REMOVABLE ANCHORING SYSTEM FOR TRAILER

[sebas-1024]

Hello,

I'm in charge of designing an anchoring system for a 8,5' wide x 48' long x 8'-11" trailer. The system is only supposed to resist loads caused by seismic and wind action, dead load is taken care of by the trailers own supporting system (basically the wheels and an additional support). The anchoring system is comprised of helical piles that will be receiving tension and compression to resist overturning and lateral loads to resist sliding, the basis of the design is pretty simple on it's own right, but once we presented the design to the client, they asked that the upper portion of the piles be removable for construction and maintenance purposes (changing the trailer and who knows what else)as they feel it will be a tripping hazard and obstruct any trucks or cranes that need to enter the area of the piles. In order to achieve this, I'm thinking of proposing a pile with a plate on top that sits at level with the grade, then a column with a base plate at it's base that will sit on top of the other plate, and 4 or more anchor bolts to keep them together; you can see a rough sketch of my proposal attached to this post. Even though it seemed like a feasible solution, some questions arose while talking to a colleague about it, so I wanted to post them here and see what you guys think.

1) Will the bolts, nuts, washers or plates suffer in any way by the disassembly and reassembly of the ensemble? Note that this should happen at 6 month intervals at most, I feel like it shouldn't be too hard on the elements, but I'm unsure as it is not the kind of thing that you design bolts for.
2) Will corrosion be a problem? I'm not referring so much to the structural integrity; as that's taken care of by assuming a corrosion rate and designing with a bit extra thickness or diameter, but to ease of disassembly and reassembly, if the bolts start to rust they'll be hard to unscrew and screw at best. Any special coatings for this type of application? Note that the bolts will be in direct contact with the soil, or at least that's the way I'm envisioning it right now.
3) Once the upper portion of the structure is removed, the bolts have to be removed as well, as they would be a tripping hazard if they protrude out of the ground. I feel that excavating under the piles base plate to unscrew the nuts is not ideal, the bolts would have to be unscrewed and screwed from above the base plate to not disturb the soil. Any thoughts on a construction detail for this specific application?
4) I'm a little lost as to how the base plate and bolts should be designed. What I mean is that anchor bolts are normally embedded into a concrete element, in this case they're only holding the two plates together, and on top of this, the base plate is not bearing on a pedestal or pile cap either, just another base plate. So, should the bolts only be designed for tension and shear without taking anything else into account? And the plate's deflection, will it be the same as what we usually consider in concrete applications or is it a whole different story?
5) Leveling the upper plate will be a problem of course, I thought maybe inserting a leveling nut between the two plates but then the plate will be bearing on the nuts instead of the lower plate. Will this have any undesirable effects for the structure? It's not supposed to support a lot of weight so it might be fine, but it's just another concern that I don't quite now how to properly address.

Sorry for the long post but this design was not as simple as I thought it would be. Thanks in advance for any help that you can provide me with and, if you have any comments on the design please let me know, I'm sure there are better solutions for this problem that I have not considered myself.

 

[dik]

can you cast a concrete cap on the screw pile, flush with grade and have threaded inserts cast into it... and bolt the anchoring post to the concrete cap? The screw pile can have headed studs welded to it to engage the concrete cap... could be 12"dia x 12" thick... any frost heave issues?


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

What are the circumstances requiring you to use piles instead of concrete?

Also, you may have to cast a concrete donut at the top of the pile to resist the lateral. Might want to talk to the pile company or a geotech to get figures on the lateral resistance of the shaft bearing against the soil.

 

[sebas-1024]

Responding to Dik: I´m not necessarily against that, but the company that I'm doing the design for is a helical pile installer so the ideal situation is one where you don't depend on concrete to provide a solution as that eliminates one of the big advantages of working with helical piles, which is not having to wait for concrete to set. That said, it does seem like a pretty sound solution, from what I'm seeing, the anchors could be taken out while maintaining a flush finish as you say. I'd say no to the frost heave issues, as the project is in California. Do these threaded inserts have any standards or manufacturers that you could point me to?

Responding to XR250: I work for a helical pile installer, so my solutions have to be based on that foundation system. On the lateral, I guess that's possible, it's just a matter of evaluating pile deflection and see how much load it can take without exceeding deflection limits for helical piles, in any case, Dik's solution would provide a good bit of lateral resistance similar to the donut that you talk about so that might solve both problems at once.

Thank you both for your replies, you've been really helpful.

 

[dik]

The concrete is used only for a transfer of the load from the trailer to the pile.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

If you are only required to resist lateral load, seems like there are easier ways to achieve this. Put your piles in at an angle flush with the ground and use cables.

 

[dik]

To prevent a tripping hazard, you want the anchor flush with the ground, maybe.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Sebas-1024:

If your company is involved with the design of screw piles, can you advise my how they design the thickness of the auger (spiral) component? and the weldment to attach it to the shaft? There are likely others that could use that info. Thanks in advance.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

If i were in your shoes, i would prefer screw pile with RC cap flush with the ground and a socket fixed in the RC pile cap. When you remove the column, the socket could be sealed with a plastic cap.

In order to show the concept,I write ( large umbrella removable base ) and searched the web..One of the outcomes,

https://www.shadeaustralia.com.au/bases/inground/inground-removable

 

[dik]

Great solution...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LittleInch]

I was thinking of some sort of bayonet style anchor to allow vertical restraint, but that looks as good as anything.

The bolts idea will work the first time then gradually fail as corrosion, dirt and mis threading, the nut coming off the lower flange etc etc.

Unless you use a proper flange you're going to get high stress concentration at the connection to the plate, you'll get water inside the tube which will then rust from the inside unnoticed.

Not a great design IMHO.

Removable anything will be some sort of compromise over a single solid tube, but many proprietary system exist like hturkats for removable posts.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

I've seen bolts used for years, with the holes periodically being high pressure sprayed to remove crud.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[sebas-1024]

Thanks for all the replies again, I like the discussion.

Responding to Dik: the thickness of the piles helicesthat my company installs (I'm guessing that's what you mean by spiral) is 0.375" thick for all sizes; what I really design for as a structural engineer is the diameter of the helix, the thickness was probably designed by a mechanical engineer at one point and is standard for all cases (I'm just guessing here). They're also factory fillet-welded to the pile shaft so I don't have any input there except that I don't really design for that either. I'm not trying to say that you can just take any piece of metal and build a helical pile by yourself, all the contrary, there are factory standards and certifications that need to be achieved by the fabricator; but my knowledge is limited to the foundation design of the piles which doesn't include those things that you're asking about. Sorry if this isn't the answer you were expecting on my part.

HTURKAK: that seems like an interesting solution but, have you seen it used in structural applications? I know it's just an example but the one you proposed is for umbrellas. Or did you mean coming up with something similar myself and have the manufacturer fabricate it?

LittleInch: regarding corrosion, the bolts will be changed periodically with each disassembly of the structure, and all elements will be designed with an "over-thickness" to account for any structural capacity loss, I feel like this will be enough to avoid those issues on the long term. What do you mean by "a proper flange", the base plate itself or some other element?. On the water inside the tube point, I'm not planning on having holes in the plates other that the ones needed for the bolts, so water inside the tube shouldn't be a problem in that case.

Again, thanks for all your replies, and sorry for the long posts.

On a side note, how do I quote other replies? I've seen other users do it and I'm just curious.

 

[dik]

Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

Yes for umbrellas but for big umbrella. I have seen similar concept at fair stands.. I just proposed to see the concept. If you cannot find a proprietary system, you may develop your solution with calculation and manufacture . It should not be big issue.