huangyhg

end grain epoxy gluing of threaded rod into timber pile
i have a consultant who has specified this unusual method of fixing a steel joist (of a pedestrian bridge) to each timber pile support. the concerns that i have are that the timber will shrink over its life and that the 40 mm diameter hole will no longer secure the epoxy and its threaded rod to the pile.
i propose a secure mechanical fixing as an alternative. does anyone have any comments?
epoxy dowel connections are sometimes used in manufactured timber beams, particularly glulam. but like you, i would be loathe to depend on a connection like that into the end grain of a pile.
simpson has products (pbvpc and cps4) that anchor a threaded rod into the end grain of a post. you might be able to get some approximate load values and embedment depths from their product.
the approach you describe is more common in europe than in the us. there are also threaded inserts that go in to the timber and accept threaded rod. do a google search for more information.
i not sure what you exact situation is, however in most case shrinkage cause the section to get smaller, so i don't think the hole will get larger.
one other thought if you are dealing with solid sawn timbers they are probably at a much higher moisture content then glulams. your bigger concern may be checking in the area of the hole.
you can get some information on the use of end-grain screws for heavy timber construction from:
ipenz transactions, vol. 24, no. 1/ce, 1997
dry timber does not shrink, it swells with the increase in moisture. the endgrain should be coated with the epoxy as well as the interior of the hole to stop moisture intrusion. the insert will squeeze out excess epoxy when placed and the connection will outlast the timber pile.
thank you all for your helpful and valuable comments. in particular there seems to have been a good deal of research undertaken in new zealand about 9 or 10 years ago into the strength of epoxy glued connections into heavy glulam beams designed for the sydney olympics. particular reference may be made to the paper by gaunt "joints in glulam using groups of epoxy grouted steel bars", ipenz transaction 1999.
the steel bars achieved large pull out and bending strength. but, my concern in still that the timber pile may have been moist / wet when the threaded rod was epoxied in place. i am unsure if epoxy will bond adequately with damp / moist timber?
regards
i would be concerned about that too. i think that a steel or aluminum sleeve placed over the pilecap and thru bolted to the pile with welded metal tabs or a kerf plate bolted to the beam would be much more appropriate.
mike mccann
mmc engineering

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