Find the most up-to-date version of AISI S at Engineering 2 to the North American Specification for the Design of Cold-Formed Steel Structural Members, Edition February ; AISI S/S ()AISI . Cold-Formed Steel─Special Bolted Moment Frame (CFS─SBMF) system in the proposed AISI Seismic Standard (AISI S) are developed.
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This first edition of AISI S represents a merging of the following previously published standards: This consolidated seismic design standard brings together all North American cold-formed steel seismic-force-resisting systems SFRS into one standard, adding a consistent capacity-based design philosophy to each. The standard also provides Canadian seismic design provisions where the seismic force modification factors, R d R oare taken as greater than or equal s110 1.
This standard focuses on the design and construction of cold-formed steel members and connections in seismic-force-resisting systems SFRS and diaphragms in buildings and other structures. In the absence of an applicable building code, the design requirements must follow accepted engineering practice for the location under consideration, as specified by ASCE Chapter A also provides the provisions for determining the material expected strength for steel. Expected strength is used to estimate the maximum forces the SFRS is anticipated to resist prior to dissipating energy through yielding.
Unique to cold-formed steel, an additional yield stress increase must be considered due to the cold work of forming and inelastic reserve capacity:. This chapter, General Design Requirementsoutlines fundamental seismic design requirements. Specifically, the available strength of the SFRS must be greater than or equal to the required strength determined from the applicable load combinations to ensure adequate performance in a design-level seismic-event.
The designated energy dissipating mechanism and methods for determining the expected strength of the various SFRS are included in Chapter E, as discussed below. This chapter, Analysisprescribes that the structural analysis should be done in accordance with the applicable z110 code and AISI S Future editions are expected to expand on analysis methods and their implementation for cold-formed steel SFRS. This chapter, General Member and Connection Design Requirementsreferences Chapters E and F for specific member and connection design and is reserved for future development.
Seismic energy is dissipated in wood structural panel shear walls through titling and bearing deformation in the aiis connections between the wood structural panel sheathing and the cold-formed steel structural members, and in the wood structural panels themselves. Two types of shear walls are included within the section:.
Sheathed shear wall analysis models.
Type I shear walls Figure 2 a are fully sheathed and require hold-downs and anchorage at each end of the shear wall.
If an opening exists, details must be provided for load transfer around the opening.
Aspect ratio shear wall height, h, divided by length, w limits for the various assemblies are also provided. Type II shear walls Figure 2b permit openings in the wall without specific design for force transfer around the openings. The nominal shear strength, V ncan be determined:. The nominal shear strength per unit length, v nis based on the values for Type I shear walls and C a is tabulated in the standard for a variety of shear wall geometries.
The expected strength of the SFRS, capped by the seismic load effects including overstrength, is to be used to design other components in the SFRS that are not part of the designated s1110 mechanism, including any collectors.
STRUCTURE magazine | AISI S/S
For this SFRS, the expected strength equals 1. To ensure the shear wall performs as intended, additional system requirements must be met as further detailed in AISI S, Section E1. Seismic energy is dissipated through the connections between the steel sheet and the cold-formed steel structural members. Yielding also occurs in the tension fields across the steel sheet. The nominal shear strength, V ncan be determined using the same equations provided in Section a except that values for v n and C a are tabulated separately in the standard.
In addition, a new effective strip method has been introduced in this edition, which can be used to determine the nominal shear strength of the shear wall analytically. The expected strength of steel-sheet sheathed shear walls is specified as 1. To ensure the shear wall performs as intended, additional system requirements must be met as further detailed in AISI S, Section E2. To perform as intended in a design level seismic event, this common SFRS aisii be designed and detailed to ensure that the diagonal tension strap yields first, thus dissipating the seismic energy, while other limit states such as fracture at the strap ends and buckling of the chord studs are avoided.
The shear wall strength is determined by the nominal strength of the strap as follows:. The s110 strength of the strap equals the expected yield strength of the strap times its gross area. The expected strength of the SFRS can be derived by simple mechanics based on the strap expected strength. Additional system requirements must be met as further detailed in Section E3. For instance, provisions must be made to guard aisu loose strap bracing either by pre-tensioning the straps or through other similar methods of installing the tension-only strap bracing.
This system is formed by cold-formed channel beams aiso HSS columns with bolted moment connections, as detailed in Figure 3. Seismic energy is dissipated through sliding and bearing deformations in the bolted connections between the beams and aisj.
The beams and columns, therefore, need to be designed to resist the expected moment M e and shear V e at the bolted connections defined as:. Detailed guidance on how to determine s10 expected strength is provided in the standard. For instance, it is limited to single story structures no higher than 35 feet. The nominal shear strength and detailed requirements are provided in Section E6 of the standard.
The expected strength of this SFRS equals 1. This chapter outlines requirements for Diaphragms. Acting to collect and distribute seismic forces to the SFRS, diaphragms must be designed to resist the forces specified by the applicable building code. The diaphragm stiffness needs to be taken into consideration in determining the required strengths of both the SFRS and the diaphragm itself since the stiffness directly affects the force distribution.
This standard currently provides the design provisions for cold-formed steel-framed diaphragms sheathed with wood structural panels. Future editions may be extended to include other common diaphragm systems.
This chapter discusses Quality Control and Quality Assurance. This chapter, Use of Substitute Components and Connections in Seismic Force-Resisting Systemspermits the substitution of components or connections in any of the SFRS specified in Chapter E as long as they aiso the applicable building code requirements and are approved by the authority having jurisdiction.
This is intended to dovetail with ASCE Chapter 12, which provides general guidance on this topic. A design guide for the seismic design of cold-formed steel framing will be published in Determine the nominal shear strength of the strap braced wall, as illustrated in Figure 4aand the expected strength of the system.
Safety and resistance factors: Braced shear wall design example. Collectors, strap connections, chord studs, other vertical boundary elements, hold-downs and anchorage connected to it and all other components and connections of the strap braced wall should be designed to resist this force.
Aug, By Rob Madsen P. Chapter A, Scope and Applicability This standard focuses on the design and construction of cold-formed steel members and connections in seismic-force-resisting systems SFRS and diaphragms in buildings and other structures.
AISI to Develop New Unified Cold-Formed Steel Seismic Design Standard
Unique to cold-formed steel, an additional yield stress increase must be considered due to the cold work of forming and inelastic reserve capacity: The modification coefficient for strength increase due to cold work of forming is determined as: Chapter B This chapter, General Design Requirementsoutlines fundamental seismic design requirements. Chapter C This chapter, Analysisprescribes that the structural analysis should be done in accordance with the applicable building code and AISI S Chapter D This chapter, General Member and Connection Design Requirementsreferences Chapters E and F for specific member and connection design and is reserved for future development.
Shear wall sheathed with wood structural panels. Cold-formed steel special bolted moment frame.
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