To: "SEAINT (E-mail)" <seaint(--nospam--at)seaint.org>
Subject: Hold downs of stacked wood shear walls
From: Steve Hiner <shiner(--nospam--at)folsom.ca.us>
Date: Thu, 20 Jan 2000 10:30:02 -0800
Here's one particularly for those involved in the structural design and/or
plan review of single-family homes of wood frame construction (custom or
The subject has to do with sizing of the hold downs on a two-story house
where a shear wall in the 2nd-story is stacked directly above a 1st-story
shear wall below (say both are 10 feet long). The standard for this type of
construction locally is to provide plywood (or OSB) only at the specified
shear wall locations ... not at the entire exterior of the house.
Statics would dictate that the hold downs at the foundation be sized
considering the overturning moment due to the force at the roof times the
moment arm to the roof "plus" the force at the second floor times the moment
arm to the 2nd-floor (less any dead load resisting moment).
Many designs do not approach it this way. Often times the foundation hold
downs are sized considering the overturning moment due to the "total" of the
force at the roof "plus" the force at the second floor times the moment arm
to the 2nd-floor only (essentially neglecting the uplift from the 2nd-story
shear wall above). This is reasonable for the situation of "in-plane
offset" shear walls ... but uplift from the 2nd-story shear wall would still
need to be addressed as far as load path through the 1st-story goes.
The reasoning often used to justify the later approach often varies from
"that's the way we have been doing it for 30 years", and/or "it's just a
house". I'm not really comfortable with either of these explanations.
Just curious what feedback any one else may have on this subject (feel free
to email me directly if you prefer).
Thank you for your time,
Steve Hiner, SE