Point of Fixity of a Pile or Drilled Shaft 1

[DWHA]

I am working on an analysis of a large Drilled Shaft and I am having trouble determining the point of fixity of the shaft. I have some texts that talk about it, but they kind of run you around in circles. The top 50 feet of the shaft is in clay. Any suggestions would be appreciated.

 

[civilperson]

Assuming the soil is uniform as depth increases and the the pier is sufficiently stiff, roughly 17 feet down.

 

[Panars]

What are you planning on doing with the point of fixity? When I get this question, the structural engineer is usually planning on modeling the drilled shaft as a fixed base column in a FE model, or looking at a buckling analysis. In this case, I will perform a lateral load analysis using LPile and calculate an equivalent cantilever length.

 

[DWHA]

I am working for the construction company that is doing the work. In the plans it states that the contractor shall provide bracing between the shafts until intil cap is placed. So I am determining the moment induced due to wind forces prior to the cap being placed.

 

[civilperson]

What is the wind blowing on and how is it attached to the drilled pile?

 

[DWHA]

Wind is blowing on the formwork and unsolidified concrete cap.

 

[civilperson]

Drive some metal stakes around the perimeter of the formwork to resist all horizontal forces and forget about the drilled pier since it is not attached to the forms.

 

[DWHA]

Ya, this is in a lake.

 

[civilperson]

DWHA,
A bit miserly in giving necessary information to get good suggestions.

 

[Panars]

If I was calculating the moment in the shaft, I would use the LPile program from Ensoft. If you dont want to (or can't) purchase the program, then the alternative would be to use the analysis method described in the NAVFAC manual. It is available here:

http://vulcanhammer.net/download/foundations.php#dm72

Look on page 7.2-235.

 

[DWHA]

Civilperson,
I understand that what I stated may have been a little misleading, however I did not ask for suggestions on how to brace the formwork.

Planars,
Thank you for the site, I looked at it quickly and it appears to be what I was looking for. At this time I do not have LPile, but I am going to research the program and see if I can get it. Thanks again.