Gravity Foundation to Resist Lateral Forces?
Gravity Foundation to Resist Lateral Forces?
(OP)
Hi there,
I am new to structural design and I am designing a foundation for a tower. The tower itself does not weigh much (450kg) and because I am in a hurricane prone area I want to ensure that the foundation stays in place in 150 mph winds. The lateral forces therefore govern. I used a very conservative estimate of the area of the tower that the wind hits (I assumed the area as a block instead of as a tubular area as shown in the attached sheets) and applied that force at the very top of the tower in the analysis. I am not sure if I went about determining the restoring moment in the right way but any advice on how to ensure this stays put with the applied forces shown in the sheets will be appreciated. The foundation will be cast on grade and on top of sturdy rock. Would I need to use anchors to anchor the concrete into the existing rock? Is the foundation too big for the application? Is my live load estimate reasonable? Also how can I determine how deep the bottom of the tower should be embedded into the concrete and how can one tie the tower into the rebar (when I get to that stage in the design)?
Points I should mention is that the tower is made of aluminium and is a tube with a diameter of 194mm.
Any help would be appreciated.
I am new to structural design and I am designing a foundation for a tower. The tower itself does not weigh much (450kg) and because I am in a hurricane prone area I want to ensure that the foundation stays in place in 150 mph winds. The lateral forces therefore govern. I used a very conservative estimate of the area of the tower that the wind hits (I assumed the area as a block instead of as a tubular area as shown in the attached sheets) and applied that force at the very top of the tower in the analysis. I am not sure if I went about determining the restoring moment in the right way but any advice on how to ensure this stays put with the applied forces shown in the sheets will be appreciated. The foundation will be cast on grade and on top of sturdy rock. Would I need to use anchors to anchor the concrete into the existing rock? Is the foundation too big for the application? Is my live load estimate reasonable? Also how can I determine how deep the bottom of the tower should be embedded into the concrete and how can one tie the tower into the rebar (when I get to that stage in the design)?
Points I should mention is that the tower is made of aluminium and is a tube with a diameter of 194mm.
Any help would be appreciated.






RE: Gravity Foundation to Resist Lateral Forces?
This shows up in the building codes as a load combination of:
0.6D + W (1/0.6 = 1.66).
This includes a bit for underestimating the dead load as well.
You included your "live load" of five people. Don't do that - just include dead load and the lateral wind per above.
Using the tower as a block and then placing all of the lateral load at the very top is pretty conservative...it's OK to be conservative but just be aware that a portion of the wind pressure on the tower doesn't have the full height moment arm.
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RE: Gravity Foundation to Resist Lateral Forces?
Thanks for your advice. That was silly of me to include the LL. I removed that and bumped up the factor of safety to 1.5 shown in the attached sheet. Any tips or advice for the other questions posed? Also in your opinion, does the foundation seem too large? If so I should perhaps reconsider the block area that I used.
RE: Gravity Foundation to Resist Lateral Forces?
RE: Gravity Foundation to Resist Lateral Forces?
Some guy-wires could change that situation.
RE: Gravity Foundation to Resist Lateral Forces?
Also, because of the relatively large box area at the top, I would check for torsion. Probably not significant but could be an issue.
Agree with JAE's comments.