Adding a 2x8 flange to 6x10 wood beam
Adding a 2x8 flange to 6x10 wood beam
(OP)
Hi everybody, this is my first post, but I have been watching for a while.
I am wondering if adding a 2x8 flange on the bottom of a 6x10 beam(actually 3-2x10s)is an acceptable way to increase the capacity and reduce the deflection of the beam.
I am considering shoring the beam to zero deflection, and gluing/screwing the 2x8 to the bottom of the beam. The 2x8 would stop just short of the supports.
This beam supports the joist (2x6) for a nearly flat roof of an older house, beam span is 17', beams spaced 8' apart, approx. dead load is 17psf. Not sure what type of wood the beam is.
Is gluing/screwing a flange to the beam an effective option?
Thanks
Mac
I am wondering if adding a 2x8 flange on the bottom of a 6x10 beam(actually 3-2x10s)is an acceptable way to increase the capacity and reduce the deflection of the beam.
I am considering shoring the beam to zero deflection, and gluing/screwing the 2x8 to the bottom of the beam. The 2x8 would stop just short of the supports.
This beam supports the joist (2x6) for a nearly flat roof of an older house, beam span is 17', beams spaced 8' apart, approx. dead load is 17psf. Not sure what type of wood the beam is.
Is gluing/screwing a flange to the beam an effective option?
Thanks
Mac





RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
I am thinking about using an adhesive with shear strength of around 300psi (wood is about 175psi).
I think it would work in theory (similar to gluelam beams), but am not sure if the actual results will be good due to the method of shoring, applying adhesive, screwing, humidity, temperature, creep of adhesive, etc.
I was relying on the adhesive to take all the shear stress and the screws to clamp the pieces together while the adhesive cures.
Mac
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
The reason that I did not want to add steel or wood to the sides of the beam was that the joist were not sitting on top of the beam, but possibly joined into the sides of the beam. This would have allowed only a 4" tall board on each side of the beam, even with steel this would not help much due to low inertia of the additional boards.
I have since found that the joist are notched with 4" sitting on top of the beam and 1.5" overlaping the side of the beam.
I will add a 2x10 on each side which will increase the depth of the beam by 1.5", the same as adding the flange.
Based on the inertia of the two cross sections, a 2x8 flange is about equal to 2-2x10 side pieces (assuming you could make the connection between the pieces adequately).
Thanks again,
Mac
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
http://www.edgest.com/wood.html
RE: Adding a 2x8 flange to 6x10 wood beam
This is analogous to a steel cover plate on a wide flange where the cover plate is used, say, in the middle third of the span.
Now if the existing beam cannot take the end shear, then yes, your statement is correct...but many times wood beams only need bending updgrades and not shear upgrades.
RE: Adding a 2x8 flange to 6x10 wood beam
Yes, but you also need to design the fastening of the two side members securely to the original member so that the three act as one. My point was that this connection can require a lot of fasteners or fasteners and glue. If the side members are not fastened properly, they may just be adding to the dead load.
RE: Adding a 2x8 flange to 6x10 wood beam
My point is that the extension of the new material to the supports is an independent issue with regard to the attachment to the existing members. Flexural capacity doesn't "know" whether the end is extended or not.
RE: Adding a 2x8 flange to 6x10 wood beam
The way I think of the connection requirements of the new members to the old is to imagine that the old beam is hanging their with a deflected shape. Now place the new members so that their center is matched up with the center of the old beam (along the side of the old beam). Assuming the new members are straight, the difference at the ends of the beam is equal to the deflection of the old beam.
The force that it would require to move the end of the new member up to the existing beam (so they both have same deflected shape) is what the connection must support.
This force would be provided by the wall if the new members were supported on the wall. I think that the force would be the total reaction force at the wall divided by 5 for each new member (because there are 5 equal size members carrying the loads, 3 old 2x10, and 2 new 2x10s)
Mac
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
I just had exactly your problem but it was a ceiling of 4 x2
timber which needed strengthening to be a strong floor equivalent to 7 x 2. we tried everthing without achieving anything then we simply affixed 3 x 1/4 steel flat to each side of every timber Plenty of big strong screws at close spacing The result was a massive rigid floor and it was done very easy and quick. If you enjoy the theoretic work
then examine the respective E values and link them to deflection formulae. This is the solution to your problem. Cheers
RE: Adding a 2x8 flange to 6x10 wood beam
RE: Adding a 2x8 flange to 6x10 wood beam
I't looks great in my opinion, approximately .5" deflection over the 17' span with 90% of the dead loads applied.
The new members are supported at the wall.
There is no sheetrock installed (so it didn't crack), the joist don't seem to have moved any due to the shoring and the roof decking will be replaced anyway.
Thanks again for all the comments.
Mac