Commercial Building Inspector B2Structural SystemsMedium
A structural engineer is designing a five-story concrete moment-resisting frame building in a high seismic area. The plans specify that the concrete for the special moment frames must have a minimum specified compressive strength. According to ACI 318, what is the minimum specified compressive strength (f'c) required for concrete used in special moment frame elements?
- A3,500 psi
- B3,000 psi
- C4,000 psi
- D2,500 psi
Show answer & explanationAnswer & explanation
Correct answer: A. 3,500 psi
ACI 318-19, Section 18.2.4.1, specifies that concrete used in special moment frame elements must have a minimum specified compressive strength (f'c) of 3,500 psi (24 MPa). This requirement ensures adequate ductility and strength under seismic loading.
Why the other options are wrong
- B. 3,000 psi is a common minimum for general structural concrete, but not sufficient for special moment frames in high seismic areas.
- C. 4,000 psi is often used for higher strength concrete applications but is not the minimum requirement for special moment frames.
- D. 2,500 psi is generally the minimum for non-structural concrete or very light-duty applications, not special moment frames.
Concrete f'c for Special Moment Frames
The minimum specified compressive strength of concrete required for structural elements designated as special moment frames, per ACI 318, for enhanced seismic performance.
- Ensures ductility and strength in seismic events.
- Applies to beams, columns, and joints of special moment frames.
- A minimum of 3,500 psi is required.
Memory trick: Seismic Special Frames need strong concrete to flex and hold.