Foundation Self Weight for Resisting Uplift

[DTS419]

What is the current code requirement for any reduction in foundation self-weight (D) when resisting wind uplift (W)?

2021 IBC contains the following verbiage:

"For load combinations that include the counteracting effects of dead and wind loads, only two-thirds of the minimum dead load likely to be in place during a design wind event shall be used."

In spite of this, there is no load combination shown that includes 0.67D.

In ASCE 7-16, combination 7 gives 0.6D + 0.6W. This is different from the two-thirds that IBC says.

 

[Celt83]

I think it is important to highlight this point:
"..only two-thirds of the minimum dead load likely to be in place during a design wind event shall be used."

In the alternative combination you shouldn't be using 2/3 of your normal dead load it should only be the dead load you reasonably assume will be there during the design event. In the case of the cast-in-place dead man 2/3 of self weight is likely reasonable. In the case of a building 2/3 of the design superimposed dead load is not likely accurate.

"..wind uplift is provided by truss manufacturer.."
usually no you as the EOR are providing the uplift to the truss manufacturer, they typically aren't figuring out the loads for themselves (some do but I think it's in TPI-1 that all loads should be provided by the EOR)

 

[phamENG]

usually no you as the EOR are providing the uplift to the truss manufacturer, they typically aren't figuring out the loads for themselves (some do but I think it's in TPI-1 that all loads should be provided by the EOR)

While we are required by chapter 16 to provide it, I've found that most truss manufacturers do come up with it themselves. A significant portion of the trusses produced are not used on engineered structures, and so the standard software has a wind module that automatically determines the wind load on a roof truss. I think it's easier for them to just enter the wind speed, building height, and exposure class and get it automatically rather than trying to manually enter the wind loads we provide.