Wood/Steel Composite Beam 1

[DYork]

I have to design a beam that must span what a 2-2x12 beam could handle. How do I calculate what a 2-2x6 beam w/ a 1/4" steel plate sandwhiched in the middle can support. Thanks for the help in advance.

Devon

 

[boo1]

A timber beam which has been strengthened by the insertion of a metal plate (flitch plate). Flitch beams are designed mainly using equivalent section fundamentals.

Assume that in the first instance the load is taken by the timbers, the calculated proportion then being transferred from the timbers to the plate by the bolts over the main span, and then transferred back from the plate to the timbers at the bearings

Flitch beams have limited strength when analyzed about the minor axis. You MUST ensure that any flitch beam is provided with adequate lateral restraint.

See:

http://www.destefanoassociates.com/tech/flitch.pdf

http://www.toolbase.org/docs/MainNav/WoodFrameConstruction/2947_flitchplate.pdf

http://www.strucalc.com

Timber Construction Manual, AITC, 3rd ed
Design of Wood Structures, Donald E. Breyer, 3rd ed

 

[corrosionman]

I recently strengthened a floor made from 4" x 2" timbers. We bolted 4" x 1/4 " steel flat bars between two joists and it totally solve the problem. My suggestion is to totally ignore the strength contribution of timber and simply calculate based on strength and elasticity of steel You will be surprised at outcome..Timber is very flexible and steel very rigid. Cheers David Whitlock.

 

[boo1]

A floor made from 4x2's sound like a crate.

A flitched beam 2-2x12 w 1/2 steel spacer fits in a stadard 4" wall cavity. Agree the steel takes the loading, but connections are critical.

 

[corrosionman]

The 4" x 2" joists were originally a ceiling but then we needed to make them sufficiently strong for a floor. We were limited to a beam depth of 4". We double up with 4x2 but still imposibly flexible.. Since rigidity is proportional to depth cubed we then calculated that we needed a 4" x 11" to have same strength as a 7x2 nornal floor beam. However a 6 mm thick steel flat was 100% satisfactory whem Bolted to side of 4x2 joist. When we fionally saw the light it was so simple .
cheers
David Whitlock.

 

[boo1]

David, why use wood at all, "C" channels back to back or 18 gauge corrugated steel decking would be easier to use.

Live load deflection = 5/384*[w(L**4) / (EI)]
gives us the functional inverse realtionship E * I and length to the fourth power