Pile Energy Capacity Equation 1

[HollyM]

Hello!

I am looking for an equation to find the ultimate pile capacity. When designing fender systems, a required energy absorption it given. I am struggling to find a refernced equation for the pile capacity.

Thank you!

 

[Ron]

HollyM...a bit more info please...

Are you trying to calculate pile capacity based on geotech parameters and loads, or are you trying to estimate capacity from a driving equation?

If the former, are you looking for lateral capacity, vertical capacity, uplift or other?

 

[Qshake]

As Ron noted you need to provide more information to properly answer your question.

Since you're working on fender systems, I would ask if you've checked out the Florida DOT guide on fender systems? This should help you determine the force-displacement relationship you may need.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[HollyM]

I am looking for lateral/impact capacity on the pile based on section and material properties.

I have come across a couple of equations, both based on impact location, E and I. One equation converts the energy requirement to a static load. I then compared the applied moment to the moment capacity. Neither are referenced.

I have been looking at the FDOT specifications, they outline what their requirements are for piles, but not how to find the energy capacity in a proposed pile.

 

[cessna98j]

Hi Holly - I do this type of calculation quite frequently when analyzing fender piles for marine terminals. I typically do an iterative approach for impacts at different heights based on the MLLW and MHHW elevations.

In short, you apply a trial static load to your fender pile or fender pile system. From there, you obtain the deflection at the impact point (accounting for the stiffness of the backing rubber fender units at the top if applicable). You can do this by hand or with a computer analysis program. You then check what the reaction should be for the calculated deflection based on the required energy absorption. Use the equation P = 2E / delta where E is the required energy absorption of your system. You increase or decrease the load applied in the model until the applied point load and the calclated "P" converge based on the deflection.

Once you know what your applied load is, you can easily determine whether or not the fender piles are overstressed for the required energy.

You should also remember to account for the depth to fixity below the mudline as part of the analysis for the fender pile(s). This is a geotechnical parameter that can be conservatively estimated using NAVFAC 7.02. The equation for depth to fixity is T=(EI/f)^(1/5), all units in inches, where f is the coefficient of variation of subgrade reaction (5 pci is usually a conservative number here). Your recommended depth to fixity below the mudline is 2T and recommended minimum pile embedment is 4T.