Design of Timber Pile Foundation

[oengineer]

I am working on designing a foundation made of a reinforced concrete pile cap supported by timber piles. I am currently using RISA Foundation software to determine the loads applied to each timber pile via the pile cap. What is the procedure to design the timber pile? I am given the tension, compression, and shear capacity of the piles. How would I check the piles for settlement? How would I check for the lateral deflection of the timber piles?

 

[JedClampett]

Design of the piles takes a Geotechnical Investigation and report. Usually this is done by a specialized Geotechnical Engineer. Pile design is a subset of the Geotechnical Engineering field. Then someone needs to specify pile type, installation and testing.
This is something you don't want to learn on a real project.

 

[mike20793]

I agree with JedClampett. This is something that your geotechnical engineer should specify or should help you with the LPile information to get it yourself.

 

[EngineeringEric]

Also treatments are rather important and should not be learned after/during

 

[oengineer]

Thank you all for your responses.

So as the structural engineer designing the foundation, does this mean that as long as the applied load does not exceed the allowable for the tension, compression, and shear capacities for the timber piles mentioned in the soil report, I should not be concerned with the settlement and/or lateral displacement? I do not have access to the Lpile software. Does Lpile determine your pile displacement?

I am reviewing an old geotech report which is the area I am putting my pile foundations. The geotechnical report states "No detail analysis was made with regards to settlements of pile foundations since they will probably be small and unimportant to the type foundation and loading. Settlements would become important if extremely large clusters of closely spaced piles are anticipated and if this case arises additional analysis should be made." Is the "additional analysis" performed by the geotechnical engineer or the structural engineer designing the foundation?

 

[mike20793]

There needs to be a new geotechnical engineer that provides a new report based on your anticipated loading.

 

[oengineer]

What I am doing is for estimating purposes to make a bid proposal.

 

[EngineeringEric]

That sounds like the report is stating that the pile (group?) was designed for one specific application, if you are using the values in a different application than it needs to be evaluated by a geotech.

Think about if you design a pile cap for 6 piles but then the contractor only installs 4 piles, your cap was not loaded how you designed it an now it may fail.... it needs to be re-evaluated

 

[DaveAtkins]

I don't know how RISA Foundation works--I use RISA 3D. For preliminary design, I would model the piles as stiff compression springs, and see what reactions you get. Historically, timber piles have been designed for an allowable load of 10 to 30 tons. If your reactions are much smaller than that, settlement should not be a problem.

I would not assume the piles can take tension.

DaveAtkins

 

[BigH]

Why not pick up MJ Tomlinson's Pile Design and Construction book. A bit of reading and you might get an idea of what you are up against.

 

[robyengIT]

If it can help.
I have an old book (dated 1955) on piles foundations, timber piles included, but in Italian.
In a note I read some bibliography :
1 - Proceedings of American Wood Preservers' Association
2 - American Railway Engineering Association Standards
3 - Broach J.B. "Method of recording and evalueting test pile data" - Wood Preserving News, 1943
4 - Bruns T.C. "Don't hit timber piles too hard" - Civ. Eng, 1941
5 - Masters "Timber friction pile foundations" - Proc. A.S.C.E., 1941
6 - Smith-Aaron J. "Rotary drill Bores holes for timber piles in clay" - Engineering News Records, 1932

 

[BUGGAR]

Bids are usually based on data available at the time. Note this in your records and if you win the bid, you may have basis for a claim if the soil is different from what the bid data showed. Happens all the time.

 

[robyengIT]

video on timber piles foundations in Venice :

https://www.youtube.com/watch?v=GTzpeTjkaKY

 

[robyengIT]

and this too

https://www.youtube.com/watch?v=B3INp81NimE

 

[oengineer]

Thank you all for your input. It has been very helpful.

Would any one happen to know what would be typical acceptable tension & shear stiffness values (in kips/in) to use in my pile design? As mentioned earlier, this is for bid purposes.

 

[robyengIT]

Hope it can help

 

[oengineer]

Thank you all for your help

 

[boo1]

try

http://www.wwpinstitute.org/documents/timber_manual.pdf

 

[Sawbux]

Try to avoid tension in the piles, it's difficult to make tension connections to the wood. There are some details that use bolted connections and bent plate brackets that embed in the cap, but they are limited in capacity.
Many times it is better to increase the foundation weight to minimize uplift on the piles. The typical uplift used is 1/2 the downward capacity or less for friction piles. If they are end bearing, even less!