Truss joint fixity
Truss joint fixity
(OP)
We are currently load rating a truss where the connections are welded using gusset plates. When we input the truss into STAAD we assumed fully fixed connections at the ends. The resultant moments in the members were relatively small, but since the members bend in the weak axis, the load rating is very low. Is there any information out there that discusses partial fixity of such connections?





RE: Truss joint fixity
The AISC code allowables assume "standard" structural assumptions will be used in a design. Pinned ended trusses is a standard assumption.
I had an old boss who believed that there should be 2 allowable stresses. One for hand design and one for computer design. When a computer design is used, every member becomes a biaxial beam column leading to a more conservative design. This exceeds the assumptions of the codes.
RE: Truss joint fixity
There are is an entire section on the design of trusses in Design of Welded Structures, by Blodgett (Lincoln Arc Welding Foundation publishes this) which includes consider for moment loads due to eccentric load of the chord sections. Perhaps you can break down your truss into several joints and check it with hand calc.
If the chords are long, perhaps local buckling is the limiting factor.
My 2-cents,
Batman2
RE: Truss joint fixity
RE: Truss joint fixity
RE: Truss joint fixity
"We are currently load rating a truss where the connections are welded using gusset plates.When we input the truss into STAAD we assumed fully fixed connections at the ends. The resultant moments in the members were relatively small..."
The only way you can develope moments in the members is to use beam elements.