Effects of plate slenderness on the ultimate strength behaviour of foam supported steel plate elements

Mahen Mahendran,Narayan Pokharel 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.4

Plate elements in fully profiled sandwich panels are generally subjected to local buckling failure modes and this behaviour is treated in design by using the conventional effective width method for plates with a width to thickness (b/t) ratio less than 100. If the plate elements are very slender (b/t >1000), the panel failure is governed by wrinkling instead of local buckling and the strength is determined by the flexural wrinkling formula. The plate elements in fully profiled sandwich panels do not fail by wrinkling as their b/t ratio is generally in the range of 100 to 600. For this plate slenderness region, it was found that the current effective width formula overestimates the strength of the fully profiled sandwich panels whereas the wrinkling formula underestimates it. Hence a new effective width design equation has been developed for practical plate slenderness values. However, no guidelines exist to identify the plate slenderness (b/t) limits defining the local buckling, wrinkling and the intermediate regions so that appropriate design rules can be used based on plate slenderness ratios. A research study was therefore conducted using experimental and numerical studies to investigate the effect of plate slenderness ratio on the ultimate strength behaviour of foam supported steel plate elements. This paper presents the details of the study and the results.

Effects of plate slenderness on the ultimate strength behaviour of foam supported steel plate elements

Pokharel, Narayan,Mahendran, Mahen Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.4

Plate elements in fully profiled sandwich panels are generally subjected to local buckling failure modes and this behaviour is treated in design by using the conventional effective width method for plates with a width to thickness (b/t) ratio less than 100. If the plate elements are very slender (b/t > 1000), the panel failure is governed by wrinkling instead of local buckling and the strength is determined by the flexural wrinkling formula. The plate elements in fully profiled sandwich panels do not fail by wrinkling as their b/t ratio is generally in the range of 100 to 600. For this plate slenderness region, it was found that the current effective width formula overestimates the strength of the fully profiled sandwich panels whereas the wrinkling formula underestimates it. Hence a new effective width design equation has been developed for practical plate slenderness values. However, no guidelines exist to identify the plate slenderness (b/t) limits defining the local buckling, wrinkling and the intermediate regions so that appropriate design rules can be used based on plate slenderness ratios. A research study was therefore conducted using experimental and numerical studies to investigate the effect of plate slenderness ratio on the ultimate strength behaviour of foam supported steel plate elements. This paper presents the details of the study and the results.

Design of Cold-formed Steel Wall Frames Lined with Pasterboard on One Side Under Axial Compression

Yaip Telue,Mahen Mahendran 한국강구조학회 2006 International Journal of Steel Structures Vol.6 No.3

plasterboard lining and are used in the construction of both the load bearing and non-load bearing walls in residential, industrialand comercial buildings. However, the design of these wall frames does not utilise the strengthening effects of theplasterboard lining in carrying axial loads. An experimental study has shown that the strength of the studs in compression wasincreased significantly when they were lined with plasterboard one or both sides. In order to fuly understand the behaviourmodel of one side lined wall frame was developed and validated using experimental results. This paper presents the details ofthe finite element modelling of one side lined steel wall frames and the results. A design method based on apropriate effectivelength factors was developed within the provisions of Australian/New Zealand standard for cold-formed steel structures topredict the ultimate loads and failure modes of one side lined stel wall frames.

Fire resistance tests of LSF walls under combined compression and bending actions

Mithum Peiris,Mahen Mahendran 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.4

Cold-formed steel wall panels sheathed with gypsum plasterboard have shown superior thermal and structural performance in fire. Recent damage caused by fire events in Australia has increased the need for accurate fire resistance ratings of wall systems used in low- and mid-rise construction. Past fire research has mostly focused on light gauge steel framed (LSF) walls under uniform axial compression and LSF floors under pure bending. However, in reality, LSF wall studs may be subject to both compression and bending actions due to eccentric loading at the wall to-roof or wall-to-floor connections. In order to investigate the fire resistance of LSF walls under the effects of these loading eccentricities, four full-scale standard fire tests were conducted on 3 m x 3 m LSF wall specimens lined with two 16 mm gypsum plasterboards under different combinations of axial compression and lateral load ratios. The findings show that the loading eccentricity can adversely affect the fire resistance level of the LSF wall depending on the magnitude of the eccentricity, the resultant compressive stresses in the hot and cold flanges of the wall studs caused by combined loading and the temperatures of the hot and cold flanges of the studs. Structural fire designers should consider the effects of loading eccentricity in the design of LSF walls to eliminate their potential failures in fire.

Shear Buckling Characteristics of Cold-formed Steel Channel Beams

Poologanathan Keerthan,Mahen Mahendran 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.3

Cold-formed steel members are increasingly used as primary structural elements in the building industries around the world due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. However, their shear capacities are determined based on conservative design rules. For the shear design of LCB web panels, their elastic shear buckling strength must be determined accurately including the potential post-buckling strength. Currently the elastic shear buckling coefficients of LCB web panels are determined by assuming conservatively that the web panels are simply supported at the junction between their flange and web elements. Hence finite element analyses were conducted to investigate the elastic shear buckling behavior of LCBs. An improved equation for the higher elastic shear buckling coefficient of LCBs was proposed based on finite element analysis results and included in the ultimate shear capacity equations of the North American cold-formed steel codes. Finite element analyses show that relatively short span LCBs without flange restraints are subjected to a new combined shear and flange distortion action due to the unbalanced shear flow. They also show that significant post-buckling strength is available for LCBs subjected to shear. New equations were also proposed in which post-buckling strength of LCBs was included.

Elastic Lateral Buckling of Cantilever Litesteel Beams Under Transverse Loading

Cyrilus Winatama Kurniawan,Mahen Mahendran 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.4

The LiteSteel Beam (LSB) is a new hollow flange channel section developed by OneSteel Australian Tube Mills using its patented dual electric resistance welding and automated continuous roll-forming technologies. The LSB has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. Its flexural strength for intermediate spans is governed by lateral distortional buckling characterised by simultaneous lateral deflection, twist and web distortion. Recent research on LSBs has mainly focussed on their lateral distortional buckling behaviour under uniform moment conditions. However, in practice, LSB flexural members are subjected to non-uniform moment distributions and load height effects as they are often under transverse loads applied above or below their shear centre. These loading conditions are known to have significant effects on the lateral buckling strength of beams. Many steel design codes have adopted equivalent uniform moment distribution and load height factors based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. The non-uniform moment distribution and load height effects of transverse loading on cantilever LSBs, and the suitability of the current design modification factors to include such effects are not known. This paper presents a numerical study based on finite element analyses of the elastic lateral buckling strength of cantilever LSBs subject to transverse loading, and the results. The applicability of the design modification factors from various steel design codes was reviewed, and suitable recommendations are presented for cantilever LSBs subject to transverse loading.

Flexural-torsional buckling tests of cold-formed steel compression members at elevated temperatures

Yasintha Bandula Heva,Mahen Mahendran 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.3

Current design standards do not provide adequate guidelines for the fire design of cold-formed steel compression members subject to flexural-torsional buckling. Eurocode 3 Part 1.2 (2005) recommends the same fire design guidelines for both hot-rolled and cold-formed steel compression members subject to flexural-torsional buckling although considerable behavioural differences exist between cold-formed and hot-rolled steel members. Past research has recommended the use of ambient temperature cold-formed steel design rules for the fire design of cold-formed steel compression members provided appropriately reduced mechanical properties are used at elevated temperatures. To assess the accuracy of flexural-torsional buckling design rules in both ambient temperature cold-formed steel design and fire design standards, an experimental study of slender cold-formed steel compression members was undertaken at both ambient and elevated temperatures. This paper presents the details of this experimental study, its results, and their comparison with the predictions from the current design rules. It was found that the current ambient temperature design rules are conservative while the fire design rules are overly conservative. Suitable recommendations have been made in relation to the currently available design rules for flexural-torsional buckling including methods of improvement. Most importantly, this paper has addressed the lack of experimental results for slender cold-formed steel columns at elevated temperatures.

Comparison of hot spot stress evaluation methods for welded structures

이제명,서정관,김명현,신상범,한명수,박준수,Mahen Mahendran 대한조선학회 2010 International Journal of Naval Architecture and Oc Vol.2 No.4

In this paper, different evaluation methods of Hot Spot Stresses (HSS) have been applied to four different welded structure details in order to compare them and to illustrate their differences. The HSSs at failure-critical locations were calculated by means of a series of finite element analyses. There was good overall agreement between calculated and experimentally determined HSS on the critical locations. While different methods and procedures exist for the computation of the structural hot-spot stress at welded joints, the recommendations within the International Institute of Welding (IIW) guideline concerning the ‘Hot Spot Stress’ approach were found to give good reference stress approximations for fatigue-loaded welded joints. This paper recommends and suggests an appropriate finite element modeling and hot spot stress evaluation technique based on round-robin stress analyses and experimental results of several welded structure details.

Direct Strength Method for Cold-Formed Steel Unlipped Channel Columns Subject to Local Buckling

Akshay Mangal Mahar,S. Arul Jayachandran,Mahen Mahendran 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.6

This paper evaluates the strength of unlipped channel columns using the Direct Strength Method (DSM), which applies to the sections with either intermediate or edge stiff eners. The local buckling behaviour of plain cold-formed steel sections (CFS) with fi xed-ends is studied by investigating the results of (i) 25 experimental studies published in the literature and (ii) a numerical study of 105 CFS sections. This paper reveals that the aspect ratio (web height to fl ange width ratio) of the cross-section signifi cantly aff ects the local buckling strength of plain unlipped channel sections. The DSM local buckling strength as specifi ed in the codes of practice ignores the eff ect of this parameter, resulting in unconservative designs for such columns. The diff erence in strength prediction can be up to about 15% for columns with a web height to fl ange width ratio of 3.0. At this aspect ratio, the inter-element stiff ness contribution in the post-buckling stage is the minimum, resulting in a lower strength estimation. To account for this inadequacy, this paper suggests a modifi ed DSM design procedure that accounts for the eff ect of stiff ness contribution from the aspect ratio of the cross-section in the post-buckling stage. The proposed modifi ed DSM design equations agree well with the results of experimental and numerical studies and preserve the target reliability of AISI- S100 (2016) for LRFD.

Post buckling mechanics and strength of cold-formed steel columns exhibiting Local-Distortional interaction mode failure

Hareesh Muthuraj,S.K. Sekar,Mahen Mahendran,O.P. Deepak 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.5

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio (0.91≤FCRD/FCRL≤4.05) (ii) non dimensional local slenderness ratio (0.88≤λL≤3.54) (iii) non-dimensional distortional slenderness ratio (0.68≤λD≤3.23) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and nonlinear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.