Piling extensions over or under engineered

[boatwright]

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.

 

[spcoolin]

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~

 

[daniel r morrison]

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.

 

[REBrueckner]

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.

 

[krush]

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.

 

[Trojan]

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

 

[oldboat]

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

 

[krush]

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?

 

[Trojan]

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

 

[krush]

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

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.

 

[jim rosenthal]

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

 

[Tinman]

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.

 

[krush]

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

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