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Re: Perforated shear wall uplift

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Jason-

In a properly designed shear wall, the uplift forces are transmitted from the sheathing into the post via the edge nailing.  The uplift forces in  the posts are transmitted to the foundation via hold downs. 

Hold downs need to be stiff enough & strong enough to restain the shearwall uplift; this will minimze the portion of uplift load that goes from sheathing into the sill. 

Minimze but not eliminate the load through that path, even with heavy hold downs, about 80% of the uplift load goes through the hold down, the other 20% goes through the sheathing into the sill and finally into the foundation through bolts meant for shear not tension.

If the hold downs do their jobs, cross grain bending will be reduced.

Having run 100's of shear wall tests on all sorts of hold downs, sheathing & nailing combinations.........IMO shear anchor bolts near shear wall hold downs should not have nuts OR  square washers........................reducing sheathing / sill UPLIFT stiffness relative to the hold down stiffness will go a long way to preventing sill failures.

cheers
Bob

On 2/2/06, Jason Christensen <jason.christensen(--nospam--at)es2eng.com> wrote:

So how does one transfer the uplift force through plywood to plate connection with out causing cross grain bending in the plate? 

Other than using 3 1/2" or 5 1/2" plate washers for 2x4 or 2x6 walls.

 

Jason

-----Original Message-----
From: Eli Grassley [mailto:elig(--nospam--at)psm-engineers.com]
Sent: Thursday, February 02, 2006 12:09 PM
To:
seaint(--nospam--at)seaint.org


Subject: RE: Perforated shear wall uplift

 

The anchor bolts (not the end holdowns) need to be designed for a "uniform uplift equal to the wall shear."  Your example of a 10' wall with 500plf shear gives you 5000# of total uplift.  That gets distributed out to all of the anchor bolts along the length of the wall.  If you have 5 anchor bolts, they each see 1000#.  The overturning holdown forces are a completely separate issue.

 

This is the code language for designing a "perforated shear wall."  It is my understanding that this requirement is worded that way because that is how the testing apparatus was set up when they were gathering data to make Table 2305.3.7.2 (shear capacity adjustment factors).

 

~~ Eli G

 

-----Original Message-----
From: Rhkratzse(--nospam--at)aol.com [mailto:Rhkratzse(--nospam--at)aol.com]
Sent: Thursday, February 02, 2006 10:21 AM
To: HoodMO(--nospam--at)ci.anchorage.ak.us; seaint(--nospam--at)seaint.org
Subject: Re: Perforated shear wall uplift

 

In a message dated 2/2/06 10:12:48 AM, HoodMO(--nospam--at)ci.anchorage.ak.us writes:

2003 IBC section 23053.7.2.6 indicates that "perforated shear wall
bottom plates at full height sheathing shall be anchored for a uniform
uplift force, t, equal to the unit shear force, v." Where v is the shear
force for which the bottom plate shear transfer has to be designed.


I have no answers, only more questions.  Does this mean that in a shear wall designed to resist 500 plf must have uplift resistance of 500#?  Or if the wall is 10' long it must have uplift resistance of 5,000#?  And if it's 100' long, 50,000#?

Ralph