Transformed Section of LVL and Wood Joists

[LPPE]

I want to sister an LVL to an existing wood joist. Anyone ever calculate transformed section properties? Do you think using the same method as a flitch beam is acceptable?
Any general thoughts on finding transformed sections?

 

[RRBegin]

Why wouldn't you ratio the moduli like you do in any other transformed section? I thought that this was valid to all materials, all the time.

And just so I can sleep tonight - what is a flitch beam?
(Most of my experience has involved bridge structures, and sometime the terminology from other areas is new to me. I assume that this is a carpentry term?)

Sorry about the responding to a question with a question business, but I was curious on both points (transformed section and flitch beam).

Thanks

 

[RockEngineer]

Since the Young's Modulous of the LVL and the sawn lumber are not that much different (largest ratio 2.0/1.0) it is not as noticable in the dimensions as steel (29.0/1.0). Your LVL just takes a little larger share of the load for the same size members. If you have DF (1.6E) wood and 1.8E LVL you don't even need to do the ratios. Use the dimensions directly to determine your section properties. The E for wood is not as consistent as steel or other homogenious materials. Actual E and published E varies a lot for sawn lumber.

 

[boo1]

RRBegin, A flitched beam refers too a steel plate sandwiched between wood members. Typically in the states the plate is 1/2" thk between two 2x12s.

HBA has a flitch desing guide see:

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

 

[RRBegin]

Holy Smokes! The design "guide" is 96 pages long!

I designed a flitched beam (just learned to word and I'm already throwing it around like I'm the king of flitched beams!) once for a friend of the boss (no, not my wife, the company president). The timber contribution was so insignificant, that I just ignored it. Of course, in that case, I added two steel plates to a timber beam, rather than one steel plate sandwiched between two pieces of lumber. But still, 96 pages?!!

All kidding aside, thanks for the post. I downloaded the guide and will keep it for future use.

Ron

 

[LPPE]

I ignore the wood and design the steel plates to take it all for a flitch beam.
As for sistering an LVL to an existing solid sawn, I was hoping for a conservative shortcut, instead of relative stiffness of each piece.

 

[RockEngineer]

Quick conservative design would be to use the properties of the original sawn lumber (Fb & E) and the crossection of the combined members. In most cases it won't make much difference because you are constrained by the LVL and/or sawn lumber standard dimensions so it is all multiples of the allowable for one. The question usually is do I have to add and LVL or sawn board to one side or both and how close of a nail or bolting pattern do I need. The LVL manufacturer data usually gives you a conservative connection pattern. 5 minute job to size the sistered lumber. Buying a little more lumber is cheaper than engineering time. Most of the engineering time is spent determining whether the structure supporting beefed up beam is adequate.