Wood flitch beam design

[structuresdesign13]

Hello
i am designing one flitch beam. i have one 4x10 sawn lumber and trying to put one channel on each side.
does any body have any reference calculation for flitch beam.

 

[MiketheEngineer]

Do a search on these forums -- it comes up rather repeatedly and there are some very good ideas and suggestions to be found.

IMHO - I would just use the channels for moment, deflection and maybe shear calcs. Wood could also carry shear loads - assuming good connections. The wood beam with good anchors will mostly just add torsional stability. It makes the calcs much simpler and more conservative. If you go through all the calcs - You will find the wood does not help all that much.

 

[SlideRuleEra]

http://www.toolbase.org/PDF/DesignGuides/flitchplate.pdf

http://www.structuremag.org/Archives/2007-6/D-From Exp Flitch Plates DeStefano-pac-5-10-07.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[nativo]

Do you need channels or can you get away with steel plates on each side? I've done flitch beams with wood "sandwiching" steel plates and vice-versa. Have not performed calcs for channel-wood beam combo so perhaps not much help then

 

[woodman88]

I agree with Mike's opinion. I would ignore the wood unless the steel is less than 5% over stress, than I would check out the steel/wood capability.

Garth Dreger PE
AZ Phoenix area

 

[ToadJones]

I'll pile on too...ignore the wood entirely for your first round of checks.

 

[BAretired]

Agree with Mike, Toad et al.

BA

 

[structuresguy]

I would also like to agree with Mike. However, many times the wood beam is the only component carrying the shear, as the steel plates/channels are not connected to the supporting columns. So all the shear has to transfer through the wood section, which now has holes in it for the bolts required to hold it all together. I have found in many cases that the limiting factor of the beam strength is the shear capacity of the wood at the support, particularly so if this is a transfer beam supporting columns above. You will have to decide based on how the beam is conencted to the support, and whether any load can be directly transfered from the steel to the support.

 

[BAretired]

If the plate or channel continues to the end of the wood beam, the load is transferred from steel to wood by bolts, then to the column by compression in the wood beam, not shear. Usually there are extra bolts over the column.

BA

 

[structuresguy]

I would agree with that, where your flitch beam extends over the support. Make sure you have adequate number of bolts over the support to transfer all the shear from the steel to the wood. If your support is small, say 4x4 post, and your beam shallow, you may not be able to achieve the required load transfer.

Here is an article describing the approach to design flitch plate beam, where both the wood and steel capacities are used in the calculation.

http://www.structuremag.org/article.aspx?articleID=399

Does anyone have a rule of thumb on how much extra capacity they can achieve using flitch plates, versus the wood section alone? I usually figure 1.5x is safe, and may be able to go up to 2x. Beyond 2x, I figure that it won't work, and look to increase the wood beam size.

That said, I typically only use flitch beams in renovation work, where we are dealing with existing conditions that somehow limit the use of deeper sections. In reno work, I have encountered the condition where I need to face mount a flitch beam to existing construction, which goes back to my point of using only the wood to transfer shear. In new construction, I rarely use them, preferring to go with an engineered wood section instead.