Restraing Compression Flange LTB
Restraing Compression Flange LTB
(OP)
Dear All
I got a composite floor slab(steel and concrete slab) where they are connected toghter using shear studs and metal decking, the problem is i have got a cantilever beam nearly 5 meters ,allowable stress considering lateral torsional buckling is exceeding allowable , i have a though to reduce LTB by providing stiffener at mid span perpendicular to web and welded to both bottom and top flanges(Both sides of the web) , i believe by this i am preventing the buckling shape of unrestrained compression flange ,anyone has got input in this?!
thanks in advance
I got a composite floor slab(steel and concrete slab) where they are connected toghter using shear studs and metal decking, the problem is i have got a cantilever beam nearly 5 meters ,allowable stress considering lateral torsional buckling is exceeding allowable , i have a though to reduce LTB by providing stiffener at mid span perpendicular to web and welded to both bottom and top flanges(Both sides of the web) , i believe by this i am preventing the buckling shape of unrestrained compression flange ,anyone has got input in this?!
thanks in advance






RE: Restraing Compression Flange LTB
The stiffeners are fine, but you still have to provide some kind of kicker to resist the twisting, stiffeners alone won't do it.
What kind of backspan do you have?
RE: Restraing Compression Flange LTB
RE: Restraing Compression Flange LTB
RE: Restraing Compression Flange LTB
In his case the tension flange is braced along the length
RE: Restraing Compression Flange LTB
A sketch would help.
BA
RE: Restraing Compression Flange LTB
I believe that the composite slab will provide adequate twist restraint.
See attached for AS4100 (Aust) recommendations.
RE: Restraing Compression Flange LTB
The test on what is adequate is that the displacement of the bottom flange, Δb under the required brace force does not exceed the assumed initial misalignment, Δ0.
The required brace force is 2% or 2.5% of the compression in the flange to be braced, depending on the code used unless a more detailed analysis is carried out.
BA
RE: Restraing Compression Flange LTB
More clarification to my question is that i have back span of composite beam(10 M) the back span and cantilever are supported on main beam.
I agree with ash060 that deflection will govern due to rotation/deflection of main beam
For calculating thickness of stiffner , i would check it under bending moment(2.5%Force in flange/2*H web)
Thanks all for your input.