CSLB General Building (B)Framing and CarpentryHard
A shear wall segment used for lateral bracing is 4 feet wide and 10 feet tall, giving an aspect ratio of 2.5:1. Per CBC wood structural panel shear wall provisions, what must be done with this segment's tabulated shear capacity before using it in design?
- AThe segment is prohibited outright because any ratio over 2:1 is not allowed under any circumstance
- BThe nail spacing must be reduced by half to compensate, without adjusting the capacity value
- CThe tabulated capacity must be multiplied by a reduction factor of 2w/h because the ratio exceeds 2:1
- DNo adjustment is needed since the ratio is below the 3.5:1 maximum allowed
Show answer & explanationAnswer & explanation
Correct answer: C. The tabulated capacity must be multiplied by a reduction factor of 2w/h because the ratio exceeds 2:1
CBC/IBC wood shear wall provisions allow segments with height-to-width ratios up to 3.5:1, but for ratios exceeding 2:1, the tabulated unit shear capacity must be reduced by the factor 2w/h. Here, 2(4)/10 = 0.8, so the design capacity is 80% of the tabulated value.
Why the other options are wrong
- A. Ratios up to 3.5:1 are permitted with the capacity reduction, not outright prohibited.
- B. Nail spacing is not the code-prescribed remedy; the capacity value itself must be reduced by 2w/h.
- D. Being under 3.5:1 avoids outright prohibition but does not exempt the wall from the 2w/h reduction once past 2:1.
Shear Wall Aspect Ratio Reduction
Wood structural panel shear walls with height-to-width ratios between 2:1 and 3.5:1 remain permitted but must have their tabulated shear capacity multiplied by the factor 2w/h to account for reduced stiffness and performance.
- Max allowed aspect ratio (h:w) is 3.5:1 for wood structural panel shear walls
- Ratios over 2:1 require capacity reduction by 2w/h
- Example: 4 ft wide x 10 ft tall wall → factor = 2(4)/10 = 0.8
Memory trick: 'Tall and skinny walls pay a penalty: 2w over h.'