Parallam epoxy creep?

[drscottuk]

I was just wondering, given the recent incident at the Boston tunnel involving creep failure of epoxy in tensile connections (

http://www.ntsb.gov/Publictn/2007/HAR-07-02.htm),

are Parallam's certified or tested against creep failure?

Given that Parallam's are more reliant on the long term strength of their binding epoxy than GLULAM's, this must be a pretty big concern.

 

[csd72]

good question,

The thickness of the epoxy is not as great as that in chemical anchors so I would think the creep properties would not be as exagerated, but....

The report did mention that some epoxy anchors did pass a creep test.

csd

 

[drscottuk]

I reckon the problem might be exacerbated if the beam was called off as a joist trimmer, due to the addition of fatigue from continual loading-unloading.

 

[csd72]

I dont think it is a fatigue problem, just a creep problem. So any load that is not continuous will not cause this type of failure.

csd

 

[RARWOOD]

You would have to contact Trus-Joist for an answer.

 

[msquared48]

Just don't call on Holloween. Like they would admit that their beams are creepy?

Mike McCann
McCann Engineering

 

[RARWOOD]

drscottuk

Have you learned any more on this topic? After thinking about the issue, I had some additional thoughts.

Wood beams experience long term creep generally equal to about 1/2 the dead load. This is true of solid sawn lumber and of glulam. I would expect that this would be true of Parallam also. My guess is that epoxy creep is not a concern because of the creep in the wood.

 

[drscottuk]

RARSWC -
I did a bit of research online and heard that the creep problem occurs with formaldehyde based epoxy adhesives.

I'm not sure the exact adhesive composition for the more common laminate / wood fibre beams on the market