Unbraced Bottom Flange Length
Unbraced Bottom Flange Length
(OP)
Dear All,
Is there min beam to beam girder depth ratio that allows you to assume that beam girders bottom flange is braced in case of negative bending?
I have a case that my beam girders are 33in deep and the beams are only 16in.
Thanks
Is there min beam to beam girder depth ratio that allows you to assume that beam girders bottom flange is braced in case of negative bending?
I have a case that my beam girders are 33in deep and the beams are only 16in.
Thanks






RE: Unbraced Bottom Flange Length
You could check the web of the beam bending like a plate (weak axis bending). The force applied at the bottom flange would be the bottom flange buckling force (2% of the bottom flange axial force would be some engineers' estimate). The moment in the web would be this force times the distance between the bottom flange and the bottom of the connection angles at the beam framing in.
DaveAtkins
RE: Unbraced Bottom Flange Length
FWIW: Another idea I have used, is to use a full height stiffener plate as both a single shear connection plate for the beam coming in, and to brace the bottom flange of the girder.
RE: Unbraced Bottom Flange Length
The connection between the intersecting beams and the girder may or may not help in resisting rotation of the supporting girder. One method of achieving this is to extend the connection through to the bottom flange such that any rotation would be effectively resisted by the connection. Now this would also probably require pretensioned bolts in the connection but even with pure bearing connections, the small slip might be allowed and still offer enough stiffness and strength to resist LTB.
RE: Unbraced Bottom Flange Length