Piling extensions over or under engineered

The existing pilings are not as tall as Lilly Marie's sheer of the boats at high tide. Wanting to add 3 feet to the existing piling height, we cut a 3 ft piece off of the butt end of a scrap piling then drilled 4 holes into the top of the existing piling and the 4 holes into the end of the scrap piece, then filled all 8 holes with thickened epoxy resin and inserted 5/8 x 16 inch rebar into the holes on one end, added more thickened epoxy to the top of the piling then put the 3 ft piece on top.

Problem is the holes and rebar are difficlut to line up even with the jig. We had difficulty with the first one and almost did not get it to come together. I would like to use one pair of holes and one piece of rebar per piling, located in the center of the piling. That would be much easier alignment, I wonder if one rebar provides enough strength?

An Internet site indicate that 5/8 rebar epoxied into concrete has a tensile strength of about 24,000 pounds. My shade tree engineering tells me that a 3 foot lever against an 8" piling base (4") radius against a length of rebar at center would be a 9 / 1 reduction ( 36" / 4" = 9) Thus the joint should stand a 2,666 lb pull to the side from the top of the piling.

Any thoughts on this?

Have you thought about sleeving it with a steel pipe over the existing piling? You would only be increasing the OD of the piling by the wall thickness of the pipe.

Sleeving the piling is a great idea! :)

Thanks,
I had not thought about sleeving it with steel pipe, sounds like an effective solution if I can put my hands on 8 to 11 diameter (the pilings' diameter varies) steel pipe that can be cut in 12-18 inch lengths. Any suggestions on where to find this without going overboard on cost?

I have been thinking about wrapping the joint with fibergalss cloth tape and epoxy, and could put some steel tabs underneath with screws through the tabs and into the pilings.

There are probably a lot of ways to increase the strength of the joint, but how much is enough. That's the engineering component of this post.

You could put a steel pipe over those pilings long enough to sit on the sea bottom. Because you only need a 3' extension I would buy large PVC pipe, cut them to a length that would allow the PVC to sit on the bottom and extend 3' over the existing pilings. I would also glue a PVC cap over the top. Those tubes should be cheaper than steel, have adequate strength, and with the nice caps, should look a lot better than rusty steel. We do that trick in the Great Lakes over small diven steel pilings to avoid damage to a boat. Over steel pilings the PVC will actually roll as a boat slides its rubrail along the piling.

Like Maynard suggested, you can sleeve them with PVC no matter what you use for the structural part of the extension. This way you could still do your fiberglass joint or some steel tabs or a steel sleeve or whatever. It won't matter how is looks because the PVC will finish it off nicely.

Thanks,
The idea of a PVC sleeve sounds like an excellent solution to put over the wood extension with one rebar dowel.

All I did was bolt a 3 X 12 to the inside of the piling. you can sink the bolts into the wood so they dont scratch your rub rail. so easy, even a caveman can do it

I assume George means "outside" the piling....anyway, that's what I was thinking....
I'd place a pair of heavy such wooden pieces perpendicular to the hull, for added strength, and thru bolt the pieces...two bolts on top two on the bottom. If you have the beam room, you could also bolt a single thicker piece of womanized lumber directly to the existing pile to extend it.....that would also serve to keep the hull and fenders off the creosote soaked piling....

Quote:

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Originally Posted by REBrueckner

you could also bolt a single thicker piece of womanized lumber directly to the existing pile .

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So does womanized lumber come from this kind of a tree?

http://gary-davison.com/wp-content/u...woman-tree.jpg

I ran into one issue on pvc pipe, the largest the plumbing supply had was 10" and several piling butts exceed that. In addition one length of 10" was >$250. Couplings were >$50 would guess end caps would be comparable. That comes to over $100 per 6' piling and I am doing 13.

Additional research indicates that fiberglass reinforced plastic has a tensile strength of 20,000 pounds per square inch. A few wraps of fiberglass cloth tape around the joint with epoxy should have the joint exceed the strength of the piling.

I think that will work best for me.

Gee Vincent, I have seen PVC pipe being used for city water mains. This stuff was big enough to crawl through. That price is hard to handle for sure.

Vincent: In several of your posts you're using the term "tensil strenght" of rebar or epoxy as an indication of the strength of the proposed joint. The problem is your piling joint will be subjected to shear (pounds/sq.in.) and bending (ft-lbs) forces and not tensil forces, generated by the boat impacting the piling. Impact forces are quite different than static forces. Impact forces generate much higher stresses than the equivelant static forces. Driviving a nail with a hummer into a wood block is much easier than driving the same nail by just pushing it down even with a static force 2 or 3 times greater than that generated by the hummer impacting the nail. So, in order to understand how a structural joint will behave, under load, you first have to have a good undestanding of the type of forces acting on that joint. The tensil strength of the joint is normally associated with a force acting along the long axis of the pile or rebar putting either one in tension until it fails (breaks).

Now I'm wondering why the hell I wrote what I wrote above. Does it serve any purpose? Well take it for what is worth, which maybe not much.

CapetaniosG

The problem I see with the original design is when your boat rub rail pushes on the pile far away from the joint. This will result in a very strong moment at the joint which will cause it to "pivot" on one side and pull the rebar out of the join OR will just bend the rebar.

Rebar is designed to be strong in tension only. If you can somehow be sure the rebar is bonded to the wood and won't release, then when a moment (push on the top of pile) is applied, the rebar will only be loaded in tension.

Shear loading will occur if your boat contacts the piling very near the joint....but I wouldn't worry about this scenario as I do not think it will cause failure.

One option I can think of that would address the above loading problems would be to bore out the center of the pile on the top and the bottom for a 4x4 or something similar. Then you can through bolt through the piling and the 4x4 on both the top and the bottom (and countersink). A large dowel would work too.

Another option is to just use doweling and then use strapping on the outside of the pile running from the top to the bottom. The strapping will take the tension and the dowel will take the shear---and the combination of the two will solve the moment problem.

And even another option is to drill continuous holes vertically in both the top and the bottom and use all thread. Drill near the circumference to allow for cutting a notch out to on put in a plate/washer and a nut. This will satisfy the loading the same way as the dowel and straps.

But really, I think ya'll should just debate shadow ghost forces and loadings on the internet LOL. Whatever you do, good luck.

Disclaimer: no expertize was used in making the above post. Everything I know I learned from Wikipedia.org. My comments are worth exactly what you paid for them.

Vincent,
You have created a " hinge " connection. Setting a sister pile
along the existing pile is the best solution. An alternate would
be the splint idea with 2"x material attached to the side as mentioned
earlier. A 3' extension will require a 6' overlap to offset the cantalever.
That's your 2 cent consultation from a humble Architect.
Mike

Quote:

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Originally Posted by George

All I did was bolt a 3 X 12 to the inside of the piling. you can sink the bolts into the wood so they dont scratch your rub rail. so easy, even a caveman can do it

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I had the same problem in my slip and solved it this way using 2x6s. Very easy and quick, just countersink the bolt heads. Then I bought a fancy Taylor foam bumper and screwed it to the inside which covered the bolts. Works great and is cheap.

Quote:

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Originally Posted by SKYCHENEY

So does womanized lumber come from this kind of a tree?

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Sky, that is just tooo funny.

That SURE is a great tree....reminds me................................................ ..............damn, can't remember now....Oh well, never mind...

"Additional research indicates that fiberglass reinforced plastic has a tensile strength of 20,000 pounds per square inch. A few wraps of fiberglass cloth tape around the joint with epoxy should have the joint exceed the strength of the piling."

I think post #13 covers it....you CANNOT count on a few fiberglass wraps to hold your boat in high winds....just not gonna work....use bolts and lumber as described above....maybe copy proven pile extensions in use in your area if you can find any examples....

WOW..You guys are over-engineering the daylights out of this simple and very crude job. :)

Crude,
Maynard, now I feel insulted, but you did answer the question. It is over engineered. But considering Krush's disclaimers. . .

This probably is Chevy rather than Jaguar engineering ( See Richard Prior's answer to Gene Wilder in SILVER STREAK ) I appreciate all the analysis and it has led me to further thought and a final solution.

A 10" x 3/4" hole was drilled in the center at one end of each piling. 10" of a 20" #5 rebar was embedded in the top piece and glued in place with filled epoxy resin. After set up, the extension piling was placed on top of the base piling with the other 10" of the rebar embedded and glued into the base piling hole. The top and hole in the base piling was coated/filled with more filled epoxy. The joint is then wrapped with 3 layers of fiberglass tape and epoxy.

As shown in the diagram below, the joint is a composite structure. When force is applied to one side of the extension, the rebar (Green) is placed in tension and one side of the piling joint fiberglass cloth (Purple) is in tension and the other compression. Everything is attached to the piling with epoxy (Red) including the rebar. As I understand it, builders secure rebar and bolts into existing concrete slabs with epoxy and the joint is stronger than the rebar. Wouldn't wood be the same, yielding a joint as strong as the weaker of either the rebar or the piling?

its not the strength of the epoxy/fiberglass layup but the bond of the epoxy to the piling. i assume the piling is pressure treated? not a strong bond. the rebar will be subjected to bending loads .the compression side in your drawing will be a fulcrom and the pileing will be a lever. a shock load at the top of the piling(missjudged docking, storm surge etc ) will shear the bond of the epoxy at the tension side and put bending load on the rebar. rebar is strong in many ways but bends fairly easily. three 2x6's per piling with counter sunk lag bolts is a better fix.

Just curious...What would be saved over having the dock guy come out, pull the short ones & reset longer pilings ?

Or if they are holding up the dock...Sinking longer ones next to the existing pilings ?

You could also plane two flat surfaces and attach another piling to the existing with bolts from dock level up (of course countersunk)

I would ask the dock guy how he recommends doing it...I'm sure he's run across it before.

Epoxy, Rebar, etc...No flex in epoxy so it will crack on first impact...I'd not entertain anything along those lines if it were my boat...I'd be up all night every time the wind blew worried about it.

Steve~

Just a thought. ever split logs for the fire, thats what dowl rods will do to the piling if put under load. why not stainless band the pile and extension above and below the joint , this should give all the strength you need and is cheap.

Vincentc: I'd give REAL serious consideration to what will hppen if just one of those connections fails. And then reinforce with external lumber and thru bolts....Anything you do now to prevent a failure during a storm will be money well spent.

I see no problem with your drawing design. It is just another way of one of doing one of the ideas I put up. The only concern is that for that design to work, you need to ensure there is good bonding with the epoxy (as people have already mentioned). I never used epoxy/glass on pressure treated pilings, so I have no experience. But, it very may well bond nicely.

I like the drawing...brings me back to 2nd year statics class. Nothing like taking tests hungover---ahh memories.

You would be further ahead to go back to your original idea using rebar. I would use 5/8" X 20" rebar, 6 pieces equally spaced 1.5" in from the outside edge. Drill over sized holes in the top and bottom pole to accommodate the epoxy. The holes must be large enough so the epoxy will ooze out so it won't hydraulic. Make a template that is centered by a centered drilled guide hole in the top of each post. A 1/2" guide hole is large enough. Make one guide template for drilling 1" thick. Make another template 5" thick using the first template as a guide. Drill these holes using a drill press. A 5" thick piece of pole will work fine. This will be used to guide and hold the rebar in place while the epoxy sets. This template will be used to hold the rebar in place and some what parallel when you epoxy the rebar in the upper pole. Place wax paper between the pole and the guide. This will be used only to locate the rebar in the extension and will be done first one at a time. When you make the patterns make sure you mark them top and bottom and place a alignment mark on the side of the fixture and on each pole to radial locate everything. Once you have all the extensions done you can start on the bottom poles. By doing the top poles first you have the added weight to get the poles to butt up. I apply a liberal amount of epoxy at the butt joint only to try and seal it all. Also if the thick pattern fixture won't slide off easy you can alter a rebar rod with a hammer until it does. You can't do this job without the patterns.
That's how I have done it in the past.

BILL

i was a little curious about which method would be best, the rebar or a sleeve so i ran a quick analysis of both. the piling i used was an eight inch diameter. the lower part is five feet long and the upper extension was three feet. the rebar was 5/8 inch diameter 16 inches long, four bars. the sleeve is 1\4 inch steel 16 inches long. the bottom of the five foot section is fixed in place. a 100 pound force is applied to the top of the upper extension. the analysis is linear for load so it can be scaled up to a higher load by dividing the real load by 100 and then multiplying the stress by that factor.
the sleeve is the clear winner for lower stress. the max stress in the sleeved version was 331 psi, for the rebar version it was 811 psi. the stress for the rebar version is concentrated around the perimeters of the rebar.
go with the sleeve if possible.
the pics are in the following order
rebar version
rebar version closeup
sleeved version

You needed an FEA calc to figure that out? The sleeve has more area to distribute the force, so isn't it obvious that it would have less stress?

What about rebar or doweling with vertical strapping on the outside?

I hope we don't need to bust out Mohr's circle---I'm a little rusty LOL

Edit: Also notice the higher stresses on the left rebar due to the "pivot" action. I'd guess that the left rebar is under greater tension which leads to the great stress. The right rebar is under more compressive loading, and it can share it's duty with the piling butts hitting each other---in theory. Can you get a diagram with stress vectors?

I have never seen a perfectly round wood dock pole. Bonding to a odd shaped pole with a sleeve would be tuff. Any extension you use would not be good in any type of major storm. You would be lucky to have any poles left. 8 inch poles are nothing in a hurricane.

Bill

Nice SPAM post.


And you know how I know I'm getting old, this guy quoted below wrote some stuff and ideas that sounds pretty smart. Wonder what happened to him?????? LOL

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Originally Posted by krush

Disclaimer: no expertize was used in making the above post. Everything I know I learned from Wikipedia.org. My comments are worth exactly what you paid for them.

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Oh, he bought a boat, and now we don't hear from him much. He's got a list that never ends.

I sleeved over my pilings with heavy gauge PVC pipe. I think It was 8". It worked well on a 45 Viking. I got the pipe from a friend that was a site contractor. You might call a few company's that lay pipe and see if they have some left overs. Chances are they will. Might get a deal!

Eventually I bought a larger boat and put some large spring pilings in.

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Originally Posted by jim rosenthal

Oh, he bought a boat, and now we don't hear from him much. He's got a list that never ends.

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I totally don't remember ANYTHING about this topic though. Now I know how old farts feel ;)