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trusses, stupid trusses

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I really hate trusses. But they are the necessary evil of most building SEs
at one time or another. There is a lot of gray area in truss, bracing, and
component design, I am glad someone else is talking about this.

This bracing thing has me heated, so I decided to double check what the
Florida Building Code has to say, since wind loading here is so critical and
it makes the truss components that much more important. I also checked the
IBC so the other 97% of the list is not ignored.

FBC 2319.17.2.1  Wood Trusses

This section covers all the responsibilities of truss design. All bracing
design and detailing, along with connections between trusses, are to be on
the truss shop dwgs. It is somewhat unclear whose responsibility it is to
design the bracing to main structure connection.

On our drawings we indicate that the truss dwgs shall show all lateral
bracing design, with reactions, and their connection to the main structure
so that we may review them and design the connection to the main structure.
Basically, we delegate all responsibility to the truss manfucturer for all
truss related design, up to connection to the main structure, where we come
in and finish the job. Doing this through the shop dwg process seems logical
to me. Now, this works great in theory, but I have had mixed success
enforcing this. Sometimes I will go ahead and supply the truss bracing
design, but we have decided that from now on to remain steadfast on the
bracing issue. The truss co. bids the job knowing this is their
responsibility, then they should bid accordingly or not at all.

 IBC 2303.4.1

Requires truss designer to indicate bracing location and the amount of axial
force for the EOR to design the bracing for. So according to them it is the
EOR's resp.

BUT, can building codes govern the scope of a contract and delegate
contractual responsibility like this? Is this enforceable? Say I put a big
note on my roof framing plan clearly stating the truss designer shall
___________ , then when I get their shop dwgs they have not done any of it.
I reject their drawings saying that it is indicated on the dwgs, then they
come back saying they cannot do it, and they don't have to, because of this
TPI document or something from the code. But they have bid on the dwgs to do
those services. Our project architect seems to think that none of these
documents are enforceable if it is on our plans and they bid on those plans.

ANother issue, even more complicated, is shear transfer. What if the depth
of the roof truss at the bearing is over a single truss top chord or bottom
chord, where toppling/truss overturning is an issue. Especially if it is
around 1-2ft, then you have to supply X-bracing or mini-shear walls or
something of this nature to transfer the roof diaph. shear to the walls. Can
this responsibility be delegated to the truss fab. if you supply all the
shear loads on the original CDs that the truss designer bids on? Has anyone
had success doing this?

Any more thoughts on these issues would be greatly appreciated. What are
others doing on this issue?


Andrew D. Kester, EI
Structural Engineer
Bentley Architects & Engineers
665 W. Warren Ave.
Longwood, FL 32750

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