Starr verankerte dünnwandige windbelastete Kreiszylinderschalen mit Dachscheibe

Anchoring forces of cirular cylindrical shells. The wind force distribution according to the new german standard DIN 1055‐4:2005‐03 “Action on structures – Wind loads” is shown and transferred into Fourier series for various values of the Reynolds constant. The values are given in tables. Using a computer program developed by the author anchoring forces of closed circular cylindrical shells are calculated, based on the shell theory, for various non‐dimensional geometries and for rigid anchors. The results of these calculations are presented in tables for easy use by designers. An example shows the influence of elastic anchors.     

Stability of circular cylindrical steel shells under combined loading

Circular cylindrical shells made of steel are used in a large variety of civil engineering structures, e.g. in off-shore platforms, chimneys, silos, tanks, pipelines, bridge arches or wind turbine towers. They are often subjected to combined loading inducing membrane compressive and/or shear stress states which endanger the local structural stability (shell buckling). A comprehensive experimental and numerical investigation of cylindrical shells under combined loading has been performed which yielded a deeper insight into the real buckling behaviour under combined loading . Beyond that, it provided rules how to simulate numerically the realistic buckling behaviour by means of substitute geometric imperfections. A comparison with existing design codes for interactive shell buckling reveals significant shortcomings. A proposal for improved design rules is put forward.     

Stählerne Kamine mit abgestufter Wanddicke – Tragverhalten und Bemessung

Steel chimneys with stepwise changing wall thickness – structural behaviour and design. Firstly, the results of analyses of the load bearing behaviour of slender wind loaded cylindrical shells with stepwise changing wall thickness are presented. Special attention is turned on the differences of the stress resultants from the beam theory at the one hand and from the one segment shell with constant wall thickness on the other hand. From it, conclusions for design are drawn. The several possibilities of numerical buckling strength verification given in the Eurocode still contain partly substantial problems, which limit their application. Therefore, proposals on the approximation of the internal forces of two segment shells are presented, which make possible the buckling strength verification by stress design in a safe manner.     

Buckling of cylindrical shells with stepwise variable wall thickness under uniform external pressure

Cylindrical shells of stepwise variable wall thickness are widely used for cylindrical containment structures, such as vertical-axis tanks and silos. The thickness is changed because the stress resultants are much larger at lower levels. The increase of internal pressure and axial compression in the shell is addressed by increasing the wall thickness. Each shell is built up from a number of individual strakes of constant thickness. The thickness of the wall increases progressively from top to bottom.Whilst the buckling behaviour of a uniform thickness cylinder under external pressure is well defined, that of a stepped wall cylinder is difficult to determine. In the European standard EN 1993-1-6 (2007) and Recommendations ECCS EDR5 (2008), stepped wall cylinders under circumferential compression are transformed, first into a three-stage cylinder and thence into an equivalent uniform thickness cylinder. This two-stage process leads to a complicated calculation that depends on a chart that requires interpolation and is not easy to use, where the mechanics is somewhat hidden, which cannot be programmed into a spreadsheet leading to difficulties in the practical design of silos and tanks.This paper introduces a new “weighted smeared wall method”, which is proposed as a simpler method to deal with stepped-wall cylinders of short or medium length with any thickness variation. Buckling predictions are made for a wide range of geometries of silos and tanks (unanchored and anchored) using the new hand calculation method and compared both with accurate predictions from finite element calculations using ABAQUS and with the current Eurocode rules. The comparison shows that the weighted smeared wall method provides a close approximation to the external buckling strength of stepped wall cylinders for a wide range of short and medium-length shells, is easily programmed into a spreadsheet and is informative to the designer.     

Shell structures: the new European standard and current research needs

Shell structures are widely used in a great variety of applications from space rockets to domestic food and drink containers. Civil engineers are principally concerned with steel shell structures such as silos, tanks, pipelines, chimneys, towers and masts, though other examples may be found in offshore structures and stadium roofs.This paper describes the treatment of terrestrial shell structures in Eurocode 3: Steel structures. It outlines the principles which are guiding the development of the standard, the range of applications covered, and some details of the current proposals. The axially compressed cylindrical shell is then chosen as an example illustrating the range of real problems which need to be addressed, and the paucity of current data on many aspects of these problems. This example is also used to outline the complexity involved even in this one area, recent progress and current needs.     

Modelluntersuchungen zur Windeinwirkung auf stählerne Doppelmantelbehälter

The model tests of wind action on the steel double‐shell tanks. The paper shows the results of the wind tunnel tests on the double shell cylindrical vertical tank models with fixed and floating roofs. During tests the pressure distribution onto both shells and onto the roofs was measured. The influence of the following parameters on the wind load value and distribution was analysed: – Distance between tank shells (3 distances) – Type of roof (floating or fixed) – Position of floating roof (4 positions). The measurement results have been presented as graphs of the pressure coefficients (C_p).     

一种竖向无约束悬挂点在悬挂式钢内筒烟囱上的应用

目前,悬挂式钢内筒烟囱的悬挂点都采用焊接的方式,钢内筒在外筒的横向位移作用下会产生一个倾斜角度,从而对承重平台钢梁产生下压力和上拔力,其在悬挂钢梁的截面设计中起控制作用。传统的计算方法并没有考虑这一对力对悬挂钢梁的不利影响,而只考虑内筒的自重作用。以莱州某百万机组工程为例,旨在通过一种竖向无约束悬挂点做法,释放传统做法产生的下压力和上拔力,使悬挂钢梁的截面更经济合理,并将这种做法与传统做法的计算结果作比较,说明竖向无约束悬挂点的优点。     

Defining University Anchor Institution Strategies: Comparing Theory to Practice

Since the 1990s, some urban universities have served as neighborhood anchors with an interest in revitalization. Current theory suggests anchors adopt ‘shared value’ approaches, leveraging resources for mutually beneficial improvement in the community. This study explores assumptions in contemporary anchor frameworks and uses a survey to examine how 22 U.S. universities approach their roles as anchor institutions. The study finds that the universities tend to prioritize place-based initiatives, while contemporary frameworks are more normative and highlight socioeconomic practices. Based on reported strategies, the author proposes an alternate typology that accounts for the ways universities most commonly describe anchor approaches, complementing contemporary theory.     

Randnahe Vierfachbefestigungen unter Querlast

Shear Loaded Quadruple Fastenings Close to edge – Experimental and Numerical Analysis Fastenings in concrete with anchor groups placed close to a free edge are often met in practice. At the connection of anchors with a steel base plate, installation tolerances are present and so the anchors are randomly placed in the clearance holes of the plate. Consequently, by shear loading of an anchorage, the individual anchors are not activated simultaneously and the group's shear capacity is strongly affected. At shear loaded quadruple anchorages close to an edge the most unfavourable configuration is reached if the first row of anchors is loaded first. Based on that, the current design of shear loaded anchor groups close to an edge according to ETAG 001 considers only the anchors near the edge for ultimate limit state (ULS). In experiments with common geometries and unfavourable anchor configurations in contrary essential higher ultimate loads are shown. To provide a basis, the influence of a single anchor on the ambient concrete surface is investigated by non‐contact Electronic Speckle Pattern Interferometry (ESPI). It enables to show the three dimensional deformation of the concrete surface in the range of micrometers, to detect micro cracks at their initiation and to measure their width. Supported by finite element simulations the influence of the most unfavourable anchor configuration on the internal flow of forces is analysed.     

边坡加固机理探讨

笔根据参与的十几个岩土边坡加固设计,审查和施工体验对边坡加固中预应力锚索传力深度,自由段概念,削坡开挖边坡安全系数,群锚形成“岩壳”,补赏张拉等问题进行了讨论。中介绍了边坡治理中开挖控制变形工法。工法的主要素为：安全监测,超前支护,分层分段开挖,及时进行坡面支护,加强边坡底部支护和施工工艺管理。中着重讨论了预应力锚索钻孔中水泥砂浆芯柱受力分析,把问题归结为压杆稳定提出了预应力锚梁结构。该结构大大提高了预应力锚索的承载力。     

拉力型和压力型预应力锚索受力分析及工程应用

根据拉力型、压力型预应力锚索结构特征，本文将拉力型预应力锚索抽象为在假想滑动面处受一个集中力P，将压力型预应力锚索抽象为在锚索孔底处受一个集中力P。工程中一般假想滑动面或锚索孔底距岩土体表面较远。基于以上假定和工程条件把预应力锚索归结到空间体内一点受集中力Kelvin问题。文中引用Kelvin应力解求得了拉力型预应力锚索钢绞线侧壁、锚索孔壁剪应力τ沿轴向分布，求得了压力型预应力锚索孔壁剪应力汲正应力σ沿轴向分布。 根据本文结果：建议岩体中拉力型预应力锚索设计时应以钢绞线与注浆体之间粘结强度作为设计依据。建议岩体中压力型预应力锚索在受力端增加一段钢管改进成压力局部分散型预应力锚索。建议土体中压力型预应力锚索采取孔底扩孔改进成扩大头式压力型预应力锚索。     

Design procedure for stiffened water-filled steel conical tanks

Since the collapse of the steel liquid-filled conical tank located in Fredericton, Canada in December 1990, a concern has been raised about the safety of existing tanks. In a previous investigation, it was shown that welding longitudinal stiffeners to the bottom part of hydrostatically loaded conical tanks would provide a significant enhancement to the buckling capacity of this type of shell structure. In the current study, an attempt is made to develop a simple procedure that can be used in designing stiffened conical tanks. The procedure is based on the theory of orthotropic shells and design formulae for unstiffened tanks previously developed by Vandepitte.The study is conducted numerically using an in-house developed shell element model to simulate both the walls of the tank and the stiffeners. The study considers stiffening existing tanks and the design of newly stiffened ones. As the application of the orthotropic theory depends on the ratio between the stiffener spacing and the shell thickness, limiting values for such a ratio have been evaluated and are presented graphically. The orthotropic design procedure is then described and applied in two examples involving a retrofitted as well as a newly designed stiffened conical tanks.     

核电厂安全壳预应力锚具静载试验

核电厂安全壳大吨位预应力锚固系统是核电站安全壳施工中重要的、复杂的部分,锚具的静载锚固性能通过钢绞线—锚具组装件的静载试验来衡量。根据核电设计单位要求,核安全壳预应力锚具静载试验时应模拟实际工况,在端部增加砼锚固块,这与常规锚具静载试验相比,纲绞线在砼锚固块处产生弯折,这大大增加了试验的难度。本文介绍模拟实际工况下核安全壳预应力锚具的静载试验,试验的成功促使了国产核电预应力锚具的应用。     

Querschnittsberechnung von Stahlbetonstäben – Stand der Forschung

Cross‐Sectional Analysis of Reinforced Concrete Beams – State of the Art Many common structures consist of one‐dimensional members. For such structures beam theory is applicable. Within beam theory, the material behaviour can be captured on cross‐sectional level. Regarding reinforced‐concrete structures, material nonlinearity has generally to be considered. The present article provides an overview of the state of the art in cross‐sectional analysis of one‐dimensional reinforced‐concrete elements. A crosssectional analysis describes the relationship between the internal forces and the generalized strains. There is a large number of different models, for which a classification is suggested here. Existing models can be classified into resultant models, truss models, uniaxial models, wall models, and finite element models. For each class, the characteristics are outlined and the most important models are presented.     

Tragfähigkeitsminderung durch lokale Instabilität bei stählernen Zylindertanks mit Doppelmantel

Reduction of load bearing capacity by local instability of double‐shell steel tanks. The structure of a double‐shell steel tank creates specific risks for its local stability and load capacity. These risks form the subject of this paper. The following three issues have been discussed: Internal shell stability risk during hydrostatic test of the tank, deformation of the bottom in between the shells by heating of the storage liquids and difference in the settlement of the bottom under the internal tank shell and the external shell resulting from different loads acting on both these parts of the bottom.     

Harmonic settlement effects on uniform and tapered tank shells

For economic reasons, foundations of large tanks for fluid storage tend to be shallow and may consequently suffer differential settlement under load. But these tanks are ductile and are able to tolerate limited settlement without distress. For an economic limitation of settlement, the structure should be analyzed rationally. In this paper, the effects of peripheral differential settlement on the shell are evaluated for the practical case of a tapering wall thickness in floating roof tanks which have a relatively flexible response to warping displacements. Previous research has centred on walls of uniform thickness, and is therefore of more limited relevance. Settlement of harmonic form is imposed at the base, and shell deformations and stresses determined in accurate finite element analysis. The significance of stresses in the primary wind girder, adjoining shell and at the bottom is assessed in relation to radial displacement at the top arising from the warping displacement. Results of recent laboratory tests particularly relevant to stress distribution are reported.     

玻璃钢螺旋锚的现场拉拔试验

回顾了FRP螺旋锚的基本结构型式,介绍现场拉拔试验的设计,完成了无灌浆和灌浆FRP螺旋锚的现场拉拔试验。无灌浆锚杆的最大拉拔力约在10 kN左右,而灌浆锚杆的拉拔力提高到15～20 kN,且拉拔位移较小。拉拔试验结果与现有拉拔力公式的计算值进行比较,并对螺旋锚的结构和施工提出一些改进意见。     

Effect of imperfections on wind-loaded cylindrical shells

The wind-induced buckling of thin-walled steel cylinders, such as silos and tanks, was investigated by wind-tunnel testing for a limited range of the parameters. While wind-buckling of short, stocky shells can be well represented by an equivalent uniform external pressure, long shells show quite a different behaviour, which is strongly influenced by the axial compression forces. This paper presents a study of this behaviour, based on numerical analyses and considering various types of imperfection shape. The effect of geometrical nonlinearity, as well as material plasticity, has also been included. A comparison with test results shows good agreement with the numerical results of imperfect shells, provided that special eigenmode-shaped modes of imperfections are excluded.     

碎石保护结构防护海底管线的机理及模型试验研究

近海海底管线会在港口锚地处因船舶走锚而受到损害,碎石结构能够防护管线免受走锚的危害,因此研究碎石结构的防护机理对保护管线有重要意义。采用极限平衡方法分析了走锚状态下土楔对形状复杂的商用霍尔锚的作用力,提出了锚冠和锚爪的受力计算模式,采用3种不同几何相似比的模型锚在模型槽中进行了拖锚试验。模型试验的结果与计算结果相互吻合。锚体整体受力分析的结果表明,霍尔锚在从砂土进入碎石保护层后因力矩不平衡引起锚体翻转,使锚爪尖位置上移而远离埋设的管线,从而使管线避免走锚的伤害。该机理也通过模型试验得到验证。此外,不同试验锚重的归一化结果还说明,霍尔锚锚爪在碎石中的稳定入土深度约为爪长的0.45,拖曳力为2.5倍锚重,可为碎石结构设计参考。     

预应力钢结构锚固节点瞬态温度场分析

根据试验数据,建议了热铸锚填料锌铜合金和冷铸锚填料环氧树脂/钢丸混合物的比热容及导热系数计算公式.基于热传导理论和ABAQUS数值传热模拟平台,进行了ISO834标准火灾下锚固节点截面瞬态温度分布的参数分析.结果表明:随着受火时间的延长,热铸锚杯壁截面温度分布非均匀性逐渐显现,锌铜合金填料的升温速率显著低于锚杯壁;冷铸锚杯壁截面温度分布较均匀,包裹钢丝的填料区域较填料其他区域温度分布非均匀性降低.总体上,锚头沿中心轴的温度分布非均匀性显著,且升温明显滞后于环境温度,无防火保护的情况下锚杯内壁界面处的填料将在较短时间内失效.所提出的热铸锚截面瞬态升温理论计算式,为预应力钢结构锚头抗火承载力验算提供了理论依据.