Local Buckling Strength Research Articles

Dynamic pulse buckling and failure analysis of the single curved composite sandwich panel using the core high-order theory

The current study aims to investigate the facesheet dynamic pulse buckling of simply supported, cylindrical composite sandwich panels using the Budiansky–Roth buckling criterion. The foam core has been modeled with isotropic elastic-perfectly plastic properties and various failure modes of the sandwich panel like facesheet fracture, foam shear fracture, and foam yield are investigated. The extended high-order sandwich panel core theory was used to model the compressibility of the core. To study the mechanical properties of the viscoelastic foam core, the Kelvin–Voigt linear viscoelastic model was applied. The transient responses and stress components obtained from the present method are compared with finite element solutions using commercial software ANSYS and those reported in the literature. Accordingly, reasonable agreement is observed. It was shown that the pulse local buckling strength of the panel increases with a decrease in the panel radius or an increase in the thickness of the panel, and facesheet fracture is considered more a likely failure mode of these sandwich panels.

Local buckling of longitudinally stiffened plates with rotational stiffness of closed-section ribs

Recent studies have shown that the rotational stiffness of longitudinally installed closed-section ribs increases the local buckling strength of thin plates. Thus, in this study, the equations for the buckling strength of compressively loaded stiffened plates, which reasonably account for the partially restrained effect, were theoretically derived using the principle of minimum potential energy. Through three-dimensional refined finite element analysis performed using ABAQUS that appropriately simulates the buckling of plates stiffened with rotational rigidities along the sides, a series of parametric numerical analyses were conducted to examine the variation in buckling stresses based on the influential parameters revealed from the theoretical formulas. Further simplified and readily applicable formulas for the strength increment factor were derived from a series of rigorous regression analyses on the parametric analysis results. A comparative study of the suggested approximate solutions and the numerical analysis results was carried out to validate the proposed method.

Analysis of uniaxially loaded short round-ended concrete-filled steel tubular beam-columns

Round-ended concrete-filled steel tubular (RCFST) columns exhibit low resistance to running water, strong y-axis bending strength and aesthetic appearance for their use in bridge piers. However, the behavior of RCFST beam-columns under uniaxial loading has not been studied numerically. This paper describes the computational simulation and design of uniaxially compressed short RCFST beam-columns. The nonlinear simulation is based on the numerical fiber-based methodology. The flange local and post-local stability in terms of outward buckling of the flat plate and circular-rectangular concrete confinement are considered in the fiber-based simulation. The simulation procedures for generating the load-strain responses, moment-curvature curves, and nonlinear strength envelopes are described. The computed axial capacity, ultimate bending strength and load-strain performance of short RCFST beam-columns are assessed against the independent experimental results. The statistical results reveal the accuracy of the fiber-based simulation for exploring the compression and bending behavior of short RCFST beam-columns. The parametric analysis is conducted using the fiber-based model to examine the local buckling, bending axis, aspect ratio, and material strength influence on the performance of uniaxially compressed RCFST short beam-columns. The design of eccentrically loaded short beam-columns based on Eurocode 4 provisions is described.

Effect of concrete infill on local buckling capacity of circular tubes

For circular steel sections, axial slenderness limits are typically defined in terms of the diameter-to-thickness ratio and indicate whether the member will first yield or locally buckle under axial compression. The common opinion is that filling a hollow structural section with concrete would enhance its resistance against local buckling by restraining its inward deformations. On the basis of this concept, the axial slenderness limits stipulated by most international design standards are notably higher for filled sections when compared to their hollow counterparts. Although there is extensive evidence in support of this approach for box sections, the available data for circular sections is limited and, in some cases, inconsistent. While some studies and most international design standards suggest that filled circular sections should have a notably higher axial slenderness limit compared to hollow circular sections, a number of studies argue that the concrete infill is in fact not very effective in increasing the local buckling strength of circular sections. Such studies are however very limited in the literature and often incomplete. Consequently, a comprehensive numerical study with over 140 analyses is conducted herein considering different material types, a wide range of slenderness values, and five initial imperfection modelling techniques to clarify the role of concrete infill in the local buckling behaviour of circular sections. Results of the study strongly suggest that the concrete infill has limited effect on enhancing the local buckling strength of circular tubes. The enhancement is found to be much lower than that implied in international design standards. The roots for this discrepancy are identified and recommendations are proposed in light of the findings of the study. The results suggest that the axial slenderness limit for hollow circular tubes can be significantly relaxed to bring it closer to that of filled circular tubes.

Elastic local buckling strength and maximum strength of cold‐formed steel members with different plate widths on adjacent plate elements

AbstractA key issue in the design of cold‐formed steel members is their local buckling strength under axial compression. In this study, we focused on the local buckling strength of rectangular section and lipped C‐section members, the adjacent plate elements of which have a different width‐thickness ratio, and we investigated their elastic and inelastic local buckling strengths through a numerical analysis. On comparing the numerical analysis results with those obtained using a conventional design method, we found that the plate restraining effect between the adjacent plate elements affected both the elastic buckling strength and maximum strength of the cold‐formed steel members.

Rotational Stiffness Requirements of Closed-Section Stiffeners for Buckling Strength Increment of Stiffened Plates Under Uniaxial Compression

In these days, closed form solutions to estimate the strength increment in the local buckling strength due to the rotational stiffness of the closed-section ribs have been proposed through theoretical approaches using the energy methods and parametric numerical analysis. In this paper, the correlations between the local buckling strength of longitudinally stiffened plates and the rotational restraint stiffness of closed-sections ribs were thoroughly investigated through numerical analyses. Three-dimensional finite element models of longitudinally stiffened plates were obtained using ABAQUS, and a series of comprehensive parametric numerical analyses were conducted in order to reveal the influential design parameters for required rotational stiffness of closed-section ribs for reaching converged buckling strengths. Then, a simplified design equation for the required rotational stiffness for the stiffened plate buckling strength has been proposed, which are applicable for both flat and curved plates to achieve optimum design sections. The comparative study and trend analysis showed that the proposed design methods have a good correlation with the numerical analysis results. Finally, a series of design examples demonstrate a design process of the longitudinally stiffened plates with closed-section ribs by using the proposed design equations.

An experimental study on the local buckling strength of an SBHS700 stub column with cruciform section

AbstractKurita‐Albrecht Young Engineers Award 2018 – SteelRecently, SBHS (Steels for Bridge High‐Performance Structure) has been introduced in Japan because of its remarkable mechanical properties. The main features of SBHS are high yield strength, improved toughness and weldability, which are superior to conventional steel materials at the corresponding tensile strength grades. In this study, these material properties of SBHS were compared with conventional steel materials through experimental studies as well as the Japanese design specifications. The main focus of this paper is the evaluation of the local buckling strength of two SBHS700 stub columns, each with cruciform section through compression tests. The load‐displacement relationship, strain bifurcation related to plate buckling and out‐of‐plane deformation are discussed. Two test specimens with different width‐to‐thickness ratio parameters RR are compared. As the results indicate, for the specimen having a larger RR, an abrupt decrease in load was observed after the peak load, whereas the decrease in load for the specimen with a smaller RR proceeded gradually after the peak load with a much larger vertical displacement. In terms of local buckling strength, it was found to be possible to evaluate the SBHS700 stub column with cruciform section based on the existing ultimate strength curves.

The effects of residual stresses and strains on lateral-torsional buckling behavior of cold-formed steel channel and built-up I-sections beams

Purpose The purpose of this paper is to focus on the influences of residual stresses which were induced during roll-forming sections on lateral-torsional buckling of thin-walled cold-formed steel channel and built-up I-sections beams. Built-up I section is made up of two back-to-back cold-formed channel beams. In this direction, at the primary stage, the roll-forming process of a channel section was simulated in ABAQUS environment and the accuracy of the result was verified with those existing experiments. Residual stresses and strains in both longitudinal and circumferential transverse directions were extracted and considered in the lateral-torsional buckling analysis under uniform end moments. The contribution of the current research is devoted to the numerical simulation of the rolling process in ABAQUS software enabling to restore the remaining stresses and strains for the buckling analysis in the identical software. The results showed that the residual stresses decrease considerably the lateral-torsional buckling strength as they have a major impact on short-span beams for channel sections and larger span for built-up I sections. The obtained moment capacity from the buckling analysis was compared to the predictions by American Iron and Steel Institute design code and it is found to be conservative. Design/methodology/approach This paper has explained a numerical study on the roll-forming process of a channel section and member moment capacities related to the lateral-torsional buckling of the rolled form channel and built-up I-sections beams under uniform bending about its major axis. It has also investigated the effects of residual stresses and strains on the behaviour of this buckling mode. Findings The residuals decrease the moment capacities of the channel beams and have major effect on shorter spans and also increase the local buckling strength of compression flange. But the residuals have major effect on larger spans for built-up I sections. It could be seen that the ratio of moment (with residuals and without residuals) for singly symmetric sections is more pronounced than doubly symmetric sections. So it is recommended to use doubly symmetric section of cold-formed section beams. Originality/value The incorporation of residual stresses and strains in the process of numerical simulation of rolled forming of cold-formed steel sections under end moments is the main contribution of the current work. The effect of residual stresses and strains on the lateral-torsional buckling is, for the first time, addressed in the paper.

Buckling strength of thin-walled steel cylindrical shells with stiffened plates

Thin-walled steel shell members are structurally superior as structural members. However, the thin-walled steel shell with stiffeners has been only studied in a part by reason of excelling dynamically on ordinary thin-walled shell without stiffeners. In this paper an investigation in regard of the increase of the buckling capacity on steel cylindrical shells with out- and inside stiffened plates is generated under pure axial compression. Then, so as to clarify the effect of the buckling capacity on thin-walled steel cylindrical shells with out- and inside stiffened plates, exact buckling strength and buckling mode shapes are generated by using the extended transfer matrix method. The buckling strength of cylindrical shell with out- and inside stiffened plates are obtained during the combination of half wave number (n) for perpendicular direction to axis and half wave number (m) for axis direction. Depending on circumstances, the local buckling strength of thin-walled shells with stiffened plates is sometimes failing by local buckling of stiffened plate to differ from local buckling of shell-panel in comparison with that of ordinary thin-walled shells without stiffener. Therefore, this study aims to plan increase of the local buckling capacity on the thin-walled steel cylindrical shells with out- and inside stiffened plates due to pure axial compression.

Elastic-plastic local buckling model of rectangular CFT columns under axial compression

Assuming that the loaded edges of steel plates are clamped, while the unloaded edges are restrained against rotation, the elastic-plastic local buckling model of rectangular CFT columns was proposed. The formula for calculating elastic-plastic local buckling strength of steel plates in rectangular CFT columns were proposed using the deformation theory of plasticity. The calculated results by formula were compared with the experimental results, showing good agreement between the calculated results and the experimental results. Based on the proposed elastic-plastic local buckling model of rectangular CFT columns, the effects of width-to-wall thickness ratios on the elastic-plastic local buckling critical stress of the steel tube in the cases of different cross-sectional aspect ratios were investigated. Finally, the reasonable limitations for width-to-wall thickness ratios and the reasonable thickness ratios of the steel plates in the cases of different cross-sectional aspect ratios are suggested for engineering design, which can ensure that the elastic-plastic local buckling of the steel tube can not occur before the steel yield.

Local and post-local buckling of fabricated high-strength steel and composite columns

High-strength structural steel plates are being increasingly used as composite columns in tall buildings, bridges and large infrastructure. The presence of concrete infill in these composite sections enhances their local buckling strength, and thus very slender steel plates can be used in their fabrication. This paper presents the results of an experimental study and numerical investigation of the local buckling slenderness limits for high-strength steel plates. A set of sixteen tests were conducted on both hollow steel and steel-concrete composite sections to explore their local and post-local buckling behaviour under axial compression. A numerical model which accounts for the effects of residual stresses and initial geometric imperfections was developed to predict the local buckling and post-local buckling response of box and I-section columns. This model was verified against the test results. Yield slenderness limits obtained from numerical results were compared with existing codes of practice for both hollow steel and composite sections incorporating high-strength steel plates.

Elastic local buckling strength analysis of stiffened aluminium plates with an emphasis on the initial deflections and welding residual stresses

ABSTRACTThis study aims at estimation of the elastic local buckling strength of stiffened aluminium plates. First, the patterns of initial deflections and welding residual stresses are studied in details. Then, the energy-method-based Fujikubo–Yao's algorithm is so modified that the assessment of the elastic local buckling strength of the stiffened aluminium plates becomes possible focusing on the specific characteristics of welding residual stresses and initial deflections. The modified algorithm is implemented into a computer code in MATLAB environment, where it is verified against the FEM. Three groups of the stiffened aluminium plates are considered and used for some further parametric studies.

Behaviour and design of cold-formed steel built-up section beams with different screw arrangements

An experimental and numerical investigation of cold-formed steel built-up beams with different screw arrangements is presented in this paper. A total of 35 beams were tested under four-point bending with different screw arrangements in the moment span. The built-up sections were assembled using self-tapping screws from either two lipped channels connected back-to-back at the web to form an open section or two plain channels connected face-to-face at the flanges to form a closed section. Finite element (FE) models have been developed and validated against the test results for the built-up open section beams and built-up closed section beams, respectively. It is shown that the FE models can accurately predict the behaviour of cold-formed steel built-up beams with different screw arrangements. A parametric study on built-up beams with larger span and various screw spacing was further carried out using the verified FE models. The test and numerical results were compared with the design strengths predicted by the direct strength method (DSM) for cold-formed steel structures, with contingent considerations of the screws when determining the elastic buckling moments in the finite strip analysis. A reliability analysis was performed to evaluate the reliability of the current DSM equations. It is shown that the current DSM equations can predict the design strengths of built-up open section beams well in this study, with the assumption that the strength of the built-up section is the sum of two component profiles. However, the design equations for local buckling strength are generally conservative for the built-up closed section beams failed by local buckling. Meanwhile, the design equations for lateral-torsional buckling (LTB) strength cannot be directly used for the built-up closed section beams with relatively large screw spacing that failed by LTB with cross section distortion or separation of two component channels. It should be noted that LTB mode with cross section distortion was found in built-up closed section beams with large screw spacing. A modified design rule based on DSM is then proposed, which is shown to improve the accuracy of the predicted strengths. Moreover, the maximum longitudinal screw spacing for built-up closed section beams was also recommended for design practice.

Effects of Moment Gradient on Elastic Flange Local Buckling of I-Shaped Beams

Recently, after clearly pointing out the flaws associated with the current AISC equation for flexural strength of I-shaped beams with slender flange, the authors proposed new equation, more accurate and more consistent than the current AISC equation, based on the mixed variational approach. However, the new equation was derived under the condition of uniform moment loading. In this paper, elastic flange local buckling strength formula for I-shaped beams with slender flange under moment gradient was proposed as a follow-up study on the basis of mixed variational approach and supplemental numerical works. The flange plate buckling coefficient predicted by the formula of this study is again shown to be much more accurate and consistent.

Numerical Slenderness Approach for design of complex aluminum extrusions subjected to flexural loading

Aluminum structural members can be extruded to various cross-sectional shapes, including additional elements projecting out of flat flanges or webs. The additional elements contribute to flexural strength increase due to local buckling strength increase. In this study, a general design approach is developed for complex extrusions, accounting for the local buckling strength increase. This approach uses numerical buckling analyses, while the overall framework of the existing specification provisions is maintained. The approach is evaluated through parametric studies of seven different kinds of cross-sections, using finite element analysis. The FEA models and the parametric study results are validated through physical tests.

Analytical solution for local buckling strength of square CFT columns subjected to eccentric compression

Theoretical study on local buckling behavior of square CFT columns subjected to eccentric compression has been carried out. Assuming that both the loaded edges and the unloaded edges of the steel plate are clamped, the analytical solution for local buckling strength of steel plates in square CFT columns subjected to eccentric compression is derived by energy method. Furthermore, the relationship between the local buckling coefficient of steel tube and the stress gradient is investigated. It is found that the local buckling coefficient of steel tube increases with the increase of the stress gradient. When the stress gradient equals 0, namely the steel plate is subjected axial compression, the minimum of the local buckling coefficient of steel tube is obtained, namely 10.312; when the stress gradient equals 2, namely the steel plate is subjected to pure bending, the maximum of the local buckling coefficient of steel tube is obtained, namely 22.713. Then, the relationship of local buckling strength of steel plates in square CFT columns subjected to eccentric compression with b / t ratios at different stress gradients is studied, resulting in the reasonable limitations for b / t ratios of the steel plates at different stress gradients in square CFT columns subjected to eccentric compression for the reference of engineering design.

Compressive stress-strain model of cold-formed circular hollow section stub columns considering local buckling

A complete stress-strain model for cold-formed circular hollow section (CHS) stub columns under compression is proposed with emphasis placed on the modeling of post-local-buckling behavior. The proposed model comprises two mathematical expressions. One of the two equations is to define the ascending portion of the proposed stress-strain curve and depict the nonlinearity caused by residual stress induced during manufacturing process of cold-formed CHS, while the other is to define the descending portion and trace the post-local-buckling behavior. The proposed stress-strain model is a single parameter model. Only if the generalized outer diameter-to-thickness ratio is given, the compressive stress-strain relationship of a CHS can be completely determined. To calibrate the proposed model and verify its accuracy, test results of forty-eight CHS stub columns under compression are collected. The previous tests cover a wide range of structural factors such as outer diameter-to-thickness ratio and yield strength, particularly including CHS stub columns with yield strength of up to 1180MPa. Comparisons between the measured results and the calculated ones indicate that the proposed model can not only predict the local buckling strength as well as corresponding strain, but also trace the post-local-buckling behavior up to large strain with high accuracy.

05.42: Evaluation of ultimate strength and plastic deformation capacity of square hollow section members under bending shear

ABSTRACTThe purpose of this study is to evaluate ultimate strength and plastic deformation capacity of square hollow section members under bending shear governed by local buckling as a function of member shapes and loading conditions. First, elastic local buckling strength under bending shear derived from theoretical analysis is shown. A new normalized width–thickness ratio SH based on elastic local buckling strength and full plastic strength is proposed. Then, after understanding the elastic local buckling behavior purely determined by member shapes and loading conditions, the large deformation behavior under monotonic bending shear is examined using numerical analysis and structural testing. The ultimate strength and plastic deformation capacity are evaluated using the new normalized width–thickness ratio SH as a function of width–thickness ratio, aspect ratio, gradient of bending moment, and angle of applied force. Finally, the large deformation behavior under cyclic bending shear is examined using structural testing. The relation between the ultimate strength or plastic deformation capacity and the new normalized width–thickness ratio SH is reported.

Strength of double skin steel-concrete composite walls

Double skin steel-concrete composite walls have been increasingly used in civil engineering applications. However, the advantages of these walls have not been fully recognized due to the lack of appropriate technical guidelines for capacity design. In this paper, the local buckling strength of steel plate were firstly reviewed in terms of specifications incorporated in several modern codes. A methodology to predict the strength of steel plate with restraint of both concrete and shear studs was proposed based on the explicit solution for local buckling of steel plate in composite shear walls subjected to uniform axial compression and with elastically rotational restraint at loaded and unloaded edges. The results were compared with various previous experimental data and good agreement was observed. Furthermore, the load carrying capacity of composite walls was derived from the superposition of the contribution of steel plate and concrete. The predicted values from the proposed equations, together with the resulted determined from modern codes, were compared with the experimental results. It was found that both the proposed method and JEAG 4618 offer reasonable predictions while AISC 360 and KEPIC-SNG always underestimate the actual values.

ASEISMATIC PERFORMANCE OF HYBRID STEEL COLUMN CONSISTS OF HIGH STRENGTH STEEL FLANGE AND CONVENTIONAL STEEL WEB

Recently in Japan, the pulse type earthquakes that cause large displacement responses have been more noticeable. Some of them are predicted to become much larger than the magnitude level used in the current design, so it is promoted to set new seismic wave levels for design and to study about new design methods. To reduce damage of buildings against huge earthquakes, it has been considered to increase the elastic limit deformation using high strength steels in columns and girders. In this study, on the contrary, we propose the frames using conventional girders and hybrid H-section columns that consist of flange manufactured from high strength steel and web made with conventional strength steel. In order to apply the hybrid H-section columns to a building, the following items should be clarified; (1) method of evaluating full-plastic strength, (2) understanding the behavior of the hybrid H-section alone, (3) understanding the behavior of the hybrid H-section column in a frame. To investigate these items, we fabricated several specimens and conducted stub column tests, bending and shear tests, and cruciform tests. The experimental findings are complemented by a finite element simulation study. In Chapter 2, at first, we derive a full-plastic moment of hybrid H-section column under combined stress, including axial force, shear force and bending moment. Secondly we assumed the application limit of the formula. The following chapter describes that the stub-column tests and bending and shear tests were conducted to comprehend the elasto-plastic behavior caused by local buckling. Chapter 5 and 6 describes that we conducted the beam-to-column subassemblages test to verify the effects on high strength steel flange caused by axial force and plastic deformation of beam-column connection. By the series of experiments and analyses, we obtained the following results; (1) Full-plastic moment of hybrid H-section column and the application limit are shown in chapter 2. (2) Within the limit of application, platicizing of conventional strength steel web has little effects on high strength steel flange, therefore the hybrid H-section column can be regarded as elastic member until it reaches full-plastic strength. Further, if the width-thickness ratio satisfies the FA rank, the axial-yield of the web in an early stage has little effects on flange local buckling strength and plastic deformation capacity. (3) The extension of axial tensile strain, which is one of the factors of the stress degradation, can be reduced by column axial force. “Break by tensile strain” of the hybrid H-section column can be avoided unless the column axial force is neutralized by the fluctuating axial force in the case of earthquakes. (4) The relationship between column-to-beam strength ratio and the deformability of a cruciform frame is revealed by finite-element analyses in chapter 6. We proposed the design method of the hybrid H-section column that consists of flange made with high strength steels and web made with conventional strength steels. We expect the hybrid H-section column to be utilized as reasonable aseismatic column member for reducing the damage against huge earthquakes.