Carta Responsiva

9.1–50

CHAPTER F BRACED-FRAME AND SHEAR-WALL SYSTEMS

This chapter provides the basis of design, the requirements for analysis, and the requirements for the system, members and connections for steel braced-frame and shear-wall systems. The chapter is organized as follows: F1. F2. F3. F4. F5. Ordinary Concentrically Braced Frames (OCBF) Special Concentrically Braced Frames (SCBF)Eccentrically Braced Frames (EBF) Buckling-Restrained Braced Frames (BRBF) Special Plate Shear Walls (SPSW)

User Note: The requirements of this chapter are in addition to those required by the Specification and the applicable building code.

F1. 1.

ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF) Scope
Ordinary concentrically braced frames (OCBF) of structural steel shall be designed in conformance withthis section. In seismically isolated structures, OCBF above the isolation system shall satisfy the requirements of Sections F1.4b, F1.5, F1.6 and F1.7 and need not satisfy the requirements of Section F1.4a.

2.

Basis of Design
This section is applicable to braced frames that consist of concentrically connected members. Eccentricities less than the beam depth are permitted if they areaccounted for in the member design by determination of eccentric moments using the amplified seismic load. OCBF designed in accordance with these provisions are expected to provide limited inelastic deformation capacity in their members and connections.

3.

Analysis
There are no additional analysis requirements.

4. 4a.

System Requirements V-Braced and Inverted V-Braced Frames
Beams inV-type and inverted V-type OCBF shall be continuous at brace connections away from the beam-column connection and shall satisfy the following requirements:
Seismic Provisions for Structural Steel Buildings, June 22, 2010 AMERICAN INSTITUTE OF STEEL CONSTRUCTION

Sect. F1.]

ORDINARY CONCENTRICALLY BRACED FRAMES (OCBF)

9.1–51

(1) The required strength shall be determined based on the loadcombinations of the applicable building code assuming that the braces provide no support of dead and live loads. For load combinations that include earthquake effects, the seismic load effect, E, on the member shall be determined as follows: (i) The forces in braces in tension shall be assumed to be the least of the following: (a) The expected yield strength of the brace in tension, Ry Fy Ag (b) Theload effect based upon the amplified seismic load (c) The maximum force that can be developed by the system (ii) The forces in braces in compression shall be assumed to be equal to 0.3Pn. (2) As a minimum, one set of lateral braces is required at the point of intersection of the braces, unless the member has sufficient out-of-plane strength and stiffness to ensure stability between adjacent bracepoints.

4b.

K-Braced Frames
K-type braced frames are not permitted for OCBF.

5. 5a.

Members Basic Requirements
Braces shall satisfy the requirements of Section D1.1 for moderately ductile members.

5b.

Slenderness
Braces in V or inverted-V configurations shall have KL /r ≤ 4 E Fy .

6. 6a.

Connections Diagonal Brace Connections
The required strength of diagonal braceconnections is the load effect based upon the amplified seismic load. Exception: The required strength of the brace connection need not exceed the following: (1) In tension, the expected yield strength of the brace multiplied by 1.0 (LRFD) or divided by 1.5 (ASD), as appropriate. The expected yield strength shall be determined as Ry Fy Ag. (2) In compression, the expected brace strength incompression multiplied by 1.0 (LRFD) or divided by 1.5 (ASD), as appropriate. The expected brace strength in compression is permitted to be taken as the lesser of Ry Fy Ag and 1.14Fcre Ag where Fcre is determined from Specification Chapter E using the equations for Fcr except that the expected yield stress Ry Fy is used in lieu of Fy. The brace length used for the determination of Fcre shall not exceed...