Monopole connection to pile cap

[engleprechaun]

I am fairly new to the design world. Currently I am working a a monopole pile foundation system and am having difficulties with the pile to pole connection. Im not really sure which direction to head as far as figuring out how thick the pile cap plate should be, and how to figure out if there is a need for gusset plates or not. Any help would be greatly appreciated. Thank you

Ross

 

[civilperson]

Use anchor bolts that embed in pile cap. Eight or a integer times eight is a good first try for number of bolts. Pick a bolt circle diameter at least 12" bigger than outside radius of pole and a plate OD 12" bigger than bolt circle. Find greatest moment condition, probably wind or seismic load combination. Solve P/A +/- Mc/I and size anchor bolt for worst case. Check embed depth by ACI appendix D, add steel reinforcemnt as necessary. Solve for thickness of base plate using greatest bolt force on proportion of base plate as a cantilever.

 

[engleprechaun]

I am looking into a concrete foundation alternative. However we are still exploring the pile foundation (24" D with a 1.375 wall thickness). It is this plate connection that I am having the problem with.

 

[civilperson]

Same proceedure, no embedment. Bolts connect welded pole plate to welded pile plate.

 

[csd72]

Generally for a monopole there is a hole in the middle of the base plate to allow services to run up into the pole. This means that any bending in the base plate from cantilever action will also induce bending in the wall of the pole.

I would always put gussets for this type of base plate.

As the pile is narrow, the typical anchor formulii do no really apply so I would usually lap the anchor bolts with the reinforcement to ensure full transfer of the tension forces.


Calculate the base plate thickness based on the bolt tension and spanning from gusset to gusset. Then calculate the gusset size based on the diagonal vector of the required reaction (as a compression force).

Blodgetts design of tubular structures has some good formulii on similar details, but I never found anything that covered this exactly.

Also for this type of structure they tend to use levelling nuts under the base plate so you would get discrete support points rather than concrete bearing. I believe we used the formula 4M/ND for bolt forces which can be calculated from first principles by estimating the bolt ring as a pipe of equivalent area.

Hope this helps.

Have fun.