Bolt Capacity in PVC/Composite Marine Piles

[phamENG]

My googling isn't helping me much here. I have a client (contractor) who is starting to build piers, docks, etc. using composite PVC/fiberglass piles with wood beams, stringers, and decking. Anyone have any good resources for PVC-as-main-member bolt connection shear capacities? I know I'm going to have some interesting action going on as the pile is hollow and the beam is a LOT thicker than the pile wall, so I'll likely have to consider some amount of bending in my bolt. But I'm really curious about shear failure in the PVC/fiberglass material.

The manufacturer's response to my question was "bolt capacities in our product seem to be comparable to other composite pile products on the market." Thanks for that.

 

[dhengr]

PhamENG:
Ask a similar question about materials properties in forum #327, ‘Composite Engineering’ here on E-Tips (not double posting??, slightly diff. topic). Leave this OP here as it seems to be an interesting Structural question. I would be as concerned about wear at the bolt bearing surface on their thin material, as the structure moves around. The bolt will act just like a rasp on that thin material edge. Look around and see what some 10 year old pier details look like, if there are any in the area. Hassle the pipe supplier a little more, ask to talk with one of their materials engineers or production engineers, not the first person who answers the phone. Ask for their complete material testing and data sheets so you can design around their material.

 

[phamENG]

Thanks, dhengr. I'll head over there and see what they have to say. No 10 year old piers around here built with this stuff. These products haven't really made it to our market yet - they seem to be fairly popular in Florida (that's where several of these companies are located) but haven't moved very far north. This contractor wants to introduce them and carve out a unique market share that doesn't exist yet locally.

They did send me some pictures of bolted connections where they notch the hollow pile and bear a beam on it...looks terrible and the mechanics of the connection are a little scary (prying on the pvc face, bolt in bending, etc.). So I don't have a ton of faith in the manufacturer's ability to provide guidance on connections.

 

[dauwerda]

I'm not sure if it would be helpful or not (I do not have a copy), but ASCE's MOP 104, "Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures" is a recent (2019?) publication that does address best practices for hardware solutions and attaching standard items (davit arms, insulators, etc.) to FRP poles. There may be some parallels to be made there.

 

[phamENG]

Well...I was about to post over there when I realized I hadn't exhausted all possible google keywords. I found the two documents, below, which will get me off to a good start. dhengr- one of them brings up shear bushings (though it's directed at preventing crushing of FRP tubes) which I think is a good method of preventing the rasp action you mentioned. The other is a fiberglass design manual with good information on connection design.

Delta Composites Design Manual

Bolted Structural Connections in Fiberglass Materials

 

[phamENG]

dauwerda - thanks. Sounds like that would be a great document. I'll check into it.

 

[HTURKAK]

I will suggest you to look to the following books;


- Composites for Construction Structural Design with FRP Materials by Lawrence C. Bank

- ASCE Manual : Design Guide for FRP Composite Connections by Ayman Mosallam

 

[phamENG]

HTURKAK - great. Thanks. Always nice to have an excuse to expand my library.

 

[dhengr]

PhamENG:
By all means, keep the bolt thread away from the bearing areas, and out of the faying planes/surfaces, contrary to what some of the details in one of the papers show. Everything else I have to offer adds to the cost and complexity, but is pretty important for longevity. The bearing thickness on the PVC/whatever pipe is always too thin for our liking. I’ve seen and thought about those shear bushings before. Epoxy them in place will improve their staying in place and really improves their bearing stress conditions. One of the papers shows our idealized idea of bearing stress [(bolt dia.)(wall thickness)] vs. the much higher bearing stress due to poor diametral fit (a Hertz stress problem).

Almost anything you do to tighten through bolts is going to start crushing and deforming the pipe section. And, you have the problem of the bolt bending through the hollow area in the pipe. Pick a bolt dia., then look for some mech. tubing (not pipe) which has an i.d. only slightly larger than the bolt dia. Cut this mech. tubing 1/16th inch, minus, shorter than the pipe o.d., drill the pipe for this larger tubing o.d., and epoxy it into the pipe. This mech. tubing has a larger bearing area on the pipe, and it controls the bolt bending, maybe rationalizing it away. Extend the mech tubing an inch or so, maybe more, and counter bore the cross beam for it and the bolt, to improve the beam bearing and shear reaction. Cross cut a piece of the pipe 12” long, then rip it into 120° sectors. Epoxy these sectors to the pipes where you will be needing to drill for through bolts. When drilling the pipe for bolts, drill a slightly larger hole than the bolt dia. Then, butter the drilled material edge with epoxy, and finally redrill for the bolt or bushing or mech. tube. This binds/bonds the loose fibers in the drilled edge and makes it more durable and resistant to abrading. You might be better off to drive the pipe, then cut it off, to length/elev., and put the cross beam on top of it with some sort of a std. pipe cap detail. This turns that detail into bearing problem on the entire pipe [(pipe dia.)(pipe thk.)], with some attention to an uplift problem from wave/storm action on the pier sections.