Timber Pile design questions 2

[pelelo]

Engineers,

I am working on the design of a platform using timber piles. I got few questions:

1 - For lateral analyses, i plan to use LPILE. LPILe doesn't offer the timber pile option, however there is a option called "Elastic Section (non-yielding)" (see attached). Do you think that is the appropriate way to perform lateral analyses on timber piles?

2 - For checking deflection. Is there a maximum deflection specified for lateral analyses in timber piles?, I know for my concrete piles i limit lateral deflection to a max of 1 inch however, i think 1 inch for timber might be too high. Any thoughts?

3 - Refer to the lateral analysis attached that i performed. The depth of the pile would based on which ever is deeper between the bending moment and the deflection diagrams, correct?. Please let me know your thoughts. When i perform analyses on concrete piles, i don't that the "equilibrium" in the deflection chart is that deep, therefore most of the time the depths are based on the bending Moment chart.

The application of these timber piles is to support a walking platform. Water will be 1 ft below top of the platform, so essentially the piles are going to be submerged. Soils in the top 10 feet are composed of loose sands. Between 10 and 20, soils are medium sands.

Please advise.

 

[Settingsun]

1. I don't have LPILE but have used it in the past. The elastic section option sounds OK for timber. The alternative is something like concrete cracked section analysis?

2. I would relate deflection limit to the structure's purpose rather than the material. That is, what would you tolerate if you didn't know what the piles were made out of? The strength checks for the timber will tell you whether you've pushed the timber too far. 1" in a long, flexible pile would induce lower stress than in a short, stiff pile.

3. Stability isn't inherently different for timber than concrete so you can use the same procedures. Since the soil response is non-linear, I like to use ultimate loads (or ultimate load divided by the capacity reduction factor) to check whether the embedment is sufficient. A geotech engineer I used to work with used ultimate load and checked for no movement at the toe.

 

[r13]

Unless the lateral load is quite small, I'll seriously consider the use of battered pile rather than dealing with wood in flexural.

 

[pelelo]

Thanks a lot for your responses.

What do you consider a small lateral load?I am dealing with lateral loads of 2,000 lbs.

 

[r13]

There is no definite line dividing the magnitude of force into large and small, rather it is relative to to pile size, number, and ease in design and construction. 2 kips lateral load seems not that small for a single wooden pile with fixed support (M=F*L), but it can be made small by providing multiple piles. The load may be high for a set of battered piles too, however, you are dealing with simple tension and compression forces, and use the wood more efficiently than subject it to bending. You need to work out the numbers and compare the results.