Steel/Wood Combined Beam
Steel/Wood Combined Beam
(OP)
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
Devon






RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
Otherwise, transformed properties.....
RE: Steel/Wood Combined Beam
See the following thread for a similar discussion: Thread507-85244
RE: Steel/Wood Combined Beam
As long as you have enough bolts over your support to transfer the steel reaction to the wood, you could use the wood bearing area without having to take the full shear of the combined section in the wood.
RE: Steel/Wood Combined Beam
If you need to use a 2x6 flitch, then I would not count on the wood and design the plate to resist the full load.
RE: Steel/Wood Combined Beam
be careful with how you design the bolts. you have use the bolts in the center of the span to transfer the force into the plate from the wood. don't forget the plate is usually not flush top with the bottom of the joist and the steel does not supply adequate bearing area for the joists. you then have to transfer the shear back into the wood at the support. i usually try to transfer the shear back in within d of the support. this allows you to transmit a greater shear into the supprt then the beam's capacity. as a side note i understand the 2002(?) NDS has essentially eliminated the exemption for point loads within d of the support. however it seams to be a logical way to do things that has worked for years
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
You MUST ensure that any flitch beam is provided with adequate bearing, fastening methods, and lateral restraint.
See:
http://www.destefanoassociates.com/tech/flitch.pdf
http://www.toolbase.org/docs/MainNav/WoodFrameConstruction/2947_flitchplate.pdf
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
My mistake. You are correct. You would need 4 of the mini-microlams 1 3/4 x 5 7/8 to equate to the (2) 2 x 12's. It still might be an easier option if you can live with the width.
RE: Steel/Wood Combined Beam
Using allowable (permissible) stress design, the required elastic section modulus, Z, is found by dividing the maximum bending moment by the adjusted allowable bending stress, Fb. As we all should know Z is a function of height squared and width. You can not use an area fuction, but must use Fb * Z equivalancy.
Live load deflection = 5/384 [wL / (EI)] gives us the functional inverse realtionship E * I
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
S=section modulus
must have had a senior moment...
RE: Steel/Wood Combined Beam
How about a W6 steel beam with wood nailers and hangers? Leave a 1/4" space above the top flange to prevent a lump in the floor when the joists shrink.
Check the deflection. I recommend span/480
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
Live load deflection = 5/384*[w(L**4) / (EI)]
RE: Steel/Wood Combined Beam
RE: Steel/Wood Combined Beam
Can you provide additional support elsewhere? i.e. breaking up the spans of the joists framing into this beam with intermediate supports? Then you may be able to reduce the req'd size.
If there happens to be a wall above the beam, in the past, I've cut into the wall 1/2" depth and used a single microlam with simpson tension straps wrapping the beam below to carry the loads.
Chip
RE: Steel/Wood Combined Beam