Cold-formed Steel Wall Frames Research Articles

Application of Direct Stiffness-Strength Method for Design of Gypsum and Plywood sheathed CFS wall panels Subjected to Bending

The cold-formed steel (CFS) wall frames need to be stiff-strong to inhibit the instability failures. The current design specifications do not have a robust design method for sheathed CFS wall panels. A safe wall frame design is possible by providing adequate bracing to resist the instability failures, which the sheathing boards can do. A new design method based on the demand and supply approach called “Direct Stiffness-Strength Method” (DSSM) is developed to fulfill sheathing-bracing design needs. Nevertheless, it is necessary to validate the suitability of the DSSM for the design of CFS wall frames with various sheathing materials. In this study, a total of 58 CFS sheathed panels were tested under out-of-plane loading with varying design parameters such as global (λe), local (λl), and distortional slenderness (λd), two sheathing board types (Gypsum and Plywood), sheathing board thicknesses (tb), and sheathing fastener connection spacing (df). The full-scale test results indicate that the resistance of the sheathing fastener connection is sensitive to the thickness of the fibrous sheathing board plywood. The full-scale test results were compared with the design strength of CFS wall panels using DSSM. The sheathed CFS wall panel design indicates that the current DSSM method is unconservative for gypsum sheathing (both 12.5 mm 15 mm thicknesses) and overly safe for 12 mm thick plywood sheathing. This can be attributed to the omission of sheathing thickness in the DSSM approach to determine the stiffness and strength of the sheathing fastener connection. Further, the reasons for the inaccurate prediction of the current DSSM method are discussed in detail. A set of new resistance factor values are proposed for the accurate design prediction of sheathed CFS wall panels. Finally, the paper presents and discusses the application of the proposed design approach and provides evidence for the benefits of DSSM.

Investigation on sheathing-fastener connection failures in cold-formed steel wall panels

Torsional buckling is a common mode of failure in highly slender Cold-formed Steel (CFS) stud wall frames. The torsional buckling mode will induce pull-through in sheathings attached on either side of wall panel leading to failure. This paper presents an experimental investigation to understand the performance of various sheathing boards against torsional buckling of CFS structural members. A total of forty-two specimens were tested including various parameters such as seven types of sheathing boards and six different types of CFS studs. In addition, the influence of different fasteners types that are used in the installation of sheathing boards on the CFS wall frames is also examined. The test results indicate that it is necessary to use the fastener with rubber washer (hex-washer head fasteners) to avoid pull-through failures in the sheathing. The load magnitudes at which the pull-through failure or the sheathing breakage occurs is reported for the different sheathing and CFS studs. In general, the sheathing board with the fiber composition performed well compared to the sheathing materials made of particle composition. In addition, the study also indicates that the performance of the sheathing board depends on the geometric dimensions of the CFS studs. The influence of CFS stud geometry in the sheathing-fastener connections is pictorially presented in the form of a plot. The force developed at each sheathing-fastener connection to achieve the target design moment in the CFS wall panels is calculated using a simple theoretical expression and compared against the experimental results obtained from this study. An appropriate sheathing board that offers resistance against torsional buckling of CFS stud is suggested based on the observed experimental failure modes.

Cyclic Loading Tests for Cold-Formed Steel Wall Frames with Lightweight Concrete

Lightweight steel framing is a method in housing and construction that have been widely used in lightweight steel construction. In this method, the structure is built by cold formed steel elements. They are cost-effective, light, and easy to assemble. However, the performance of lateral load resisting systems in cold-formed steel structures specially the behavior of cold-formed steel shear walls filled with lightweight structural concrete under seismic loads has not been studied in detail. In this study, an experimental investigation on cold-formed steel frames filled with lightweight structural concrete has been conducted and the results are presented. Six full-scale cold-formed steel frames filled with lightweight structural concrete with two different configurations were studied. The test was performed under a standard cyclic loading regime. This study is focused on the ultimate lateral load capacity and seismic response modification factor of cold-formed steel walls filled with lightweight concrete subjected to cyclic loads. Based on the test observation, detailed discussions on the failure modes of cold-formed steel wall specimens are given. Finally, shear load resistance, seismic response modification factor, failure modes, energy dissipation and stiffness of tested shear walls are proposed and discussed. The results show that although lower height to width ratio leads to a greater shear load resistant, energy dissipation, and stiffness for shear wall filled with lightweight concrete, its seismic modification factor is lower than those shear walls, which have higher height to width ratio.

Fragility curves for thin-walled cold-formed steel wall frames affected by ground settlements due to land subsidence

This report presents the results of a study on the performance of thin-walled cold-formed steel wall frames with different sheathing systems affected by angular distortions simulating ground differential settlements due to land subsidence. The wall frames are sheathed with different systems: expanded polystyrene, OSB, calcium silicate and gypsum board. Using experimental testing and numerical simulation, moment–rotation curves were calculated for the studs. A non-linear static pull-down analysis was performed producing several degrees of angular distortion simulating ground settlements. Lastly, fragility curves were calculated based on three levels of damage for wall frames with different sheathing systems.

Monotonic and cyclic loading tests for cold-formed steel wall frames sheathed with calcium silicate board

This research is concentrated on the structural strength and behavior of cold-formed steel wall frame sheathed with calcium silicate board under shear load. Test specimens with two different thicknesses of sheathing were assembled, 9mm and 12mm, with one-side or two-side of attachment. Monotonic shear and cyclic loading tests are conducted on wall specimens utilizing two C sections connected back-to-back to be as chord studs and calcium silicate board sheathing on the exterior. Based on the test results, detailed discussions on the strength, stiffness, energy absorption, ductility ratio, and failure mode of cold-formed steel wall specimens are given. It is noted that the failure mostly occurred at the bottom track of wall specimens due to the large deformation or tearing failure of track. The wall strength is not affected by the change of sheathing's thickness significantly, but wall frames attached with two-side calcium silicate board sheathing provide higher resisting strength and stiffness than those attached with one-side sheathing. In this study, test results are also used to compare with the previous study that single chord stud was used in the assembly of wall frame. In addition, the suggested response modification factor of the wall sheathed with calcium silicate board is proposed for design purpose.

Monotonic shear tests of cold-formed steel wall frames with sheathing

This research is focused on the experimental study of the structural strength of cold-formed steel wall frames with sheathing under monotonic shear loading. Two aspect ratios, 1.0 and 2.0 were utilized in the design of wall specimens. Three different kinds of sheathing material, gypsum board, calcium silicate board, and oriented-strand board, with two different thicknesses (9 and 12mm) were adopted in the test specimens. The ultimate strength, stiffness, energy absorption, and ductility ratio were studied for each test specimen. In final, the ductility ratios of the cold-formed steel wall frames similar to the wall configuration conducted in this study are proposed.

Performance of cold-formed steel wall frames under compression

This study presents the strength of braced and unbraced cold-formed steel wall frames consisting of several wall studs acting as columns, top and bottom tracks, and bracing members. The strength and the buckling mode of steel wall frames were found to be different due to the change of bracing type. In addition, the spacing of wall studs is a crucial factor to the strength of steel wall frames. The comparisons were made between the test results and the predictions computed based on AISI Code. The related specifications do not clearly provides the effective length factors for the member of cold-formed steel frame under compression. This paper proposes effective length factors for the steel wall frames based on the test results. A theoretical model is also derived to obtain the modulus of elastic support provided by the bracing at mid-height of steel wall frames in this research.

Numerical modelling and design of unlined cold-formed steel wall frames

Cold-formed steel wall frame systems using lipped or unlipped C-sections and gypsum plasterboard lining are commonly utilised in the construction of both the load bearing and non-load bearing walls in the residential, commercial and industrial buildings. However, the structural behaviour of unlined and lined stud wall frames is not well understood and adequate design rules are not available. A detailed research program was therefore undertaken to investigate the behaviour of stud wall frame systems. As the first step in this research, the problem relating to the degree of end fixity of stud was investigated. The studs are usually connected to the top and bottom tracks and the degree of end fixity provided by these tracks is not adequately addressed by the design codes. A finite element model of unlined frames was therefore developed, and validated using full scale experimental results. It was then used in a detailed parametric study to develop appropriate design rules for unlined wall frames. This study has shown that by using appropriate effective length factors, the ultimate load and failure modes of the unlined studs can be accurately predicted using the provisions of Australian or American cold-formed steel structures design codes. This paper presents the details of the finite element analyses, the results and recommended design rules for unlined wall frames.

Behaviour and design of cold-formed steel wall frames lined with plasterboard on both sides

Gypsum plasterboard is a common lining material used in cold-formed steel wall frame systems. It is used either with lipped or unlipped (plain) C-section studs in the construction of both the load bearing and non-load bearing walls in residential, industrial and commercial buildings. The design of these wall frames does not utilise the full strengthening effects of the plasterboard in carrying the axial loads. An experimental study has shown that the strength of the studs in compression was increased significantly when they were lined with plasterboard on one or both sides. In order to fully understand the behaviour of both sides lined steel wall frames, a finite element model was developed and validated using experimental results. This was followed by a detailed parametric study using finite element analyses. This paper presents the details of the finite element modelling of both sides lined wall frames and the results. A design method based on appropriate effective length factors was developed within the provisions of Australian/New Zealand Standard for cold-formed steel structures to predict the ultimate loads and failure modes of both sides lined steel wall frames.

Racking strength and stiffness of cold-formed steel wall frames

A combined experimental and theoretical study on the racking strength and stiffness of cold-formed steel wall frames is presented. A variety of bracing methods including no bracing, bracing with cement particle board or oriental strand board, and bracing with single or double X strap are investigated. The deformation behaviour and failure modes of each frame under racking are observed, and its racking strength and stiffness measured. Theoretical analysis is performed for frames with metal strap bracing. The predicted failure loads are in close agreement with those measured. The cross-sectional area of a strap significantly affects the deflection (stiffness) of a frame, but has little influence on its racking load capacity. Amongst the bracing methods studied, frames with 2 side X-straps have the best racking performance. By careful selection of the bracing method, individual member section, strap geometry and connection method, the frame performance can be optimised.

Behaviour of cold-formed steel wall frames lined with plasterboard

Gypsum plasterboard is a common lining material for steel wall frame systems used in combination with cold-formed steel studs (C or lipped C-sections). However, the design of these wall frames does not utilise the full strengthening effects of plasterboard in carrying axial loads. Therefore an experimental study was conducted to investigate the local and overall buckling behaviour of the studs in these frames using a total of 40 full-scale wall frame tests and stub column tests. The tests included unlined, both sides lined and one-side lined wall frames and studs. Test results were compared with predictions from the Australian standard AS 4600 (1996) and the American specification AISI (1996). This paper presents the details of the experimental study, the results, and comparisons with design code predictions.

Lateral Behavior of Plasterboard-Clad Residential Steel Frames

This paper presents a detailed investigation into the contribution of plasterboard to the lateral resistance of cold-formed steel-framed residential structures. It details the development of a finite-element model for laterally loaded plasterboard-lined cold-formed steel wall frames for residential construction. The model utilizes nonlinear element properties and three-dimensional geometrical configurations and is capable of simulating the influence of boundary conditions such as corner return walls and ceiling cornices. The analytical results from the finite-element model were successfully verified against experimental racking test results. A sensitivity analysis was conducted using the model to study the influence of return walls, ceiling cornices, and wall length on the lateral capacity of the wall system. It is concluded that a wall with corner return walls, ceilings cornices, and skirting boards has more than three times the lateral capacity of an identical isolated wall panel. The relationship between the wall length and the ultimate lateral load-carrying capacity of the wall system is dependent on the presence of these boundary conditions.