Lateral Torsional Buckling Behavior Research Articles

Experimental and numerical analysis of lateral–torsional buckling behaviour of monosymmetric simply supported beam

Experimental and numerical analysis of lateral–torsional buckling behaviour of monosymmetric simply supported beam

ANALYSIS OF ELASTIC LATERAL TORSIONAL BUCKLING OF CANTILEVER I SECTIONS BY THE COMPLEMENTARY FUNCTIONS METHOD

In this study, an important stability problem, in the design of cantilever I-beams under lateral torsional buckling behavior is theoretically investigated. The elastic lateral torsional buckling behavior of cantilever I beam loaded from shear centers is examined for four different loading types. The governing differential equation is transformed into a set of first-order ordinary differential equations. The Complementary Functions Method (CFM), which is an effective method in solving the first-order differential equation set, is used. Fifth Order Runge-Kutta (RK5) algorithm is used for numerical integrations in CFM, which can transform the boundary value problem into an initial value problem. The obtained results were compared with the existing results in the literature. It has been shown that CFM can be used effectively in the analysis of elastic lateral torsional buckling behavior of I beams.

On the evaluation of lateral-torsional buckling of web-tapered cantilevers with doubly symmetric I-section

Recently, structural engineers have tended to design stronger and lighter structures due to economic reasons, technical developments in computer-aided design, and improvements in manufacturing. The demand for designing stronger and lighter structures has led to the compulsory considering structural efficiency and stability loss at the design level. Lateral-torsional buckling (LTB) is a major stability loss for web-tapered cantilevers with doubly symmetric I-section, which are aesthetic and structurally efficient. The elastic LTB loads of these cantilevers should be calculated at the design level since the LTB may happen before bending stress reaches yield. Studies related to the LTB of cantilevers are rare and require numerical solutions since the LTB mode shape of cantilevers is complex compared to simply supported beams. The present study introduces an analytical procedure based on the energy method for calculating elastic LTB of web-tapered cantilevers with doubly-symmetric I-section in two different forms. The analytical model considers different transverse load types, positions of loads, and web tapering degrees. The analytical solutions were validated with one-dimensional finite element analysis using a beam element. Excellent accordance between results was demonstrated. The general LTB behavior of web-tapered cantilevers with doubly symmetric I-section was clarified with detailed comments based on results obtained from the presented analytical model.

Lateral torsional buckling analysis of corrugated steel web girders using homogenization approach

Corrugated web beams have become popular in recent years due to their high strength-to-weight ratio, ductility and high shear resistance without stiffeners. The developments in the automated production of corrugated steel plates have further amplified their use as structural elements in bridges and buildings. In this paper, we develop a strain energy-based homogenization scheme to convert corrugated sections into equivalent flat sheets with modified elastic properties. The thin-walled theory is implemented in a one-dimensional (1D) finite element (FE) framework along with a modified analytical expression to study the lateral torsional buckling of corrugated web girders. The homogenization-based FE modelling reduces the computational requirement of finer mesh sizes on the corrugation profile. The present thin-walled FE model is implemented to different corrugation profiles and lengths, and their responses are compared with methodologies available in the literature. The effects of the geometrical parameters and loading on the lateral torsional buckling behaviour are investigated and important observations are made for structural designs.

Impact of web perforation size and shapes on structural behavior: a finite element analysis

Purpose Various designs of corrugated webs include trapezoidal, sinusoidal, triangular and rectangular profiles. The increasing use of curved plates has prompted the creation of I-sections made of steel with a corrugated web design. This study aims to examine the effectiveness of an I-beam steel section that features a perforated-triangular web profile. Design/methodology/approach In the current study, finite element analysis was conducted on corrugated-perforated steel I-sections using ANSYS software. The study focused on inspecting the design of the perforations, including their shape (circle, square, hexagon, diamond and octagon), size of perforations (80 mm, 100 mm and 120 mm) and layout (the position of web perforation), as well as examining the geometric properties of the section in term of bending, lateral torsional buckling, torsion and shear behavior. Findings The study revealed that perforations with diamond, circle and hexagon shapes exhibit good performance, whereas the square shape performs poorly. Moreover, the steel section’s performance decreases with an increase in perforation size, regardless of loading conditions. In addition, the shape of the web perforations can also influence its stress distribution. For example, diamond-shaped perforations have been found to perform better than square-shaped perforations in terms of stress distribution and overall performance. This was because of their ability to distribute stress more evenly and provide greater support to the surrounding material. The diagonal alignment of the diamond shape aligns with principal stress directions, allowing for efficient load transfer and reduced stress concentrations. Additionally, diamond-shaped perforations offer a larger effective area, better shear transfer and improved strain redistribution, resulting in enhanced structural integrity and increased load-carrying capacity. Originality/value Hence, the presence of lateral-torsional buckling and torsional loading conditions significantly impacts the performance of corrugated-perforated steel I-sections.

Rapid evaluation of lateral-torsional buckling of European standard I-section cantilevers

Lateral-torsional buckling (LTB) is the primary failure mode for thin-walled steel members where the cantilever beams experience nonuniform twisting and buckling about their weak axes. Much research exists in the literature, and modern codes have presented simple formulations for calculating of elastic LTB load of simply-supported beams. However, there are limited numbers of treatments for predicting of elastic LTB load of cantilevers, most of which are numerical, because as different from the simply supported beams, the LTB failure mode of the thin-walled cantilevers is much more complicated. The present study aims to develop a simplified equation for calculating the elastic LTB of the cantilevers with the European standard I-section. First, an analytical model considering first-order bending distribution, load height level, and monosymmetry property of the section has been introduced. Then, a simplified formula for cantilevers has been introduced utilizing the analytical model and two dimensionless coefficients called the slenderness and the load case parameters. The presented analytical solutions were verified with the finite element analysis (FEA), and the effects of slenderness and loading positions on the LTB behavior of cantilevers with European standard I-section have been investigated. It is found analytical solutions are quite compatible with FEA, and the proposed equation could be safely used for calculating the elastic LTB of the cantilevers.

Lateral torsional buckling behaviour of tapered steel section with web opening – finite element analysis

PurposeRecently, this steel section has found increasing popularity in residential, industrial and commercial buildings with their high load-carrying capacity due to the nature of high strength to weight ratio properties. However, the rise on the price of steel section should be more emphasized; therefore, the optimization in steel section design is needed to overcome the issue of material cost. As such, tapered steel sections save on material use, while the introduction of web openings allows the placement of mechanical and electrical services, plumbing and also aesthetic design considerations.Design/methodology/approachThe purpose of this study is to investigate the lateral torsional buckling behavior of a tapered steel section with an ellipse-shaped opening by analyzing its structural parameters. To achieve this, the finite element analysis (FEA) of the section is modeled using LUSAS software, which allows for a detailed analysis of the section's behavior under varying loads and conditions. It involves the variation in web opening size, opening layout, opening rotation angle and the tapering ratio. Eigenvalue buckling analysis is adopted to know the parametric effects of each 108 model. The size of opening varies from 0.2 to 0.5 d of the total depth where the opening located. There are three type of layouts applied in this study, which are the layouts A, B and C. There are three types of rotation angles for the ellipse-shaped opening, including the non-rotated vertical opening and two additional types formed by rotating the opening 45 degrees clockwise and counterclockwise around the center-point of the ellipse. A fixed-free boundary condition was applied, resulting in a simulation of a cantilever beam. The models are fixed at one end with a larger depth, and free at the other end with a smaller depth. Loading condition is an application of 10 kN/m uniform distributed load in the direction of gravity along the mid-span of the top flange.FindingsIt is observed that the model 82 with Layout A, tapering ratio 0.3, opening size 0.5 d and opening rotated in 45 degree anti-clockwise direction results in the highest structural efficiency among the 108 models. Therefore, the buckling moment of model 82 is 1,013.08 kNm with structural efficiency of 481.26, which shows an increase of 3.17% compared to the controlled model.Originality/valueThe FEA results shows a significant increase in ductility and stiffness of the tapered steel section with elipse shape opening and consequently changes in the behaviour of yield point.

Theoretical and experimental study on overall stability for the thin-walled double cantilever photovoltaic stent under uniform pressure

As an important part of the solar-energy system, the bearing capacity design is crucial to the photovoltaic stent structure. It consists of thin-walled steel components, which are prone to bending and torsional buckling after being stressed. However, it is rare to conduct a comprehensive analysis and experimental research on the lateral-torsional buckling (LTB) behavior of the photovoltaic stent. In this study, Rayleigh-Ritz method is utilized to analyze the stability of the Z-shaped thin-walled Double Cantilever Photovoltaic Stent (DCPS) under uniform pressure, and the theoretical formulas for its critical load are derived. In addition, the stability failure experiment and Finite-Element (FE) simulation of the thin-walled DCPS under uniform pressure are carried out. Through mutual verification of the theoretical derivation, experimental data and FE modeling results, the failure modes of the DCPS under uniform pressure is studied, the effects of different influencing factors on the bearing capacity of the structure are studied through the parametric analysis, and the theoretical formula of torsional restraint stiffness Kr is given based on laboratory test data. The research results can provide a reference for the design of photovoltaic structures.

Experimental Evaluation on Lateral Torsional Buckling Resistance of Continuous Steel Stringers

An extensive experimental study evaluated lateral torsional buckling resistance of two-span, continuous, steel beams in a test assembly that included three beam lines, an interior transverse support (floor beam), and transverse diaphragms at the end supports. Funded by the Louisiana Transportation Research Center (LTRC), this study was conducted to better understand continuous stringer behavior so that simplified analyses would better capture their lateral torsional buckling (LTB) behavior. Current practice produces Louisiana Department of Transportation and Development (LA DOTD) bridge ratings often conservatively controlled by stringer LTB capacity and, in many cases, necessitates posting; thereby imposing significant and often unnecessary operational restrictions. Forty-seven elastic tests were completed. The tests encompassed a variety of unbraced lengths and support conditions with steel diaphragms or timber ties acting as bracing members. The interior beam in the test assembly was loaded orthogonal to its strong axis at the middle of one or both spans using a spreader beam that minimized restraint and prevented the development of follower forces. Tests demonstrated that minimal bracing could significantly increase lateral torsional buckling resistance and justify a higher LTB resistance than what is currently used. Although the tests were conducted on assemblies used to represent a bridge floor system, the results provided an extensive set of valuable data that could be used by structural steel researchers interested in examining flexural resistance of continuous beams.

Full beam formulation for the lateral torsional buckling analysis of elastic frames by considering the structural detail of beam-to-column joint

The total potential energy formulation plays an essential role in investigating the flexural–torsional instability of elastic plane frames composed of thin-walled members. However, the work conjugateness between the internal moments and rotation variables of typical frame member cannot be restored completely when applying the conventional potential energy approaches. This paper aims to fully consider the virtual work done by the induced conservative and nonconservative moments in the planar frame prone to lateral buckling. The proposed full beam formulation can help identify those neglected moments that are necessary for fulfilling the equilibrium at the critical state no matter which potential energy formulation is concerned. It has been found that the relative significance of the virtual work done by the neglected moments with respect to the first variation of total potential energy is served as an indicator as whether the conventional potential energy equation can be used for investigating the lateral torsional buckling behavior of the frame. In the out-of-plane buckling investigation of benchmark elastic frames, it has been demonstrated in cases where the neglection of non-zero virtual work done by the nonconservative moment or an approximate account of the induced bimoment through the kinematic warping model may result in incorrect critical load. The lateral torsional buckling strength of the elastic frames can only be correctly determined by taking into account the structural configuration of beam-to-column joint.

Experimental Studies on the Influence of Different Support Conditions and Structural Systems for the Lateral Torsional Buckling Behaviour of Steel Structures

AbstractThe use of slender steel members promotes the competitiveness of steel structures in structural engineering. However, it requires an efficient design, especially for the stability behaviour including lateral torsional buckling which is usually verified by the simplified design method with reduction factors. This method is based on the model of a simply supported member with ideal fork boundary conditions at the ends. However, commonly used joints in engineering practice, such as typical main and secondary beam joints, deviate from the idealisations of these ideal fork restraints. And at system level, there are only a few simply supported members, more common are structural systems such as continuous girders or frames. So far, there is a lack of knowledge on the influence of common joints used in engineering practice and structural system effects on the load‐bearing capacity. This paper deals with the results of experimental studies carried out within a German national (FOSTA) research project. The lateral torsional buckling behaviour of different support and boundary conditions as well as structural systems is investigated for hot‐rolled steel members with doubly and mono‐symmetric sections. In total, 14 tests on support conditions are carried out at the University of Stuttgart and 20 tests on two‐span members at the Ruhr‐Universität Bochum. The aim is to develop easy‐to‐use design rules that consider the effects of realistic conditions and structural system effects on the lateral torsional buckling resistance.

Investigations on the lateral-torsional buckling of an innovative U-shaped steel beam

An innovative solution of a steel-concrete composite beam was developed for buildings with beam spans between 6 and 12 m, taking into consideration the fire situation and the construction stage. The beam is composed of an U-shaped steel part, connected to a reinforced concrete part. In the construction phase, the beam is supporting the slab and constitutes a formwork for the reinforced concrete part. When casting concrete, the steel beam is filled at the same time as the slab, this allows considerable time savings on site. In the exploitation stage, the beam behaves as a steel-concrete composite beam.The developed U-shaped section is composed of three steel parts; a hot rolled steel plate (180x8x6300 mm, and two cold-formed steel plates (470x4x6300 mm) before folding. The section was assembled together with four self-drilling screws longitudinally spaced of 150 mm.In the construction stage, the U-shaped steel beam without restraints is prone to lateral torsional buckling instability. In this paper, the mechanical behaviour of the steel beam at the construction stage, in particular its lateral-torsional buckling stability, was studied. In order to characterize this instability without lateral support, a four-point bending test was carried out on a life-size specimen. The load introduction system was developed especially for the test to allow for all displacements due to LTB. The test clearly showed the lateral torsional buckling behaviour of the steel beam. The test results are compared with numerical simulations and analytical studies. A parametrical study, covering 200 geometrical configurations of the U-shaped beam, is carried out to validate the use of the curve “b” for the design of the steel beam for lateral torsional buckling according to Eurocodes 3.

Lateral-torsional buckling strength of corrugated web girders – Experimental study

Current standards and specifications do not provide specific design methods to determine the lateral-torsional buckling (LTB) strength of girders with trapezoidally corrugated web. In the international literature there are some previous investigations available focusing on the LTB strength of corrugated web girders. Based on numerical calculations analytical solutions have been derived in the past, however, there is a lack of experimental test results to prove or improve these design proposals. The authors performed an extensive experimental research program including eleven large-scale test specimens. All the test girders have different flange sizes, beside, having the same corrugation profile. The test specimens are loaded by pure in-plane bending having simply supported boundary conditions. The tested specimens have limited warping and rotational restraint at the supports. No web distortional type failure is observed. During the tests the longitudinal strains are captured in characteristic cross-sections and the displacements in vertical and lateral directions are measured as well as the rotation of the mid-span cross-section. The measured LTB strength of the test specimens is compared with existing analytical proposals regarding corrugated web girders and the differences are evaluated. It is observed that the imperfections have key role in the LTB behavior. Based on the experimental results buckling curve “b” from Eurocode 3 is preliminary proposed for the determination of the lateral-torsional buckling strength of trapezoidally corrugated web girders. The executed test program gives useful background to further numerical studies.

Effects of Shear on the Elastic Lateral Torsional Buckling of Doubly Symmetric I-Beams

The theoretical lateral-torsional buckling solutions for I-beams utilized in many design specifications may the overestimate lateral torsional buckling (LTB) resistance when significant shear is present due to web distortion. This paper investigates the effects of shear on the elastic LTB of doubly symmetric steel I-beams through computational models. A parametric study was conducted considering a range of geometric parameters and loading conditions commonly found in design applications in buildings and bridges. The results show that shear can have a substantial impact on the LTB resistance under many practical design circumstances. The impact of shear on LTB is more significant for sections with larger web slenderness ratios and smaller depth-to-flange width ratios. Postbuckling shear resistance does not significantly impact the reductions in LTB resistance due to shear. A practical design method that accounts for shear effects on the LTB behavior in stiffened and unstiffened beams was proposed and verified by comparison with computational solutions. Design examples demonstrating the proposed method are provided.

Parametrical Study of Lateral Torsional Buckling Behaviour for Triangular Web Profile Steel Section

A triangular web profile (TRIWP) steel section is a structural steel section that is made up of two flanges connected to a web plate of triangular profile. As a newly proposed section, limited research have been carried outto study the characteristic, behaviour and the advantages offered by this section compared to the normal flat web (I-beam) and other types of corrugated web steel section. One of the area that still not been studied is the capability of this section to resist thelateral torsional buckling moment compared to the normal flat web. The objective of this thesis is to study the lateral torsional buckling behaviour of triangular web profile (TRIWP) steel section. This study involved modelling of 60 beam models (30 TRIWPand 30 FW) derived from four main model using LUSAS Modeller version 14.0 to investigate buckling resistance. There are three spans that have been used which are 3 m, 4 m and 4.8 m. For a conclusion TRIWP steel section has higher buckling moment resistance, Mcr compared to FW steel section.

Estimation of Web Distortion Effect on the Elastic and Plastic Limiting Lengths for Lateral Torsional Buckling through the Web Strain Results

The present study is aimed to estimate the influence of the web distortion on the elastic (Lr) and plastic (Lp) limiting lengths given in the American Institute of Steel Construction (AISC code) for the lateral torsional buckling behavior of steel beams. For this aim, the W44x335 beam is adopted in the buckling analyses carried out by the ABAQUS finite element (FE) program. The strain results at mid-height of the web at mid-span of the beam are taken into account as monitoring parameters. The web strain results are found highly greater than the yield strain value when L/Lr is equal to 1.0. Hence, the elastic limiting length (Lr) is required to be considered greater than the calculated length as per the code formulation. The section is obtained to reach the maximum strain value at the web before the unbraced length (L) is equal to the plastic limiting length (Lp). Therefore, the calculated Lp is estimated with the given analytical formulation to be highly shorter than the length through the FE analysis. These outcomes prove that the formulations of the limiting lengths proposed in the AISC code don’t consider the influence of the web distortion that is predicted to lead to reducing the torsional and warping rigidity of the section. With the study, it is proposed to determine a reduction coefficient by performing more numerical analyzes for different cross sections and free openings in the regulation.

Lateral–torsional buckling behaviour of welded Q690 steel I-beams with double lateral restraints along the length

This paper presents experimental and numerical investigations of lateral–torsional buckling behaviour of welded Q690 steel I-beams with double lateral restraints along the length. In the experimental programme, 11 steel beams with different beam depths, load ratios and span ratios were tested under two concentrated point loads. Lateral–torsional buckling resistance of beams was obtained through experimental tests. Comparisons between experimental bending moments and calculated values suggest that existing design methods in different national codes cannot accurately predict the critical moments of beams in the selected range of slenderness. Besides, numerical models were also established and verified against test data. Parametric studies showed that the buckling factor of beams increased with increasing ratio of the middle span over the clear span and with increasing ratio of concentrated point loads on beams. It was also concluded from numerical results that the Chinese code and the American code are not safe when used for calculating the buckling factor of beams with intermediate slenderness, whereas Eurocode 3 is rather conservative. Comparisons between buckling factors of continuous and single beams also indicate that the buckling factor of beams can be substantially underestimated if only the beam segment in the middle span is considered by neglecting the restraints provided by adjacent beams. Finally, a modification factor was proposed for welded Q690 steel beams with unequal bending moments at the two ends, which can predict the buckling factor of beams with fairly good accuracy.

Lateral torsional buckling capacity of corroded steel beams: A parametric study

Thickness reduction due to uniform corrosion increases the tendency of lateral torsional buckling (LTB) of open cross-sections and it reduces the moment capacity of the beam. The effect of the various corrosion cases on the LTB moment capacity (M b,rd) of the I-beams are investigated in this paper. An analytical framework for patch corroded I-beams is introduced to provide a guideline for simulating the nonlinear lateral torsional buckling behaviour of patch corroded simple beams. Hence the effect of different corrosion scenarios to reduce the buckling reduction factor (η LT) is investigated by conducting a parametric study. Twelve different beam lengths were considered to obtain different non-dimensional slenderness ratios (λ LT) in this parametric study. The degraded buckling curves were obtained for each corrosion scenarios.

Investigation of residual stresses on the fire resistance of unrestrained cellular beams

AbstractIt is being a common engineering practice to use steel beams with web openings in buildings requiring long spans, besides giving an important additional advantage of allowing services through instead of underneath the beams. The presence of these openings is penalizing the carrying capacity at ambient temperature and in the case of fire due to large cells and double nonlinearity geometric and material a complex behaviour take place. In this study, numerical models for beams having closely spaced large openings are simulated with ISO834 fire loading including both nonlinearities cited above in the primal investigation. Followed as a second investigation, is the effect of residual imperfections added to the numerical model mentioned above and simulated for different diagrams as presented within updated literature. All simulations were done using the finite element software ANSYS, to analyse the results captured for lateral torsional buckling (LTB) behaviour in terms of vertical and lateral displacement, von Mises stresses for different sections at ambient and fire conditions. For this parametric study, the change in cross‐section geometries, opening spacing, beam length on the LTB of cellular beams is analysed.

Nonlinear imperfect analysis of corrugated web beams subjected to lateral-torsional buckling

In this paper the lateral-torsional buckling (LTB) behavior of steel trapezoidally corrugated web girders is studied by advanced nonlinear finite element (FE) analysis in order to develop new computer-based design method for the determination of the LTB strength of such innovative members subjected to pure bending. Due to the low number of previous investigations the rules of FE modelling for strength determination is not unified nor regulated in the case of corrugated web girders. In addition, standards and specifications do not provide any prescriptions on how to determine the LTB strength of corrugated web girders. The required imperfections have key role in the LTB strength determination. The paper discusses the FE modelling issues on the basis of own test results. Advanced FE model is developed, mathematically verified, and validated by experimental test results. Standards provide equivalent geometric imperfections for conventional flat web I-girders. These proposals have not been, however, investigated for the application to corrugated web girders. Thus in this paper a detailed imperfection sensitivity studies are performed and finally modelling prescriptions and required imperfections – including residual stresses and initial geometric imperfections – are developed and proposed to promote a novel FE analysis based design method for these innovative structures.