Live Load Reduction for Stud Walls
Live Load Reduction for Stud Walls
(OP)
I want to apply live load reduction to a wood stud wall. The problem is (for me at least) that I don't know how to determine what the Tributary area should be for the wall.
If I consider the wall on a "per foot" basis then the tributary area is only a 1 ft strip of all of the floors that this wall carries. Doing it like that, It'll be almost imposible to get the area of influence over 400 ft^2.
Obiously, how much trib area I use will depend on the width of wall that I consider in my analysis. I think that the width I choose should somehow reflect the ability of the wall to distribute the load out. For example, I would choose a smaller width for a wood stud wall than I would for a masonry wall.
Either way, I need some algorithm do determine how much tributary area I should be assigning to the wall for the purpose of live load reductions. What is everyone else doing??
If I consider the wall on a "per foot" basis then the tributary area is only a 1 ft strip of all of the floors that this wall carries. Doing it like that, It'll be almost imposible to get the area of influence over 400 ft^2.
Obiously, how much trib area I use will depend on the width of wall that I consider in my analysis. I think that the width I choose should somehow reflect the ability of the wall to distribute the load out. For example, I would choose a smaller width for a wood stud wall than I would for a masonry wall.
Either way, I need some algorithm do determine how much tributary area I should be assigning to the wall for the purpose of live load reductions. What is everyone else doing??






RE: Live Load Reduction for Stud Walls
RE: Live Load Reduction for Stud Walls
(1.6L + 0.5S)/1.6 or
(0.5L + 1.6S)/1.6
http://www.awc.org/Standards/wfcm.html
HTH
Buddy Showalter, P.E.
AF&PA/AWC
RE: Live Load Reduction for Stud Walls
For live loads, I wouldn't use a live load reduction for wood stud walls as there is no mechanism to calculate the spread of the load across the sheathing to adjacent studs. This is because the usual specified nailing for the sheathing does not take into account this kind of shear transfer.
Also, the floor or roof framing is also usually of wood and these place the gravity loads directly onto the top plate which directly transfers it to the stud. Statistically, you still have a good probability of loading one individual joist to 100% of the live load which in turn will load the stud 100%.
Your trib area then is the spacing of your studs times half the span of the supported members.
Now for perpendicular loads, such as wind, I would consider a larger tributary area in determining component wind loads as the sheathing does have some ability to distribute "hot spots" in the wind across more than one stud. We usually count on between 3 or 4 studs all acting together (4x8 sheet spread across the studs - 48" / 16" o.c. = 3 spaces = 4 studs)
RE: Live Load Reduction for Stud Walls
Buddy,
Can you give me more information about the WFCM? Specifically, is the document actually referenced by any of the model codes? I was under the impression that the WFCM was more of a "recommendation" kind of thing -- albeit a very usefull one. Is there an extension of this method for 3 story wood frame buildings? Thanks again.
Adam
RE: Live Load Reduction for Stud Walls
RE: Live Load Reduction for Stud Walls
Unfortunately, I don't know of any code or spec formulae that would give a standard way to look at it.
RE: Live Load Reduction for Stud Walls
The 1995 WFCM is referenced in all major model building codes in the U.S. including:
» 2000 IBC International Building Code: 2308.2.1 for winds > 100 mph (3 sec. gust)
» 2000 IRC International Residential Code: 301.2.1.1
» Currently adopted in 1997 SBCCI Standard Building Code
» 1999 BOCA National Building Code
» Approved by State of Florida Board of Building Codes and Standards
» Approved by North Carolina - Department of Insurance
» Approved by Georgia - Department of Community Affairs
The new 2001 WFCM is an ANSI approved document and is being adopted in the 2003 IBC, 2003 IRC, and new 2002 NFPA Building Code.
Here's the webpage to see code approvals for other wood standards, like NDS and LRFD:
http://www.awc.org/Codes/bldgcode.html#acceptance
HTH
Buddy
RE: Live Load Reduction for Stud Walls
RE: Live Load Reduction for Stud Walls