Wood Truss Fix...
Wood Truss Fix...
(OP)
Hi all,
I have a 24' long Spruce Pine Fir Fink Truss (all 2x4) that have a broken top and bottom chord along the left end of truss before the web splice plates. The peak is 4' high and the web diagonals connect the bottom chord at 8' from the end (spacing is 8-8-8). The top chord connection for the webs is about 6'6" along the top chord from the end (corresponding to about 6 feet in the x direction from the bottom chord end). I want to design a fix since replacement would be way to costly.. My loads are 50# snow and 12# DL.. The spacing is 2 feet on center. Currently I plan on splicing along the top chord, second web leg, and bottom chord on good wood using 3/4" CDX sheathing and a plethora of 10d?? nails/screws. Any idea on a pattern, size, length of the splices/gussets on the members?
I have a 24' long Spruce Pine Fir Fink Truss (all 2x4) that have a broken top and bottom chord along the left end of truss before the web splice plates. The peak is 4' high and the web diagonals connect the bottom chord at 8' from the end (spacing is 8-8-8). The top chord connection for the webs is about 6'6" along the top chord from the end (corresponding to about 6 feet in the x direction from the bottom chord end). I want to design a fix since replacement would be way to costly.. My loads are 50# snow and 12# DL.. The spacing is 2 feet on center. Currently I plan on splicing along the top chord, second web leg, and bottom chord on good wood using 3/4" CDX sheathing and a plethora of 10d?? nails/screws. Any idea on a pattern, size, length of the splices/gussets on the members?






RE: Wood Truss Fix...
See if you can find a grade mark on the members that need to be spliced. If they are MSR (machine stress rated) then they might be alot stronger than the material that you are going to splice with. Either obtain the same MSR material from a truss supplier or make sure that you use something equivalent in strength.
RE: Wood Truss Fix...
Sounds like it could be bad materials or knot locations. If so, be cautious with the fix.
Mike McCann
MMC Engineering
RE: Wood Truss Fix...
1/2" plywood should be fine but nothing wrong with 3/4"
I would use 8d 2-1/2" max length nails if you have the room you can use 12d or 16d and get double shear, but I have seen this poorly done in the field many times. They drive all the nails from one side pushing the plywood on the opposite face out away from the truss.
RE: Wood Truss Fix...
I like both the screws and the glue foor the same reason: they help to hold the repair tightly together.
I used to work for the Wood Truss Council of America. Alhough the industry doesn't advertise it much, both truss plates and nails have a tendancy to work their way out over time. This is particularly the case where there are large fluctuations in the ambient humidity. Scary, I know...
Plate manufucturers usually provide values for their plates assuming that the plates will not be snug tight against the wood. Ostensibly, this is to account for truss fabrication tolerances though.
RE: Wood Truss Fix...
RE: Wood Truss Fix...
http
RE: Wood Truss Fix...
RE: Wood Truss Fix...
As to the actual fix - and not knowing all the details - probably sister rafters on each side about 4' long would more then solve the problem. IF the break is at a panel point where the webs come in - then 1/2'' or 3/4'' plywood is the rule.
This is a SMALL truss - so the forces are really quite low.
Try fixing a 70' or 80 truss - now you have some problems...
Good luck
RE: Wood Truss Fix...
RE: Wood Truss Fix...
A low value for 10D common nails in single shear on OSB is about 95# ea more or less right?