Commercial Building Inspector B2Structural SystemsMedium
A structural engineer is designing a steel-framed building in a high seismic zone. The design includes a special concentrically braced frame (SCBF). According to AISC 341, which of the following is a primary requirement for the bracing members in an SCBF?
- AThey must be proportioned such that their expected compressive strength is greater than their expected tensile strength.
- BThey must be designed to buckle elastically under expected seismic forces.
- CThey must have a slenderness ratio (KL/r) not exceeding 200.
- DThey must be designed to yield in compression before buckling.
Show answer & explanationAnswer & explanation
Correct answer: C. They must have a slenderness ratio (KL/r) not exceeding 200.
AISC 341-16, Section F2.3, specifically states that the slenderness ratio (KL/r) of bracing members in SCBFs shall not exceed 200. This limit helps ensure stable and predictable performance under seismic loading by preventing premature buckling.
Why the other options are wrong
- A. The design focuses on stable behavior in both tension and compression, with specific limits like the slenderness ratio, rather than a direct comparison of expected strengths in this manner.
- B. Bracing members are expected to yield and buckle inelastically under seismic forces, dissipating energy.
- D. SCBF braces are designed to buckle in compression, but the goal is controlled, stable buckling, not necessarily yielding before buckling.
SCBF Bracing Slenderness
A critical design parameter for bracing members in Special Concentrically Braced Frames (SCBFs) to ensure stable and ductile behavior under seismic loads.
- Limits the slenderness ratio (KL/r) to 200.
- Prevents premature, unstable buckling.
- Promotes energy dissipation through controlled inelastic action.
Memory trick: SCBFs: Seismic Control, Bracing Flexibility, controlled buckling.