Gusseting flat trusses w/ OSB

Question

Gusseting flat trusses w/ OSB

Patman (Structural)

(OP)

6 Feb 03 01:43

I'am actually a Entry Level BLDG Inspector and I've been presented w/ a Contractor who has completely gusseted some flat roof trusses which have been damaged in a fire resulting in a negative camber of at least 4", he has jacked up the trusses and applied 7/16' OSB across the entire span of the flat truss, My concern is: has the excessive rigidity imposed on the required deflection enough that the load transfer has gone from Vertical to a Lateral Shear imposing on the exterior walls?

Watermelon (Structural) · Answer 1 · 2003-02-06 13:33:01

From your description, it is hard for me to understand clearly what is going on. What do you mean by gusseting?

If it was my problem, I'd insist on the involvement of a professional engineer. Get a report and an approval/disapproval.

Patman (Structural) · Answer 2 · 2003-02-07 02:14:18

I should describe it as completely sandwhiching the flat truss with OSB from top to bottom and end to end, OSB was applied to one side of the truss he then removed the uprights and webs and applied OSB to the other side leaving only the top and bottom chords between the 2 sheets of OSB, you can no longer see the truss itself only OSB across the entire span.

JAE (Structural) · Answer 3 · 2003-02-11 13:14:37

Patman - if you are the "building official" per the governing code, you probably have the authority to order a load test on the trusses.

Review your applicable code to understand how this works.  In the UBC or IBC, Chapter 17 governs in-situ load tests.  (see 1713 in the IBC 2000)

So basically, you can request that the contractor hire a structural engineer to validate the new "design" through calculations and his certification ...  OR ... you should request that the contractor perform a load test to verify that he indeed meets the load carrying capability that is required.

Anything else would be putting the public at risk.

rlflower (Structural) · Answer 4 · 2003-02-11 20:18:44

A couple of thoughts:
1.) Although I have not had the opportunity to investigate such a case, the American Plywood Association provides a clear step by step guideline for the calculations for plywood gusseted box beams. Worth looking into.

2.) Perhaps we are overlooking a consideration that may be more important: The deflection in the middle of the trusses might prevent proper drainage of the rainwater on the roof.

SteveBausch (Computer) · Answer 5 · 2003-07-26 09:55:00

What 'required deflection'?

Keep in mind that firemen have their own opinions regarding what they like, or don't like in construction techniques.

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Gusseting flat trusses w/ OSB