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Re: Perforated shear wall uplift[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Perforated shear wall uplift
- From: Robert Kazanjy <rkazanjy(--nospam--at)gmail.com>
- Date: Fri, 3 Feb 2006 19:53:03 -0800
Show me the statics. :)
Sounds like phantom forces to me
Guys who write code put their pants on one leg at a time........... and are sometimes wrong & often unclear.
From whence does this "uniform uplift equal to the wall shear" come?
I submit that shearwalls (perforated or not) do not work by anchoring the sills but by "anchoring" (holding down) the wall boundary elements (posts).
Anchoring sills w/o adequate boundary hold downs is asking for trouble.
By this logic, an 8x8 sheawall with a vanishingly small "perforation" would require its shear anchors to also be capable of uplift restraint? !
I am not talking about the end of wall uplift forcing, I am talking about the "uniform uplift equal to the wall shear" that each anchor bolt must designed for in a "perforated shear wall".
From: Robert Kazanjy [mailto:rkazanjy(--nospam--at)gmail.com]
Sent: Thursday, February 02, 2006 11:58 PM
Subject: Re: Perforated shear wall uplift
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.
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.
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
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#?
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