Post-buckling Strength of LiteSteel Beams in Shear

This paper presents the details of experimental and numerical studies on the shear behaviour of a recently developed, cold-formed steel beam known as LiteSteel Beam (LSB). The LSB sections are produced by a patented manufacturing process involving simultaneous cold-forming and electric resistance welding. It has a unique shape of a channel beam with two rectangular hollow flanges. Recent research has demonstrated the presence of increased shear capacity of LSBs due to the additional fixity along the web to flange juncture, but the current design rules ignore this effect. Therefore they were modified by including a higher elastic shear buckling coefficient. In the present study, the ultimate shear capacity results obtained from the experimental and numerical studies of 10 different LSB sections were compared with the modified shear capacity design rules. It was found that they are still conservative as they ignore the presence of post-buckling strength. Therefore the design rules were further modified to include the available post-buckling strength. Suitable design rules were also developed under the direct strength method format. This paper presents the details of this study and the results including the final design rules for the shear capacity of LSBs.

Lateral-torsional buckling of cold-formed steel beams at ambient temperature

Cold-formed steel beams are increasingly used as floor joists and bearers in residential, industrial and commercial buildings. Their structural behaviour and moment capacities are influenced by lateral-torsional buckling and hence a research study was undertaken to investigate the lateral-torsional buckling behaviour of cold-formed steel lipped channel beams at ambient and elevated temperatures. For this purpose a finite element model of a simply supported cold-formed steel lipped channel beam under uniform bending was developed first and validated using available numberical and experimental results. It was then used in a detailed parametric study to simulate the lateral-torsional behaviour of cold-formed steel beams under varying conditions. The moment capacity results were then compared with the predictions from the current ambient temperature design rules in Australia, New Zealand, American and European codes for cold-formed steel structures. Some very interesting results have been obtained. European design rules are found to be conservative while Australian and American design rules are unsafe. This paper presents the results of finite element analyses for ambient temperature conditions, and the comparison with the current design rules.

Elastic shear buckling characteristics of LiteSteel Beams

LiteSteel beam (LSB) is a new cold-formed steel hollow flange channel beam. The unique LSB section is produced by a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. To date, limited research has been undertaken on the shear buckling behaviour of LSBs with torsionally rigid, rectangular hollow flanges. For the shear design of LSB web panels, their elastic shear buckling strength must be determined accurately including the potential post-buckling strength. Currently the elastic shear buckling coefficients of web panels are determined by assuming conservatively that the web panels are simply supported at the junction between the flange and web elements. Therefore finite element analyses were carried out to investigate the elastic shear buckling behaviour of LSB sections including the effect of true support conditions at the junction between their flange and web elements. An improved equation for the higher elastic shear buckling coefficient of LSBs was developed and included in the shear capacity equations of Australian cold-formed steel codes. Predicted ultimate shear capacity results were compared with available experimental results, both of which showed considerable improvement to the shear capacities of LSBs. A study on the shear flow distribution of LSBs was also undertaken prior to the elastic buckling analysis study. This paper presents the details of this investigation and the results including the shear flow distribution of LSBs. Keywords: LiteSteel beam, Elastic shear buckling, Shear flow, Cold-formed steel structures, Slender web, Hollow flanges.

Molecular dynamics study of dynamic buckling properties of nanowires with defects

Based on the embedded atom method (EAM) and molecular dynamics (MD) method, the deformation properties of Cu nanowires with different single defects under dynamic compression have been studied. The mechanical behaviours of the perfect nanowire are first studied, and the critical stress decreases with the increase of the nanowire’s length, which is well agreed with the modified Euler theory. We then consider the effects to the buckling phenomenon resulted from different defects. It is found that obvious decrease of the critical stress is resulted from different defects, and the largest decrease is found in nanowire with the surface vertical defect. Surface defects are found exerting larger influence than internal defects. The buckling duration is found shortened due to different defects except the nanowire with surface horizon defect, which is also found possessing the largest deflection. Different deflections are also observed for different defected nanowires. It is find that due to surface defects, only deflection in one direction is happened, but for internal defects, more complex deflection circumstances are observed.

Behaviour and design of cold-formed steel beams subject to lateral-torsional buckling

Cold-formed steel beams are increasingly used as floor joists and bearers in buildings. Their behaviour and moment capacities are influenced by lateral-torsional buckling when they are not laterally restrained adequately. Past research on lateral-torsional buckling has concentrated on hot-rolled steel beams. Hence a numerical study was undertaken to investigate the lateral-torsional buckling behaviour of simply supported cold-formed steel lipped channel beams subjected to uniform bending. For this purpose a finite element model was developed using ABAQUS and its accuracy was verified using available numerical and experimental results. It was then used in a detailed parametric study to simulate the lateral-torsional buckling behaviour and capacity of cold-formed steel beams under varying conditions. The moment capacity results were compared with the predictions from the current design rules in many cold-formed steel codes and suitable recommendations were made. European design rules were found to be conservative while Australian/New Zealand and North American design rules were unconservative. Hence the moment capacity design equations in these codes were modified in this paper based on the available finite element analysis results. This paper presents the details of the parametric study, recommendations to current design rules and the new design rules proposed in this research for lateral-torsional buckling of cold-formed steel lipped channel beams.

Numerical study of cold-formed steel beam subject to lateral-torsional buckling

The use of cold-formed steel members as structural columns and beams in residential, industrial and commercial buildings has increased significantly in recent times. This study is focused on the use of cold-formed steel sections as flexural members subject to lateral-torsional buckling. For this purpose a finite element model of a simply supported lipped channel beam under uniform bending was developed, validated using available numerical and experimental results, and used in a detailed parametric study. The moment capacity results were then compared with the predictions from the current ambient temperature design rules in the cold-formed steel structures codes of Australia, New Zealand, North America and Europe. European design rules were found to be conservative while Australian and American design rules were unsafe. This paper presents the results of the numerical study, the comparison with the current design rules and the new proposed design rules.

Lateral torsional buckling behaviour of cold-formed steel beams at elevated temperatures

Abstract: This paper presents the details of a study into the behaviour and moment capacities of cold-formed steel lipped channel beams (LCB) subject to lateral-torsional buckling at elevated temperatures. It was based on a validated numerical model of a simply supported and laterally unrestrained LCB subjected to a uniform moment. The ultimate moment capacities from this study were compared with the predicted values using ambient and fire design methods. This study showed that the lateral torsional buckling capacity is strongly influenced by the level of non-linearity in the stress-strain curves of steel at elevated temperatures. Hence most of the current design methods based on a single buckling curve were not adequate to determine the moment capacities. This paper proposes a new design method for the cold-formed steel LCBs subject lateral-torsional buckling at elevated temperatures.