0.6D overturning uplift foundation metal building continuation
0.6D overturning uplift foundation metal building continuation
(OP)
thread507-352021: .6D + W for footing bearing pressure?
so, ya.. kinda clear as mud as far the application i need clarity on (unless ofcourse im reading it wrong again)....
when you are doing footing designs for METAL Building frames with no slab to count for contributory weight, it is a BIG DEAL to have to reduce your required concrete footing weight to .6D to counteract the uplift .9D would be acceptable, but how bout a similar note as ASCE 12.13.14 regarding an additional 25% overturning (uplift) reduction for seismic, but for wind instead ... is there one for wind? That would make the footings more manageable. Despite my love of conservativism, I have a hard time justifying the need for say 250 yards in a footing as opposed to 160 because of the 0.6D we are all used to.
so, ya.. kinda clear as mud as far the application i need clarity on (unless ofcourse im reading it wrong again)....
when you are doing footing designs for METAL Building frames with no slab to count for contributory weight, it is a BIG DEAL to have to reduce your required concrete footing weight to .6D to counteract the uplift .9D would be acceptable, but how bout a similar note as ASCE 12.13.14 regarding an additional 25% overturning (uplift) reduction for seismic, but for wind instead ... is there one for wind? That would make the footings more manageable. Despite my love of conservativism, I have a hard time justifying the need for say 250 yards in a footing as opposed to 160 because of the 0.6D we are all used to.






RE: 0.6D overturning uplift foundation metal building continuation
The additional weight you're trying to avoid is the whole intended point of the factor you're talking about.
It's easy to justify the necessary concrete, since it's required to provide safety against the building flipping over in an extreme event.
RE: 0.6D overturning uplift foundation metal building continuation
RE: 0.6D overturning uplift foundation metal building continuation
RE: 0.6D overturning uplift foundation metal building continuation
RE: 0.6D overturning uplift foundation metal building continuation
I can't help you with the anchor bolt issue. I'm not really all that conversant in current ASD practices in the US.
I wouldn't suggest using skin friction of your foundation except in some very controlled situations. If you want help from the soil against uplift, why don't you put a spread footing at the bottom?
RE: 0.6D overturning uplift foundation metal building continuation
In ASD, all your material strengths are factored down. Your allowable resistance is some fraction of the ultimate resistance. This is how you get your factor of safety. Just think of the 0.6 factor as the allowable uplift resistance per pound of dead load. It's the same thing.
RE: 0.6D overturning uplift foundation metal building continuation
"C12.13.4 Reduction of Foundation Overturning. Since the vertical distribution of forces prescribed for use with the equivalent lateral force procedure is intended to envelope story shears, overturning moments are exaggerated. (See Section C12.13.3.) Such moments will be lower where multiple modes respond, so a 25 percent reduction is permitted for design (strength and stability) of the foundation using this procedure. This reduction is not permitted for inverted pendulum or cantilevered column type structures, which typically have a single mode of response.
Since the modal response spectrum analysis procedure more accurately reflects the actual distribution of shears and overturning moments, the permitted reduction is only 10 percent."