Design of Footing with very large moment
Design of Footing with very large moment
(OP)
Good day!
I believe this one is just simple, what makes it complex is the large moment to be considered in the design.
I have an anchored steel pole with base reactions M=220kN-m, P=28kN, V=14kN,. (M=moment, P=Axial, V=Shear).
I have already design the pedestal to support the pole, my concern is the footing.
May i ask for idea how can i design the footing with these much moment in it. it might be critical for overturning.
what i found in textbooks are just those with minimal to no moment considered in the footing design.,
Thanks
I believe this one is just simple, what makes it complex is the large moment to be considered in the design.
I have an anchored steel pole with base reactions M=220kN-m, P=28kN, V=14kN,. (M=moment, P=Axial, V=Shear).
I have already design the pedestal to support the pole, my concern is the footing.
May i ask for idea how can i design the footing with these much moment in it. it might be critical for overturning.
what i found in textbooks are just those with minimal to no moment considered in the footing design.,
Thanks






RE: Design of Footing with very large moment
RE: Design of Footing with very large moment
1) Large footing with enough mass to resist the overturning. The simplest and usually the most economical. Do your first one by trial and error. You will soon get a feel for it.
2) Bored pile which resists the overturning by passive soil pressure. Often used for lighting towers.
3) Pile group with pile cap designed to resist overturning by push-pull on the piles. Relatively common for portal frame buildings, especially those with cranes.
4) Footing with ground anchors, in which the anchors provide tension force, soil pressure on footing bottom provides compressive force.
RE: Design of Footing with very large moment
- all depends on your ground conditions and ability to excavate / pile / get good bearing pressures
- if your steel pole is sensitive to deflections at the top, ie a camera on top of a mast, then a piled solution may be better
- for a simple steel post (say lighting post) where there is lots of room then a pad is likely to be simple & cheap (if not massive!) - a first guess is something like 2.5 x 2.5 x 1.2 m !
RE: Design of Footing with very large moment
RE: Design of Footing with very large moment
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Design of Footing with very large moment
RE: Design of Footing with very large moment
I've often had trouble making spread footings work in a reasonable size (plus the fact that I work in areas with huge frost depths tend to make them uneconomical). I've had problems in the field installing the caps for multiple pile installations. The types of contractors that do these little jobs aren't necessarily the most experienced and you end up having a few critical reinforcing details where things can get a little congested. Even with fairly detailed drawings I've found issues on site inspections. Depending on your depth you can also end up having to do a very annoying strut and tie model with several different cases including load reversals to check everything properly.
ishvaaag, I don't know if you need to go so far as the whole beam on a spring foundation system you're describing. In this kind of situation you're likely to have a very thick slab to so your internal deflection is going to be fairly negligable. You can likely just assume that the slab deflects as a block and assume a reaction that varies linearly with the distance from the neutral axis. If you're concerned at the end, you can check the deflection at the tip of the foundation under the applied soil reaction and make sure it's insignificant in comparison to the expected soil deflections. The more complicated analysis obviously wouldn't hurt, though, if you can do it quickly.
RE: Design of Footing with very large moment
Good luck
RE: Design of Footing with very large moment
Is having pad footing design section that would be very useful and informative reference for your case here, it lists the analysis and design into simple steps.
RE: Design of Footing with very large moment
http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."
RE: Design of Footing with very large moment
http://www.eng-tips.com/viewthread.cfm?qid=272903
http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."