Elastic Buckling Capacity Research Articles

Stability of laterally unsupported shear links in eccentrically braced frames

AbstractI‐shaped links in eccentrically braced frames (EBFs) are susceptible to lateral or lateral torsional buckling when subjected to cyclic link rotations. Lateral bracing should be provided at the ends of the I‐shaped links in order to prevent these failures. Requirements for such braces are available in widely used design specifications such as the AISC Seismic Provisions for Structural Steel Buildings (AISC341‐16) and EC8. These requirements limit the use of I‐shaped links in bridge piers and elevator shafts. A combined experimental and numerical study was undertaken to investigate the behavior of laterally unsupported I‐shaped links under cyclic loading. The experimental study consisted of testing of six nearly full‐scale EBFs where the link length, link length ratio, and presence of lateral supports were considered as the prime variables. The test results demonstrated that short links with link length ratios less than 1.22 can experience inelastic link rotations greater than the codified limit of 0.08 rad even without lateral bracing. A numerical parametric study was conducted to develop more generalized design recommendations for laterally unsupported I‐shaped shear links. Stability of one‐story one‐bay EBFs was studied using geometrically and materially nonlinear finite element analysis including imperfections. The numerical results showed that I‐shaped links without lateral bracing can provide a stable response when the link length ratio is less than 1.15. In addition to this limit, the ratio of the elastic critical buckling capacity to the plastic shear capacity should be greater than 3.5 and 2.5 for links with and without axial force, respectively.

Buckling behavior of composite double-layer space-grid structures

In order to better understanding the structural response of double-layer flat grids, the effects of using of a reinforced concrete (RC) topping in composite action with double-layer space-grid structures on the buckling behavior of such grids are studied. Both non-composite and composite flat grids (with and without any integral RC topping) with different span lengths are considered. The base models with span lengths of 15, 30 and 60 meters are initially selected and designed employing the well-known weight–density procedure. The finite element models are then developed in the ABAQUS environment with special consideration in the modeling procedure for beam type elements of pin connections at two ends in order to employ the capabilities of the software for buckling and post-buckling analyses. Elastic buckling analyses as-well-as non-linear analyses incorporating both the geometric and material non-linearities emphasizing the structural stability and post-buckling behavior are performed. It was found that the presence of a RC cover in composite action with double-layer flat grids can lead a decrease in the weight of steel around 29 % as-well-as maximum vertical deflection around 61 %. The presence of a RC layer can also improve the elastic buckling capacity up to 94 %. The results showed that the ultimate strength of such structures in composite state increases significantly. Finally, the RC layer can improve the post-buckling behavior which can lead an increase in the structural reliability from progressive failure or sudden loss of the structural strength.

Flexural behaviour and design of modular construction optimised beams

The use of modular construction shows continuous growth leading to cost-effective and fast construction methods. Modular Construction Optimised (MCO) beams are employed in steel-framed modular units owing to their enhanced structural performance. MCO beams fall under the hollow flange beam family and can be produced using roll forming techniques, with lesser cost compared to general built-up beams. However, there is no dominant research on the design approach to predict the section moment capacity of MCO beams. To bridge this knowledge gap, this paper aims to investigate the section moment capacity of MCO beams using numerical analysis. Numerical models were developed as simply supported four-point bending arrangement in ABAQUS. The validity of the numerical models in terms of failure capacity prediction and failure modes were ensured comparing the experimental results of the hollow flange and lipped channel beams. Subsequently, a comprehensive parametric study was conducted including various dimensional and strength parameters to generate a section moment capacity results database. The results were compared with the codified Direct Strength Method (DSM) predictions and appropriate design recommendations were proposed. Based on the results, a simplified calculation method to predict the critical elastic buckling capacity of the MCO beams was also developed. New findings arising from this study would enhance the applicability of MCO beams in steel modular structures.

DAİRESEL BOŞLUKLU KİRİŞLERDE EĞİLME VE YANAL BURULMALI BURKULMA DAVRANIŞININ İNCELENMESİ

3D Finite Element Analysis (FEA) was performed to determine flexural and elastic lateral-torsional buckling behavior of cellular beam by using European steel shape and quality. An experimental study from literature was chosen for verification of the Finite Element Model (FEM). Parametric studies were carried out with a verified numerical model to investigate the effect of some geometrical properties of the cellular beam such as hole diameter, hole spacing, and various types of rigidity plates on elastic buckling and flexural capacity of the beam. Geometric and material nonlinear behavior were included in FEM. In the other part of the study, the theoretical calculation method of Lateral Torsional Buckling (LTB) with gross section and with net section properties was also investigated. The study showed that the LTB calculation method given by AISC360-16 and TSDC-2016 design guides provided more accurate result with net cross-section for European steel shapes and quality.

Local Buckling Analysis of Cold-Formed Steel Webs with Rectangular Openings

The cold-formed steel members often require web openings to save interior space and allow for building services such as mechanical piping, electrical wiring, and air conditioning systems. Stress distribution in members with openings is different from members without holes, and therefore, their characteristics, shape, and modes of buckling are dissimilar which results in distinct behavior that could increase or decrease elastic buckling capacity and ultimate strength. In this study, analytical solutions for the local buckling of cold-formed steel webs with rectangular holes subjected to compression, bending and their combination are developed and summarized. The effects of flanges and other forces such as shear and torsion are not considered. The main variables are height of openings to height of web, aspect ratio of openings, and stress distribution gradient above or under the hole. These solutions can be used for a wide range of rectangular web openings for any sections. Analyses were conducted using energy-based methods, and the results were compared with numerical data obtained from the commercial finite element software (ABAQUS). The numerical results demonstrate that the three of the six proposed formulas can be used to predict the critical buckling stress of cold-formed steel webs with rectangular holes with regard to the aspect ratio of the web opening.

Experimental investigation of buckling response of pretwisted structural steel columns

This paper explores an attempt to experimentally investigate the axial capacity of prismatic and pretwisted structural steel sections under pinned-ended conditions. The main aim is to study the improvement in the elastic and inelastic buckling capacity for a selected Universal Column (UC100 × 100 × 17) section due to pretwisting. Short and slender UC sections were permanently twisted at a range of rotations between 0° and 60°, then tested under axial compression. The experimental results were utilized to verify a nonlinear finite element model that was developed to carry out a parametric investigation to incorporate several more lengths, angles of twists, and boundary conditions for the same UC section. Results revealed that pretwisting is more effective in improving the elastic buckling of slender columns since elastic buckling is primarily influenced by the section’s inertia as opposed to inelastic buckling which is affected by material yielding as well. Considerable buckling capacity improvement of up to 50% was achieved for fixed-ended pretwisted columns.

Investigation on the Collapse Behavior of Diagonal Stiffened Composite Plate Girders Subjected to Shear Loading

In this study, a new analytical method is presented to estimate the shear capacity of diagonally stiffened steel–concrete composite plate girders. This method is formulated based on tension field action in steel girder web and failure mechanism of concrete slab deck. To validate the accuracy of the proposed method, the obtained results are compared with three-dimensional finite element analysis of composite plate girders with different configuration of stiffeners. The results of analytical and numerical investigations indicate that the proposed method can accurately estimate the ultimate shear capacity of composite plate girders. In addition, it is shown that the diagonal stiffeners on one hand can reduce the buckling effects of shear panel of girders and on the other hand can increase the strength of elastic shear buckling and ultimate shear capacity of girders well in comparison with the unstiffened thin steel plate girders.

Buckling behaviour and design of complex-shaped aluminium mullion sections

Thin-walled aluminium mullions are the vertical framing members of the façade systems used in buildings. This article investigates the buckling behaviour of these complex-shaped aluminium mullions. For this purpose, the aluminium mullion sections were simplified into elements of varying thickness and modelled using CUFSM finite strip analysis programme. Elastic buckling analyses were performed with and without considering the availability of glass panel restraints for both negative and positive wind actions, and the results are presented in this article. The effect of providing return flanges to enable a good connectivity between the male and female mullions was also evaluated. The lateral restraints provided by glass panels were simulated using the spring stiffness option available in CUFSM, and the analyses were performed for spring stiffness values in the range of 0–1 N/mm/mm. The applicability of the buckling analysis results to the design of aluminium mullions was then evaluated using the direct strength method. For this purpose, the section moment capacities of mullions were determined from finite element analyses and compared with the direct strength method predictions using the CUFSM buckling analysis results. This comparison showed that direct strength method–based design can be adopted for the complex-shaped aluminium mullions provided their elastic buckling capacities are available. Overall, this study has provided good understanding of the buckling behaviour of mullion sections under both positive and negative wind actions and has proposed the use of direct strength method for the design of aluminium mullion sections.

Elastic imperfect tip-loaded cantilever cylinders of varying length

A number of recent publications have explored the crucial relationship between the length of a thin cylindrical shell and the influence of pre-buckling cross-sectional ovalisation on its nonlinear elastic buckling capacity under bending. However, the research thus far appears to have focused almost exclusively on uniform bending, with ovalisation under moment gradients largely neglected.This paper presents a comprehensive computational investigation into the nonlinear elastic buckling response of perfect and imperfect thin cantilever cylinders under global transverse shear. A complete range of practical lengths was investigated, from short cylinders which fail by shear buckling to very long ones which exhibit local meridional compression buckling with significant prior cross-section ovalisation. Two imperfection forms were applied depending on the length of the cylinder: the linear buckling eigenmode for short cylinders and a realistic weld depression imperfection for long cylinders. The weld depression imperfection was placed at the location where the cross-section of the perfect cylinder was found to undergo peak ovalisation under transverse shear, a location that approaches the base support with increasing length. Compact closed-form algebraic expressions are proposed to characterise the elastic buckling and ovalisation behaviour conservatively, suitable for direct application as design equations.This study contributes to complete the understanding of cylindrical structures of varying length where the dominant load case is global transverse shear, including multi-strake aerospace shells with short individual segments between stiffeners and long near-cylindrical wind-turbine support towers and chimneys under wind or seismic action.

Cyclic analyses of corrugated steel plate shear walls

SummaryCorrugated steel plate shear wall (CoSPSW), which consists of a steel boundary frame and a corrugated steel wall panel with the corrugation in the horizontal or vertical direction, is a new type of lateral load‐resisting system in the family of steel plate shear walls. Compared with the unstiffened special plate shear walls (SPSW), CoSPSW would have greater elastic buckling capacity and more resistance to the gravity loads transferred to the wall panel or neatly avoid them, depending on the corrugation direction. The main research contents of this paper is on the cyclic behavior of CoSPSWs and comparison with SPSWs. Nonlinear push‐over and cyclic analyses were conducted on a group of CoSPSW and SPSW models, and parametric studies were performed with different panel and frame configuration, as well as gravity load effects. It turns out that CoSPSWs with deep corrugation have higher lateral stiffness, lateral strength, and energy dissipation than SPSWs, whereas CoSPSWs with shallow corrugation have higher lateral stiffness and ductility, but lower lateral strength than SPSWs. For all cases investigated, CoSPSWs have stable hysteric curves with no almost pinching, and they are much less sensitive to the influence of gravity loads or weaker boundary frames, compared to SPSWs.

Development of Closed-Form Equations for Estimating the Elastic Local Buckling Capacity of Pultruded FRP Structural Shapes

AbstractThe main objective of this paper is to develop closed-form equations for estimating the elastic local buckling capacity of pultruded fiber-reinforced polymer (FRP) structural shapes. This i...

Simplified semi-analytical model for elastic distortional buckling prediction of cold-formed steel flexural members

The expressions for elastic distortional buckling stress predictions available in literature are used with reasonable accuracy, but are either iterative or involve increased calculation effort for design. It is an accepted fact among researchers that these expressions are not evaluated enough for the distortional stress prediction of sections with complex lip stiffeners. In this paper, a candidate model for distortional buckling stress predictions is presented which is semi analytical in nature and is simple to incorporate in the direct strength method (DSM) of cold-formed steel design. The proposed expression incorporates the effect of complex lip stiffeners on the elastic distortional buckling capacities of cold formed steel flexural members. In the proposed model, the (i) translational stiffness at lip-flange junction and (ii) rotational stiffness at the flange-web junction, are derived from regression analysis of wide range of cross sectional dimensions. The proposed method is calibrated with semi-analytical finite strip method presented in the literature and this formulation has been demonstrated to be good in comparison with recently published numerical based distortional buckling predictions.

On the improvement of buckling of pretwisted universal steel columns

This paper investigates the improvement in elastic buckling capacity of pretwisted columns using Linear Perturbation Approach. Three different Universal Column (UC) sections of various lengths were considered in the proposed study assuming fixed–fixed and pinned–pinned end conditions. Linear perturbation analysis was first verified by comparing the critical loads of the simulated straight columns with analytical results. Numerical analysis was then extended to simulate the buckling improvement of pretwisted columns considering four different lengths of 4m, 5m, 6m and 7m, and a range of twisting angles between 0° and 180°. The results showed that the initial twisting has positively impacted the axial capacity of the pretwisted columns. This noticeable improvement is supported by the significant increase in the buckling capacity for the three UC sections, particularly at angles of twists between 120° and 150°.

Local Buckling of Cold-Formed Steel Members with Edge Stiffened Holes

Cold formed steel members with edge stiffened holes are a new generation of cold formed members recently developed by the building industry. Very little research has been performed on such sections to determine their local and distortional buckling capacity. This article provides the numerical results of elastic local buckling analysis of cold-formed lipped channels with edge stiffened holes. For flexural elements values of critical buckling moments are calculated and the influence of hole spacing and diameter on elastic buckling capacity is determined.

Elastic flexural and torsional buckling behavior of pre-twisted bar under axial load

According to deformation features of pre-twisted bar, its elastic bending and torsion buckling equation is developed in the paper. The equation indicates that the bending buckling deformations in two main bending directions are coupled with each other, bending and twist buckling deformations are coupled with each other as well. However, for pre-twisted bar with dual-axis symmetry cross-section, bending buckling deformations are independent to the twist buckling deformation. The research indicates that the elastic torsion buckling load is not related to the pre-twisted angle, and equals to the torsion buckling load of the straight bar. Finite element analysis to pre-twisted bar with different pre-twisted angle is performed, the prediction shows that the assumption of a plane elastic bending buckling deformation curve proposed in previous literature (Shadnam and Abbasnia 2002) may not be accurate, and the curve deviates more from a plane with increasing of the pre-twisting angle. Finally, the parameters analysis is carried out to obtain the relationships between elastic bending buckling critical capacity, the effect of different pre-twisted angles and bending rigidity ratios are studied. The numerical results show that the existence of the pre-twisted angle leads to "resistance" effect of the stronger axis on buckling deformation, and enhances the elastic bending buckling critical capacity. It is noted that the "resistance" is getting stronger and the elastic buckling capacity is higher as the cross section bending rigidity ratio increases.

Increasing Girder Elastic Buckling Strength Using Split Pipe Bearing Stiffeners

Warping restraining devices can result in substantial improvements in the girder elastic buckling capacity; however, calculating this increase can be complex. This paper presents a simplified method to evaluate the increase in elastic buckling strength and corresponding unbraced length due to improved warping restraint provided by split pipe stiffeners located at the ends of doubly symmetric W-shapes. The solution is based on analytical studies and results from a finite-element parametric study validated using large-scale laboratory tests. The laboratory tests include specimens exposed to concentrated loads with split pipe warp-restraining devices and others with standard plate stiffeners. The proposed analytic method is based on uniform moment and shows that warping restraint can increase the elastic buckling capacity of a girder by 30–100%. The improved warping stiffness can result in increases in the unbraced length in the range of 20–35% compared with systems with plate stiffeners.

Experimental evaluation of the elastic buckling and compressive capacity of laced columns

To investigate the static behavior of laced columns, 18 tests were conducted on sample columns constructed from pairs of u-section profiles with various lengths and various distances between the main chords, all with an initial imperfection. To study the behavior of built-up columns in the plane parallel to the lacing planes, the test set-up was arranged in such a way that buckling occurred in this plane. There was generally good agreement between the test results and the theoretical results for the elastic critical loads. The SSRC method overestimated the results with a high error, whereas Engesser's method was more conservative, with a minor error. Bleich's method and Paul's method both led to results with moderate error. The compressive capacity of the sample columns, obtained by the tests, were compared to those obtained by the Ayrton–Perry and capacity curves methods, of which the first gave conservative results and the second led to the results being slightly overestimated. The experimental results showed that the amount of initial imperfection has a significant effect on reducing the compressive capacity of the samples.

Numerical modelling and design of LiteSteel Beams subject to lateral buckling

The LiteSteel Beam (LSB) is a new hollow flange channel section developed using a patented dual electric resistance welding and cold-forming process. It has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a slender web, and is commonly used as flexural members. However, the LSB flexural members are subjected to a relatively new lateral distortional buckling mode, which reduces their moment capacities. Unlike lateral torsional buckling, the lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist and cross sectional change due to web distortion. Therefore a detailed investigation into the lateral buckling behaviour of LSB flexural members was undertaken using experiments and finite element analyses. This paper presents the details of suitable finite element models developed to simulate the behaviour and capacity of LSB flexural members subject to lateral buckling. The models included all significant effects that influence the ultimate moment capacities of such members, including material inelasticity, lateral distortional buckling deformations, web distortion, residual stresses, and geometric imperfections. Comparison of elastic buckling and ultimate moment capacity results with predictions from other numerical analyses and available buckling moment equations, and experimental results showed that the developed finite element models accurately predict the behaviour and moment capacities of LSBs. The validated model was then used in a detailed parametric study that produced accurate moment capacity data for all the LSB sections and improved design rules for LSB flexural members subject to lateral distortional buckling.

Elastic buckling capacity of bonded and unbonded sandwich pipes under external hydrostatic pressure

Elastic buckling capacity of bonded and unbonded sandwich pipes under external hydrostatic pressure

Elastic and inelastic local buckling of stiffened plates subjected to non-uniform compression using the Galerkin method

A solution for the elastic and inelastic local buckling of flat rectangular plates with centerline boundary conditions subjected to non-uniform in-plane compression and shear stress is presented. The loaded edges are simply supported, the longitudinal edges may have any boundary conditions and the centerline is simply supported with a variable rotational stiffness. The Galerkin method, an effective method for solving differential equations, is applied to establish an eigenvalue problem. In order to obtain plate buckling coefficients, combined trigonometric and polynomial functions that satisfy the boundary conditions are used. The method is programmed, and several numerical examples including elastic and inelastic local buckling, are presented to illustrate the scope and efficacy of the procedure. The variation of buckling coefficients with aspect ratio is presented for various stress gradient ratios. The solution is applicable to stiffened plates and the flange of the I-shaped beams that are subjected to biaxial bending or combined flexure and torsion and shear stresses, and is important to estimate the reduction in elastic buckling capacity due to stress gradient.