Footing w/ Large Moment
Footing w/ Large Moment
(OP)
I've been asked by a client to design a footing foundation for an H-Frame (Substation Equipment (see link for a reference pic - http://www.sabretubularstructures.com/Substation.a...). There are two columns and I've been given the loads at each base plate.
Axial and shear forces are not really a concern, it's the moment of 900 kN-m (factored to 1.5 SF - 600kN-m unfactored) on each base plate that is governing the design. Keeping with the pier-footing idea, I've come up with 1.5" dia. anchors embedded to 2'-6". I'm finding that to get a concrete breakout resistance with that embedment depth, I need a lot of edge distance and that is making the pier quite large. I'm getting a 10'x12' pier x 4'-6" deep (basically just a large concrete block). This would be on top of a footing 16'x14' x 1'6" thick. The concrete is all required to keep the bearing pressure in compression. This volume of concrete seems like a lot - wondering if a different foundation type is better or more suited for this
I'm still inexperienced with foundations in general (< 1 year out of school) and I've never worked with something like this so I have nothing to draw on. Couldn't find any typical foundations for this type of structure either. Just wondering if anyone has experience with something similar and could advise if this design is in the ballpark or not.
Appreciate any input, cheers
Axial and shear forces are not really a concern, it's the moment of 900 kN-m (factored to 1.5 SF - 600kN-m unfactored) on each base plate that is governing the design. Keeping with the pier-footing idea, I've come up with 1.5" dia. anchors embedded to 2'-6". I'm finding that to get a concrete breakout resistance with that embedment depth, I need a lot of edge distance and that is making the pier quite large. I'm getting a 10'x12' pier x 4'-6" deep (basically just a large concrete block). This would be on top of a footing 16'x14' x 1'6" thick. The concrete is all required to keep the bearing pressure in compression. This volume of concrete seems like a lot - wondering if a different foundation type is better or more suited for this
I'm still inexperienced with foundations in general (< 1 year out of school) and I've never worked with something like this so I have nothing to draw on. Couldn't find any typical foundations for this type of structure either. Just wondering if anyone has experience with something similar and could advise if this design is in the ballpark or not.
Appreciate any input, cheers






RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
As far as the overall foundation goes: that kind of overturning moment screams for a pile group. Reinforced concrete caissons seem like the way to go. If that is a problem (I don’t know what your geotechnical report says) that you may want to try a combined footing (I don’t know how far apart those columns of that bent are, or what direction the moment is in).
RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
Another wrinkle is that these structures usually are set on leveling nuts and are not grouted so all of the loads are carried through the bolts.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Footing w/ Large Moment
Brian C Potter, PE
http://simplesupports.wordpress.com
RE: Footing w/ Large Moment
http://www.bechtel.com/assets/files/TechPapers/des...
RE: Footing w/ Large Moment
But from the diagrams the structures seem pretty light on to me.
What is it thats causing this large moment in the footings?
RE: Footing w/ Large Moment
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
I also 'second' the paper that Slickdeals referenced. AND would add that ACI 355.3R-11 is helpful as well.
RE: Footing w/ Large Moment
Strap beam is not a good solution.
Probably go for combined bored pile and pad as suggested above.
RE: Footing w/ Large Moment
This would avoid moment on the pad footing.
RE: Footing w/ Large Moment
RE: Footing w/ Large Moment
Some outfits still build new truss-like frames but the ones we built for were using the newer tubular ones.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Footing w/ Large Moment
What I was suggesting was a simple tension brace from top of gable to an independant footing. Only applies if land is available.
But your solution is another option.
RE: Footing w/ Large Moment