A technician is performing a special inspection for seismic detailing on a reinforced concrete column in a special moment frame. The plans indicate that the spacing of transverse reinforcement (hoops) in the column's confined region must meet specific requirements. According to ACI 318, which of the following is NOT a governing factor for the maximum spacing of these hoops?
- AOne-fourth of the minimum member dimension.
- BOne-half of the largest longitudinal bar diameter.
- CSix inches (150 mm).
- DSix times the diameter of the longitudinal reinforcement.
Show answer & explanationAnswer & explanation
Correct answer: B. One-half of the largest longitudinal bar diameter.
ACI 318-19, Section 18.7.5.3, specifies the maximum spacing (s) for transverse reinforcement in the confined regions of special moment frame columns. The spacing s shall not exceed the least of: (a) one-fourth of the minimum member dimension (h); (b) six times the diameter of the smallest longitudinal bar (6db); (c) 6 inches (150 mm). One-half of the largest longitudinal bar diameter is not a governing factor for maximum spacing; it often relates to minimum cover or bar spacing requirements, but not maximum hoop spacing in confined regions.
Why the other options are wrong
- A. This is one of the governing factors for maximum hoop spacing (h/4).
- C. This is one of the governing factors for maximum hoop spacing (6 inches or 150 mm).
- D. This is one of the governing factors for maximum hoop spacing (6db, where db is longitudinal bar diameter).
ACI 318 Hoop Spacing (Seismic)
Specific maximum spacing requirements for transverse reinforcement (hoops) in the confined regions of concrete special moment frame columns to ensure ductility and prevent buckling of longitudinal bars during seismic events.
- Crucial for seismic performance.
- Prevents longitudinal bar buckling.
- Defined as the least of h/4, 6db, or 6 inches.
Memory trick: Hoops hug the column tight, keeping bars from flight.