hippo11
Structural
- Mar 21, 2003
- 161
I always hear that when you are doing preliminary lateral design for a bldg, you should check that there's no net uplift at the frame column foundation, in other words, make sure that
0.9 D - 1.0 E > 0 and
0.9 D - 1.3 W > 0
But my question is, what's wrong if you have a bit more than zero? What's so evil about 2 kips of net uplift, heck, what's wrong with 30 kips of net uplift?
It's not like your frame column will fly up into space at 1 kip net uplift.
What's wrong with the foundation losing contact with the soil in an earthquake or hurricane, as long as your structure is still stable?
A frame column that has lifted up 0.05" off the soil still has about the same amount of tension in it as a frame column that is still in contact with the soil. It just seems like an arbitrary threshold...as long as you can show thru a P-delta analysis that you are still stable, you should be okay even with net uplift occuring...right?
0.9 D - 1.0 E > 0 and
0.9 D - 1.3 W > 0
But my question is, what's wrong if you have a bit more than zero? What's so evil about 2 kips of net uplift, heck, what's wrong with 30 kips of net uplift?
It's not like your frame column will fly up into space at 1 kip net uplift.
What's wrong with the foundation losing contact with the soil in an earthquake or hurricane, as long as your structure is still stable?
A frame column that has lifted up 0.05" off the soil still has about the same amount of tension in it as a frame column that is still in contact with the soil. It just seems like an arbitrary threshold...as long as you can show thru a P-delta analysis that you are still stable, you should be okay even with net uplift occuring...right?