties of these structures. Here, the performances of the thin walled composite beam under matrix cracking damage having material uncertainties are studied. The cross-sectional stiffness properties are obtained using thin walled beam formulation, which is based on a mixed force and displacement method. The stochastic behaviors of material properties are obtained from previous experimental and analytical studies. The effects of matrix cracking are introduced through the changes in the extension, extension–bending and bending matrices of composites. The effects of matrix cracking on out-of-plane bending, inplane bending and torsion cross-sectional properties are studied at different crack densities for stochastic material properties. Further, the effects of matrix cracking and uncertainties on measurable properties such as deflections and frequencies are studied. Results show that the beam responses at different crack densities get mixed due to the material uncertainties. The estimates of variance obtained for observable system properties due to uncertainty can be used for developing more robust damage detection algorithms.     

A global approach for three‐dimensional analysis of tall buildings

In the literature, several approximate approaches have been proposed to analyse the lateral loading distribution of external loads in high‐rise buildings; in this paper, a general method is proposed for the analysis of the lateral loading distribution of three‐dimensional structures composed of any kind of bracings (frames, framed walls, shear walls, closed and/or open thin‐walled cores and tubes) under the customary assumption of floor slabs being undeformable in their planes. This general formulation allows analyses of high‐rise structures by taking into account the torsional rigidity of the elements composing the building without gross simplifications, even in the case of very complex shapes and with the contemporary presence of different kinds of bracing. The method is aimed at gaining an insight into the force flow in the structure, in order to understand how the building response is governed by decisive structural parameters and to compare preliminary calculations with other approaches such as the structural finite element analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

任意形状薄壁钢截面双轴压弯恢复力分析

为适应高耸结构非线性分析的需要，将任意形状薄壁钢截面划分成适当数目的薄壁直边，通过建立薄壁边截面的面内弯矩及轴力与相应变形之间的广义本构关系合成整个截面的双轴压弯恢复力模型。     

Mindestbewehrungskonzept für dickwandige Querschnitte

Minimal reinforcement concept for thick‐walled cross‐sections. The objectives of this contribution is the evaluation of thick walled torrential barriers, regarding the reinforcement. For the evaluation several cross sections are verified. The minimal reinforcement according ÖNORM B 4700 [1] or Eurocode 2 [3] just depends on the geometry. The limits of these simplified rule types are shown. Especially for thick‐walled construction elements a proposal of enhancement is generated. The detailed study relies on numerical studies of the fracture behaviour.     

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。     

Eine Finite‐Elemente‐Lösung auf der Basis eines erweiterten eindimensionalen Querschnittselementes für die freie Torsion dünnwandiger prismatischer Stäbe

A finite element solution on the basis of an extended one‐dimensional cross‐section‐element for the Saint‐Venant torsion of thin‐walled prismatic beams. It is presented a finite element solution on basis of an extended one‐dimensional cross‐section‐element to the calculation of the warping function, the torsional properties and the shear stresses, dependent on it, for thin‐walled prismatic beams under Saint‐Venant torsion. The formulated finite two‐node‐element with six element degrees of freedom can capture through inclusion of the torsion around the element axis the linear term of the variance of warping function perpendicular to the element axis. Only the shear stresses of the ring shear flows in the closed section parts unchangeable over the wall thickness can be calculated with the simple two‐node‐element with two element degrees of freedom. The extended two‐node‐element supplies in addition also the shear stresses of the cut open cross‐section linearly changeable over the wall thickness.     

Ermittlung von Eigenwerten und Eigenformen für Stäbe und Stabwerke

Determination of eigenvalues and modal shapes for members and frames. For the calculation of stability‐endangered members and frames the determination of eigenvalues and modal shapes has central meaning. Because from the literature numerous, partly strong different analyses are known, the question will be clarified, which procedure will be best suitable due to the specific problem definition. The paper deals with two solutions in detail, with a modified vector iteration method and a particularly adapted matrix decomposition method. Beyond that the determination of eigenvalues and modal shapes by EDV‐programs and the evaluation of their results are explained.     

Collapse analysis of real RC spatial structures using known failure schemes of ferro‐cement shell models

Large‐span reinforced concrete (RC) shells collapses that occurred in the last decade caused many death toll as well as significant losses to national economies. The most famous cases were the collapse of the aqua park cover in Moscow on February 2004 and the 2E terminal roof destruction at Charles de Gaulle Airport near Paris on May 2004. Following the publications of the appropriate commissions that have studied the reasons of these events, the influence of concrete creep and changes in the shell geometry on buckling of RC thin‐walled shells was not properly considered in the design. This study is focused on buckling of such shells, taking into account geometrical and physical nonlinear behaviour of compressed concrete. Other important reasons of concrete shells collapse are also analysed. The study is based on available experimental and theoretical investigations of ferro‐cement shells' models previously performed by the first author. The results of these investigations, obtained for small‐scale ferro‐cement models of thin‐walled shallow RC shells, are discussed. Behaviour of the tested models is compared with that of the above‐mentioned real shells and similar structures, which also collapsed. The critical buckling loads for the shells are obtained. It is shown that these loads are lower than the actual ones; thus, the shells buckling was unavoidable. To prevent brittle shell failure, they should be designed using other dominant failure modes that appear before the buckling. Possible failure schemes of real RC shells can be predicted using dominant failure modes obtained by laboratory testing of scaled models. Copyright © 2012 John Wiley & Sons, Ltd.     

Vibration characteristics of tall buildings braced by shear walls and thin‐walled open‐section structures

An analytical method is presented for the three‐dimensional frequency analysis of buildings braced by shear walls and thin‐walled open‐section structures. Owing to the asymmetry of the structure, the centre of gravity and the centre of flexural rigidity of the floor plan do not coincide, and hence the flexural vibration in two mutually perpendicular directions and the warping torsional vibrations are all coupled. Based on the continuum approach and D'Alembert's principle, the governing differential equation of free vibration and its corresponding eigenvalue problem for asymmetric shear walls and thin‐walled open‐section structures are derived. Based on the theory of differential equations, an analytical method of solution is proposed to solve the eigenvalue problem and a general solution is derived for determining the natural frequencies of the structures. Results obtained from the proposed method for the example structure show good agreement with those of finite element analysis. It is also shown that the proposed analysis is efficient and accurate enough to be used both at the concept design stage and for final analysis. Copyright © 2007 John Wiley & Sons, Ltd.