Buckling Of Members Research Articles

Estimation of ultimate capacities of Moment-Resisting Frame’s subassemblies with Mid-Storey Pin connection based on elastoplastic local buckling

This research proposes a novel method of Mid-Storey Pin Moment-Resisting Frames’ (MSP MRFs) ultimate capacity estimation. Shell and solid numerical models with initial imperfections are defined and calibrated against the experimental results. Parametric studies are conducted, presenting the influence of structural parameters on the performance and failure mode of the frame dictated by the elastoplastic local buckling of members. It is shown that commonly used control over column-to-beam plastic moment ratio is insufficient; the need for column-to-beam stiffness ratio consideration is highlighted. Finally, innovative yet simple equations are proposed to estimate the frame’s storey drift capacity and ultimate strength ratio.

Seismic evaluation of concentrically braced steel frames equipped with yielding elements and BRBs

As a way of increasing lateral load resistance, Concentrically Braced Frames (CBFs) are employed in steel structures. Structures with CBF display high lateral stiffness and experience lesser story drifts than structures with Moment Resisting Frame (MRF). Despite the advantages, there are some major problems in the performance of the braced frames, such as low capacity in energy dissipation, buckling of conventional brace members, and degradation of strength and stiffness. To increase the energy dissipation of braced frames, central yielding elements in the intersection of braced members have been proposed in the past. In this study, BRB elements were placed in the bracing system to improve energy dissipation and lateral stiffness and to reduce buckling in the bracing. Designing a structure that includes the stated lateral-load-resisting system necessitates seismic performance parameters to be evaluated. As the study's main purpose, by pursuing the FEMA P695 methodology, seismic parameters, including response modification factor, over-strength factor, and deflection amplification factor (R-, Ω-, and Cd-factor), are specified. Several archetypes with various properties were considered to reflect the possible application of this bracing system. Based on FEMA P695, static pushover analyses are implemented to establish over-strength factors for archetypes. Subsequently, Incremental Dynamic Analyses (IDA) are implemented to specify Adjusted Collapse Margin Ratios (ACMRs). Finally, the acceptance of the abovementioned assumed factors for the system is scrutinized by comparing ACMRs values with the values which are acceptable in FEMA P695.

Enhancements to the Direct Strength Method of cold-formed steel member design

The design of thin-walled cold-formed steel members must consider various forms of buckling. The Direct Strength Method simplifies strength prediction with a common approach utilizing adaptations of the Winter plate buckling formula. Recent modifications to the Direct Strength Method were developed for flexural members not symmetric about the axis of bending, which introduced a new general form to the direct strength equation. The versatility of this form provides one strength curve for the entire range of slenderness, including inelastic reserve strength. This new form was investigated for local and distortional buckling of compression members, members with holes, beam–columns, and beam–columns with holes. The proposed formulas for members without holes gave strength predictions nearly identical to the current AISI expressions. For members with holes, the proposed strength predictions were compared to test data and showed improvement over the current AISI expressions. Shear buckling strength was also investigated using the new direct strength equation form which gave equivalent predictions. Enhancement to the global buckling strength curve for flexural members was explored for alignment with column buckling and to facilitate further consistency for global buckling of beam–columns. The proposed enhancements provide improvements with a consistent set of simpler equations, advancing a new cleaner appearance to the Direct Strength Method.

Energy-based collapse assessment of concentrically braced frames under mainshock-aftershock excitations

Concentrically braced frames (CBFs) collapse mainly because of soft story formation at one or a few stories in which excessive brace buckling occurs. This study provides an intuitive understanding of the collapse mechanism of CBFs with 3–18 stories subjected to mainshock-aftershock sequences. Such understanding will support development of design methods that preclude low-capacity collapse modes specially under multi-shock excitations. This paper assesses the collapse mechanism as a stage in which the imposed seismic energy fails to dissipate and eventually leads to uncontrolled kinetic energy. The investigation focuses on the role and distribution of the various energy measures and different dissipating mechanisms throughout the structures. The employed structural models simulate softening-induced dynamic instability by modeling various inelastic damage modes including buckling of the brace members. Collapse mechanism is identified for various combinations of the utilized mainshock-aftershock pairs that are gradually scaled following the IDA process. The distribution of input and dissipated energies along various stories reveals the role of upper stories in damping the imposed energy. Furthermore, the similarity between the height profile of the residual drifts and the story imposed energies highlights the characteristic of the structures in adapting their drift response to a mode with the highest energy absorption.

Revision of EN 1993‐1‐1 – Design rules for structural analysis, cross‐sectional resistance and member buckling

Revision of EN 1993‐1‐1 – Design rules for structural analysis, cross‐sectional resistance and member buckling

Revision of EN 1993‐1‐1 – Design rules for structural analysis, cross‐sectional resistance and member buckling

AbstractIn the framework of the revision of Eurocode 3, Part 1–1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow chart connecting the global analysis (first or second order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been conducted across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral–torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3, Part 1–1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This article presents in a systematic way the new implementations in the formal vote version FprEN 1993‐1‐1 of the code.

Generalized response spectrum analysis based computational morphogenesis for metal gridshells with buckling-restrained braces subjected to seismic loading

Structural morphogenesis is widely used as a parametric tool to find an optimal structural shape of shell structures for a prescribed objective function and a given design load. However, the current optimization methods are limited to finding a geometry under only a specific static load like the dead load or an equivalent static seismic load for predefined geometrical shapes, and so can not be applied to free-form gridshells. This poses a challenge to achieving an efficient free-form shell structure in high seismic hazard areas. This paper aims to resolve this by presenting a computational morphogenesis method to obtain form-found shell structures by considering the dynamic seismic loads and the response reduction effects of seismic energy-dissipating devices using generalized response spectrum analysis. The method was applied to optimize the buckling-restrained brace layouts on target spherical metal gridshell structures with different diameter-to-height ratios. The resulting form-found structures had an efficient roof geometry, along with an efficient damper layout (to prevent member buckling and the dropout of finishing materials). Dampers were found to be more efficient if placed in the (relatively heavy) supporting structure instead of the roof, and a flattened but locally bulged roof shape proved to be the most efficient in mitigating the seismic response. The generalized response spectrum analysis significantly reduced the computation time while evaluating the displacement response with sufficient practical accuracy, although it slightly underestimates the acceleration response if compared to the conventional nonlinear response history analysis results.

Design and analysis of novel negative stiffness structures with significant energy absorption

Negative stiffness structures (NSS) are a type of mechanical metamaterials that absorb energy via buckling of negative stiffness members. However, these structures have limitations in energy absorption and reusability. Therefore, this study aimed to design, simulate, fabricate, and perform experimental tests on novel designed negative stiffness (NS) structures and improve the performances of negative stiffness structures in terms of energy absorption and keeping their original configuration under cyclic loading. First, the finite element method (FEM) and parametric study of the geometrical dimensions of NS members were considered to investigate the activation/non-activation snap-through mechanisms in the designed structures under quasi-static compression loading. Subsequently, two designed structures were manufactured via the Fused deposition modeling (FDM) printing method and one cyclic loading with a quasi-static state was carried out. The results of the FE simulation and experimental tests were compared, and good agreements were found between them. Afterward, the dissipated energy values and loss factor values of the designed structures under two cyclic loading (two loading/unloading processes) were investigated. Considering both the parameters of the energy absorption values and the remaining members in the elastic region, the proposed NSS was presented for energy absorber structures.

Flexural behaviour of pultruded circular tubular GFRP composite truss bridges with novel non-corrosive connections

Five multiplanar truss bridges (MTBs) made of glass-fibre reinforced polymer (GFRP) circular tubular profiles incorporating different innovative non-metallic connections with adhesives, grouted GFRP rods and GFRP laminate wrapping are proposed. These MTBs were tested under flexure with static loading, and their performance surpassed the design load demands required by pedestrian bridges. One of the MTBs showed sufficient load capacity for heavy load platforms in Australian road bridge applications. Failure of the MTBs was triggered by member connections, and no damage such as local or member buckling of the individual members was observed. It was found that the combined effect of GFRP rods and GFRP wrapping on the connections increased the ultimate strength and the ductility of the MTBs. The capacity of the members and connections for the MTBs were calculated using available design guidelines and analytical equations which were compared and discussed with the experimental results.

Experimental and numerical study on the axial compression performance of the prestressed sleeved members

The progressive collapse of large-span spatial structures can be triggered by the buckling of compression members. To further improve the stable load capacity of compression members, this study proposes a prestressed sleeved member by combining a prestressed stayed column system with a sleeved member. The experimental results show that the prestressed sleeved members possess a high load capacity, large secondary stiffness and moderate recovery performance, with the buckling modes of the members including first-order and second-order buckling. A nonlinear finite element (FE) model for the prestressed sleeved members is developed based on the experimental model. In addition, a series of parametric analyses are conducted to investigate the effects of the initial imperfection amplitude ratio, inner tube length to slenderness ratio, strand cross-sectional area ratio, inner and outer tube cross-sectional stiffness ratio and central support plate equivalent height ratio on the axial compression performance of the specimens. Furthermore, a simplified calculation model of the prestressed sleeved members is proposed for the case of second-order buckling, and theoretical calculation formulas are presented for three key points of the axial force–displacement curves of specimens. In contrast to the theoretical and FE results, the maximum errors of axial displacement and axial force do not exceed 15%. In addition, the steel strand tension, the contact force, and the lateral deflection of the middle section of the inner half-tube are highly consistent, which verifies the proposed relevant assumptions and theoretical calculation formulae.

Impact resistance and simplified evaluation method for square CFST members subjected to transverse impact

Recently, the impact behavior and anti-impact design of concrete-filled steel tubes (CFSTs) have attracted increasing attention; the existing analytical theories have mainly focused on equivalent static methods. Thus, this study presents numerical and analytical analyses of simplified evaluation methods for square CFST members subjected to transverse impacts, by adopting dynamic impact action (i.e., impact mass and impact velocity) to evaluate the impact resistance. A finite element model was first established and benchmarked based on 38 test results collected from existing studies with a wide range of test parameters. The impact process, distribution and development of the internal force, and development of the stress, strain, and strain rate were comprehensively analyzed. The dynamic overall buckling of the CFST members under coupling actions of the axial load and transverse impact was investigated and compared with the control groups for CFST members without an axial load. Based on the parametric analyses, the yield strength of steel, section width, steel ratio, and axial load level (n) are important factors affecting the impact resistance. A simplified formula was therefore proposed to evaluate the impact resistance of CFST members with n ≤ 0.5. A machine learning method was also employed to predict the impact resistance of CFST members covering a wider range of axial load levels (n ≤ 0.9).

Revision of EN 1993‐1‐1 – Design Rules for Member Buckling

AbstractIn the framework of the revision of Eurocode 3 Part 1‐1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow‐chart connecting the global analysis (1st or 2nd order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been carried out across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side.For example, a new formulation for lateral torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3 Part 1‐1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This paper presents in a systematic way the new implementations in prEN 1993‐1‐1.

Influence of the Shape of Initial Imperfections on Single Web and Flange Steel Plates at Elevated Temperatures

AbstractIn the last decades the buckling of steel members in fire has attracted the attention of the scientific community, but considerations about the choice of the initial imperfections have been rarely the focus of scientific publications. However, initial imperfections play a primary role in the definition of the resistance, especially when local buckling is investigated. Although the lowest buckling mode is usually employed, the definition of an appropriate imperfection shape providing, for instance, the lowest resistance is not straightforward. Even more so when the local behaviour at elevated temperatures is being studied, since the buckling behaviour may differ from the one at ambient temperature, owing to the steel degradation and possible load redistributions. In this paper steel plates in compression at elevated temperatures are studied considering different shapes of imperfection. A parametric analysis on webs and flanges composing Class 4 HE and IPE sections with S355 steel grade is presented, considering five temperatures in a relevant range (400–800°C) and several plate aspect ratios. The influence of the imperfection shapes on the resistance depending on the temperature, the length and the slenderness of the web and flange plates is discussed.

Structural Stability Verification for Steel Beam‐columns in Fire ‐ a Consistent Approach with Ambient Temperature Rules

AbstractSteel structures are characterized by a slender design, which makes stability verifications particularly important. While the design methods for steel members at ambient temperatures have been continuously developed and revised for the second generation of Eurocode 3, the method for elevated temperatures in prEN 1993‐1‐2 is still based on the corresponding rules of ENV 1993‐1‐1 of 1992. This leads to a divergence of methodology for ambient and elevated temperatures and to unnecessarily complex design methods for the engineering practice. Therefore, a harmonization of design models for ambient temperature and fire design is desirable.This paper presents a theoretical and numerical study on the stability behaviour of steel members at elevated temperatures. The structural fire behaviour of steel beams, columns and beam‐columns, i.e. flexural buckling under pure compression, lateral torsional buckling under major axis bending and spatial buckling of members under combined bending and axial compression has been investigated. Based on results available in the literature as well as an extensive numerical parametric study, reduction factors and interaction factors were determined. The new reduction and interaction factors were used to develop a design model for the member stability verification in fire that follows the format of FprEN 1993‐1‐1. Thus, engineering practice is provided with a harmonized verification method for steel members in bending and compression for ambient temperature and fire design.

A sequential investigation of the residual stresses and strains influence on the buckling of cold-formed thin-walled members

In this study, a specific formulation and its corresponding computational code are developed using: (i) an alternative 3D finite strain elastoplastic theory based on the multiplicative Flory decomposition, (ii) a node-surface contact algorithm to model sheet folding and (iii) a 3D prismatic solid-based finite element with high order approximation. Employing the developed code, a sequential analysis is presented that involves (i) folding an initially flat sheet in the dimensions of the studied thin-walled U-member, from which results the residual stresses of the manufacturing process, (ii) changing the boundary conditions to enable the application of linear basic loads that generate the buckling situation and (iii) solving the buckling of the cold-formed thin-walled U-member. We used literature benchmarks to show that the proposed 3D elastoplastic theory is sufficiently accurate to study the influence of residual stresses and geometric defects (residual deformations) – arising from the folding process – on the critical loads of the studied U-member.

Analysis of titanium alloy pyramidal lattice core sandwich panels under bending load using acoustic emission

Due to their superior strength and shock resistance, lattice core sandwich panels (LCSPs) have potential applications in many fields. In this work, acoustic emission (AE) technology was adopted to monitor three-point bending tests of titanium alloy pyramidal LCSPs. Simultaneously, AE signals which were collected during the bending process were post-processed by cluster analysis. The AE signals can be divided into three classes which correspond to three damage modes, specifically face-sheet wrinkling, core member buckling and face-sheet crushing. These results offer guidance for deploying AE technology for structural health monitoring of titanium alloy pyramidal LCSP components during active service.

Buckling of Conventional and High-Strength Vanadium Steel Single- and Double-Angle Compression Members and Truss Subassemblies: Experimental and Computational Correlation Study

High-strength, low-alloy vanadium (HSLA-V) steel offers higher strength and toughness than conventional steel. The resulting lighter weight and more slender structural members are more susceptible to buckling in compression. This study establishes an understanding of buckling in this material and the ability to predict it analytically. A series of conventional ASTM A572 Grade 50 steel and HSLA-V (nominal Grade 80) steel angle compression members were tested at Lehigh University’s Advanced Technology for Large Structural Systems (ATLSS) laboratory. A general-purpose finite element (FE) software was used in this study to simulate the buckling and post-buckling behavior of the structural members. The objective of these simulations was to establish confidence in the ability to accurately predict buckling response. The influence of the following modeling parameters on the accuracy of the compression angle member simulation results was investigated: variation in material stress-strain relationship, residual stresses, and the shape and magnitude of geometric imperfections. For the truss subassembly simulations, the influence of the following parameters was also investigated: bracing and boundary element stiffness and design code assumptions of end conditions.

Collapse Mechanism of Transmission Tower Subjected to Strong Wind Load and Dynamic Response of Tower-Line System

Transmission towers are prone to collapse under strong wind load, resulting in significant economic losses. In order to investigate the collapse mechanism and failure modes of the transmission tower under strong wind load and whether the wind vibration factor can greatly reflect the increasing effect of the fluctuating wind, the finite element method (FEM) is utilized to analyze the ultimate bearing capacity of a typical 220 kV transmission tower. The results show that the collapse of the tower under strong wind loads is usually due to the buckling of the leg members. When the reference wind speed is equal to 27 m/s, a small part of the main leg members reaches their yield strength, while the diagonal members are still in the elastic range, and the deformation of the transmission tower is unapparent at this wind speed. When reference wind speed is equal or greater than 30 m/s, the growing variety of main legs is totally into the plastic yield stage, and the overall deformation of this tower is visible. Therefore, the transmission tower is collapsed due to the large deformation caused by the elastic-plastic buckling of leg members. Based on the aforementioned study, a finite element model involving three transmission towers and four span transmission lines is established to analyze the dynamic response of the tower-line system below fluctuating wind. Results show that the wind-induced coefficients designed by current code not only notably satisfy the stress response of tower components subjected to fluctuating wind loads in the elastic phase but also accurately assess the collapse displacement of the transmission tower. The increasing effect of displacement on the top tower under fluctuating wind, unfortunately, could not considerably reply with the investigated factor, and the load-carrying capacity of the transmission tower in the plastic phase can be overestimated by static calculation results.

Experimental research on local buckling of BS700 high-strength steel thin-walled box-section members under axial compression

Experimental research on local buckling of BS700 high-strength steel thin-walled box-section members under axial compression

Eccentric compression behaviour of diagonal rib-stiffened thin-walled square concrete filled steel tubes

Thin-walled square concrete filled steel tubular (CFST) members have attracted more attention in practice because of less steel consumption, high construction efficiency, and convenient arrangement for furniture or curtain wall. Compared with circular members, the local buckling of thin-walled square CFST members is a big concern since tube buckling often results rapid strength and ductility degradation. So in this investigation, diagonal ribs were welded on the internal tube corners to improve the performance of square CFST members. Nine diagonal rib-stiffened square CFST specimens, with large width-to-thickness ratio B/t=100, were experimentally investigated under eccentric compression. The main test parameters included column slenderness ratios (λ=13.9, 34.6, 55.4) and loading eccentricities (2e/B=0, 0.25, 0.50, 1.00). Detailed finite element models were established and verified. The composite effect of the stiffened column was elaborated through combining test results and the finite element analysis, followed by feasibility of column–column connection details and parametric studies. Finally, design methods for calculating the member resistances subjected to axial and eccentric compression were proposed.