Wood Truss Repair-Wood Gusset Plate Design
Wood Truss Repair-Wood Gusset Plate Design
(OP)
I have a truss problem and was hoping that someone could point me in the right direction to come up with a solution.
I am helping some friends get there house ready to sell and went in the attic and saw that someone had chopped a couple of trusses apart to install a set of pull down stairs. It is a simple gable roof using fink trusses. They cut out the bottom cord and 1 web member from each truss. I am a civil engineer but my specialty was geotechnical engineering and I haven't resolved truss load conditions in 35 years so I am woefully unqualified to come up with a fix.
I have tried to find the truss manufacturer to no avial. The house is 22 y/o, the builder is long gone, and the truss stamps are illegible as to who built them even if they are still in existence. I have contacted many people but keep getting told that they can't do anything to help.
I have a good friend who is a structural engineer and he designed the fix for the bottom cord using very conservative wood properties, 1/2" diameter bolts, etc. So no problem there.
The web member that was removed is creating the most difficulty. It seems that the solution would be to put back the missing web member and then tie the joints together with a gusset plate. I was thinking a plywood gusset plate for simplicity and wouldn't really care how big it was. However, I can't seem to find a direction to go to get someone to help.
Does anyone here have any ideas on how to proceed?
Thanks for any help you can provide.
I am helping some friends get there house ready to sell and went in the attic and saw that someone had chopped a couple of trusses apart to install a set of pull down stairs. It is a simple gable roof using fink trusses. They cut out the bottom cord and 1 web member from each truss. I am a civil engineer but my specialty was geotechnical engineering and I haven't resolved truss load conditions in 35 years so I am woefully unqualified to come up with a fix.
I have tried to find the truss manufacturer to no avial. The house is 22 y/o, the builder is long gone, and the truss stamps are illegible as to who built them even if they are still in existence. I have contacted many people but keep getting told that they can't do anything to help.
I have a good friend who is a structural engineer and he designed the fix for the bottom cord using very conservative wood properties, 1/2" diameter bolts, etc. So no problem there.
The web member that was removed is creating the most difficulty. It seems that the solution would be to put back the missing web member and then tie the joints together with a gusset plate. I was thinking a plywood gusset plate for simplicity and wouldn't really care how big it was. However, I can't seem to find a direction to go to get someone to help.
Does anyone here have any ideas on how to proceed?
Thanks for any help you can provide.






RE: Wood Truss Repair-Wood Gusset Plate Design
BA
RE: Wood Truss Repair-Wood Gusset Plate Design
If so, take down the stair, restore the trusses to their original design and reinstall the stair in the proper orientation.
Have structural engineer do the repair design as BAretired noted.
RE: Wood Truss Repair-Wood Gusset Plate Design
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: Wood Truss Repair-Wood Gusset Plate Design
BA
RE: Wood Truss Repair-Wood Gusset Plate Design
I generally prefer to use screws in existing trusses. Nailing is often difficult - lack of room, etc. And the vibrations it generates can start cracking drywall - esp the bottom chord.
Testing has shown that adding glue doesn't really help much - seems that the glue "cracks" or fails before the fasteners fail - or at least that was what I was told. That said - I still like a good dose of Liquid Nails. That stuff is amazing.
RE: Wood Truss Repair-Wood Gusset Plate Design
How have you justified the existing press plates on the adjacent trusses? From calcs I have seen, they design these right down to the wire.
Recently, I had a 4' deep truss spanning 17' (depth needed for architectural purposes). The owner wanted to put a new mechanical unit on this roof. The truss members worked easily for the new loads, but the truss calcs indicated that the press plates were designed to .99 unity.
RE: Wood Truss Repair-Wood Gusset Plate Design
You do have to check everything!! Sometimes - you get lucky - many times not so much
RE: Wood Truss Repair-Wood Gusset Plate Design
Thanks so much for the input. I spent many hours this morning tracking down a structural engineer who was well versed in residential wood framing AND was interested in doing the work. A very difficult combination! Anyhow, I did find someone. He discussed several possible solutions but until he came and viewed the situation and went back an made calculations he couldn't come up with a definite solution.
The one interesting thing I have had to do was to explain to the homeowners why they have a problem. This condition has existed for 10 years, and last year we had a series of snow storms that left about 48-inches of snow on the ground and roofs. No problem at all with the roof. They look at me with a very odd expression as I try to tell them it really is a problem.
Not really knowing how truss capacities are determined, I assume that they are modeled as simply supported structures. If this is so that doesn't take into account all of the redundancies built into homes by default, such as interior walls that, while not designed as such, still act as load bearing walls, drywall, roof sheathing, etc. Am I correct in these assumptions? I know that modeling this is difficult at best but the reality is that all of these components contribute in some fashion.
Anyhow, I will post an update on the solution once it is known, which looks like it will be in a couple weeks.
And again, thank you for all of the input. It really pushed me to searching hard to find the right person to do the work.
RE: Wood Truss Repair-Wood Gusset Plate Design
However, a Fink truss with one diagonal missing is an unstable structure and needs to be addressed.
BA
RE: Wood Truss Repair-Wood Gusset Plate Design
The nice thing as you mentioned is for the last decade they didn't have any problems. Its cause the system is stronger than the individual components. Sheathing, factor of safety in the adjacent trusses, and other redundancies (partitions are a huge redundancy, as someone mentioned above) all kick in to keep the roof up in view of the damaged component.
When replacing missing webs, tell the contractor to ensure a tight fit between the new member and the existing members. A max. gap of 1/8" is recommended between new and existing members.
Plywood is the method of choice for this reinforcement. Preferably both sides. If using a gusset on one side, i recommend driving the nails through the lumber face and clinching them on the plywood face.
If you find a truss engineer, they should be able to detail this for you easily.
RE: Wood Truss Repair-Wood Gusset Plate Design
When clinching of nails at the plywood or OSB face I use a decease value (usually 66% for the clinched side) for the connection. This is due to the damage I have seen done to the plywood and OSB when the nails are clinched.
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.