薄壁钢结构的材料和几何非线性等参样条有限条法的研究进展

给出了等参样条有限条法(ISFSM)用于分析开孔薄壁钢结构的材料非弹性和几何非线性的研究进展。简要介绍了ISFSM理论。提出了运动学方程、应力-位移关系和假定的本构关系。通过增量平衡条件,推导出正切刚度矩阵。讨论了板带连续和边界条件的要求。特别强调了塑性理论和求解速率方程的方法,以及相关的欧拉后退法和材料模量一致的假定。开孔薄壁钢结构的非弹性后屈曲性能分析的准确性和有效性,证实了目前的等参样条有限条法的有效性。     

Material and geometric nonlinear isoparametric spline finite strip analysis of perforated thin-walled steel structures—Numerical investigations

The theoretical developments of a material inelastic and geometric nonlinear analysis by use of the isoparametric spline finite strip method (ISFSM) are presented in a companion paper (Yao and Rasmussen (submitted) [1]). In the present paper, the numerical implementation of the analysis is reported, including nonlinear solution techniques, inelastic material models, selective reduced integration strategies, convergence criteria, and solution procedures. The reliability and efficiency of the method are demonstrated by a number of numerical examples, including analyses of flat plates with different material plasticity models, a classical nonlinear shell problem, perforated flat and stiffened plates, and perforated stiffened channel section storage rack uprights.     

Inelastic restrained distortional buckling of continuous composite T-beams

This paper develops a method of inelastic buckling analysis of thin-walled sections to study buckling characteristics of single span and two-span composite T-section beams in the inelastic range of structural response. The method is based on a bubble-augmented spline finite strip method, developed elsewhere by the authors, and confirmed as both accurate and efficient for the elastic buckling analysis of thin-walled structural members and plates. The method admits both flexural and membrane buckling deformations and it allows for consideration of structures with intermediate supports and a variety of boundary conditions that may be prescribed at the ends of plate assembly. The analysis includes the so-called Tendon Force Concept developed at Cambridge University for residual stresses caused by the process of fabrication, and the non-linear stress-strain properties of the structural steel from which the joist section is made. The inelastic restrained distortional buckling (RDB) of continuous composite T-section beams under transverse loading and moment gradient is investigated, and conclusions are drawn that address the influence of geometry, residual stresses, member length, the rigid restraint provided by the concrete and the degree of reinforcement in the concrete element.     

Inelastic buckling analyses of beams, columns and plates using the spline finite strip method

A method of inelastic buckling analysis of thin-walled structural members and plates is described. The method is based on the spline finite strip method of structural analysis. The analysis takes into account the non-linear material stress-strain properties, strain hardening and residual stresses. The plastic theories used in the study are the flow theory of plasticity and the deformation theory of plasticity. The method of inelastic buckling analysis is applied to a variety of instability problems including plates, cold-formed columns, hot-rolled columns and welded tee section beams. The buckling modes and loads computed are compared with theoretical values and test results.     

Structural behaviour and design of lightweight structural panels using perforated cold-formed thin-walled sections under compression

Cold-formed thin-walled steel sections are widely used as primary loadbearing members in lightweight panels that form walls in residential and other low rise structures. In cold regions, the webs of the steel sections are often perforated to reduce the cold bridging effect in order to increase thermal comfort and reduce energy waste. Perforating the web of a steel section will reduce its loadbearing capacity. This paper presents the results of an experimental and numerical study to investigate the compression behaviour of lightweight structural panels using perforated sections. The primary objective of the tests is to provide experimental data to validate the numerical simulations, which were carried out using the commercial finite element analysis software ABAQUS. The validated FE analysis was used to develop a simple design calculation method to convert a section with perforated web to a section with solid web. In the equivalent solid web, the thickness of the solid web would have the same elastic local buckling strength as the original perforated web with the gross thickness while the thickness of the unperforated flanges remains unchanged. By converting a thin-walled section with perforated web to a solid section with an effective web thickness, the conventional design methods for thin-walled structures can be applied.     

薄壁受压构件的非弹性有限条法

最近几年,证实了有限条法(FSM)分析薄壁结构构件屈曲模态的有效性。提出了一个能估算均匀压力下无初始曲率薄壁非弹性构件的屈曲应力的FSM公式。在该公式中,利用塑性流方程考虑了塑性,得到了一个考虑非弹性剪切刚度的表达式,避免了之前的塑性流理论关于屈曲模型问题的缺陷。     

Elastic buckling analysis of perforated thin-walled structures by the isoparametric spline finite strip method

This paper presents the application of the isoparametric spline finite strip method to the elastic buckling analysis of perforated folded-plate structures. The general theory of the isoparametric spline finite strip method is introduced. The kinematics assumptions, strain–displacement and constitutive relations of the Mindlin plate theory are described and applied to the spline finite strip method. The corresponding matrix formulation is utilised in the equilibrium and stability equations to derive the stiffness and stability matrices. A number of numerical examples of flat and folded perforated plate structures illustrate the applicability and accuracy of the proposed method.     

Cyclic behavior of thin-walled steel structures—numerical analysis

In the present paper, results of a numerical study on cyclic behavior of thin-walled steel structures are presented. Analyses are conducted on steel plates with or without stiffeners, steel stub columns of pipe-sections, and steel cantilever columns of box or pipe sections. To trace with good accuracy the inelastic cyclic behavior of steel, a modified two-surface model developed at Nagoya University is employed for material nonlinearity. Discussions of the results are concerned with the cyclic behavior, strength and ductility of the structures. Especially, a series of proposed formulas are given to obtain the strength and ductility of various types of structures, and it is expected that the formulas are useful to researchers and practical engineers.     

Buckling analysis of thin-walled cold-formed steel structural members using complex finite strip method

In this paper, a generalised complex finite strip method is proposed for buckling analysis of thin-walled cold-formed steel structures. The main advantage of this method over the ordinary finite strip method is that it can handle the shear effects due to the use of complex functions. In addition, distortional buckling as well as all other buckling modes of cold-formed steel sections like local and global modes can be investigated by the suggested complex finite strip method. A combination of general loading including bending, compression, shear and transverse compression forces is considered in the analytical model. For validation purposes, the results are compared with those obtained by the Generalized Beam Theory analysis. In order to illustrate the capabilities of complex finite strip method in modelling the buckling behavior of cold-formed steel structures, a number of case studies with different applications are presented. The studies are on both stiffened and unstiffened cold-formed steel members.     

Analysis and design reliability of axially compressed members with high-strength cold-formed thin-walled steel

High-strength cold-formed thin-walled steel has been widely used in developed countries in the last several years. However, the application and popularization of the new materials in China is still very limited, and there are no related provisions in current design codes for reference in engineering practice. In this paper, considering the effects of the variations from material strength in structural members, geometrical parameters of sections, analysis methods for limit load-carrying capacity and external loadings, the second-order moment probability method was used for conducting the design reliability analysis of 550 MPa high-strength cold-formed thin-walled steel structures, from which the reasonable target reliability index, the corresponding resistance partial coefficient and the design strength values were discussed and proposed. Existing experimental data related have been collected and used to demonstrate the suitability and reasonability of the proposed results, which shows that, with reasonable determination of the design strength value of 550 MPa high-strength cold-formed thin-walled steel sections, the effective width-to-thickness ratio method considering coupling stability of plates recommended by “Technical Code of Cold-formed Thin-Walled Steel Structures (GB50018-2002)” can be efficiently used to estimate the load-carrying capacities of the axially compressed elements of high-strength cold-formed thin-walled steel structures, and well satisfy the target reliability index in structural design.     

屈服强度550MPa高强冷弯薄壁型钢结构轴心受压构件可靠度分析

本文采用二阶矩概率法,考虑强度、截面几何参数、计算模式、外荷载等不定因素的影响,针对屈服强度550MPa高强冷弯薄壁型钢轴心受压构件的可靠度进行了分析,并考虑材料特性,在已有试验的基础上对其承载力计算方法、目标可靠指标及强度设计指标的合理选取进行了研究。结果表明,在按厚度分类合理确定高强冷弯薄壁型钢的强度设计指标后,可依据现行的《冷弯薄壁型钢结构技术规范》(GB 50018—2002)给定的考虑板组稳定计算截面有效宽厚比的方法对其轴心受压构件的极限承载力进行有效分析,并满足预定设计可靠指标的要求。     

Analysis of thin-walled structures by finite strip and finite layer methods

The finite strip and finite layer methods are powerful tools for the analysis of thin-walled structures. In this paper, the finite strip method is applied to study the behavior of cold-formed steel beams including webs with longitudinal stiffeners. Comparisons are made with AISI specifications and published data. The finite layer method is used to investigate the buckling behavior of sandwich panels with thin facings and rigid foam cores. Effects of variable core stiffnesses (due to uneven curing, etc.) on the buckling strength are quantified and presented.     

Linear elastic isoparametric spline finite strip analysis of perforated thin-walled structures

This paper describes the application of the isoparametric spline finite strip method to the linear elastic analysis of tri-dimensional perforated folded plate structures. The general theory of the isoparametric spline finite strip method is introduced. Kinematics assumptions and the procedure for combining in-plane (membrane) and bending effects are set out. Particular attention is paid to the procedure for rotating the stiffness matrix and load vector from local to global coordinates. The reliability of the method is demonstrated by comparisons with finely meshed finite element analysis results. Square stiffened perforated plates in compression and bending are analysed.     

Strength of slender concrete filled high strength steel box columns

The use of thin walled steel sections coupled with concrete infill has been used on various building projects with great advantage. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections. However, there is limited research work in the literature available which is concerned with slender concrete filled thin-walled steel columns. This paper presents a comprehensive experimental study of thin walled steel sections utilising high strength steel of a thin walled nature and filled with normal strength concrete. A numerical model is developed herein in order to study the behaviour of slender concrete filled high strength steel columns incorporating material and geometric non-linearities. For this analysis, the equilibrium of the member is investigated in the deformed state, using the idealised stress–strain relationships for both the steel and concrete materials, considering the elastic and plastic ranges. This paper presents both an experimental and theoretical treatment of coupled local and global buckling of concrete filled high strength steel columns sometimes termed interaction buckling. The experimental results of columns with high strength steel casings conducted herein by the authors are used for comparison. The effect of the confined concrete core is also addressed and the method shows good agreement with the experimental results of concrete filled steel columns with compact sections. The behaviour of concrete filled steel slender columns affected by elastic or inelastic local buckling is also investigated and compared with relevant experimental results. The paper then concludes with a design recommendation for the strength evaluation of slender composite columns using high strength steel plates with thin-walled steel sections, paying particular attention to existing codes of practice so as not to deviate from current design methodologies.     

Short-term behaviour of shallow thin-walled concrete dome under uniform external pressure

Thin-walled spherical concrete shells or domes find widespread use in many applications, including in many iconic engineering structures of historical and religious significance. Despite this, very few experimental investigations have been reported in the open literature of shallow spherical concrete domes which allow for the effects of geometric and material non-linearities and of imperfections to be identified. This information is essential, however, in order to validate sophisticated numerical treatments, as well as to calibrate practical design and construction guidelines and is therefore much-needed. This paper reports an experimental study of a shallow thin-walled concrete dome under short-term loading, without the use of reinforcement in the concrete. The dome is 30 mm thick and has a base diameter of 3 m, being supported on a steel ring beam. The testing of the dome to failure under a uniform external pressure is described in the paper, and it is shown that it failed in a non-axisymmetric buckling mode well before the concrete reached its compressive strength. The failure pressure is compared with the ‘theoretical’ buckling results and the analytical results based on finite element analyses. In particular, this paper presents a comprehensive set of experimental data for the load–displacement and load–strain relationships and their distributions across the spherical dome throughout the loading regime.     

Nonlinear inelastic analysis of building frames with thin-walled cores

A second-order inelastic analysis by combining the theories of stability and plasticity is proposed for studying frames with thin-walled cores. In the proposed approach, steel frameworks surrounding the cores are modelled by using the plastic hinge beam-column approach, and core walls modelled by using the thin-walled beam-column approach. Transformation procedures are proposed to consider the kinematic relationship between beams, columns, core walls and floor diaphragm. Nonlinear solution procedures are incorporated for the incremental analysis. The proposed inelastic analysis is used to investigate the inelastic behaviour and ultimate strength of core-braced frames.     

Elasto-plastic analysis of perforated core structures subjected to applied torque

This paper presents a method of analysis, based on Vlasov's thin-walled beam theory in conjunction with the continuum approach, for investigating the elasto-plastic behaviour of perforated core structures subjected to torsional loading. A closed section analogy is utilized in the analysis. It is assumed that the plastic hinges form at the ends of the lintel beams and the lintel beams will fail prior to any yielding of the walls when the limiting rotational ductility is reached. The analysis enables the behaviour of a perforated core structure to be traced from working load to ultimate condition.     

Stability analysis of large diameter thin-walled tube beam-columns

Based on a blind spot in the current design standard of steel structures, the large diameter thin-walled tube beam-columns are analyzed using nonlinear finite element method in this paper. The influence of several factors on stability capacity of the large diameter thin-walled tube beam-columns is taken into account. Thus, according to the correlative design standard of steel structures, and on the basis of the numerical analytical results by the finite element methods, the calculation formulas of the stability bearing capacity are presented for beam-column members of the large diameter thin-walled tubes. Three tests of thin-walled steel tube beam-columns were reported. Test results for deformations and ultimate strength are found to be in a good agreement with the corresponding values predicted by the calculation formulas, and the proposed methods can be used in design practice. __________ Translated from China Civil Engineering Journal, 2007, 40(3): 11–17 [译自: 土 木 工 程 学 报]     

Application of linear structural analysis program for steel frame ultimate limit state analysis

This paper describes the feasibility of applying a modified linear structure analysis computer program in the ultimate limit state design of unbraced steel frames. The elastic–plastic hinge zone concept and the linear elastic structural analysis computer program SAP90, are used to simplify the nonlinear steel frame structural analysis model. Most steel structures are designed by plastic theory, called ‘ultimate limit state design’. In practice, most steel structure analysis is performed by linear elastic computer programs that do not take into account either inelastic behavior or calculation of the ultimate strength. Herein, a modified analysis approach is presented and its design implications discussed. The results obtained from the modified approach are provided and compared with both experimental data and the inelastic structural analysis computer program DRAIN‐2DX with respect to the ultimate strengths and the lateral displacements of unbraced steel frames. Copyright © 1999 John Wiley & Sons, Ltd.     

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns,Part I: Modeling

High strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns under eccentric loading may undergo local and overall buckling. The modeling of the interaction between local and overall buckling is highly complicated. There is relatively little numerical study on the interaction buckling of high strength thin-walled rectangular CFST slender beam-columns. This paper presents a new numerical model for simulating the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular CFST slender beam-columns with local buckling effects. The cross-section strengths of CFST beam-columns are modeled using the fiber element method. The progressive local and post-local buckling of thin steel tube walls under stress gradients is simulated by gradually redistributing normal stresses within the steel tube walls. New efficient Müller's method algorithms are developed to iterate the neutral axis depth in the cross-sectional analysis and to adjust the curvature at the columns ends in the axial load–moment interaction strength analysis of a slender beam-column to satisfy equilibrium conditions. Analysis procedures for determining the load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns incorporating progressive local bucking and initial geometric imperfections are presented. The new numerical model developed is shown to be efficient for predicting axial load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns. The verification of the numerical model and parametric studies is given in a companion paper.