OSB or Plywood for Truss Gussets?

[LD1]

The "two other engineered" pieces are actually where most of the strength lies. As with any beam or I beam, the two biggest things that effect strength is 1. Extreme most fibers. In this case the dimensional lumber on top an bottom. And 2. How far apart they are from each other. The web offers very little in strength. You could double the web thickness and get very little increase in strength. But double the flanges and the difference is huge.

Cause under load, the bottom is trying to tear apart and the top is trying to compress. The webbing does little.

 

[mikehaugen]

Maybe I'm missing something, but I don't think shear strength is the important factor in truss gussets. Not sure what they would call it for plywood, but tensile strength or "tear" strength would be the determining factor I would think.

 

[BethelHntr]

The "two other engineered" pieces are actually where most of the strength lies. As with any beam or I beam, the two biggest things that effect strength is 1. Extreme most fibers. In this case the dimensional lumber on top an bottom. And 2. How far apart they are from each other. The web offers very little in strength. You could double the web thickness and get very little increase in strength. But double the flanges and the difference is huge.

Cause under load, the bottom is trying to tear apart and the top is trying to compress. The webbing does little.

Yup and those webs can be utilized for hvac and plumbing traveling perpendicular.

 

[spitter]

biggest thing is the glue and nails. Dont use avantec osb repells lots of glue and most manufactures dont warenty their product if glued to it. In humid conditions i have seen osb swell to twice there size .Use 3/4 inch plywood coate both sides with yellow exterior wood glue clamp smack teco nails in it .After glue dries you will never get it apart.:drink:

 

[gdicks]

Everything I've read indicates that the Sheer strength of OSB is superior for truss gussets:

Plywood vs. OSB Truss Repairs | SBC Magazine

Seems to make a compelling argument for both the sheer strength and dowel bearing strength which I assume is a proxy for the nail / staple bearing strength.

These tables show there are generally only slight differences between the design capacities for structural plywood and OSB for a given span rating. An exception, however, occurs with shear through-the-thickness capacities, where OSB provides considerably higher values. Based on this difference, if a truss repair specifies only OSB, plywood should not be substituted without written permission from the registered design professional who prepared the truss design repair drawing.

Another design capacity to consider is dowel bearing strength, which determines the allowable lateral resistance provided by the nails, screws or bolts that attach the wood structural panel to the truss. Table 11.3.2B of the National Design Specification® for Wood Construction (NDS®) lists the dowel bearing strengths for various wood structural panels (see Table 3). All grades of OSB, Structural 1 and Marine plywood are assigned the same dowel bearing strength, whereas all “other grades” of plywood have a lower dowel bearing strength. Since the majority of plywood used for construction applications in the U.S. is NOT Structural 1 or Marine, lower lateral resistance values (i.e., more fasteners) typically must be used for a repair using plywood than for one using OSB.

I havnt seen any data on the impacts of moisture wicking of OSB resulting in loss of strength over time. is anyone aware of any source of this data or is this generally anecdotal?

 

[EddieWalker]

I think you guys are all missing the point of what the gusset does. It is there to keep the boards in the truss lined up and in position. In theory, the truss should work without a gusset or plate by fitting all the boards together that make up the truss nice and tight. The gusset is just there to keep them from moving around.

As mentioned by a few, the glue that holds them in place is what matters. Glue is stronger then the wood. The nails or screws are just there to hold the wood in place until the glue dries and makes it permanent. Half inch plywood is the norm and it's what I've always used, but in just about every other building use, I prefer OSB over plywood.

Eddie

 

[Capricious]

Everything I've read indicates that the Sheer strength of OSB is superior for truss gussets:

Plywood vs. OSB Truss Repairs | SBC Magazine




Compares OSB to exposure-rated sheathing ply, which i already have posted that I would not use.

Also mentions marine ply, which I have already posted that I WOULD use.

If I am building my own structure, there is a good posibility that the trusses will be up and exposed to the weather for some time before i could get a roof on it. I would not want OSB (Oriented Sh__ Board) up there soaking in the rain.

Now, if i were hiring a framing crew to throw this building up in a matter of a few days, then MAYBE I might consider letting them use their OSB.

Also, my gussets would be through-bolted. Yea, a bit slower than shooting nails through everything, but that is how one builds something to last.

That is how I would do it- others may do as they please.

 

[Capricious]

"..The gusset is just there to keep them from moving around..."



Gussets are an important structural element of a truss. The I-35 bridge collapsed due to failure of a gusset.

 

[EddieWalker]

When a gusset fails, it allows the components of the truss to move. They do not hold anything up and their only structural value is to keep those boards in place. The lumber carries all the load. There is no load or weight bearing consideration on the gussets. This is true for bridges and roofs.

Eddie

 

[Capricious]

"...There is no load or weight bearing consideration on the gussets..."



Gussets provide the connections between those members.

No gusset, no connection. No connection, no truss.

They carry a load.