flitch beam

[BLUEPUPIL]

A timber beam sandwiched between two cold formed U-sections, all bolted together. Can I assume, that the U-sections are restrained against lateral torsional buckling?

 

[structSU10]

I would say it depends on where the bolts are placed to restrain that kind of deformation. If you have a line of bolts down the mid height only, it probably might be tougher to justify than a double line of bolts near the top and bottom flange.

 

[Ron247]

Depends on how wide the timber beam is for one. Also, how are the U-sections turned in relation to the timber beam. I would think you could still have localized buckling of the cold-formed flanges but maybe not global buckling of the entire section.

 

[CANPRO]

Lateral torsional buckling is a global failure of the member, so you should be checking this failure state with the built-up section (cold-form/timber/cold-form), not the individual sections.

 

[KootK]

CFM is tricky this way because of the multitude of possible buckling modes. one line of fasteners down the middle will prevent global LTB but, then, is the compressed half of the section likely to flop over in some distortional mode that only an eastern block mathematician could possibly understand? It would be a row of fasteners high and a row of fasteners low for me, at minimum.

 

[BLUEPUPIL]

It’s a small flitch beam from a porch. 1..The timber beam is rectangular; height to width ratio 2:1; 6x3(75x150mm) 2..U-sections are facing each other on both sides of the timber beam, with their closed lateral sides; 3..Bolts are placed at the flanges as near as possible. 4..I can tie upper flanges (even the lower ones if needed) with a thin steel plate, 5 inches wide and 4 bolts, every feet or so.