Shearwalls - add in roof uplift?
Shearwalls - add in roof uplift?
(OP)
Hi - quick question for all of you shearwall experts out there....
Do you consider roof uplift when calculating the loads for your shearwall holdowns?
What I usually do when calculating my shearwall holdowns is take the unit shear times the wall height, then subtract out 0.6 times the wall dead load that is tributory to the side of the shearwall I'm calculating the holdown load for. (I usually neglect the roof dead load.)
However, another engineer I recently spoke with said that for shearwalls parallel to the ridge line he always adds in the roof uplift as well.
Any comments?
Do you consider roof uplift when calculating the loads for your shearwall holdowns?
What I usually do when calculating my shearwall holdowns is take the unit shear times the wall height, then subtract out 0.6 times the wall dead load that is tributory to the side of the shearwall I'm calculating the holdown load for. (I usually neglect the roof dead load.)
However, another engineer I recently spoke with said that for shearwalls parallel to the ridge line he always adds in the roof uplift as well.
Any comments?






RE: Shearwalls - add in roof uplift?
Mike McCann
MMC Engineering
RE: Shearwalls - add in roof uplift?
Mike McCann
MMC Engineering
RE: Shearwalls - add in roof uplift?
Re the direction of the wind... parallel to the ridge (the longitudinal direction in Figure 6-2), the wind pressures shown for the 0° roof angle are negative, so I was assuming that an uplift would occur on the roof for wind loading in that direction as well.
RE: Shearwalls - add in roof uplift?
1. The wind should not be C&C wind but MWFRS wind as the design you are performing is for an overall main wind design.
2. The uplift is usually taken by the individual studs and the shearwall anchor bolts, not the holddowns. The holddowns are typically there for the uplift due to the overturning of the lateral force.
3. The shearwall anchor bolts between the holddowns would then take lateral shear and uplift combined.
4. The shearwall anchor bolts between the holddowns might then have to be a little more densely spaced than in non-shearwall walls.
5. The wind uplift is based on the tributary area of the exposed structure adjacent to the shearwall. Where roof members are parallel to the shearwall, there may not be much uplift to consider. Where roof members are perpendicular to the shearwall there would be higher wind uplift countered by the roof dead load (i.e. use net wind uplift based on the appropriate load combinations)
RE: Shearwalls - add in roof uplift?
RE: Shearwalls - add in roof uplift?
RE: Shearwalls - add in roof uplift?
However, I rarely take any contributory dead load into consideration at corner shearwalls either...although there is some, just rarely enough to make a substantial ifference.
Mike McCann
MMC Engineering
RE: Shearwalls - add in roof uplift?
JAE is correct as usual! The individual load for the anchors is subjected to tributary shear and tension, thus capacity is reduced by interaction.
Keep in mind that, in theory, if holddowns have significantly higher capacity than the anchors, they will accept a portion of the uplift load, as they are mobilized first under certain wind directions and roof configurations.
RE: Shearwalls - add in roof uplift?
Garth Dreger PE
AZ Phoenix area