Simpson Mending Plate for custom made wood truss

[structurebeton]

A client did some "custom" floor trusses with simpson "MP-36" and "MP-24" mending plates. The plates very specifically say that they are NOT to be used for trusses.

I have to verify the trusses. Any one has had any experience in using these plates as truss connectors?

The client did install nails through the plates "to make sure it stay in place"...

Any thoughts?

 

[UcfSE]

If the manufacturer says they are not structural and you approve using them as structural, you assume all the responsibility if they fail. Plus you're going against the manufacturer who has specific knowledge of the product. That's a very bad idea imo.

 

[ctcray]

perhaps you can design the proper connection to use overtop of the mending plates.

 

[MiketheEngineer]

Start over .... these will never perform as you might hope

 

[boo1]

can you say "Liability"
CTcray is on the right path....

 

[structurebeton]

I talked to a Simpson Engineer, and accordingly, mentioned that the plate has no "hold" value for structural purposes, however, since nails have been installed through the 20ga plate, an analysis of the plate could be done as a "shear" side plate connection, after reducing the plate capacity due to the holes generated by the "dents"...

 

[COEngineeer]

Simpson catalog doesnt give any value for shear to any direction so theoratically you cant proof it unless you do lab test and divide the number by 4.

Never, but never question engineer's judgement

 

[ARJ1]

It clearly says "Connectors are not load rated." So basically you have to pretend like they are not there and have the truss repaired accordingly. Don't wait for someone to tell you what you want to hear. It isn't worth the risk.

 

[ctcray]

I don't think you have to do lab tests and divide by 4. You can evaluate the existing connection per NDS nail values for 20gage lapped shear connections. Of course, then you'll find that they don't come close to working in a floor truss application.

When you say "floor truss" is it 1.5" wide or 3.5" wide? Or perhaps a better question is what side of the lumber are the plates on, the wide face or the narrow face?

Also, what's the span, spacing, and depth of the truss?

 

[ctcray]

they don't look like this, do they?

=)

"Thar easier to put up this way."

 

[structurebeton]

Trusses are 18" deep, spaced at 16" o.c., for spans varying from 20' up to 25' max. for a residential loading. They are assembled in a "flat" manner, i.e. they are made of 2x4's, but the truss is 3.5" wide, including the webs. He installed plates on each side of the truss on each joint, and drove 1 nail to each web member thru each plate. So far they look pretty good.

The bottom chord is double, with a splice on each layer (staggered) He also, installed a mending plate at the splice, which is located about 1/3 of the span.

I like the idea of the shear plate calculation

 

[RARWOOD]

I think boo1 pretty welled summed it up. Based on experience my opinion would be that the liability you would be taking on if you try to show that the mend plates work, would be too high.

When someone so clearly violates the code, it would make me wonder what other items also violate the code.

 

[COEngineeer]

ctcray, I disagree. The 20 gage has spikes holes so you cant say it is a plate unless you take the account of that also. Plus I dont even know how they create these holes. I have a feeling if you put 10d nails trough there it can easily tear trough the plate. I do agree with adding connection over it, maybe use simpson straps. I dont understand why one would make custom trusses when you can easily order it from the manuf.

Never, but never question engineer's judgement

 

[structurebeton]

Apparently he saved 50% on the cost by doing them himself. He ordered 1 truss, and copied the fabrication. But now, he will have to pay what he saved on engineering to make the analysis and design the repair.

 

[boo1]

Check the grade of material in the site built truss. Often the bottom cord of floor trusses are #1 grade SYP

 

[structuralaggie]

18" floor trusses spanning 25' will have huge forces. There is no way those little mp plates will be big enough even if you assumed they had some structural value. Did he stack several together or something?

 

[HouseBoy]

"Apparently he saved 50% on the cost by doing them himself."

Aparently he does not realize that the truss that are built in a controlled environment with dimensional and procedural controls have much higher allowable capacity due to the controlled methods and related QC proceedures. These CAN NOT be duplcated in the field.
Beyond that, I wonder how much of the materials used in the truss manufacture he accurately "copied". It would appear that he did not correctly copy the truss plates.
What about lumber grades? Do you suppose he did any better with that.
Full scale load testing would be a valid method of evaluation but it is unlikely to be successful at developing adequate strength. I would also be concerned about long term performance.
The fact that the Simpson plates are specifically stamped as NOT for truss application seems like something that will be hard to get around.