Local buckling and ultimate strength of slender elliptical hollow sections in compression (original) (raw)
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Postbuckling strength of slender elliptical hollow sections in compression
Numerical analysis of the local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression has been performed. After validating the model against previous experimental results, a parametric study comprising a total of 270 elliptical sections was conducted in order to examine the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for lower cross-section aspect ratios the behaviour of the elliptical hollow sections (EHS) was similar to that of cylindrical shells across a number of metrics; as the aspect ratio increased, more plate-like stable postbuckling behaviour was observed. A design method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local buckling with increasing slenderness, but also recognises the improved postbuckling stability with increasing aspect ratio.
Numerical analysis and design of slender elliptical hollow sections in bending
Thin-Walled Structures
The local buckling behaviour and ultimate cross-sectional resistance of slender tubular elliptical profiles in bending are examined by means of numerical modelling. After successful validation of the numerical model against previous experimental results, a parametric study comprising 240 simulations was conducted in order to investigate the influence of cross-section aspect ratio, axis of bending, geometric imperfections and local slenderness on structural behaviour. The ultimate moments, moment-curvature relationships and failure modes obtained are discussed. It was found that, overall, postbuckling stability increases and imperfection sensitivity decreases with increasing elliptical hollow section (EHS) aspect ratio. A design method is proposed for Class 4 EHS members that reflects the reduction in resistance due to local buckling with increasing slenderness and extends the range of applicability of existing provisions. A reliability analysis was performed in accordance with EN 1990,
Elastic local post-buckling of elliptical tubes
Journal of Constructional Steel Research, 2011
The elastic local post-buckling behaviour of elliptical tubes under compression is analysed in this paper. A brief outline of the local, distortional and global buckling behaviour of EHS tubes is firstly provided, where it is shown that local buckling modes govern the stability of short to intermediate length tubes while distortional modes control the stability of intermediate length to moderately long tubes and global buckling dominates the behaviour of longer tubes. Following this, an in-depth numerical study employing shell finite element modelling, of the elastic local post-buckling behaviour of compressed elliptical hollow section (EHS) tubes is presented. It is concluded that EHS tubes with a low to moderate aspect ratio can support loads up to their limit loads but are imperfection sensitive (shell-type behaviour), while EHS tubes with a moderate to high aspect ratio can carry loads higher than their limit loads (plate-type behaviour) and are imperfection insensitive. The slope of the ascending post-buckling path increases with the EHS aspect ratio and can reach values up to 40% of the slope of the linear primary path. The bound imperfection amplitude concept, separating the imperfection amplitude ranges where the EHS tube is sensitive and insensitive, is proposed. It is also found that, for increasing EHS aspect ratio, the compressive stresses grow and accumulate near the zones of minimum radius of curvature while the zones of maximum radius of curvature possess an approximately uniform and relatively low compressive stress level. Therefore, it is expected that an approach based on the effective width concept widely used for the evaluation of the strength of flat plates may be adapted to the design of EHS tubes with moderate to high aspect ratios.
SSRN Electronic Journal, 2021
Tubular structural members with slender cross-sections are susceptible to failure through local buckling of their tube walls. Previous numerical studies of steel elliptical hollow sections in compression predicted the local buckling modes and the ultimate loads of particularly slender specimens, with the results used to calibrate design methods for slender elliptical sections. Although these numerical parametric studies were conducted across a wide slenderness range, it was only possible to validate the models against experimental results in the low slenderness range since commercially available steel EHS are intended to satisfy non-slender geometric limits prescribed by structural design codes. Such limitations to the experimental scope are circumvented in the present study through testing of highly slender specimens produced using additive manufacturing techniques. A total of eight specimens of various cross-sectional aspect ratios and tube wall thicknesses were fabricated at London South Bank University using additive manufacturing techniques, which were then tested in compression; the observed load-deflection behaviour, ultimate loads, longitudinal strains and failure modes are discussed. Through appropriate rescaling of relevant parameters, design predictions for the ultimate load of the 3D-printed analogues are obtained using a design method intended for use with steel elliptical hollow sections. It is shown that the design predictions are safe-sided when compared to the present experimental results, with the accuracy generally increasing with aspect ratio and slenderness.
Journal of innovative engineering and natural science, 2024
Square hollow sections (SHSs) have been receiving a great deal of attention for use as load-carrying components in a broad range of application fields, including construction and automotive, due to their many promising mechanical advantages over solid sections, such as a higher strength-to-weight ratio [1-6]. This important mechanical quality offered by SHSs makes them very ideal for use in specific applications where high strength with low weight is required [7]. As with other hollow section members possessing different section shapes including rectangular and circular, understanding their failure mechanism under loads is highly imperative for reliable design. The robust design of SHSs is generally achieved by considering both adequate-strength and local stability requirements in a balanced way [8-11]. Taking into account the adequate-strength criterion alone can lead the SHS to suffer local buckling prior to reaching its maximum load-carrying capacity, which brings additional material cost [8, 12]. In other words, a critical elastic local buckling load of the SHS needs to be considered its collapse load since the SHS cannot sustain any additional load after undergoing local elastic buckling [13-15].
Elastic buckling of elliptical tubes subjected to generalised linearly varying stress distributions
Thin-Walled Structures, 2012
The structural behaviour of elliptical hollow sections has been examined in previous studies under several loading conditions, including pure compression, pure bending and combined uniaxial bending and compression. This paper examines the elastic buckling response of elliptical hollow sections under any linearly varying in-plane loading conditions, including the most general case of combined compression and biaxial bending. An analytical method to predict the elastic buckling stress has been derived and validated against finite element results. The predictive model first identifies the location of the initiation of local buckling based on the applied stress distribution and the section geometry. The critical radius of curvature corresponding to this point is then introduced into the classical formula for predicting the elastic local buckling stress of a circular shell. The obtained analytical results are compared with results generated by means of finite element analysis. The comparisons between the analytical and numerical predictions of elastic buckling stress reveal disparities of less than 2.5% for thin shells and, following an approximate allowance for the influence of shear, less than 7.5% for thick shells.
Compressive resistance of hot-rolled elliptical hollow sections
Engineering Structures, 2008
In recent years, hot-rolled elliptical hollow sections have attracted significant attention from engineers and architects owing to their complementary qualities of aesthetic appearance and structural efficiency. However, there is currently a lack of design guidance for elliptical hollow sections inhibiting more widespread use in construction. The present paper addresses this shortcoming for the fundamental loading condition of axial compression. Laboratory testing, numerical modelling and the development of design rules are described herein. The experimental programme comprised 25 tensile coupon tests and 25 stub column tests. All tested elliptical hollow sections had an aspect ratio of two and section sizes ranged from 150×75 up to 500×250 mm. Results, including geometric imperfection measurements and full load-end shortening curves have been presented. Non-linear finite element models were developed and validated against the generated test data. The validated numerical models were employed to perform parametric studies in order to investigate elliptical hollow sections of varying slenderness and varying aspect ratios. The resulting structural performance data have been used to establish a relationship between crosssection slenderness and cross-section compressive resistance, which demonstrates that the Class 3 slenderness limit of 90 from Eurocode 3 for circular hollow sections can be safely adopted for elliptical hollow sections based upon the proposed cross-section slenderness parameter. The equivalent semi-compact slenderness limit given in BS 5950-1, non-compact limiting slenderness in AISC 360-05 and yield slenderness limit given in AS 4100 are also valid. A modified effective area formula from BS 5950-1 can also be safely adopted. Further investigation into effective area formulations for slender (Class 4) elliptical hollow sections is currently underway.
Elasto-plastic behaviour and design of semi-compact circular hollow sections
Thin-Walled Structures, 2020
Existing cross-section and member buckling test data on CHS were collected; Numerical simulation was conducted to generate further data on CHS; New design rules were developed to capture the elasto-plastic behaviour of semi-compact CHS; Accuracy of the current Eurocode 3 and proposed methods were assessed and compared; Reliability of the proposed design rules was confirmed through statistical analyses.
Local Buckling Strength of Uniformly Compressed Octagonal Thin Walled Section Members
Journal of Structural and Construction Engineering (Transactions of AIJ)
Cold-formed steel members are widely applied in columns and other axial members in steel structures. One of the key issues in design of cold formed steel is local buckling strength under axial compression. As a means to avoid premature local buckling, we have paid an attention to the application of octagonal section members. In this paper, we conducted numerical analyses (Finite Strip Analysis and Finite Element Analysis) and stab column tests, to investigate both the elastic and the post buckling strengths of octagonal section members including those where the adjacent plate elements have different width-thickness ratios. These tests and numerical analysis results indicated that the post buckling strengths of the plate elements were affected by the restraining effect from the adjacent plate elements. However, the overall strengths of the members were in line with those estimations by the traditional effective-width method, where simply supported conditions were assumed. This was caused possibly by a trade-off effect between the adjacent plate elements on their local buckling strengths.
Influence of Open Cross-Section Shape on Compression Members Buckling Resistance
The Bulletin of the Polytechnic Institute of Jassy, Construction. Architecture Section, 2013
The methodology designs of the uniform compression member with open cross-section, according to EN 1993-1-1/2006. Eurocode 3: Design of steel structures, is briefly presented. The influence of the open cross-section shape on the compression member buckling resistance for six constructive cross-section shapes is also numerically analysed.