# SEAOC Vol 2 - Example 5 part 9c - Subdiaphragm Question



## Agostage (Jan 26, 2014)

Referencing SEAOC Vol 2 (2009) - Example 5 part 9c

Tilt-Up building with wood flexible diaphram:

pg. 305

In this example the main diaphragm is designed for the N-S direction and a nailing zone diagram is created to reflect the varying shear demand that exists (The E-W direction is not shown but would need to be computed in practice).

In part 9c. a subdiaphragm is designed in the E-W direction (using out-of-plane Fp forces), simple beam analysis to yield a shear demand.

However, they use the previous main diaphragm N-S capacities to compare to the subdiaphragm shears developed from an E-W load. Is this correct?

It seems to me that the main diaphragm in the N-S direction is a NDS Case 4 while the subdiaphragm is a Case 2 that should be checked against the main diaphragm E-W capacities.

Appreciate any guidance.


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## Agostage (Jan 28, 2014)

They do the same thing in this APA diaphragm guide:

http://www.ce.udel.edu/courses/CIEG407/APA%20Diaphragms%20and%20Shear%20Walls.pdf

Example 12 subdiaphragm assumes Example 10 main diaphragm capacities, shears not in the same direction.


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## Agostage (Feb 3, 2014)

Is the question clear? If the question isn't clear I can write something up. I have the question out to a couple wood design experts and I will follow-up with the responses here.


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## TehMightyEngineer (Feb 4, 2014)

I don't have my SEAOC in front of me so I can't reference the question but, from what you described; yes the two diaphragms would have different capacities.


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