Commercial Building Inspector B2Footings and FoundationsHard
A commercial building inspector is reviewing the structural design for a multi-story building to be constructed in a seismic design category D area. The foundation system includes concrete shear walls. According to the IBC, what is the minimum required amount of vertical reinforcement for concrete shear walls in such a seismic category?
- A0.0012 times the gross cross-sectional area of the wall
- B0.0015 times the gross cross-sectional area of the wall
- C0.0020 times the gross cross-sectional area of the wall
- D0.0025 times the gross cross-sectional area of the wall
Show answer & explanationAnswer & explanation
Correct answer: C. 0.0020 times the gross cross-sectional area of the wall
For concrete shear walls in Seismic Design Categories C, D, E, and F, ACI 318 (referenced by IBC Chapter 19) requires a minimum ratio of distributed vertical reinforcement (ρv) of 0.0020 times the gross cross-sectional area of the wall. This is a specific seismic detailing requirement to ensure ductile behavior.
Why the other options are wrong
- A. This is typically the minimum for non-seismic walls or for horizontal reinforcement in some cases, but not vertical in SDC D.
- B. This value is incorrect for vertical reinforcement in concrete shear walls in SDC D.
- D. This value is higher than the minimum required by code for this condition.
Seismic Shear Wall Vertical Rebar (SDC D)
The minimum ratio of vertical reinforcing steel required in concrete shear walls for buildings in high seismic zones.
- 0.0020 times gross wall area.
- Applies to SDC C, D, E, F.
- Ensures ductility and energy dissipation in earthquakes.
Memory trick: For seismic walls, two thousandths or more, keeps the structure from falling to the floor.