split in timber truss
split in timber truss
(OP)
I have encountered a split in one of the trusses I posted about previously.
http://www.eng-tips.com/viewthread.cfm?qid=322881
I'd like to get some feedback from the forum on the significance of the condition and thoughts about a repair. I have attached a photograph of the split.
On the negative side the split occurs at a split ring connection, is rather wider and deeper that I would expect for a check, and it occurs where the tension load is highest: about 6 Kips total in the (2)3x6 diagonal webs coming up to the connection from the right. I am also concerned that there are no secondary drains on the roof and that the loads could be potentially higher.
On the positive side, the split looks rather old (subjective opinion), only one of the two 3x12 top chords is split, and the bolt passes through the 3x8 compression web which is also not split. According to my preliminary calcs the split rings are good for about 5K each and per the plan there are 6 split rings total at the connection.
I am considering several solutions for a potential repair if I determine that the connection is compromised. The simplest and most direct involves adding a thru-bolt or SDS screws in the tension web above the check. My concern here is that I would be adding some further rotational restraint to the connection.
Thanks all.
http://www.eng-tips.com/viewthread.cfm?qid=322881
I'd like to get some feedback from the forum on the significance of the condition and thoughts about a repair. I have attached a photograph of the split.
On the negative side the split occurs at a split ring connection, is rather wider and deeper that I would expect for a check, and it occurs where the tension load is highest: about 6 Kips total in the (2)3x6 diagonal webs coming up to the connection from the right. I am also concerned that there are no secondary drains on the roof and that the loads could be potentially higher.
On the positive side, the split looks rather old (subjective opinion), only one of the two 3x12 top chords is split, and the bolt passes through the 3x8 compression web which is also not split. According to my preliminary calcs the split rings are good for about 5K each and per the plan there are 6 split rings total at the connection.
I am considering several solutions for a potential repair if I determine that the connection is compromised. The simplest and most direct involves adding a thru-bolt or SDS screws in the tension web above the check. My concern here is that I would be adding some further rotational restraint to the connection.
Thanks all.






RE: split in timber truss
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RE: split in timber truss
RE: split in timber truss
BA
RE: split in timber truss
BA
RE: split in timber truss
To me this means that the single member diagonal connection is twice the capacity of the two member diagonal connection. Kinda of an uneven shear distribution through the web members and uneven forces on the bolts causing splitting in the top chord...?... possibly?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: split in timber truss
...and yes, the compression load at the single web is about 12 kips, more than twice the load at the double tension webs.
You kinda hafta make an educated guess where the split rings are. The plan is a little ambiguous.
RE: split in timber truss
Also the Wood Handbook (another free download) from Http://www.fpl.fs.fed.us/products/publications/sev... (see page 8-24, Cross Bolts)
Both articles seems to be concerned with end splits only, not with your condition of mid-member check/split. But they may be of interest to you.
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: split in timber truss
Seems like another bolt through both tension members near the top of the chord would help a bit, but not as much as split ring connectors.
BA
RE: split in timber truss
RE: split in timber truss
Does anyone see any issues with using a flat probe or long fine wood drill bit to feel up or down between the plies for the split rings? The trusses shouldn't see significant load again until the winter.
Thanks again all.
RE: split in timber truss
There are concrete rebar detectors there that give a visual representation of the rebar and might work here to see if the ring is present without any of the drilling or probing though.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: split in timber truss
Portable Concrete and Rebar Test Equipment
thread507-325906: Portable Concrete and Rebar Test Equipment
Called the Hilti Ferroscan... Haven't used it yet, but might consider it.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: split in timber truss
Thanks again all.
RE: split in timber truss
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: split in timber truss
Back to the missing split ring(s). I would want to take one of the side webs off to examine the installation. Pick one near centre span where the web force is small if all joints are meant to have split rings.
How did you discover the missing split ring? Was there that much of a gap? If so, cross grain shrinkage would be a reason for that as well. You discovered one missing, but did you find others that are there?
RE: split in timber truss
The shrinkage of 3X (2-1/2") members is about 1/8" so in some places the ring between the plies can be seen.