Chemical timber fastening epoxy??? 1

[flyingdebris]

I am an Australian forum user and I was after some info on the existence of a timber epoxy used to fasten threaded rods into timber beams. Does it exist? Are there technical resources available with design pullout values etc? I know tasbeam used to publish design data years ago using a hilti and ramset product. They don't do that anymore. I haven't seen anything used since. Maybe there is a reason for that?????

 

[flyingdebris]

anyone?

 

[shobroco]

google Rotafix, a UK company. Sika also makes suitable products. We have done this since the 1970s in Canada with Sika products.

 

[focuseng]

check out the following:

http://www.strongtie.com/products/connectors/CPS-PBV_APG.asp#

I have not investigated where they are getting the values from but the fine print says "testing divided by a reduction factor of 4." Probably worth it to look up the Code Evaluation report. Essentially they are assigning a withdrawal value of 4490 lbs for a 10" embedment with epoxy.

______________
MAP

 

[msquared48]

Boy, despite the cited testing results, I have real reservations regrding that connector, and the use of epoxy in that regard.

The AITC has long recommended against the use of any tension values for nails in end grain, which, in effect, the rod becomes. Just feels funny to me and I would never use it without further justification beyond any report from Simpson and the State of Florida...

Mike McCann
MMC Engineering

 

[shobroco]

There is a big difference between the friction holding a nail and an adhesive that develops a greater strength than the fibre strength of the wood. The wood around an epoxied rod will fail, not the adhesive bond, so the strength of the connection depends upon the length and area (diameter) of attachment, and the strength if the wood in shear parallel to the grain, not on withdrawal like a nail.

 

[msquared48]

OK, but in both cases, you are still pulling with the grain, not across it, so any allowable tension should be much less for the same fastener. With the 4K or so capacities being generated in the Simpson table, I just do not sense that.

I guess I will have to check my old tables the pullout for the same diameter and depth lag screw in side grain when I get back into the office. I have to prove this to myself, one way or the other.

Mike McCann
MMC Engineering

 

[chicopee]

Not pointed by the above responders is the effects of shear forces perpendicular to the end grain of the wood.

 

[TXStructural]

As the wood dries, it will shrink away from the adhesive and fastener. A nail or screw hasn't removed wood, only compressed it, but drilling makes a hole that will grow over time. Especially if you are subject to tangential shrinkage - wood shrinks across the grain more than along it. I would look to install a mechanical fastener at some depth, rather than relying on adhesive, unless you have a way to key the (creep-free) adhesive into the wood, creating a mechanical bond.

 

[shobroco]

Any hole parallel to the grain will most often get smaller, not larger if the wood dries, depending upon its location with respect to growth rings. Also, the wood in question is existing in its existing service conditions and is unlikely to change much. Trust me, 35 years of experience with this method shows up most of the situations that you will encounter.