Wood Truss repair

[surjaan]

Home owner has removed few vertical and diagonal members in an existing wood truss. Of course the wood truss is sagging and they want to repair it. I am recommending to jack up the truss and bring it to level point, add those missing members.
Do you thing adding 3/8" plywood sheathing on each side of the truss ( make it like a box) will help to get the original stabilty, ot it is not necessary. Any other suggestions.
Truss is 30 ft long and 80" deep with 2x4 members.I am planning to use 1/4" steel gussets plates with bolts for attaching the vertical and diagonals.

 

[msquared48]

Add the original diagonals and verticals. With the bolts, you might need to go to 2X6 material. Check it thoroughly.

Using the 3/8" plywood could make the truss stiffer than the ones to either side, causing an unsightly read at the roof.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

I have had good results using plywood gussets with glue and nails or all-purpose screws. Analyze your forces. Recut the mising members to fit and then design the gusset and fasteners.

I often specify all-purpose screws becasue nailing may cause vibrations that can wreck/crack the ceiling drywall.

 

[BAretired]

I agree with MiketheEngineer. I have done the same thing upon occasion.

Bolts are not a good idea on 2x4 chord members because they tend to split the chords. 1/4" gusset plates are overkill. Light gauge (20 ga. or 16 ga.) steel plates with pre-drilled holes and screws or nails would be another option, but I still prefer Mike's solution using plywood gussets, glue and nails or screws.

BA

 

[jenDL]

My repair of choice is a plywood gusset each side secured with nails or Simpson SDS screws. The SDS require no predrilling and have a decent load value.

If you have enough of a stub of web member left you can just sandwich the stubs with a 2x each side.

But, like Mike the Engineer said, check your forces.

 

[Ron]

I have also used plywood gussets, nailed or screwed. msquared48 brought up a good point about compatibility between adjacent trusses. You might want to go with repairing more than just the modified ones...go beyond on either side.

 

[dik]

Mike's got the right idea... Jack things up so there's a slight 'pre-load' and then use Bulldog Premium caulked adhesive (or some other suitable waterproof adhesive) with nails to hold the 1/2" Doug Fir plywood gussets in place. The adhesive will provide far greater holding capacity than the fasteners.

Dik

 

[woodman88]

I prefer to use the nails to hold the plywood (or OSB) gussets on with. The nails transfer the force directly across the thickness of the gusset not just to the side. The adhesive attaches to the side of the plywood (or OSB) and if the joint is broken, usually the 2x member adhesive with fibers of the gusset remains, as the side of the gusset is the weak link.
Specify the required gusset and member sizes, the number of nails required for each member. I use 1/2” thick gussets with 2” long nails to avoid the ends of the nail ends from protruding into the other gusset with an adhesive to be used, where the forces are high, and state to remove the jacks so the nails will take all the force. When the adhesive dries it will help the connection and control splitting of the wood members from the nails. Where the forces are low just the nails can be used.

Garth Dreger PE
AZ Phoenix area

 

[BAretired]

woodman88,

With 1/2" gusset plates, the overall thickness is 2.5". You could use 3" nails clinched in order to obtain double shear. Nail heads should alternate each side of the connection.

BA

 

[surjaan]

I was thinking to use light gage (16-18) ga steel plates with 3/8" bolts.
Thank you all for your help.

 

[msquared48]

Clarification here...

I have no problem with the plywood gussets - a good idea and have done so too.

My concern was in sheathing the whole truss which would change the stiffness realative to the adjacent trusses.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

surjaan...16 gage plates with 3/8" bolts is an incompatibility of sorts...no need for 3/8" bolts and more chance of splitting wood. Stick with numerous nails or No. 8 to No. 10 screws, even if using steel plates.

Mike..I agree..just use plywood at the joints

 

[Stillerz]

Good input here...
I totally agree that you wont want to sheath the whole truss in this case. Pointless. The bolts and thick plates seem overkill when you consider how the original truss connections are made on light residential trusses.
I have sheathed large portions of girder trusses that showed up on jobs damaged. Of course, relative stiffness was of little concern since they were girders. It's a great fix, but I wouldn't use it in this case either.