ASCE 7-05 table 12.12-1 tall wood wall story drift

[cg3375]

I posted this in wood engineering but perhaps should have posted it here.

ASCE 7-05 table 12.12-1 is for allowable story drift.

In an occupancy II wood wall structure, this is saying that I am allowed .025 x wall height for drift (no odd torsional design or high seismic). This means an 18 foot tall wall can have 5.4 inches of drift at the top? Hopefully no glass in that wall or nobody tries to force the upper limits of that design allowance.

Assume all the components meet the l/xxx requirements. Sum the four up (cord, sheathing Gt, nail, and anchor), bring in the amplification factor of 4 for wood walls, and this table seems a bit non-restrictive with tall wood walls. Any thoughts or am I missing something?

Thanks.

 

[JAE]

That table is for seismic drift (with the amplification factor already in the drift calculation). Seismic drift can be thought of as the drift that occurs under a code seismic event - which can be very large drifts.

Since the code only deals with life safety for seismic, the concept is that the design should allow the building to be highly ductile (i.e. bend a lot) but not fall down and kill people. As a result, your deflection (which is your elastic deflection times the deflection amplification factor) is usually very high.

The code also requires you to ensure that attachments have deformation compatibility with those deflections, such as glass window walls.