Load Bearing Wood Walls - Live Load Reduction
Load Bearing Wood Walls - Live Load Reduction
(OP)
IBC 2000, live load reduction is based on tributary area associated with the loaded element. In a load bearing wood wall, does the code consider the entire wall or the individual stud as the element to consider for the tributary area. My understanding is that if there is a mechanism for redistribution of load, then the wall would be considered the element to determine the tributary area. Would a double top plate be considered adequate for a load distribution element, or would the wall need to be sheathed in plywood to consider distribution to occur?
Thanks in advance for any insight.
AUCE98
Thanks in advance for any insight.
AUCE98






RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
DaveAtkins
RE: Load Bearing Wood Walls - Live Load Reduction
The repetitive member factor of 1.15 only appies to bending stress. In general the design of wood members is based on the design of single individual members without accounting for system effects. On that basis I think I would not apply live load reduction
Also in many cases loads are transfered to the walls through closely spaced members such as floor trusses, I-joists and solid sawn joists. The load applied to these elements are going to be transfered into the supporting studs below, with some distribution occuring as a result of the top plates and wall sheathing.
Live Load reduction is based on a probability of the entire design load being present at one time. I think it is reasonable to apply that to the design of a stud wall, although I don't think you could justify by code provision.
My logic is this, the live load caused by people will occur all over the floor area. One person is standing over one floor joist and another over a different one. Also on the floor above there may be nobody standing on that joist.
In addition a distribution of load occurs through the sheathing or wood decking when closely space members deflect. The repetitive member factor is based on this distribution.
One final comment there are some new publications available from AFPA which due account for system effect. Accounting for systems effects may be more useful than applying live load reduction.
RE: Load Bearing Wood Walls - Live Load Reduction
using the multiplier when checking combined stresses will show a stud to be adequate when it may not be so if the stresses are checked without the multiplier.
RE: Load Bearing Wood Walls - Live Load Reduction
Note that IBC and ASCE-7 both restrict live load reductions for one-way slabs. Stud walls would seem to behave similarly to one-way slabs.
RE: Load Bearing Wood Walls - Live Load Reduction
I think you can apply the repetitive member adjustment to the bending stress whenever you meet the requirement of 4.3.4 of the 1997 N.D.S. (4.3.9 2001 N.D.S.). The N.D.S.indicates that the repetitive adjustment applies to studs.
It is my understanding that in the combine stress equations you determine your allowable bending stress based on what would be allowed if you had bending only.
One thing you might look into is designing using LRFD. I am not familair with LRFD but it is my understanding that some of the confusion in the past regarding some adjustment factors has been cleared up.
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
RE: Load Bearing Wood Walls - Live Load Reduction
See paragraph 2306.2.1 in both IBC 2000 and IBC 2003 for the details.
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