Journal of Structural Engineering

A LiteSteel beam (LSB) is a new cold-formed steel hollow flange channel section produced using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. The LSBs are commonly used as floor joists and bearers with web openings in residential, industrial, and commercial buildings. Their shear strengths are considerably reduced when web openings are included for the purpose of locating building services. However, no research has been undertaken on the shear behavior and strength of LSBs with web openings. Therefore, experimental and numerical studies were undertaken to investigate the shear behavior and strength of LSBs with web openings. In this research, finite-element models of LSBs with web openings in shear were developed to simulate the shear behavior and strength of LSBs including their buckling characteristics. They were then validated by comparing their results with available experimental test results and used in a detailed parametric study. The results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LSBs with web openings. Improved design equations have been proposed for the shear capacity of LSBs with web openings based on both experimental and parametric study results. An alternative shear design method based on an equivalent reduced web thickness was also proposed. It was found that the same shear strength design rules developed for LSBs without web openings can be used for LSBs with web openings provided the equivalent reduced web thickness equation developed in this paper is used. This is a significant advancement as it simplifies the shear design methods of LSBs with web openings considerably.

The work reported in this paper is part of an ongoing numerical investigation aimed at (1) assessing the buckling, postbuckling, strength, and collapse behavior of cold-formed steel continuous beams and simple frames and (2) developing an efficient methodology, based on the direct strength method (DSM) approach, to design such structural systems. The results available at this stage concern two- and three-span lipped channel beams subjected to nonuniform bending, and they include the assessment of how accurately the beam ultimate strengths can be predicted by the current DSM design curves. The numerical results presented and discussed are obtained through analyses based on generalized beam theory (elastic buckling analyses) and shell finite-element models (all the remaining analyses). Ultimate strength values yielded by geometrically and materially nonlinear shell finite-element analyses are compared with estimates provided by the DSM equations, and on the basis of this comparison, it is possible to identify some features that must be included in a DSM approach applicable to continuous cold-formed steel beams.

The paper presents an attempt to predict the load carrying capacity of perforated rack columns by the direct strength method (DSM). The investigation is focused on two different issues: the prediction of the elastic buckling loads of members with multiple perforations; and the evaluation of the accuracy of the current DSM buckling curves when applied to rack columns. In relation to the first issue, a model for the calculation of the reduced thickness of the perforated strip to be used in finite-strip buckling analysis is developed. Regarding the study of the DSM curves, it is demonstrated that they can be used to accurately determine the strength of rack cross sections whose failure is governed by distortional buckling or global buckling (with no significant participation of local buckling). This is an interesting result because it will allow substituting the distortional buckling tests, that are currently carried out in the process of design of these columns, by a simple and easy to apply calculation procedure.

This paper presents procedures for the design of fixed- and pin-ended equal-leg angle columns with short-to-intermediate lengths. First, some remarks concerning the buckling and postbuckling behavior of the angle columns are presented that (1) illustrate the main differences between the fixed- and pin-ended column responses and (2) demonstrate the need for specific design procedures. Then, the paper reports an in-depth investigation aimed at gathering a large column ultimate strength data bank that includes (1) experimental values collected from the literature and (2) numerical values obtained from shell finite-element analyses carried out in the code ABAQUS. The set of experimental results is comprised of 41 fixed-ended columns and 37 pin-ended columns and the numerical results obtained include 89 fixed-ended columns and 28 pin-ended columns; various cross-section dimensions, lengths, and yield stresses are considered. Finally, the paper closes with the proposal of new design procedures for fixed- and pin-ended angle columns based on the direct strength method (DSM). The two procedures adopt modified global and local strength curves, and it is shown that the proposed DSM approach leads to accurate ultimate strength estimates for short-to-intermediate columns covering a wide slenderness range.

Experiments were conducted on cold-formed steel C-section joists with rectangular unstiffened web holes. The presence of holes decreased joist capacity and amplified distortional buckling deformation. Distortional buckling was accompanied by unstiffened strip buckling of the compressed web. When hole depth approached the web depth, sudden buckling of the compressed flange and web above the hole was observed. Critical elastic buckling moments for local, distortional, and global buckling were calculated for each specimen including the influence of holes with recently introduced engineering expressions and finite strip analysis. Forthcoming direct strength method equations for cold-formed steel joists with holes were demonstrated to be viable predictors of flexural capacity for the specimens considered in the experimental program.

The paper starts with a selective review of some basic contributions related to local-overall buckling mode interactions in thin-walled steel members. Then, the results of an intensive experimental study carried out at the Politehnica University of Timisoara with the purpose of evaluating the erosion of a theoretical bifurcation load in the distortional-flexural buckling interaction range in pallet rack uprights are presented. Two different sizes of cross sections, with and without perforations, have been studied. To evaluate and quantify the erosion, the erosion of the critical bifurcation load approach is applied. This approach enables one to use the European buckling curves in the Ayrton-Perry format, expressing the imperfection factor ($\alpha$) in terms of the erosion coefficient ($\psi$). It allows estimation of the member’s ultimate capacity, taking into account the interaction of sectional (local or distortional) and member (flexural, torsional, or flexural-torsional) instability modes. Test results and the evaluation procedure for the erosion coefficient ($\psi$) and imperfection factor ($\alpha$), applied on tested specimens, are presented.

Stainless steel is gaining increasing use in construction because of its durability, favorable mechanical properties, and aesthetic appearance, with the austenitic grades being the most commonly used. Austenitic stainless steels have a high nickel content (8–11%), resulting in high initial material cost and significant price fluctuations; this, despite its desirable properties, represents a considerable disadvantage in terms of material selection. Ferritic stainless steels, having no or very low nickel content, may offer a more viable alternative for structural applications, reducing both the level and variability of the initial material cost while maintaining adequate corrosion resistance. There is currently limited information available on the structural performance of this type of stainless steel. Therefore, to overcome this limitation, a series of material, cross section, and member tests have been performed, covering both the standard EN 1.4003 grade (similar to the chromium weldable structural steel 3Cr12) and the EN 1.4509 grade (441), which has improved weldability and corrosion resistance. In total, 20 tensile coupon tests, 16 compressive coupon tests, eight stub column tests, 15 flexural buckling tests, and eight in-plane bending tests were carried out. Precise measurements of the geometric properties of the test specimens, including the local and global geometric imperfections, were also made. The experimental results are used to assess the applicability of the current European (EN 1993-1-4) and North American (SEI/ASCE-8) provisions to ferritic stainless steel structural components. In addition, the relative structural performance of ferritic stainless steel to that of more commonly used stainless steel grades is also presented, showing ferritic stainless steel to be an attractive choice for structural applications.

In this paper, the behavior of deep trapezoidal sheeting with perforated webs is studied. The analyzed panel has longitudinal stiffeners both in the webs and flanges, which improves the load-bearing capacity but makes the behavior more complicated. The considered panel is produced with and without web perforations. When web perforation is applied, it is located in the middle part of the web. The primary aim of web perforation is to enhance noise resistance, but it also has an influence on the static behavior. Because reliable design rules for web-perforated trapezoidal sheeting panels are not available, an experimental program is undertaken: panels with and without web perforations are tested in parallel. The test setup and specimens are designed to provide information on all the behavior modes. On the basis of the test results, it is possible to define the degrading effect of web perforation on the rigidity, bending, and shear resistances and on the resistance to direct transverse forces close to and far from the panel end. The experimental results are compared with proposals found in the relevant literature. On the basis of the test results, reduction factors might be proposed to consider the effect of web perforation in the design of the investigated sheeting panel.

This paper examines the accuracy of equations specified by the North American and Australasian steel structures codes for determining the net section tension capacity of a channel brace. It points out that there are three distinct factors affecting the net section efficiency of a cold-formed steel channel brace bolted at the web. These factors include (1) the in-plane shear lag associated with stress concentration around a bolt hole that is also present in flat sheets, (2) the out-of-plane shear lag that is also present in an I-section bolted at the flanges only, and (3) the bending moment arising from the connection eccentricity with respect to the neutral axis. Each of the relevant factors is explicitly incorporated into the equation proposed in this paper for determining the net section tension capacity of a cold-formed steel channel brace bolted at the web. The proposed equation is demonstrated through laboratory tests on low-ductility channel braces having practical aspect ratios that were bolted onto flexible plates, to be more reliable than the code equations and those existing in the literature.

This article presents 93 unpublished experimental results for rupture in the net section of bolted connections in cold-formed steel angles and channels. The article includes a study of the strength reduction coefficient in order to account for the shear lag effect. Predictions of connection strength by Brazilian and American design codes are considered. By comparing experimental results with design code predictions, model error (professional factor) statistics are evaluated. Model errors are incorporated in reliability analyses of typical connections to investigate their effects on connection safety. It is shown in the article that model errors have a significant impact on connection safety. Consideration of model errors leads to significant reductions in reliability indices, which are found to be less than the recommended target reliability levels. The model error statistics obtained herein are used to find the resistance factors that would be required to achieve the target reliability index in the design of bolted connections for net-section rupture. These factors are smaller than the current $\varphi =0.65$ used in the American Iron and Steel Institute code. Other suggestions for improvement of the North American code are also presented.

The current design rules of double shear bolted connections in the North American and Australian/New Zealand specifications for cold-formed steel structures are mainly based on the design rules of single shear bolted connections. The design rules may not be applicable for elevated temperature conditions because the design rules of single shear bolted connections were based on tests conducted at ambient temperature. A total of 153 double shear bolted connection specimens were tested, where 102 specimens were tested using a steady-state test method and 51 specimen tests were conducted using a transient-state test method. Three thicknesses of thin sheet steel were used in the investigation. The connection strengths obtained from the tests were compared with the nominal strengths calculated from the North American, Australian/New Zealand, and European specifications for cold-formed steel structures. The current modification factor in the bearing strengths calculation for double shear bolted connections was evaluated at an ambient temperature. The reduced tensile strengths of the thin sheet steels obtained from tensile coupon tests at elevated temperatures were used to calculate the nominal strengths of the connections. It is shown that the strengths of the double shear bolted connections predicted by the three specifications are generally conservative at elevated temperatures. Five failure modes were observed in the tests: bearing, tear-out, net section tension, bolt shear, and material.

Currently, there is a need for a design method for cold-formed steel (CFS) stud and track walls that use traditional sheathing materials to brace against compressive load. The objective of this paper is to provide a robust design method for these walls. Existing design methods are unable to handle dissimilar sheathing attached to the CFS stud flanges [e.g., oriented strand board (OSB) on the exterior face and gypsum board on the interior face] and provide no clarity on the impact of key properties including sheathing shear rigidity and stud spacing. A series of tests on axially loaded sheathed single studs and sheathed full walls using OSB, gypsum board, or an unsheathed face (and combinations thereof) is performed to elucidate the basic behavior and limit states. The stiffness that the fastener-sheathing system supplies to the stud as bracing is characterized analytically and experimentally. The characterization clarifies how both local fastener deformations and global sheathing deformations contribute to sheathing bracing. The impact of sheathing on elastic stability of the stud in local, distortional, and global buckling modes is provided. Both computational and analytical methods for stability determination including bracing stiffness from sheathing are detailed. An extension to current design methods that uses the enhanced elastic stability provided by sheathing bracing is proposed for member strength prediction. The design method is shown to agree well with the performed tests, providing consistent predictions for the limit state and the strength for walls with sheathing, including sheathing on one side only, and dissimilar sheathing on the two stud flanges.

A system that controls the rocking behavior of multistory shear walls is proposed as an innovative damage-control system for cold-formed steel structures. In this system, we have developed a new hold-down equipped with a fuse function (HDF) that controls the rocking behavior and is placed on the foundation of multistory shear walls. The HDF contributes to reducing damage to both structural and nonstructural members in cold-formed steel framed buildings, dissipating seismic input energy in the event of a large earthquake. The present paper describes the shake table tests performed using one-story, one-span, real-size specimens to investigate the fundamental behavior of the developed system. By using shake table tests in which the type of hold-down and the magnitude of input ground motion were varied as parameters, it was clarified that the plasticization of HDFs could reduce the base shear of specimens and that the energy dissipation by the HDFs could subdue the uplift deformation of the specimens. It is also shown that specimens that were not connected with foundations had the least base shear, but their uplift deformation was difficult to control because of their rocking-free condition. Overall, it was shown that incorporation of HDFs was effective in both reducing the base shear and controlling the rocking behavior in a stable manner.

Light-gauge steel frames with load-bearing walls have become one option in robust structural systems for low-rise buildings. This structural system is often used in steel-framed houses and in typical load-bearing walls consisting of a light-gauge steel frame with plywood and gypsum boards fastened by self-drilling screws. These load-bearing walls dissipate seismic energy mainly through local bearing failure of the cladding boards at the screw connections, exhibiting significant slip and pinching behavior. This behavior tends to decrease the energy dissipation capacity of the bearing walls because of the small areas of the cyclic hysteresis loops. To improve the energy dissipation capacity, corrugated shear diaphragms failing in the end-failure mode were studied by conducting monotonic and cyclic loading tests of simple shear panels under ideal boundary conditions with pure shear loading. A full-scale load-bearing wall using corrugated steel sheets with end failure was also studied under cyclic loading to verify that the wall exhibits improved seismic performance. It was found that corrugated shear diaphragms failing in the end-failure mode could increase the seismic performance of steel-framed houses.

This paper describes an experimental investigation of steel-sheathed cold-formed steel-framed shear walls by means of dynamic shake table tests. The objective was to evaluate the seismic performance and to identify whether the shear-wall behavior was consistent with past static tests, to obtain measures of damping and natural period of vibration, to investigate the influence of a second story, and to validate and improve the accuracy of the numerically predicted force-deformation response. The scope of study comprised five single-story and five double-story walls of the platform framing technique. Each wall was subjected to a suite of excitations: impact test to measure the linear-viscous damping ratio, harmonic excitation to estimate the natural period of vibration, and ground motions representative of the seismic hazard in Canada. An overview is presented of the test setup and dynamic loading protocols, as well as the test results and numerical model.

Cold-formed thin-walled steel residential building systems, because of their good environment protection, seismic performance, and high construction efficiency, have been widely used in the United States, Canada, Japan, and Australia, and recently, they also have had good application in China. Although a variety of studies have been carried out all over the world in the last 20 years, there is no related design code for this kind of building in China. For this reason, a series of research has been conducted in China recently, considering the consistency of standard systems in structural design in China and the newest development in the world. The contents of the paper can be divided into two parts. First, the major research works conducted by the authors over the last 5 years and the main findings are reviewed and summarized. Second, based on a Chinese professional standard, a brief summary of the design methods for cold-formed thin-walled steel framing residential buildings developed by the authors and other researchers in China is introduced.

This paper presents the method and results of a study whose objective was to investigate the seismic performance of a new light-frame cold-formed steel-frame system. The system includes floor trusses, open panels, V-braced panels, columns, and connections. To do this, a series of reversed-cyclic tests were conducted on subassemblies. The results of this experimental program provided insight into the behavior of the subassemblies under cyclic loading, which in turn provided key information for numerical modeling of the subassemblies and the whole system as well as failure mechanisms of the frame. Nonlinear time history analyses were performed using a new formulation for a 4-story frame using a suite of earthquake ground motions to demonstrate the behavior of a typical V-braced system in a moderate earthquake. Both test results and numerical analysis indicate that the system has good ductility as a result of the screwed plate connections between the light-gauge members and between the light-gauge members and square columns. The frame system performed very well at four stories making it a viable midrise construction option in seismic regions of the United States and around the world.

The paper summarizes the main new design provisions included in the recently revised Australian standard for steel storage racks. The standard features multitiered analysis provisions ranging from basic linear-elastic analysis-based provisions to highly advanced integrated design-analysis [geometric and material nonlinear analysis with imperfections (GMNIA)] provisions that allow the analysis and design to be completed in one step. The GMNIA provisions distinguish between beam element–based and shell element–based analysis according to cross section slenderness and provide rules for the imperfections to use for the two types of analysis, including imperfections in the local and distortional buckling modes for the shell element–based analysis. The selection of the system-based reliability (resistance) factor (${\mathit{\varphi }}_s$) is discussed. The standard is seen as the most advanced design code of its type currently available for frame-type steel structures. The paper also provides an in-depth discussion about the use of linear and nonlinear elastic analysis methods for the design of steel storage racks and how torsion may be considered in determining design capacities while not in the structural analysis.

The North American specifications for the design of cold-formed steel (CFS) structural members provides equations for determining the sheet shear strength in bolted connections when standard holes are used. In applications of oversized holes, the specification requires experimental analysis to be conducted to ensure satisfactory performance. A research project was recently completed at the University of North Texas to investigate the behavior and performance of CFS bolted connections using oversized holes. This paper presents the findings on the sheet shear strength for oversized hole applications. The studied parameters in this research included the following: sheet thickness from 0.762 to 2.997 mm; connection type of single shear and double shear with a single bolt; and bolt diameters of 6.4, 9.5, 12.7, and 15.9 mm. The experimental results indicate that the use of oversized holes without a washer did not significantly weaken the sheet shear strength. Recommendations are provided for predicting the nominal sheet shear strength.