Timber Shear Wall Uplift - Dead Load Resistance?
Timber Shear Wall Uplift - Dead Load Resistance?
(OP)
For an isolated shear wall, how do you go about calculating the uplift force at the end of the wall panel?
My question specifically is how do you go about applying dead load to your wall to resist the uplift. This is the dead load derived from the load equation 0.6D + W/0.7E.
I have run into two methods for calculation this value:
1) The typical method for this calculation is to find the dead load of the entire shear panel as well as any dead load supported by this wall. This load is applied at its own centroid and is used in a moment equation to resist the uplift force calculated from the applied lateral load.
2) The second method I have seen is to only apply the dead load that is tributary to the shear wall chord that is subjected to the uplift. ie. for a typical wall with studs at 16” o.c. only an 8” width of wall dead load and 8” of the dead load supported by the wall are used to resist the uplift.
While method (2) is obviously extremely conservative, I can find no concrete evidence supporting the use of the method (1).
Method (1) really begins to break down when the shear wall panel is significantly longer then it is high. In this case, the wall is going to deflect under the uplift force and would therefore not be engaging its full dead load to resist.
Does anyone know of any testing or research done into how much of a wall dead load can realistically be expected to resist the uplift? I shudder to think of the strapping that will result from the use of method (2), but without some justification, do I have a choice?
Thanks for your help.
My question specifically is how do you go about applying dead load to your wall to resist the uplift. This is the dead load derived from the load equation 0.6D + W/0.7E.
I have run into two methods for calculation this value:
1) The typical method for this calculation is to find the dead load of the entire shear panel as well as any dead load supported by this wall. This load is applied at its own centroid and is used in a moment equation to resist the uplift force calculated from the applied lateral load.
2) The second method I have seen is to only apply the dead load that is tributary to the shear wall chord that is subjected to the uplift. ie. for a typical wall with studs at 16” o.c. only an 8” width of wall dead load and 8” of the dead load supported by the wall are used to resist the uplift.
While method (2) is obviously extremely conservative, I can find no concrete evidence supporting the use of the method (1).
Method (1) really begins to break down when the shear wall panel is significantly longer then it is high. In this case, the wall is going to deflect under the uplift force and would therefore not be engaging its full dead load to resist.
Does anyone know of any testing or research done into how much of a wall dead load can realistically be expected to resist the uplift? I shudder to think of the strapping that will result from the use of method (2), but without some justification, do I have a choice?
Thanks for your help.






RE: Timber Shear Wall Uplift - Dead Load Resistance?
Your method two seems to indicate a shear wall can "tear through" the diaphragm above--how could it if it is being held down by roof and/or floor framing?
DaveAtkins
RE: Timber Shear Wall Uplift - Dead Load Resistance?
Mike McCann
MMC Engineering
RE: Timber Shear Wall Uplift - Dead Load Resistance?
For example:
In this case only the dead load which is applied to the deflected section of the wall will be resisting the uplift. The remainder of the dead load on the wall does not seem to be helping.
Thoughts?
RE: Timber Shear Wall Uplift - Dead Load Resistance?
RE: Timber Shear Wall Uplift - Dead Load Resistance?
DaveAtkins
RE: Timber Shear Wall Uplift - Dead Load Resistance?
I am assuming this is based on 4' wide sheathing panels.
I believe the point of all our calculations for nailing and blocking is to make the entire shearwall work as one unit.
In order to treat it as a series of 4' wide panels we would need to have hold downs every 4'. This is not a situation I have ever heard of as this would have a significant impact on the construction costs.
RE: Timber Shear Wall Uplift - Dead Load Resistance?
RE: Timber Shear Wall Uplift - Dead Load Resistance?
RE: Timber Shear Wall Uplift - Dead Load Resistance?
You wouldn't need holddowns every 4' because the sum of the vertical forces in the stud you are holding is down is equal to 0. One 4' wall's tension chord is the adjacent 4' wall's compression chord.
RE: Timber Shear Wall Uplift - Dead Load Resistance?
DaveAtkins
RE: Timber Shear Wall Uplift - Dead Load Resistance?
Now if there was an uplift point load at the end of the wall coming from, I don't know an above story column or something external to the rest of the wall, I think you need to look a little more closely at the wall's behavior than what is normally done. The typical shear connections along the wall may not be enough to transfer the internal forces required to pick up the adjacent roof dead load along the entire wall's length (which would be required to resist the overturning induced from the external point load at one end).
RE: Timber Shear Wall Uplift - Dead Load Resistance?
It is true that not all shear walls have holddowns, or need them, but they are usually pretty lightly loaded anyway with little uplift due to the long moment arm of the length, so the chance of that kind of deflection occurring in the real world is pretty minimal in my opinion.
I also concur with the 4' SW analogy presented above too.
Mike McCann
MMC Engineering
RE: Timber Shear Wall Uplift - Dead Load Resistance?