• Steel and Composite Structures
• /
• v.53 no.1
• /
• pp.61-75
• /
• 2024

Thin-walled concrete-filled U-shaped steel beams have been recently used in building structures for shortening the construction period and cost efficiency of structural members. In this study, the flexural and shear behavior of newly developed bolt-connected U-shaped steel beams filled with concrete was experimentally evaluated considering load conditions for positive and negative moments, and types of U-shaped steel sections. Because the cross sections are not symmetrical about a horizontal axis, compressive buckling of bottom plates was observed along with web shear buckling under negative moment loading, while the slab concrete under compression was crushed under a positive moment loading. Despite such different shear failure modes depending on load conditions, the shear strength of the composite beams can be conservatively predicted using AISC 360-16 and Eurocode 4. Although the shear contribution of filled concrete is neglected according to the current design codes, the shear capacity of the steel web considering the shear buckling coefficient corresponding to the web width-to-thickness ratio reasonably predicts the test results. In addition, for deep composite beams, the longitudinal lips of a U-shaped steel section anchored into filled concrete can improve the interfacial bond between steel and concrete, thereby enhancing the shear contribution of the steel web.

• Steel and Composite Structures
• /
• v.16 no.4
• /
• pp.437-454
• /
• 2014

The influence of spacers on the behaviour and ultimate capacity of intermediate length CFS open section columns under axial compression is investigated in this paper. The focus of the research lies in the cross- section predominantly, failed by distortional buckling. This paper made an attempt to either delay or eliminate the distortional buckling mode by the introduction of transverse elements referred herein as spacers. The cross-sections investigated have been selected by performing the elastic buckling analysis using CUFSM software. The test program considered three different columns having slenderness ratios of 35, 50 & 60. The test program consisted of 14 pure axial compression tests under hinged-hinged end condition. Models have been analysed using finite element simulations and the obtained results are compared with the experimental tests. The finite element package ABAQUS has been used to carry out non-linear analyses of the columns. The finite element model incorporates material, geometric non-linearities and initial geometric imperfection of the specimens. The work involves a wide parametric study in the column with spacers of varying depth and number of spacers. The results obtained from the study shows that the depth and number of spacers have significant influence on the behaviour and strength of the columns. Based on the nonlinear regression analysis the design equation is proposed for the selected section.

• Steel and Composite Structures
• /
• v.19 no.5
• /
• pp.1299-1319
• /
• 2015

This paper presents a detailed parametric study, conducted using finite element tools to cover a range of several geometric and material parameters, on the behaviour of thin-walled partially encased composite (PEC) columns. The PEC columns studied herein are composed of thin-walled built-up H-shaped steel sections with concrete infill cast between the flanges. Transverse links are provided between the opposing flanges to improve resistance to local buckling. The parametric study is confined to eccentrically-loaded columns subjected to major axis bending only. The parameters that were varied include the overall column slenderness ratio (L/d), load eccentricity ratio (e/d), link spacing-to-depth ratio (s/d), flange plate slenderness ratio (b/t) and concrete compressive strength ($f_{cu}$). The overall column slenderness ratio was chosen to be the primary variable with values of 5, 10 and 15. Other parameters were varied within each case of L/d ratio. The effects of the selected parameters on the behaviour of PEC columns were studied with respect to the failure mode, peak axial load, axial load versus average axial strain response, axial load versus lateral displacement response, moment versus lateral displacement behaviour and the axial load-moment interaction diagram. The results of the parametric study are presented in the paper and the influences of each of the parameters investigated are discussed.

• Steel and Composite Structures
• /
• v.45 no.6
• /
• pp.775-796
• /
• 2022

In this study, a new type of energy absorbers with a functionally graded thickness is investigated, these type of absorbers absorb energy through expanding-folding processes. The expanding-folding absorbers are composed of two sections: a thin-walled aluminum matrix and a thin-walled steel mandrel. Previous studies have shown higher efficiency of the mentioned absorbers compared to the conventional ones. In this study, the effect of thickness which has been functionally-graded on the aluminum matrix (in which expansion occurs) was investigated. To this end, initial functions were considered for the matrix thickness, which was ascending/descending along the axis. The study was done experimentally and numerically. Comparing the experimental data with the numerical results showed high consistency between the numerical and experimental results. In the final section of this study, the best energy absorber functionally graded thickness was introduced by optimization using a third-order genetic algorithm. The optimization results showed that by choosing a minimum thickness of 1.6 mm and the exponential coefficient of 3.25, the most optimal condition can be obtained for descending thickness absorbers.

• Advances in materials Research
• /
• v.11 no.1
• /
• pp.59-73
• /
• 2022

In the construction industry, thin-walled frame elements with very slender open cross-sections and low torsional stiffness are often subjected to a complex loading condition where axial, bending, shear and torsional stresses are present simultaneously. Hence, these often fail in instability even before the yield capacity is reached. One of the most common instability conditions associated with thin-walled structures is Lateral Torsional Buckling (LTB). In this study, a first order Generalized Beam Theory (GBT) formulation and numerical analysis of cold-formed steel lipped channel beams (C80×40×10×1, C90×40×10×1, C100×40×10×1, C80×40×10×1.6, C90×40×10×1.6 and C100×40×10×1.6) subjected to uniform moment is carried out to predict pure Lateral Torsional Buckling (LTB). These results are compared with the Finite Element Analysis of the beams modelled with shell elements using ABAQUS and analytical results based on Euler's buckling formula. The mode wise deformed shape and modal participation factors are obtained for comparison of the responses along with the effect of varying the length of the beam from 2.5 m to 10 m. The deformed shapes of the beam for different modes and GBTUL plots are analyzed for comparative conclusions.

• Steel and Composite Structures
• /
• v.1 no.1
• /
• pp.17-32
• /
• 2001

The Rosette-joining system is a completely new press-joining method for cold-formed steel structures. One Rosette-joint has a shear capacity equal to that of approximately four screws or rivets. The Rosette thin-walled steel truss system presents a new fully integrated prefabricated alternative to light-weight roof truss structures. The trusses are built up on special industrial production lines from modified top hat sections used as top and bottom chords and channel sections used as webs which are joined together with the Rosette press-joining technique to form a completed structure easy to transport and install. A single web section is used when sufficient but can be strengthened by double-nesting two separate sections or by using two lateral profiles where greater compressive axial forces are met. An individual joint in the truss can be strengthened by introducing a hollow bolt into the joint hole. The bolt gives the connection capacity a boost of approximately 20%. A series of laboratory tests have been carried out in order to verify the Rosette truss system in practice. In addition to compression tests on individual sections of different lengths, tests have also been done on small structural assemblies and on actual full-scale trusses of a span of 10 metres. Design calculations have been performed on selected roof truss geometries based on the test results, FE-analysis and on the Eurocode 3 and U.S.(AISI) design codes.

• Advances in Computational Design
• /
• v.3 no.1
• /
• pp.71-86
• /
• 2018

Thin-walled cross-sections can be optimized to enhance their resistance and progress their behaviour, leading to more competent and inexpensive structural system. The aim of this study is to afford a methodology that would facilitate progress of optimized cold formed steel (CFS) column section with maximum ultimate strength for practical applications. The proposed sections are designed to comply with the geometrical standards of pre-qualified column standards for CFS structures as well as with the number of industrialized and practical constraints. The stiffening evaluation process of CFS lipped channel columns, a five different cross section are considered. The experimental strength and behaviour of the proposed sections are verified by using the finite element analysis (FEA). A series comprehensive parametric study is carried out covering a wide range of section slenderness and overall slenderness ratio of the CFS column with and without intermediate web stiffeners. The ultimate strength of the sections is determined based on the Direct Strength Specification and other design equation available from the literature for CFS structures. A modified design method is proposed for the DSM specification. The results indicate that the CFS column with complex edge and intermediate web stiffeners provides an ultimate strength which is up to 78% higher than standard optimized shapes with the same amount of cross sectional area.

• Steel and Composite Structures
• /
• v.10 no.3
• /
• pp.223-243
• /
• 2010

This paper reports recent developments concerning the application of Generalised Beam Theory (GBT) to the structural analysis of steel-concrete composite bridges. The potential of GBT-based semi-analytical or finite element-based analyses in this field is illustrated/demonstrated by showing that both accurate and computationally efficient solutions may be achieved for a wide range of structural problems, namely those associated with the bridge (i) linear (first-order) static, (ii) vibration and (iii) lateral-torsional-distortional buckling behaviours. Several illustrative examples are presented, which concern bridges with two distinct cross-sections: (i) twin box girder and (ii) twin I-girder. Allowance is also made for the presence of discrete box diaphragms and both shear lag and shear connection flexibility effects.

• Steel and Composite Structures
• /
• v.6 no.5
• /
• pp.401-415
• /
• 2006

Based on a non-linear model taking into account flexural-torsional couplings, analytical solutions are derived for lateral buckling of simply supported I beams under some representative load cases. A closed form is established for lateral buckling moments. It accounts for bending distribution, load height application and pre-buckling deflections. Coefficients $C_1$ and $C_2$ affected to these parameters are then derived. Regard to well known linear stability solutions, these coefficients are not constant but depend on another coefficient $k_1$ that represents the pre-buckling deflection effects. In numerical simulations, shell elements are used in mesh process. The buckling loads are achieved from solutions of eigenvalue problem and by bifurcations observed on non linear equilibrium paths. It is proved that both the buckling loads derived from linear stability and eigenvalue problem lead to poor results, especially for I sections with large flanges for which the behaviour is predominated by pre-buckling deflection and the coefficient $k_1$ is large. The proposed solutions are in good agreement with numerical bifurcations observed on non linear equilibrium paths.

• Journal of Korean Society of Steel Construction
• /
• v.23 no.6
• /
• pp.647-657
• /
• 2011

This paper describes the moment capacity of flexural members with local buckling based on a series of FE and experiment results. Thin-walled flexural members undergo local, lateral-torsional, or interactive buckling according to the section geometries and lateral boundary conditions. Flexural members with large width-to-thickness ratios in the flanges or the web may undergo local buckling before lateral-torsional buckling. Local buckling has a negative effect on the flexural strength based on the lateral-torsional buckling of flexural members. This phenomenon should be considered in the estimation of the flexural strength of thin-walled sections. Flexural members with various width-to-thickness ratios in their flanges and web were analyzed. Initial imperfections in the local buckling mode, and residual stresses, were included in the FE analyses. Simple bending moment formulae for flexural members were proposed based on the FE and test results to account for local and lateral-torsional buckling. The proposed bending moment formulae for the thin-walled flexural members in the Direct Strength Method use the empirical strength formula and the grosssection modulus. The ultimate flexural strengths predicted by the proposed moment formulae were compared with the AISC (2005), Eurocode3 (2003), and Korean Highway Bridge Design Specifications (2010). The comparison showed that the proposed bending moment formulae can reasonably predict the ultimate moment capacity of thin-walled flexural members.