Concrete pile sizing for 25-ton overhead crane

[BoomerSooner7]

Hi,

I am working on a project to install a 25-ton overhead crane with free-standing columns spaced @ 25 feet apart. The column sizes were specified by the crane manufacturer's application engineer. However they will not be liable for the sizing of the concrete piles for the columns, arggg! I am having trouble getting a hold of a local structural PE to consult with. I have more specific information, column loading, drawing etc..if anyone is interested in throwing me a bone here. My initial thought is 4' x 4' x 6' deep concrete piles, not really based on any calculations, just a huge mass of concrete. Please help!!

thanks in advance.

 

[JedClampett]

You're going to need to hire a Geotechnical Engineer to do borings and design this. Normally you'd get a Geotechnical Report and then have a structural engineer to design the foundation, but if it's limited to a foundation only, I'd say a Geotechnical Engineer can take on the whole thing.
You don't want to swag or guess this. Whatever you pay is going to be less than the cost of the crane.

 

[apsix]

As JedClampett said, you will require specific site information for this.
Free standing columns make this requirement particularly important.

 

[JAE]

And Eng-Tips isn't licensed in your state.

 

[BoomerSooner7]

Thanks for the responses. I understand fully that I will ultimately have to get consultation from a licensed engineer. Right now, I am just trying to put some budgetary numbers up for this project and the concrete work is one of the missing peices.

 

[InDepth]

Like everyone else get a geotech.

Well, you could estimate it based on minimum code values and be conservative. With crane footings, usually there is higher bearing capacity for incidental loads. And more than likely depending on the soils settlement will control (especially with fill).

So, conservatively, for a footing use a bearing pressure of 2000 psf get you approximately 6' x 6' x 2' footings.

For friction piles using 200 psf side friction maybe 2x 24" dia piles 19 foot deep. or a single pile 40 ft deep. Alternatively use a design build design with micropiles.

 

[Nickn1944]

Like others said, all depends on the soils. After that, it's pretty simple to design a foundation. A 25ton crane isn't very large, but crane beams need to remain level, so you don't want much differential settlement. Depending on horizontal loading (wind or other), I'd use piles under pile caps to get more horizontal stability. Given the relatively light loading, timber piles will work. They cost a lot less than steel or concrete piles. I'd be a little afraid of 2,000 psf until a geotech blessed it for the site. It is usually conservative, but I have worked on sites where reality was actually less than 1,000 psf.

 

[hokie66]

For your crane, my first choice would be a two pile cap with two bored piles. This arrangement is good for resisting both moment and shear, and for development of the piles into the cap.

 

[FLCraneBuilder]

IT's all about the MOMENT on this one...

I assume you mean colums are free standing as in not braced to anything. If so, you did not identify the height! 10 ft tall or 50 ft tall... BIG difference in Moment

Suggest A-frame columns if owner can allow the space they take up. Footers will be very long in that direction anyway.

we typically use a rectangular footer that is sized relative to the moment loads the crane system induces.
Longitudal direction (parallel to runway beam) is usually less since the longitudal load is divided by number of columns along the run - up to a max of 150 ft or so.

 

[BoomerSooner7]

The moment at the base plate was given to me from the crane manufacturer at 48,000 Ft.-Lb. This is a double girder overhead bridge crane with a span of 43', columns spaced at 25' apart. The free standing columns will be around 12' tall. We have also discussed tying back to existing columns that support a 3-ton crane on the adjacent side of the shop to help support the load. Hope this helps.

 

[Ron]

I see flags here!

First, you described a shallow foundation (footing) but called it a deep foundation (pile). This tells me you are unfamiliar with the terminology, thus likely unfamiliar with the design necessities. Nothing wrong with unfamiliarity unless you attempt this on your own.

Your configuration implies a lateral load of 4 kips, which will likely be a dynamic load. With a double girder bridge crane I assume you have at least 4 columns. On average, your vertical load is 12.5 kips per footing...not a lot; however, temporarily you could experience nearly the crane capacity at each footing, individually.

As others have noted, a Geotech is necessary here. Unless you have adverse soil conditions, a shallow foundation will probably work...it will be large, but workable. Also, most Geotechs will not attempt the structural design of the foundation, even a simple one....they are usually singly focused on dirt, not rebar and concrete.

I would not consider bracing to the much lighter crane system without some significant analysis. Bracing a 4 kip lateral load against a crane that likely was only designed for a few hundred pounds of lateral load might not be a good idea.

 

[FLCraneBuilder]

I see lateral load is more in the range 6 kips (per side):
AISC 9th,5-29 - lateral load is 20% of sum of Load + Hosit weight. (assumed a 6 to 8 kip hoist).
Also, the height is based on top of runway rail, which is often much higher than column (assuming runway beams are on top of column as opposed to framed in to it)