Dynamic FE simulations of buckling process in thin-walled cylindrical metal silos

The buckling of cylindrical steel silos is caused by the wall friction force due to shearing between the silo fill and silo wall. The aim of this paper is to investigate the stability process in a silo composed of thin-walled isotropic plain rolled sheets using a static and dynamic finite element analysis by taking both the geometric and material non-linearity into account during eccentric discharge. Silo shells were subjected to axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. The differences between the results of static and dynamic analyses were comprehensively discussed. The advantages of a dynamic approach were outlined.     

Strength enhancements induced during cold forming of stainless steel sections

The material properties of stainless steel are sensitive to plastic deformation which causes an increase in yield strength by a process termed cold working. The different strain paths experienced around cold-formed cross sections during manufacture create unique material strength distributions for sections from different forming routes and also influence residual stress patterns. The research program presented herein has examined experimentally the material and residual stress distributions found in two types of cold-formed sections-cold-rolled box sections and press-braked angles. Predictive tools to harness the observed strength enhancements have been proposed and incorporated into models. Subsequent comparisons have shown that these strength enhancements, in particular those observed for cold-rolled box sections, should be employed in structural design to avoid considerable underestimation of member resistance.     

Seismically induced cyclic buckling of steel columns including residual-stress and strain-rate effects

Compression buckling tests were performed on four full-scale W-shaped column specimens to investigate the buckling response of columns in multi-storey braced steel frame structures subjected to seismic strong ground motions. The test protocols included monotonically and cyclically applied concentric and eccentric axial loading. One test was conducted under dynamic cyclic loading. End moments were applied on one cyclic test. The columns were W310×129 compact (class 1) sections made with ASTM A992 steel. Weak axis buckling was studied and the column had an effective slenderness ratio of 48. The response of the test columns was also examined using numerical simulations based on fibre discretization of the member cross-section. Column residual stresses and strain rate effects on the material properties were both characterized and accounted for in the numerical models. The study showed that steel columns can sustain several cycles of inelastic buckling under seismic induced loading while maintaining sufficient compressive resistance to support the applied gravity loads. Residual stresses affected the column response only at the first buckling occurrence with a gradual reduction of the columns’ tangent stiffness prior to buckling as well as a reduction of the column’s compressive resistance. High strain rates anticipated during strong earthquakes increased the column buckling and post-buckling strengths. The cyclic buckling response of steel columns can be predicted adequately when using nonlinear beam-column elements and cross-section fibre discretization provided that residual stresses and strain rate effects are included in the modelling.     

The characterisation of friction stir welding process effects on stiffened panel buckling performance

The introduction of advanced welding methods as an alternative joining process to riveting in the manufacture of primary aircraft structure has the potential to realise reductions in both manufacturing costs and structural weight. However, welding processes can introduce undesirable residual stresses and distortions in the final fabricated components, as well as localised loss of mechanical properties at the weld joints. The aim of this research is to determine and characterise the key process effects of friction stir welding assembly methods on stiffened panel static strength performance. Utilising experimentally validated finite element modelling methods, it is demonstrated that welding induced residual stresses have a significant influence, and that collapse behaviour is less sensitive to advanced process effects and process effect magnitudes than panel initial buckling behaviour.     

Calculating the global buckling resistance of thin-walled steel members with uniform and non-uniform elevated temperatures under axial compression

This paper develops a method, based on the Direct Strength Method (DSM) global buckling curve, to calculate the global buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members under uniform and non-uniform elevated temperatures. The assessment is carried out by checking the DSM curve-based results with numerical simulation results using the general finite element software ABAQUS. The numerical model has been validated against a series of ambient temperature and fire tests on panels made of two different lipped channel sections tested to their ultimate load carrying capacities at ambient temperature or to their fire resistance at different load levels. The validated numerical model has been used to generate a database of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections under different boundary and loading conditions and with different dimensions. It is concluded that the DSM global buckling column curve is directly applicable for uniform temperature but a simple modification is required for non-uniform temperature distributions.     

On the buckling of axially restrained steel columns in fire

This paper describes the behaviour of restrained steel columns in fire. It follows the introduction of extra load into the column through the axial restraint of the surrounding cooler structure and the consequential buckling. Key to this understanding is the post-failure behaviour and re-stabilisation of the column, which is discussed with reference to a finite element model and an analytical model. Through bi-directional control of the temperature, the finite element model allows the snap-back behaviour to be modelled in detail and the effects of varying slenderness and load ratio are investigated. The analytical model employs structural mechanics to describe the behaviour of a heated strut, and is capable of explaining both elastic and fully plastic post-buckling behaviour.Through this detailed explanation of what happens when a heated column buckles, the consequences for steel-framed building design are discussed. In particular, the need to provide robustness is highlighted, in order to ensure that alternative load paths are available once a column has buckled and re-stabilised. Without this robustness, the dynamic shedding of load onto surrounding structures may well spread failure from a fire’s origin and lead to progressive collapse.     

Inelastic buckling and strengths of steel I-section arches with central torsional restraints

The elastic flexural–torsional buckling behaviour of arches with a central elastic torsional restraint has been reported elsewhere by the authors, and it was found that a central elastic torsional restraint restricts the buckling shape of an elastic arch and increases its elastic buckling resistance. However, both the inelastic buckling and strength of arches with a central elastic torsional restraint have hitherto not been investigated. It is not known whether the threshold stiffness for elastic buckling can be applied to arches which buckle inelastically, nor is it known how to determine the strength of steel arches with a central elastic torsional restraint. This paper modifies a finite element model for the nonlinear inelastic flexural–torsional analysis of steel I-section arches by including the effects of elastic restraints, and uses it to investigate the influence of central elastic torsional restraints on the inelastic flexural–torsional buckling and strength of steel I-section arches. It is found that a central elastic torsional restraint increases the strength of steel arches, but that the increase in strength decreases as the modified slenderness of the arches decreases. The threshold value of the stiffness of a central elastic torsional restraint at which the inelastic strength of an arch is equal to that of the corresponding arch with a rigid restraint is related to both the modified slenderness and included angle of the arch. For an arch with a low modified slenderness and with a small included angle which buckles inelastically, the threshold restraint stiffness is much smaller than that for an arch which buckles elastically. Design formulae for the strengths of steel I-section arches in uniform bending and in uniform compression with a central elastic torsional restraint are proposed. Comparisons with finite element results show that the proposed formulae provide good predictions for the strength of thin-walled steel I-section arches with a central elastic torsional restraint.     

钢结构大楼中箱型柱的制造工艺

介绍了钢结构大楼中箱型柱的制造工艺过程 ,从下料、切割、加工以及装配与焊接等方面进行了论述。指出该制造工艺经过实践验证为成熟技术 ,具有一定的借鉴作用。     

Application of the Direct Strength Method to local buckling resistance of thin-walled steel members with non-uniform elevated temperatures under axial compression

This paper assesses the applicability of the Direct Strength Method (DSM) to calculating the local buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members with non-uniform elevated temperature distributions in the cross-section. The assessment was carried out by checking the DSM calculation results with numerical simulation results using the general finite element software ABAQUS which was validated against ambient and uniform elevated temperature tests on short lipped channel sections. The validated numerical model was used to generate an extensive database (372 models) of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections, under different boundary and loading conditions and with different dimensions and lengths. It was concluded that the DSM local buckling curve was directly applicable for columns with uniform temperature distributions in the cross-section. For columns with non-uniform temperature distributions, a modification to the local buckling curve was necessary and this paper has proposed a new curve.     

Buckling analysis of thin-walled sections under localised loading using the semi-analytical finite strip method

Thin-walled sections under localised loading may lead to web crippling of the sections. This paper develops the Semi-Analytical Finite Strip Method (SAFSM) for thin-walled sections subject to localised loading to investigate web crippling phenomena. The method is benchmarked against analytical solutions, Finite Element Method (FEM) solutions, as well as Spline Finite Strip Method (SFSM) solutions. The paper summarises the SAFSM theory then applies it to the buckling of plates, and channel sections under localised loading. Multiple series terms in the longitudinal direction are used to compute the pre-buckling stresses in the plates and sections, and to perform the buckling analyses using these stresses. Solution convergence with increasing numbers of series terms is provided in the paper. The more localised the loading and buckling mode, the more series terms are required for accurate solutions. The loading cases of Interior One Flange (IOF) and Interior Two Flange (ITF) are investigated in this paper using simply supported boundary conditions.     

Comparative experimental study of hot-rolled and cold-formed rectangular hollow sections

Square and rectangular hollow sections are generally produced either by hot-rolling or cold-forming. Cross-sections of nominally similar geometries, but from the two different production routes may vary significantly in terms of their general material properties, geometric imperfections, residual stresses, corner geometry and material response and general structural behaviour and load-carrying capacity. In this paper, an experimental programme comprising tensile coupon tests on flat and corner material, measurements of geometric imperfections and residual stresses, stub column tests and simple and continuous beam tests is described. The results of the tests have been combined with other available test data on square and rectangular hollow sections and analysed. Enhancements in yield and ultimate strengths, beyond those quoted in the respective mill certificates, were observed in the corner regions of the cold-formed sections—these are caused by cold-working of the material during production, and predictive models have been proposed. Initial geometric imperfections were generally low in both the hot-rolled and cold-formed sections, with larger imperfections emerging towards the ends of the cold-formed members—these were attributed largely to the release of through thickness residual stresses, which were themselves quantified. The results of the stub column and simple bending tests were used to assess the current slenderness limits given in Eurocode 3, including the possible dependency on production route, whilst the results of the continuous beam tests were evaluated with reference to the assumptions typically made in plastic analysis and design. Current slenderness limits, assessed on the basis of bending tests, appear appropriate, though the Class 3 slenderness limit, assessed on the basis of compression tests, seems optimistic. Of the features investigated, strain hardening characteristics of the material were identified as being primarily responsible for the differences in structural behaviour between hot-rolled and cold-formed sections.     

Numerical and experimental investigations on the buckling of steel semi-spherical shells under various loadings

In this paper, the buckling and post-buckling of steel thin-walled semi-spherical shells are investigated under different loadings, both experimentally and numerically. Various vertical compression loadings are applied to specimens using the following methods: a rigid flat plate and some rigid bars with circular, square and spherical cross sections, a rigid tube, a plate with a hole, and an indented tube. The effects of geometrical parameters of specimens on the buckling load, such as the diameter and thickness, are studied. The numerical analysis is carried out by ABAQUS software and the experimental tests are performed using an Instron 8802 servo-hydraulic machine. The numerical and experimental results are similar to one another. Therefore, the numerical results are valid.     

Effect of higher order constitutive terms on the elastic buckling of thin-walled rods

In this paper we revisit an elastic constitutive equation proposed in two previous works and extend it in order to include all higher-order terms on the deformations. Our purpose is to assess the influence of these terms on the elastic buckling of thin-walled rods. The resulting material model was incorporated into a geometrically exact rod formulation and implemented into a nonlinear finite element code. By means of simple numerical examples we show that the higher order terms may play a significant role on the values of the buckling loads and on the post-buckling behavior of thin-walled beams and columns.     

Influence of autoclaving process parameters on the buckling and postbuckling behaviour of thin-walled channel section beams

The postbuckling behaviour and load carrying capacity of thin-walled composite channel sections subjected to uniform compression are presented. An analysis of the influence of parameters of the composite manufacturing process on strength properties and load carrying capacity of the thin-walled structure made of this composite has been conducted. The microstructure characteristics of composites is presented and discussed. The postbuckling behaviour and load carrying capacity of thin-walled channel section columns subjected to compression have been determined with the finite element method. The ANSYS software has been employed.     

The finite element analysis of the ultimate behavior of thin-walled carbon steel bolted connections

Finite element analysis (FEA) procedures were recommended for predicting the structural behaviors of single shear bolted connections in thin-walled stainless steel and carbon steel based on a previous numerical study with Kuwamura’s test results. The ultimate behaviors such as ultimate strength, fracture mode and curling occurrence predicted by FEA were in good agreement with those of test results. Especially, the effect of curling on the mechanical behavior of a stainless steel bolted connection has been focused. In this paper, an additional experiment for estimating in detail the block shear fracture mechanism and curling influence on thin-walled carbon steel bolted connections has been conducted. Finite element analysis was performed for test specimens. Bolted connections with a short end distance showed the typical block shear fracture. In contrast, connections with a relatively long end distance led to the ultimate state accompanied by out-of-plane deformation; curling. The ultimate strength reduction gets larger with the increase of end distance and the reduction ratio ranged from 4% to 17%. Moreover, this paper describes the comparison of strain distribution between specimens with curling and specimens without curling.     

Influence of friction stir welding residual stresses on the compressive strength of aluminium alloy plates

The mechanical behaviour of welded structures can be significantly affected by the effects of the employed joining process. The main goal of this work is to assess the influence of the longitudinal residual stresses on the overall compressive performance of aluminium friction stir welded plates. Longitudinal residual stress distribution was measured by means of the contour method and introduced as initial condition into a finite element model of the compressed assembly. Also, the sensitivity of the plates to the magnitude of the initial geometrical imperfections was analysed. It can be inferred that both factors influence the plate's mechanical behaviour.     

The development of the direct strength method for welded steel members with buckling interactions

The direct strength method (DSM) has been adopted by the NAS (2004) and AS/NZS 4600 (2005) for the design of cold-formed steel members. The method can be successfully applied to the design of welded and hot-rolled sections. This paper reviews the development of the DSM for welded steel structural members. The design strength formulae for welded section columns and beams for the DSM are provided based on the tests performed on welded H-section, C-section, circular and rectangular hollow section columns fabricated from steel plates whose nominal yield stress is 235 MPa or 315 MPa. The comparison between the design strength of welded sections predicted by the DSM and that estimated by existing specifications is provided. This paper verifies that the DSM which adopts the nominal axial strength and flexural strength in the AISC (2010) or EC3 (2004) can properly predict the ultimate strength of welded section columns and beams.     

Numerical evaluation on shell buckling of empty thin-walled steel tanks under wind load according to current American and European design codes

Liquid storage steel tanks are vertical above-ground cylindrical shells and as typical thin-walled structures, they are very sensitive to buckling under wind loads, especially when they are empty or at low liquid level. Previous studies revealed discrepancies in buckling resistance of empty tanks between the design method proposed by the American Standard API 650 and the analytical formulas recommended by the European Standard EN1993-1-6 and EN1993-4-2. This study presents a comparison between the provisions of current design codes by performing all types of numerical buckling analyses recommended by Eurocodes (i.e. LBA-linear elastic bifurcation analysis, GNA-geometrically nonlinear elastic analysis of the perfect tank and GNIA-geometrically nonlinear elastic analysis of the imperfect tank). Such analyses are performed in order to evaluate the buckling resistance of two existing thin-walled steel tanks, with large diameters and variable wall thickness. In addition, a discussion is unfolded about the differences between computational and analytical methods and the conservatism that the latter method imposes. An influence study on the geometric imperfections and the boundary conditions is also conducted. Investigation on the boundary conditions at the foot of the tank highlights the sensitivity to the fixation of the vertical translational degree of freedom. Further, it is indicated that the imperfection magnitude recommended by the EN1993-1-6 is extremely unfavorable when applied to large diameter tanks. Comments and conclusions achieved could be helpful in order to evaluate the safety of the current design codes and shed more light towards the most accurate one.     

The effect of semi-rigid joints and an elastic bracing system on the buckling load of simple rectangular steel frames

A linear stability analysis for establishing the combined effect of joint flexibility and an elastic bracing system on the buckling load of steel plane frames is presented herein. Based on the beam-to-column model of Eurocode 3, the subsequent study shows that joint flexibility is a very important parameter that needs to be incorporated into the stability analysis of frames with semi-rigid connections. It was found that assuming flexible connections in such frames always leads to a reduction of their buckling load, which is proven to be significant in many characteristic cases. Numerical results for simple elastically braced or unbraced frames with semi-rigid connections, in tabular and graphical form, reveal the pronounced effect of joint flexibility and elastic bracing on their buckling load. The results presented herein can be readily used for the design of simple frames against buckling, while the flexible connection concept can be applied to all types of steel frames.     

Recent advances on postbuckling analyses of thin-walled structures: Beams, frames and cylindrical shells

The lateral postbuckling response of thin-walled structures such as bars and frames with members having steel rolled shapes as well as circular cylindrical shells under axial compression is thoroughly reconsidered. More specifically via a simple and very efficient technique it is found that beams with rolled shapes (symmetric or non symmetric) under uniform bending and axial compression exhibit a stable lateral-torsional secondary path with limited margins of postbuckling strength. New findings for the static and dynamic stability of frames with crooked steel members-due to the presence of residual stresses-are also reported. It is comprehensively established that the coupling effect due to initial crookedness and loading eccentricity may have a beneficial effect on the load-carrying capacity of the frames. Moreover, simple mechanical models are proposed for simulating the buckling mechanism of axially compressed circular cylindrical shells. Very recently Bodner and Rubin proposed an 1-DOF mechanical model whose buckling parameters correlated to those of the shells by using an empirical formula based on experimentally observed shell buckling loads. In the present analysis a new 2-DOF model for the static and dynamic buckling of axially compressed circular cylindrical shells, which can include mode coupling, is presented.