Numerical and experimental investigations on the compression behaviour of stiffened plates

The main objective of this paper is to present the results of the finite element method for non-linear analysis of stiffened plates subjected to axial compression load considering post-buckling behaviour up to collapse. For this purpose two series of well executed experimental data on longitudinally stiffened steel plates with and without transversal stiffeners subjected to uniform axial in-plane load carried out to study the buckling and post-buckling up to final failure have been chosen. The first series are those of Ghavami where the influences of stiffener cross-section of the type rectangular (R), L and T, their spacing and the presence of rigid transversal stiffeners have been studied. The second series of Tanaka & Endo, where the behaviour of stiffened plates having three and two flat bars for longitudinal and transversal stiffeners respectively were analysed. For the purpose a well-established commercially available Finite Element program ANSYS has been chosen. The selected element was SHELL43, which can trace the full-range, elastic-plastic behaviour of the stiffened plates. It is seen that the simulated results of FEM are in good consistency with the test results.     

Transverse-stiffener requirements for the post-buckling behaviour of a plate in shear

The optimum stiffener rigidity in a transversely-stiffened web under pure shear is sought in the post-critical range. An energy-based large-deflection scheme is employed to study the post-critical strength of the system up to the initiation of material yielding for the usual range of plate geometries and varying stiffener rigidities. Several criteria for “optimum” rib stiffness are assessed including stiffener deflection, the effective halving of the plate length and, finally, the strength of the plate itself. Tentative conclusions are reached on the basis of comparing optimal rib rigidities for the two instances of elastic and post-buckling regimes.     

Computational modelling of flange crushing in cold-formed steel sections

The computational modelling of the flange crushing phenomenon in cold-formed steel profiles is described in this paper, with particular emphasis to the development of shell finite element (SFE) models and performance of quasi-static analyses with an explicit integration scheme. Web crippling failure is widely recognised as the most relevant collapse mode of cold-formed steel members subjected to transverse concentrated loads. However, it has been experimentally and numerically observed that a somewhat different collapse mode may occur, due to the heavy stress concentrations stemming from the adoption of narrow bearing plates. This phenomenon, termed flange crushing, should not be confused with web crippling. Usually, the web crippling phenomenon is numerically investigated by means of non-linear static SFE models with an implicit integration scheme. In this study, SFE models are developed in ABAQUS code to study the flange crushing failure of a plain channel beam subjected to Internal Two Flange (ITF) loading conditions. These models are described in detail, as well as additional modelling concerns regarding quasi-static analyses and the explicit integration method. Different parameters are discussed in this article and the numerical results obtained are commented throughout. Such parameters include the (i) SFE type and mesh, (ii) load rate, mass scaling, adoption of smoothed displacement amplitude curves and control of inertial effects, (iii) contact and friction definitions, (iv) effects of forming cold-work and manufacturing process and (v) geometrical imperfections. Finally, the load–displacement response obtained with the quasi-static model and an equivalent non-linear static analysis are compared with the experimental test curves. It is concluded that very good results are achieved with the quasi-static approach, not only in terms of the ultimate load prediction, but also regarding the post-collapse load–deflection curve and the failure mechanism.     

Semi-analytical models for the post-buckling analysis and ultimate strength prediction of isotropic and orthotropic plates under uniaxial compression with the unloaded edges free from stresses

This paper introduces two semi-analytical models developed for the nonlinear analysis of stability of isotropic and orthotropic plates under uniaxial compression. The possibility of considering fully free in-plane displacements at longitudinal edges (or unloaded edges) is the innovation of these models over existing models, where these displacements are always assumed constrained to remain straight. Contributions for the large deflection theory of plates related to the derivation of analytical solutions for the Airy stress function which satisfy Marguerre׳s equations for isotropic and orthotropic plates are presented. Namely, the extension of the Coan and Urbana solution for isotropic plates in order to consider all the terms of the unknown amplitudes of the out-of-plane displacements and the derivation of a solution for orthotropic plates. Comparisons between the semi-analytical model and nonlinear finite element model results are presented in order to discuss the effect of in-plane displacement boundary conditions on behaviour and strength of plates similar to bottom flanges used in steel box girder bridges. This study shows that the semi-analytical models have a clear potential to provide accurate solutions, requiring only a short computer time. It is also shown that the in-plane displacement boundary conditions for the unloaded edges significantly influence the behaviour and strength of plates and this problem cannot be neglected in the definition of the design rules.     

Comparison of measured distributions of concentrations of trace elements in air particulates with normal and lognormal probability functions

Concentrations of Cd, Cr, Cu, Fe, Mg, Mn, Pb, V and Zn in air particulates were measured at several sites in Québec. A computer program was written to perform a statistical analysis of this data. We found that the distributions of these concentrations are generally better described by a log normal rather than a normal probability function. Also the position of the median and the value of the coefficient of skewness are useful indicators of normality or lognormality of the measured distribution.     

Experimental and numerical investigation on the shear behaviour of friction-welded bar-plate connections embedded in concrete

Friction-welded bar-plate connections are a basic structural component of Bi-steel steel-concrete-steel sandwich construction. In Bi-steel members, the bar-plate connections, embedded in concrete, are subject to tension, shear and bending. The static and fatigue behaviour of the embedded connections subjected to bar tension is described in another paper [Xie M, Chapman JC. Static and fatigue tensile strength of friction-welded bar-plate connections embedded in concrete. Journal of Constructional Steel Research [in press]]. This paper presents experimental and numerical studies on the static behaviour of the friction-welded connections with the bar loaded in shear. Finite element analysis is carried out to examine the effects of variations in geometric and material parameters. The experimental results are used to derive an empirical equation for predicting the shear strength of embedded connections, and compared with existing test results and code specifications. Further papers will describe fatigue behaviour of the embedded connections subjected to bar shear, and static and fatigue tests on Bi-steel beams.     

Nonlinear analysis of concrete-filled square stainless steel stub columns under axial compression

Concrete-filled stainless steel tubes (CFSST) can be considered as a new and innovative kind of composite construction technique, and have the potential to be used extensively in civil engineering. This paper employs a nonlinear analysis of square CFSST stub columns under axial compression. A three-dimensional nonlinear finite element (FE) model is developed using ABAQUS, where nonlinear material behaviour, enhanced strength corner properties of steel, and initial geometric imperfections are included. Close agreement is achieved between the test and FE results in terms of load-deformation response and ultimate strength. In light of the numerical results, the behaviour of stainless steel composite columns is compared with that of carbon steel composite columns. A simple model is proposed to calculate the ultimate strength of square CFSST stub columns.     

Ultimate strength of cracked plate elements under axial compression or tension

In addition to corrosion, fatigue cracking is another important factor of age related structural degradation, which has been a primary source of costly repair work of aging steel structures. Cracking damage has been found in welded joints and local areas of stress concentrations such as at the weld intersections of longitudinals, frames and girders. Fatigue cracking has usually been dealt with as a matter under cyclic loading, but it is also important for residual strength assessment under monotonic extreme loading, because fatigue cracking reduces the ultimate strength significantly under certain circumstances.In this paper, an experimental and numerical study on the ultimate strength of cracked steel plate elements subjected to axial compressive or tensile loads is carried out. The ultimate strength reduction characteristics of plate elements due to cracking damage are investigated with varying size and location of the cracking damage, both experimentally and numerically. Ultimate strength tests on cracked steel plates under axial tension and cracked box type steel structure models under axial compression are undertaken. A series of ANSYS nonlinear finite element analyses for cracked plate elements are performed. Based on the experimental and numerical results obtained from the present study, theoretical models for predicting the ultimate strength of cracked plate elements under axial compression or tension are developed. The results of the experiments and numerical computations obtained are documented. The insights developed will be very useful for the ultimate limit state based risk or reliability assessment of aging steel plated structures with cracking damage.     

The role of frame members and sheathing in partition wall panels subjected to compression

This paper presents an experimental study on the role of frame members and sheathing by means of strain/stress distributions in each of the constituents of a cold-formed steel wall panel. Vertical compression loading was applied, and strain gauges were extensively used during the tests. At a given cross-section of the middle stud, strains/stresses experienced by its flanges are found to be significantly different from those on the web, indicating that the middle stud is not balanced in simple compression mode. However, the averaged stress on the flanges and that on the web follow the same trend as that recorded by the load cell, and can be used to work out the load carried by the stud. Screw connections between the stud and the board not only restrain the lateral displacement of the stud, but also support and re-distribute a portion of the load to the board and then to the bottom track. Upon loading, the axial force experienced by a typical screw is negligibly small initially, increasing slowly with load until substantial stud buckling occurs, resulting in often its pulling-out from the board or the stud/track. The board acts as a shearing member to steady the whole panel, a supporting member to enhance the overall/local buckling performance of the middle stud and sidetracks, as well as a structural member to support part of the vertical load.     

Monitoring of small landscape elements in The Netherlands

An investigation was carried out to build an adequate but economical system for monitoring small landscape elements in The Netherlands. Many organizations concerned with landscape management and policy support such a system as an aid to stop the deterioration of the landscape. The designed monitoring system was tried out in three areas with different landscape types. Results showed that the system can answer a lot of questions about the development of landscape quality. With the aid of local volunteers the monitoring system is economical.     

Monitoring of small landscape elements in The Netherlands

An investigation was carried out to build an adequate but economical system for monitoring small landscape elements in The Netherlands. Many organizations concerned with landscape management and policy support such a system as an aid to stop the deterioration of the landscape. The designed monitoring system was tried out in three areas with different landscape types. Results showed that the system can answer a lot of questions about the development of landscape quality. With the aid of local volunteers the monitoring system is economical.     

Experiments of edge-stiffened plates in uniform compression

There is a large body of literature on the experimental behaviour of steel plates under a variety of loading and edge support conditions. Typically the longitudinal plates edges were either laterally restrained (stiffened) or laterally unrestrained (unstiffened). There are no such plate experiments reported in the literature of plates with a longitudinal edge stiffened with an edge-stiffener (partially stiffened). This paper presents 30 plate tests of plates simply supported on three sides, with the remaining (longitudinal) edge stiffened with an edge-stiffener. The edge-stiffener was increased in size from zero (unstiffened plate) to a size sufficient to create a stiffened edge (stiffened plate). Edge-stiffeners of an intermediate size resulted in partially stiffened plates. The behaviour of partially stiffened plates is fully documented with the aid of a 3D photogrammetry system, and the adequate size of edge-stiffeners required in order to create a stiffened plate edge are discussed. Edge-stiffener types investigated are simple lips, simple inclined lips and complex lips. Design procedures for partially stiffened elements previously inferred from numerical studies are shown to accurately and reliably determine the plate strengths, and further validate the procedure for use as a general strength approach in current international cold-formed steel specifications.     

Geochemistry of some rare earth elements in groundwater,Vierlingsbeek, The Netherlands

Groundwater samples were taken from seven bore holes at depths ranging from 2 to 41m nearby drinking water pumping station Vierlingsbeek, The Netherlands and analysed for Y, La, Ce, Pr, Nd, Sm and Eu. Shale-normalized patterns were generally flat and showed that the observed rare earth elements (REE) were probably of natural origin. In the shallow groundwaters the REEs were light REE (LREE) enriched, probably caused by binding of LREEs to colloids. To improve understanding of the behaviour of the REE, two approaches were used: calculations of the speciation and a statistical approach.For the speciation calculations, complexation and precipitation reactions including inorganic and dissolved organic carbon (DOC) compounds, were taken into account. The REE speciation showed REE(3+), REE(SO(4))(+), REE(CO(3))(+) and REE(DOC) being the major species. Dissolution of pure REE precipitates and REE-enriched solid phases did not account for the observed REEs in groundwater. Regulation of REE concentrations by adsorption-desorption processes to Fe(III)(OH)(3) and Al(OH)(3) minerals, which were calculated to be present in nearly all groundwaters, is a probable explanation.The statistical approach (multiple linear regression) showed that pH is by far the most significant groundwater characteristic which contributes to the variation in REE concentrations. Also DOC, SO(4), Fe and Al contributed significantly, although to a much lesser extent, to the variation in REE concentrations. This is in line with the calculated REE-species in solution and REE-adsorption to iron and aluminium (hydr)oxides. Regression equations including only pH, were derived to predict REE concentrations in groundwater. External validation showed that these regression equations were reasonably successful to predict REE concentrations of groundwater of another drinking water pumping station in quite different region of The Netherlands.     

住宅小区景观设计中的乡土元素

在探讨乡土景观的概念和特性的基础上,提出了乡土元素在住宅小区中应用的重要原则和相关方法,并具体探讨了自然元素和文化元素在乡土景观设计中的应用,提出了乡土景观在现代住宅小区应用的意义。     

The local bearing capacity perpendicular to grain of structural timber elements

The accuracy and reliability of empirical models for the local bearing capacity perpendicular to grain of timber beams is questionable as it is not based on any fundamental principal. This study shows that a physically based stress dispersion model can successfully be applied for a wide range of practical design situations. The credibility of this model is based on experiments, FEM and optical techniques used to assess and quantify the strength affecting parameters. This model is a potential candidate to be incorporated in future structural timber design standards.     

历史地段景观环境的特征及其构成要素

从空间形态特征、美学特征、景观环境特征三方面论述了历史地段景观环境的基本特征,分析了历史地段景观环境的构成要素,以期对此类景观环境设计的研究有所助益。     

An equivalent stiffness approach for modelling the behaviour of compression members according to Eurocode 3

The development of design procedures based on inelastic advanced analysis is a key consideration for future steel design codes. In advanced analysis the effect of imperfections has to be modelled in such a way that the incremental analysis fully captures this effect in the process of moment redistribution. In modelling the influence of imperfections on the behaviour of individual members of real structures, different approaches have been used to globally represent this effect in the overall analysis of structural systems. They are referred to as the initial bow imperfection approach or as the equivalent transverse load approach. When using the abovementioned approaches in analysis of multiple member structural systems, the designer is required to arrange the directions of bow imperfections or equivalent transverse loads in such a way that the imperfection arrangement leads to the least constrained solution, i.e. the lowest ultimate load predicted from all possible sets of member initial imperfection arrangements. Since there is still ongoing research on the development of simple application rules ensuring that the designer obtains a unique solution when choosing a certain set of member initial imperfections, there is at the same time interest in the development of alternative approaches to modelling the influence of member imperfections on the behaviour of structural systems. This paper provides the necessary background information as well as describes the formulation and modelling techniques used in the development of a new approach to modelling the influence of imperfections on the stability behaviour of structural components and systems. This new approach, called hereafter an equivalent stiffness approach, has an advantage over the previously described approaches since an imperfect member is treated as a hypothetically straight element, flexural and axial stiffnesses of which at each load level are predicted in a continuous fashion dependent upon the actual force and deformation states. This type of modelling does not require any explicit modelling of equivalent geometric imperfections or equivalent forces and their directions in advanced analysis; therefore also it does not require any buckling mode assessment. Moreover, the effects of strain hardening and section class may conveniently be included in modelling. Finally, European buckling curves are used to estimate the values of parameters of the developed model that can be immediately used in advanced analysis conducted according to Eurocode 3.     

谈施工过程中某些构件之间的连接问题

分析了建筑工程施工过程中不同构件之间的相互连接问题，指出框架结构的填充墙与框架梁、隔墙与楼板、构造柱或装饰柱与各种梁等承重与非承重构件之间在相互连接时应注意的有关事项。     

地理要素对中国传统民居建筑形制的影响

从中国气候、地形、抗震角度,通过对中国传统民居建筑形制的再分析、再认识和再思考,并结合实例解读了地理要素对中国传统民居建筑形制的影响,为21世纪的建筑设计提供重要参考及借鉴价值。     

岩土工程事故中的人为因素影响

着眼于规划、设计、施工和运营这些工程阶段当中,探讨了工程事故的出现阶段及其原因,得出工程事故的发生绝大部分是由人为决策等因素导致的,而这些缺陷可以通过意识到自身专业的局限,继续教育,修改设计和施工体系,还有抵抗外部不平衡的压力来改正。