A building inspector is reviewing the structural plans for a new multi-story wood-framed apartment building. The plans utilize wood structural panels (plywood or OSB) for shear walls. According to the 2021 IBC, what is the maximum aspect ratio (height-to-width) permitted for a wood structural panel shear wall segment that is designed to resist seismic forces in Seismic Design Category D?
- A4.5:1
- B2:1
- C3.5:1
- D5.5:1
Show answer & explanationAnswer & explanation
Correct answer: C. 3.5:1
The 2021 IBC, which references the National Design Specification (NDS) for Wood Construction and its Special Design Provisions for Wind and Seismic (SDPWS), limits the aspect ratio (height-to-width) of wood structural panel shear walls. For shear walls designed to resist seismic forces in Seismic Design Category D, the maximum aspect ratio is generally 3.5:1 (h/w ≤ 3.5). This is found in SDPWS Table 4.3.4.1 (or IBC Table 2305.3.3.1 for general shear wall limits).
Why the other options are wrong
- A. 4.5:1 is generally the maximum for wind-only or lower seismic categories, or for specific wall types with hold-downs at intermediate posts.
- B. 2:1 is a common limit for certain types of walls or specific conditions, but not the general maximum for SDC D wood structural panel shear walls.
- D. 5.5:1 is typically too high for seismic shear walls and would require specialized engineering.
Wood Shear Wall Aspect Ratio (Seismic)
The maximum permissible height-to-width ratio for wood structural panel shear walls, specified by the IBC and SDPWS, to ensure adequate shear capacity and prevent buckling under seismic loads.
- Crucial for seismic performance and stability.
- Limits wall slenderness.
- Generally 3.5:1 for SDC D.
Memory trick: Tall walls need to be wide enough to resist seismic sway.