The structure is a 36x64 acorn shaped barn, with a peak almost 30ft in the air! My project is adding a 24ft loft/second floor but my beam requirement is a strange one... I want to run girders across the width of the barn, a 24ft clear span at a 9ft ceiling, and run joists lengthwise. The girders would be bearing on the MAIN stringers of the barn, which are spaced 8ft apart. That would make three girders, joists just under 8ft long, 2x10 and 16" centers (even though for that short I could go 2x8 or 24" center). Problem is I can't find the I do on what size beams I need. And running clearspan trusses widthwise is out of he question monetarily, the cost would two fold
I'm looking at lvl, but would engineer my own16 or 18 inch laminate beam if I have to
So hopefully somebody a thing or two aboit this...
Again, three 24 ft clearspan girders, 8 ft apart, supporting 2x10 joists spaced 16", at least standard load- l/360 40psf live 12psf dead blah blah blah.
Stiffer may be better because I plan to put a 6ft slate pool table right in the middle :p
Thanks in advance
I don't fully understand the description so I'll answer the last paragraph's summary. No loads other than the floor load. 24' clear span x 8' tributary width=192 sf x 52 psf=9984lbs load
Span is 24' or 288"... at L/360 you are at about 13/16" deflection under full load. A pool table is going to be interesting if anyone moves.
http://www.timbertoolbox.com/Calcs/beamcalc.htm
LVL Fb=2800
E=2.0
Fv=285
The lightest 2 ply girder I passed with was a 2 ply 20" deep with about 11/16" deflection under uniform load... the pool table in midspan probably gets closer to a point load at midspan, it wouldn't hurt to bump the 10,000 lb design load upwards.
Depth creates stiffness much faster than width.
The LVL supplier can do the engineering for the girders as part of servicing the sale.
I may not be understanding your response. 2 ply 20" lvl sounds right based on other examples ive read about around this forum and others, but im having an issue putting this in comparison to real life buildings ive experienced.
you think a point load of roughly 600lbs midspan will be too much? the same table previously sat in the middle of the kitchen in my hundred year old farmhouse (there when I bought the place). dimensional 2x8 joists clearspanned about 17ft. the floor was sagged by roughly an inch but it never bounced.
also, does that take into account the table being centered between two girders? that's going to split the floor loading considerably.
in any case, for code sake I threw out 52psf, but that floor is not structural and itll never see a 10000lb load even spread over the full 24ft length.
im sorry if I sound a little funny, I understand the concept of engineering a floor but trying to clearspan such a distance in the manner im trying to do it is unconventional
I didn't take the table into account at all. Given a weight of 600 lbs... divide by 40=15 sf. If it is over 15 square feet then it weighs less than design load. The dancing crowd around it might be worth thinking about.
I've run into that lack of bounciness in an overloaded, overspanned floor before, a sagged out joist has no ring, it is fully damped.
The design load is specified in the building code but ultimately the load is up to you. If this is ag you can pile hay mighty heavy, I've seen more beams broken in barns than anywhere. Off topic, I was in two barns yesterday, the 200 year old barn is in need of some TLC, the 60 year old barn will collapse in the next winter or two if we don't drop it first. How we are built and then stressed through life plays a big part in aging. Anyway, when in doubt or if the inspector requires a stamp.. I'll size it during preliminary design and then ask for them to check it and send a stamped letter with the beam. I'm not happy with that beam deflection to be honest. That is where I would be asking for their guidance.
Now reread your original specs, at least X load and calling for stiff. Read your last specs. It is so easy to make things work on paper with little tweaks of the numbers, reality grades the paper. Ultimate bending strength and shear strength in the beam material is greater than allowable design strength. There is a factor of safety on those allowable design values, just as with any material where life safety is involved. The deflection numbers are "true", this is really a performance issue rather than a life safety issue. It is an unadjusted number intended to predict actual deflection. Deflection was the limiting factor in the 20" deep beam, not strength. This explains some of why you often see smaller material in non engineered work. Deflection is ignored and they are operating somewhere under ultimate material strength, well until a beam breaks. They don't know where they are in the safety margin.