Timber beam weight support

Hello I am new to the sight and have some Timber frame questions. First Day give you my senario. I am a log home and timber frame enthusiast. I've done some work with a guy who is a builder and have done some tenon and mortising. I am no way a professional. So I bought a property with a small hay barn on it. It's 22x32. The barn was used as a hunting cabin for 30 yrs. In the Lower level there are  2 8x8 x16 ftBeams running the length of the barn in the center aligned with the roof peak. The upper level floor has some sagging. Near the center. I am wondering if anyone knows if the beams are thick enough to carry the load of 16ft. One has a round steel post at 8ft. The other has none.Any information would be very much appreciated.

Is there a load on the floor from above or is it an open span with the roof load bearing on the foundation walls?

Or is it full of hay or other heavy stuff right now?

I'd guess that it's sagging due to years of hay and if it's not heavily loaded any more, it probably is fine (safety wise).  But hard to tell without more info.  

Just looking at that picture, I'm a bit frightened.  Those are LONG spans. You need to get a qualified engineer to give you expert advice.  

The height of the beam is the critical dimension, not the width.  Generally, the rule of thumb is an inch of height in the beam per foot of span.  Thus, a 15' span requires a 15" beam.  A 2" x 12" foot floor joist is rated to span a 16' distance, even though the board is only 1.5 inches thick.  An 8 x 8 beam can't carry as much load as a smaller 6 x 10 beam if it's vertically oriented, even though the 6 x 10 has less actual mass.  Normally, in post and beam construction, the vertical posts are square (8 x 8), while any beam spanning a gap and carrying a load is rectangular (12 x 8).

An 8 x 8 will sag under it's own weight if you're trying to use it to span anything much wider than 12 feet or so, and that's before you put a load on it.  

Pick up Ted Benson's book "Building the Timber Frame House."  It's got tables and formulas for sawing your beams.  

The other variable is that you need quality lumber.  Fast growing doug fir is not nearly as strong as a slow growing hardwood.  Grading lumber is a science (as is structural engineering).  

Best of luck;
m

It seems well underbuilt for hay storage, depending on the wood used.. using wood strength of 875PSI Fb, for #2 doug fir, my amateur spreadsheet says allowable bending load per square foot foot on the top floor would be about 20lbs.

That's only around one third a bale of hay per foot..

Switch to dense select structural doug fir at 1900Fb and it more than doubles to about 42 pounds per square foot. Still not great.

Switch to something crummier than #2 doug and it could halve the initial number, perhaps..

It should hopefully be quite easy to reinforce with screw-style steel post jacks if desired.. or wood posts. Do take note of whatever they are transferring the force to at the base..


I personally warrant that the above numbers are worth every cent you paid for them. Most of my knowledge of this math comes from the back of Rob Roy's 'Timber Framing For the Rest of Us'.