From to , the AISI Committee on Framing Standards developed nine different framing standards to cover specific aspects of cold-formed steel framing. Six of these standards addressed the design of structural elements, such as general provisions, wall studs, floor joists, trusses, headers, and shear walls. The other standards addressed such topics as a code of standard practice, the definition of standard product, and prescriptive design for residential applications. But, why would AISI develop six discrete framing standards as opposed to one design manual? This has been an often asked question by framing design engineers. The simple reason is, it was easier to develop small single-topic documents versus a more comprehensive multi-topic document.
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From to , the AISI Committee on Framing Standards developed nine different framing standards to cover specific aspects of cold-formed steel framing. Six of these standards addressed the design of structural elements, such as general provisions, wall studs, floor joists, trusses, headers, and shear walls. The other standards addressed such topics as a code of standard practice, the definition of standard product, and prescriptive design for residential applications.
But, why would AISI develop six discrete framing standards as opposed to one design manual? This has been an often asked question by framing design engineers. The simple reason is, it was easier to develop small single-topic documents versus a more comprehensive multi-topic document.
This new standard includes design provisions for wall systems, floor and roof systems, lateral force-resisting systems, as well as truss and header assemblies.
This article focuses on AISI S which applies to cold-formed steel structural members subject to gravity loading, wind loading, and seismic loading, except when specific seismic detailing is required.
These cold-formed steel framing standards are available as free downloads at www. Also, for ease of use, S contains a section reference table between the S provisions and the previous provisions Table 2. It outlines the scope, which is for design and installation of cold-formed steel framing of a floor and roof systems, b structural walls, c shear walls, strap braced walls, and diaphragms to resist in-plane lateral loads, and d trusses for load-carrying purposes in buildings.
The chapter also includes:. The previous design standards limited their application to framing members having a maximum base steel thickness to mils 0.
This limitation has been eliminated from AISI S; however, it should be remembered that mils is still the maximum thickness of standard products in the United States and 97 mils 0. ASTM C has historically stipulated manufacturing tolerances for cold-formed steel structural framing members. In , the manufacturing tolerance values were extended to the flange width and stiffening lip length. This chapter contains design provisions for cold-formed steel framing members and assemblies, as previously included in AISI S, S, S, and S For curtain wall systems, the standard now permits the use of the bracing combination of sheathing attached to one side of the wall stud and discrete bracing for the other flange Figure 1.
The discrete braces are limited to not greater than 8 feet 2. However, AISI S now incorporates an exception for a built-up axial load bearing section comprised of two studs oriented back-to-back forming an I-shaped cross-section. The exception applies where the built-up section is seated properly in a track, and the top and bottom end bearing detail of the studs consists of a steel or concrete support with adequate strength and stiffness to preclude relative end slip of the two built-up stud sections.
The ends of a built-up compression member are connected by a weld having a length not less than the maximum width of the member or by connectors spaced longitudinally not more than 4 diameters apart for a distance equal to 1.
This new exception provides for a more economical built-up member, as is often used as a jamb stud or shear wall boundary member. For roof or floor diaphragms with a maximum aspect ratio of , framed with cold-formed steel and covered with non-steel sheathings, the in-plane nominal shear strength can be determined by tests in accordance with ASTM E The use of ASTM E results in higher nominal shear strength values as compared with the cantilever test method historically used for steel deck diaphragms.
Beneficial for the design engineer is a new Effective Strip Method that enables the calculation of the nominal in-plane shear wall strength for Type I shear walls Figure 2.
The method assumes a sheathing strip carries the lateral load via tension field action. This computational method is applicable for walls sheathed with steel sheet. This method provides an alternative approach to determine the shear wall strength, especially for those that are outside the limitations of the tested systems. The effective strip method is permitted to be used within the following range of parameters:.
This chapter provides installation requirements previously contained in the various framing standards. This newly developed chapter provides minimum requirements for quality control and quality assurance for material control and installation for cold-formed steel light-frame construction. This chapter contains design, manufacturing quality criteria, and installation requirements for cold-formed steel trusses as previously included in AISI S This new chapter lists applicable AISI test standards for cold-formed steel framing members, connections, and systems.
This appendix contains requirements for the determination of the rotational stiffness that structural sheathing provides to framing members to facilitate the design for distortional buckling. The truss component structural performance load test and full-scale truss confirmatory test methods, previously included in AISI S, are provided in this appendix.
Table 1. Format defines design considerations. Table 2. Section reference table S and previous standard. Figure 1. Sheathing and discrete bracing. Figure 2. Effective strip method model for steel-sheet sheathing. No Comments. Leave a Comment Click here to cancel reply. First Name Last Name. Email Website. Your message Submit Comment. Download this article.
While consideration of bracing is important for any structural element, this is especially true for thin, singly symmetric cold-formed steel CFS framing members such as wall studs. Without proper consideration of bracing, excessive buckling or even failure could occur. Bracing is required to resist buckling due to axial or out-of-plane lateral loads or a combination of the two. One is sheathing braced design and the other is steel braced design. Sheathing braced design has limitations, but it is a cost effective method of bracing studs since sheathing is typically attached to wall studs.
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This article provides the design requirements and methods to anchor, or complete the load path, for the lateral bracing bridging of axially loaded cold-formed steel stud walls. The bridging forces are assumed to accumulate linearly with respect to the number of studs, and the load path must be completed for the bridging forces. The forces accumulate and must be removed periodically as the force in the bridging row reaches the design capacity of the bridging member. The method of bridging anchorage may vary depending upon the magnitude of bridging force accumulated in the bridging row, as well as the preference of the design engineer. One of the common methods of bridging anchorage consists of flat-strap cross bracing attached from the bridging line to the bottom of the wall on each side of the stud Figure 2.
Tag: AISI S211