Cold-formed Steel Lipped Channel Sections Research Articles

Behaviour of cold-formed steel lipped channel sections subject to eccentric axial compression

The use of light-gauge steel framed (LSF) wall systems in low- and mid-rise buildings has increased due to the fast and clean construction and robust structural performance. Cold-formed steel studs used as the primary load-bearing component in LSF walls are often subjected to combined axial compression and bending actions caused by loading eccentricity. Research on the effects of loading eccentricity on the compression capacity has been limited while the currently used AS/NZS 4600 and AISI-S100 DSM design guidelines significantly underestimate the load bearing capacities. In this study, 35 lipped channel columns of 0.6 to 1.5 m lengths were tested under concentric and varying levels of eccentric axial compression loading and the resulting load versus axial shortening curves and failure modes were analysed. Non-linear finite element models of tested columns were developed and validated using the test results. Comparison of the ultimate capacities obtained from the tests and finite element analyses against those predicted by the DSM design guidelines showed that the current DSM design guidelines underestimate the capacities whereas a closer agreement was obtained from the improved DSM design guidelines proposed in a recent research study. This paper recommends the improved DSM design method to enable economical and safe designs.

Experimental Study and Proposal to Improve the EWM Design of Cold‐Formed Steel Lipped Channel Columns with Circular Holes under Axial Compression

The cold‐formed steel (CFS) lipped channel section with circular holes has been widely used in low‐rise and multistory building structures as the column. However, the circular hole in the web makes the lipped channel column become susceptible to buckle. A total of 54 CFS lipped channel axial compression columns with and without circular holes were used to study the buckling behavior and the effective width design method. The interaction of the local buckling and the distortional buckling were observed for the short and intermediate columns, while the slender columns were controlled by the interaction of the local buckling, distortional buckling, and flexural buckling or flexural‐torsional buckling. The experimental failure loads were gradually decreased with the increase in the diameter of the circular hole for the specimens with the same section. The failure loads of the specimens with two holes were lower than those of the specimens with one hole with same section and same diameter of holes. Then, the experimental results were used to validate a nonlinear finite element model (FEM) previously developed by the authors. The validated FEM was subsequently used to obtain additional 36 numerical failure results concerning the effects of the length, the section, and the diameter and the number of the circular holes. Furthermore, the proposal to calculate the distortional buckling coefficient of the CFS lipped channel section with circular holes were put forward based on numerical analysis considering the reduction of effect of holes. Finally, a proposal to improve the effective width method (EWM) design approach for CFS lipped channel sections with circular holes under axial compression was presented. The comparisons between experimental and numerical capacities and their calculations provided by the proposed EWM design method illustrate a great application of the proposed approach.

Experimental study on ultimate strength of bolted L shaped sleeve joints between CFS lipped channel sections

This study aims to understand the behavior of bolted L shape sleeve joint connecting two Cold-Formed Steel (CFS) channel sections. A total of thirty-two specimens were experimentally tested under three-point bending. Three different series namely, (A) control specimen with two different span lengths, (B) sleeved specimen with the flange of sleeve connector capping the compression zone, and (C) sleeved specimen with the flange of sleeve connector capping the tension zone were tested. The parameters considered in this study include (i) the span length (Lt), (ii) sleeve length to section depth ratio (β), and (iii) thickness of sleeve connector (LS). The experimental results revealed that the ultimate moment resistance of specimens with a 2.5 mm thick sleeve connector was 19 to 73% higher than 2.0 mm thick sleeve specimens. The moment capacity of series C specimens was about 90–103% of that of the series B specimens. Based on the experimental results, design predictor equations were suggested to determine the moment resistance of sleeve specimens with respect to β. In addition, reliability studies were done for test series B to determine the safety and resistance factors for allowable strength design (ASD) method and load and resistance factor design (LRFD) method respectively. The equivalent and design uniformly distributed load (UDL) was determined based on the combined effect of shear and bending.

Web crippling behaviour and design of aluminium lipped channel sections under two flange loading conditions

Aluminium alloys have recently drawn significant attention in structural applications due to its outstanding mechanical characteristics. Thin-walled members fabricated by aluminium alloys can be more competitive in construction industries than the conventional cold-formed steel sections, particularly in areas with high humidity and severe environmental conditions. Nevertheless, they are more vulnerable to various types of instability due to their relatively low elastic modulus compared to steel. Applying high concentrated load transversely on thin-walled members can cause critical damage to the web of the cross section called web crippling. Although a large number of studies has been performed to investigate the web crippling mechanisms on different types of sections, the existing studies are primarily of the empirical nature and thus merits further investigations. To fill the research gap, this study was thus performed based on our previously conducted experimental work to further comprehend the web crippling phenomenon of the roll-formed aluminium lipped channel (ALC) sections under the loading conditions of end-two-flange (ETF) and interior-two-flange (ITF). This was done through numerical investigations followed by a parametric study which are reported herein in details. A wide range of roll-formed ALC sections covering web slenderness ratios ranged from 28 to 130, inside bent radii ranging between 2 mm and 8 mm, bearing lengths ranged from 50 mm to 150 mm, and three sheeting aluminium alloy grades (5052-H32, 5052-H36 and 5052-H38) were considered in the parametric study. The acquired web crippling database was then used to assess the consistency and accuracy of the current design rules used in practice. It was found that the web crippling capacity determined by the current international specifications are unsafe and unreliable, whereas the predictions of the recently proposed equations agree very well. Furthermore, a Direct Strength Method (DSM)-based capacity prediction approach was proposed and then validated against the web crippling database acquired here as well as the experimental and numerical data for cold-formed steel lipped channel sections used in the literature.

Strength and stiffness of floor trusses fabricated from cold-formed steel lipped channels

This paper reports findings of an experimental study on floor trusses fabricated from cold-formed steel lipped channel sections. In design, the members of these trusses are generally considered as pin-ended and their capacities are assessed under pure compressive and tensile loads by making use of commonly accepted design specifications. Seventeen full-scale floor trusses were experimentally investigated through four point bending tests. Thickness of lipped channels, number of connection fasteners, and type of diagonal connection were considered as the prime variables. Test results indicate that there are marked differences between the design and measured values in terms of both the strength and stiffness. The service load stiffnesses of the trusses were found to be lower than the stiffnesses obtained using two dimensional truss models due to the neglect of connection flexibility in analysis models. Additional experiments on screw connections were conducted to find out their axial stiffness. The results from connection tests were used to develop analytical expressions which can be used to simulate connection flexibility. Similar to the stiffness, the strength of the trusses were found to be lower than the predicted strength using the pin-ended member under compression approach. In addition, the observed failure modes are markedly different than the code predictions. The sources of these differences were found to arise from the unfolding of lips at the diagonal to chord member connections and the global bending effects. The strength and failure mode of trusses can be more accurately predicted by considering local buckling of channel sections with unfolded lips.

Nonlinear behavior of axially loaded back-to-back built-up cold-formed steel un-lipped channel sections

Back-to-back built-up cold-formed steel un-lipped channel sections are used in cold-formed steel structures; such as trusses, wall frames and portal frames. In such built-up columns, intermediate fasteners resist the buckling of individual channelsections. No experimental tests or finite element analyses have been reported in the literature for back-to-back built-up coldformed steel un-lipped channel sections and specially investigated the effect of screw spacing on axial strength of such columns. The issue is addressed in this paper. The results of 95 finite element analyses are presented covering stub to slender columns. The finite element model is validated against the experimental tests recently conducted by authors for back-to-back built-up cold-formed steel lipped channel sections. The verified finite element model is then used for the purposes of a parametric study to investigate the effect of screw spacing on axial strength of back-to-back built-up cold-formed steel un-lipped channel sections. Results are compared against the built-up lipped channel sections and it is shown that the axial strength of un-lipped built-up sections are 31% lesser on average than the built-up lipped channel sections. It was also found that the American Iron and Steel Institute (AISI) and the Australian and New Zealand Standards were over-conservative by around 15% for built-up columns failed through overall buckling, however AISI and AS/NZS were un-conservative by around 8% for built-up columns mainly failed by local buckling.

Two-level optimization for a new family of cold-formed steel lipped channel sections against local and distortional buckling

The objective of this paper is to provide the development of a new algorithm that produces a family of minimal weight cold-formed steel lipped channels with the smallest number of individual cross-sections (family size) that are still capable of covering the current engineering design demands as commonly found in light steel framing. Current research in cold-formed steel optimization has largely sought optimal cross-sections for single members under a single applied action. In this paper, the optimization effort is extended to a broad set of axial (P) and bending (M) demands. A two-level optimization framework is proposed: level one focuses on member optimization of the P-M demand space as derived from current commercially available lipped channel sections in the United States; while level two focuses on the selection of a new family of optimal lipped channel sections that have the same efficiency in covering the design space, but utilize a minimal family size. As the focus of the effort is on the two-level optimization the cross-section optimization is simplified in this case to lipped channels against local and distortional buckling only; however the adopted algorithms are readily extensible. The results show that a new family of shapes with only 12 sections can achieve the same or better performance as the 108 sections commercially available in the United States. The developed family of shapes provides a direct demonstration of the potential for optimization to improve cold-formed steel manufacturing. In the future, the first-level member optimization will include new cross-section shapes, e.g., sigma sections, as well as global buckling, and will be performed along with the second family-level optimization to demonstrate additional potential benefits.

Experimental and Analytical Study of Various Shear Connectors Used for Cold-Formed Steel-Ferrocement Composite Beam

This work presents the experimental tests carried out to evaluate the behaviour of different types of shear connectors proposed for cold formed steel (CFS) section integrated with ferrocement slab as potential used for composite beam. Ten push-out test specimens of cold-formed steel lipped channel sections connected with ferrocement slab were tested. Three types of shear connectors were studied comprised of bolts, self-drilling-screw and bar angle. The connection behavior is analysed in terms of its load-slip relationship and the failure mode. The parametric studies were performed to investigate the effect on the shear connector’s capacity by varying the number of layers of wire mesh used in ferrocement slab and types of shear connector used. A theoretical analysis (Eurocode 4) was carried out to verify the experiment results. The results show that the experimental and theoretical proved to have good agreement with each other.

Finite Element Modelling of Innovative Precast Cold-Formed Steel Ferrocement as Composite Beam

This paper describes Finite Element Modeling (FEM) of a composite beam comprised of cold formed steel section and concrete slab designed as ferrocement. Software (ANSYS, version 11) was adopted to carry out the modeling of the proposed composite beam. Experimental tests were also been carried out for three simple supported composite beams. The proposed innovative precast composite beam specimens of cold-formed steel lipped channel sections (CFS) connected with ferrocement slab were tested till failure, under two point loads positioned atquarter length of the span from support. The results showed that close agreement was observed between the FEM and experimental results for ultimate loads and load-deflection responses.