Improving the shear capacities of lipped channel beams with web openings using plate stiffeners

Cold-formed steel lipped channel beams (LCB) are used extensively in residential, industrial and commercial buildings as load bearing structural elements. Their shear capacities are considerably reduced when web openings are included for the purpose of locating building services. Past research has shown that the shear capacities of LCBs were reduced by up to 70% due to the inclusion of these web openings. Hence there is a need to improve the shear capacities of LCBs with web openings. A cost effective way of eliminating the detrimental effects of large web openings is to attach suitable stiffeners around the web openings and restore the original shear strength and stiffness of LCBs. Hence detailed experimental studies were undertaken to investigate the behaviour and strength of LCBs with stiffened web openings subject to shear, and combined bending and shear actions. Both plate and stud stiffeners with varying sizes and thicknesses were attached to the web elements of LCBs using different screw-fastening arrangements. Simply supported test specimens of LCBs with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. Numerical studies were also undertaken to investigate the strength of LCBs with stiffened web openings. Finite element models of LCBs with stiffened web openings under shear, combined bending and shear actions were developed to simulate the behaviour of tested LCBs. The developed models were then validated by comparing their results with experimental results and used in further studies. Both experimental and finite element analysis results showed that the stiffening arrangements recommended by past research and available design guidelines are not adequate to restore the original shear strengths of LCBs. Therefore new stiffener arrangements were proposed based on screw fastened plate stiffeners. This paper presents the details of this research study and the results.

Behaviour of LSF floor systems with improved joist sections under fire conditions

Fire safety design of buildings is essential to safeguard lives and minimize the loss of damage to properties. Light-weight cold-formed steel channel sections along with fire resistive plasterboards are used to construct light gauge steel frame floor systems to provide the required fire resistance rating. However, simply adding more plasterboard layers is not an efficient method to increase FRR. Hence this research focuses on using joists with improved joist section profiles such as hollow flange sections to increase the structural capacity of floor systems under fire conditions and thus their FRR. In this research, the structural and thermal behaviour of LSF floor systems made of LiteSteel Beams with different plasterboard and insulation configurations was investigated using four full scale tests under standard fires. Based on the ultimate failure load of the floor joist at ambient temperature, transient state fire tests were conducted for different Load Ratios. These fire tests showed that the new LSF floor system has improved the FRR well above that of those made of lipped channel sections. The joist failure was predominantly due to local buckling of LSB compression flanges near mid-span with severe yielding of tension flanges. Fire tests have provided valuable structural and thermal performance data of tested floor systems that included time-temperature profiles, and failure times and temperatures. Average failure temperatures of LSB joists and reduced yield strengths were used to predict their ultimate moment capacities, which were compared with corresponding test capacities. This allowed an assessment in relation to the accuracy of current design rules for steel joists at elevated temperatures. This paper presents the details of full scale fire tests of LSF floor systems made of LSB joists with different plasterboard and insulation configurations and their results along with some important findings.

Web crippling tests of rivet fastened rectangular hollow flange channel beams under two flange load cases

Recent research on hollow flange beams has led to the development of an innovative rectangular hollow flange channel beam (RHFCB) for use in floor systems. The new RHFCB is a mono-symmetric structural section made by intermittently rivet fastening two torsionally rigid closed rectangular hollow flanges to a web plate element, which allows section optimisation by selecting appropriate combinations of web and flange widths and thicknesses. However, the current design rules for cold-formed steel sections are not directly applicable to rivet fastened RHFCBs. To date, no investigation has been conducted on their web crippling behaviour and strengths. Hence an experimental study was conducted to investigate the web crippling behaviour and capacities of rivet fastened RHFCBs under End Two Flange (ETF) and Interior Two Flange (ITF) load cases. It showed that RHFCBs failed by web crippling, flange crushing and their combinations. Comparison of ultimate web crippling capacities with the predictions from the design equations in AS/NZS 4600 and AISI S100 showed that the current design equations are unconservative for rivet fastened RHFCB sections under ETF and ITF load cases. Hence new equations were proposed to determine the web crippling capacities of rivet fastened RHFCBs. These equations can also be used to predict the capacities of RHFCBs subject to combined web crippling and flange crushing conservatively. However, new capacity equations were proposed in the case of flange crushing failures that occurred in thinner flanges with smaller bearing lengths. This paper presents the details of this web crippling experimental study of RHFCB sections and the results.

Behaviour and strength of hollow flange channel sections under torsion and bending

Hollow flange channel section is a cold-formed high-strength and thin-walled steel section with a unique shape including two rectangular hollow flanges and a slender web. Due to its mono-symmetric characteristics, it will also be subjected to torsion when subjected to transverse loads in practical applications. Past research on steel beams subject to torsion has concentrated on open sections while very few steel design standards give suitable design rules for torsion design. Since the hollow flange channel section is different from conventional open sections, its torsional behaviour remains unknown to researchers. Therefore the elastic behaviour of hollow flange channel sections subject to uniform and non-uniform torsion, and combined torsion and bending was investigated using the solutions of appropriate differential equilibrium equations. The section torsion shear flow, warping normal stress distribution, and section constants including torsion constant and warping constant were obtained. The results were compared with those from finite element analyses that verified the accuracy of analytical solutions. Parametric studies were undertaken for simply supported beams subject to a uniformly distributed torque and a uniformly distributed transverse load applied away from the shear centre. This paper presents the details of this research into the elastic behaviour and strength of hollow flange channel sections subject to torsion and bending and the results.

Bending and torsion of hollow flange channel beams

The LiteSteel beam (LSB) is a cold-formed high strength steel channel section made of two torsionally rigid closed flanges and a slender web. Due to its mono-symmetric characteristics, its centroid and shear centre do not coincide. The LSBs can be used in floor systems as joists or bearers and in these applications they are often subjected to transverse loads that are applied away from the shear centre. Hence they are often subjected to combined bending and torsion actions. Previous researches on LSBs have concentrated on their bending or shear behaviour and strengths, and only limited research has been undertaken on their combined bending and torsion behaviour. Therefore in this research a series of nine experiments was first conducted on LSBs subject to combined bending and torsion. Three LSB sections were tested to failure under eccentric loading at mid-span, and appropriate results were obtained from seven tests. A special test rig was used to simulate two different eccentricities and to provide accurate simple boundary conditions at the supports. Finite element models of tested LSBs were developed using ANSYS, and the ultimate strengths, failure modes, and load–displacement curves were obtained and compared with corresponding test results. Finite element analyses agreed well with test results and hence the developed models were used in a parametric study to investigate the effects of load locations, eccentricities, and spans on the combined bending and torsion behaviour of LSBs. The interaction between the ultimate bending and torsional moment capacities was studied and a simple design rule was proposed. This paper presents the details of the tests, finite element analyses, and parametric study of LSBs subject to combined bending and torsion, and the results.

Experimental studies of lipped channel beams subject to web crippling under ETF and ITF load cases

Lipped channel beams (LCBs) are commonly used as floor joists and bearers in buildings. However, they are subjected to specific failure modes such as web crippling. Despite considerable web crippling research, recent studies [1-6] have shown that the current web crippling design rules are unable to predict the test capacities under ETF and ITF load cases. In many instances, the predictions by the available design standards such as AISI S100, AS/NZS 4600 and Eurocode 3 Part 1-3 [7-9] are inconsistent. Hence thirty-six tests were conducted to assess the web crippling behaviour and strengths of LCBs under two flange load cases. Experimental web crippling capacities were then compared with the predictions from the current design rules. These comparisons showed that AS/NZS 4600 and AISI S100 design equations are very unconservative for LCB sections under ETF load case and are conservative for ITF load case. Hence improved equations were proposed to determine the web crippling capacities of LCBs. Suitable design rules were also developed using the direct strength method. This paper presents the details of this study and the results including improved design rules.

Numerical study of LSF floors made of hollow flange channels in fire

Light gauge steel frame (LSF) floor systems are generally made of lipped channel section joists and lined with gypsum plasterboards to provide adequate fire resistance rating under fire conditions. Recently a new LSF floor system made of welded hollow flange channel (HFC) section was developed and its fire performance was investigated using full scale fire tests. The new floor systems gave higher fire resistance ratings in comparison to conventional LSF floor systems. To avoid expensive and time consuming full scale fire tests, finite element analyses were also performed to simulate the fire performance of LSF floors made of HFC joists using both steady and transient state methods. This paper presents the details of the developed finite element models of HFC joists to simulate the structural fire performance of the LSF floor systems under standard fire conditions. Finite element analyses were performed using the measured time–temperature profiles of the failed joists from the fire tests, and their failure times, temperatures and modes, and deflection versus time curves were obtained. The developed finite element models successfully predicted the structural performance of LSF floors made of HFC joists under fire conditions. They were able to simulate the complex behaviour of thin cold-formed steel joists subjected to non-uniform temperature distributions, and local buckling and yielding effects. This study also confirmed the superior fire performance of the newly developed LSF floors made of HFC joists.

Elevated temperature mechanical properties of hollow flange channel sections

The fire performance of cold-formed steel members is an important criterion to be verified for their successful use in structural applications. However, lack of clear design guidance on their fire performance has inhibited their usage in buildings. Their elevated temperature mechanical properties, i.e., yield strengths, elastic moduli and stress–strain relationships, are imperative for the fire design. In the past many researchers have proposed elevated temperature mechanical property reduction factors for cold-formed steels, however, large variations exist among them. The LiteSteel Beam (LSB), a hollow flange channel section, is manufactured by a combined cold-forming and electric resistance welding process. Its web, inner and outer flange elements have different yield strengths due to varying levels of cold-working caused by their manufacturing process. Elevated temperature mechanical properties of LSBs are not the same even within their cross-sections. Therefore an experimental study was undertaken to determine the elevated temperature mechanical properties of steel plate elements in LSBs. Elevated temperature tensile tests were performed on web, inner and outer flange specimens taken from LSBs, and their results are presented in this paper including their comparisons with previous studies. Based on the test results and the proposed values from previous studies and fire design standards, suitable predictive equations are proposed for the determination of elevated temperature mechanical properties of LSB web and flange elements. Suitable stress–strain models are also proposed for the plate elements of this cold-formed and welded hollow flange channel section.

Thin-walled timber and FRP-timber veneer composite CEE-sections

This paper compares the structural performance between thin-walled timber and FRP-timber composite Cee-sections. While, thin-walled composite timber structures have been proven to be efficient and ultra-light structural elements, their manufacturing is difficult and labour intensive. Significant effort and time is required to prevent the cracking of the transverse timber veneers, bent in the grain direction, when forming the cross-sectional shape. FRP-timber structures overcome this disadvantage by replacing the transverse veneers with flexible, unidirectional FRP material and only keeping the timber veneers which are bent in their natural rolling direction. The Cee-sections investigated in this study were 210 mm deep × 90 mm wide × 500 mm high and manufactured from five plies. For both section types, the three internal plies were thin (1 mm thick) softwood Hoop pine (Araucaria cunninghamii) veneers, orientated along the section longitudinal axis. The two outer layers, providing bending stiffness to the walls, were Hoop pine veneers (1 mm thick) for the timber sections and glass fibre reinforced plastic (0.73 mm thick) for the FRP-timber sections orientated perpendicular to the inner layers. The manufacturing process is briefly introduced in this paper. The profiles were fitted with strain gauges and tested in compression. Linear Variable Displacement Transducers also recorded the buckling along one flange. The test results are presented and discussed in this paper in regards to their structural behaviour and performance. Results showed that the use of FRP in the sections increases both the elastic local buckling load and section capacity, the latter being increased by about 24 percent. The results indicate that thin-walled FRP-timber can ultimately be used as a sustainable alternative to cold-formed steel profiles.

Experimental studies of lipped channel beams subject to web crippling under two-flange load cases

Lipped channel beams (LCBs) are commonly used as flexural members such as floor joists and bearers in the construction 6 industry. These thin-walled LCBs are subjected to specific buckling and failure modes, one of them being web crippling. Despite considerable 7 research in this area, some recent studies have shown that the current web crippling design rules are unable to predict the test capacities under 8 end-two-flange (ETF) and interior-two-flange (ITF) load conditions. In many instances, web crippling predictions by the available design 9 standards such as AISI S100, AS/NZS 4600 and Eurocode 3 Part 1-3 are inconsistent, i.e., unconservative in some cases, although they 10 are conservative in other cases. Hence, experimental studies consisting of 36 tests were conducted in this research to assess the web crippling 11 behavior and capacities of high-strength LCBs under two-flange load cases (ETF and ITF). Experimental results were then compared with the 12 predictions from current design rules. Comparison of the ultimate web crippling capacities from tests showed that the design equations are 13 very unconservative for LCB sections under the ETF load case and are conservative for the ITF load case. Hence, improved equations were 14 proposed to determine the web crippling capacities of LCBs based on the experimental results from this study. Current design equations do 15 not provide the direct strength method (DSM) provisions for web crippling. Hence, suitable design rules were also developed under the DSM 16 format using the test results and buckling analyses using finite-element analyses.

Experimental studies on web crippling strength of hollow flange channels under EOF and IOF load cases

LiteSteel beam (LSB) is a hollow flange channel made from cold-formed steel using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. LSBs are currently used as floor joists and bearers in buildings. However, there are no appropriate design standards available due to its unique hollow flange geometry, residual stress characteristics and initial geometric imperfections arising from manufacturing processes. Recent research studies have focused on investigating the structural behaviour of LSBs under pure bending, predominant shear and combined actions. However, web crippling behaviour and strengths of LSBs still need to be examined. Therefore, an experimental study was undertaken to investigate the web crippling behaviour and strengths of LSBs under EOF (End One Flange) and IOF (Interior One Flange) load cases. A total of 23 web crippling tests were performed and the results were compared with the current AS/NZS 4600 and AISI S100 design standards, which showed that the cold-formed steel design rules predicted the web crippling capacity of LSB sections very conservatively under EOF and IOF load cases. Therefore, suitably improved design equations were proposed to determine the web crippling capacity of LSBs based on experimental results. In addition, new design equations were also developed under the Direct Strength Method format. This paper presents the details of this experimental study on the web crippling behaviour and strengths of LiteSteel beams under EOF and IOF load cases and the results.

Web crippling tests of hollow flange channel beams with flanges fastened to supports under two flange load cases

Thin-walled steel hollow flange channel beams known as LiteSteel beam (LSB) sections were developed for use as joists and bearers in various flooring systems. However, they are subjected to specific buckling and failure modes, one of them being web crippling. Despite considerable research in this area, much of the current design predictions for cold-formed steel sections are not directly applicable to LSBs. This is due to the geometry of the LSB, which consists of two closed rectangular hollow flanges, and its unique residual stress characteristics and initial geometric imperfections. Hence an experimental study was conducted to investigate the web crippling behaviour and capacities of LSBs with their flanges fastened to supports. Thirty nine web crippling tests were conducted under two flange load cases (End Two Flange (ETF) and Interior Two Flange (ITF)). Test results showed that for ETF load case the web crippling capacities increased by 50% on average while they increased by 97% for ITF load case when flanges were fastened to supports. Comparison of the ultimate web crippling capacities from tests showed that AS/NZS 4600 and AISI S100 web crippling design equations are conservative for LSB sections with flanges fastened to supports under ETF and ITF load cases. Hence new equations were proposed to determine the web crippling capacities of LSBs with flanges fastened to supports. This paper presents the details of the experimental study into the web crippling behaviour of LSB sections with their flanges fastened under ETF and ITF load cases, and the results.

Shear tests of rivet fastened rectangular hollow flange channel beams

The intermittently rivet fastened Rectangular Hollow Flange Channel Beam (RHFCB) is a new cold-formed hollow section proposed as an alternative to welded hollow flange channel beams. It is a monosymmetric channel section made by intermittently rivet fastening two torsionally rigid rectangular hollow flanges to a web plate. This process enables the end users to choose an effective combination of different web and flange plate sizes to achieve optimum design capacities. Recent research studies focused mainly on the shear behaviour of the most commonly used lipped channel beam and welded hollow flange beam sections. However, the shear behaviour of rivet fastened RHFCB has not been investigated. Therefore a detailed experimental study involving 24 shear tests was undertaken to investigate the shear behaviour and capacities of rivet fastened RHFCBs. Simply supported test specimens of RHFCB with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. Comparison of experimental shear capacities with corresponding predictions from the current Australian cold-formed steel design rules showed that the current design rules are very conservative for the shear design of rivet fastened RHFCBs. Significant improvements to web shear buckling occurred due to the presence of rectangular hollow flanges while considerable post-buckling strength was also observed. Such enhancements to the shear behaviour and capacity were achieved with a rivet spacing of 100 mm. Improved design rules were proposed for rivet fastened RHFCBs based on the current shear design equations in AISI S100 and the direct strength method. This paper presents the details of this experimental investigation and the results.

Experimental and numerical studies of hollow flange channel beams subject to web crippling under ETF and ITF load cases

This paper presents the details of experimental and numerical studies on the web crippling behaviour of hollow flange channel beams, known as LiteSteel beams (LSB). The LSB has a unique shape of a channel beam with two rectangular hollow flanges, made using a unique manufacturing process. Experimental and numerical studies have been carried out to evaluate the behaviour and design of LSBs subject to pure bending actions, predominant shear actions and combined actions. To date, however, no investigation has been conducted into the web crippling behaviour and strength of LSB sections under ETF and ITF load conditions. Hence experimental studies consisting of 28 tests were first conducted in this research to assess the web crippling behaviour and strengths of LSBs under two flange load cases (ETF and ITF). Experimental web crippling capacity results were then compared with the predictions from AS/NZS 4600 and AISI S100 design rules, which showed that AS/NZS 4600 and AISI S100 design equations are very unconservative for LSBs under ETF and ITF load cases. Hence improved equations were proposed to determine the web crippling capacities of LSBs. Finite element models of the tested LSBs were then developed, and used to determine the elastic buckling loads of LSBs under ETF and ITF load cases. New equations were proposed to determine the corresponding elastic buckling coefficients of LSBs. Finally suitable design rules were also developed under the Direct Strength Method format using the test results and buckling analysis results from finite element analyses.