Cold-formed Steel C-sections Research Articles

Experimental study of composite cold-formed steel C-section floor joists

Twelve large-scale slab specimens and twenty-two companion push-out specimens were tested to study the behavior and capacity of composite slab joists consisting of cold-formed steel C-sections and concrete. Four shear transfer mechanisms, including surface bond, pre-fabricated bent-up tabs, pre-drilled holes, and self-drilling screws, were employed on the surface of the flange embedded in the concrete to provide shear transfer capacity. Results indicated that specimens employed with shear transfer enhancements showed a marked increase in strength and reduced deflection compared with those relying only on a natural bond between steel and concrete to resist shear. Of the three shear transfer enhancements investigated, bent-up tabs provided the best performance at both the strength and serviceability limit states, followed by drilled holes in the embedded flanges. The use of self-drilling screws resulted in the lowest strength increase. The correlation of shear transfer capacity of push-out specimens with the ultimate capacity of large-scale specimens indicated that the average experimental flexural capacity of the slab specimens was approximately 1.16 times the average predicted value based on push-out test results.

A new formulation for distortional buckling stress in cold-formed steel members

Distortional buckling of compression members usually comprises rotation and translation of each flange and lip about the flange-web connection in opposite directions. The present procedures for the calculation of elastic distortional buckling stress in the literature are very complex, cumbersome and have long expressions. In this paper a new neural network (NN) based formula is proposed for the determination of the elastic distortional buckling stress of cold-formed steel C-sections with both end sections pinned. The focus of this study is on the distortional buckling, for which existing results are for sections subjected to pure compression and/or pure bending only. The data used for training and testing NNs is taken from Schafer’s report. The NN-based estimates are compared with the experimental, numerical and analytical results of different researchers and methods. It was found that the proposed NN based-formula is practical in predicting the elastic distortional buckling stress of cold formed steel C-sections.

Design Expressions Based on a Finite Element Model of a Stiffened Cold-Formed Steel C-Section

The design of cold-formed steel (CFS) C-sections that have bearing stiffeners installed between their flanges is a challenging task because complex interactions occur between the stiffener and the C-section when the assembly is loaded to failure. These interactions make it impractical to derive design expressions from first principles. Described in this paper is the application of a finite element (FE) model of a stiffened CFS C-section that was used to carry out parametric studies of the behavior of the stiffened joist assembly. Based on the results of these FE studies and experimental work, design expressions are proposed for the web crippling capacity of a stiffened C-section; the magnitude of the forces that develop in the fasteners connecting the joist to the stiffener; and the equivalent stiffness of the fasteners. These design expressions are fundamental components in the development of practical design expressions for the ultimate strength of stiffened C-sections.

Pilot study: lateral braced C-sections under bending

The overall behavior under uniform load of cold-formed steel C-sections assemblies was investigated. Each test assembly consisted of C-sections acting as beams having a track section to restrain its ends. A lateral brace to restrain the C-sections from rotation was provided at mid-span. To better understand the influence of the brace on the flexural behavior, an experimental investigation was carried out with particular emphasis placed on the study of the effect of the mid-span brace connection when wallboard was attached to the tension flange. The tested moment capacities are compared to predictions based on the 1996 edition American Iron and Steel Institutes' Specification for design of cold-formed steel structural members.

Bending and Shear Behavior of Web Elements with Openings

Cold-formed steel C-sections are frequently used as wall studs and floor joists in both commercial and residential construction. To facilitate installation of ancillary systems such as electrical wiring and plumbing, the C-section is manufactured with a web opening. Although the opening offers construction advantages, it may degrade the structural integrity of the member. To quantify the degrading effect of a web opening, a study has been conducted at the University of Missouri-Rolla (UMR). The UMR study included the loading conditions of bending, shear, web crippling, and the combinations thereof. This paper summarizes the results of an experimental study which addressed the behavior of combined bending and shear. A total of 68 beam specimens, with varying magnitudes of bending moment and shear force were tested. Based on the findings of this study, it was concluded that the interaction equation employed by the American Iron and Steel Institute (AISI) specification will provide an adequate strength prediction, provided that the shear and bending capacities are modified to account for the influence of the web opening.