OSB i-Beam size requirements?

[GloriainX]

Hi everyone,

I'm helping a friend build a structure in his shed which is 16' x 16'. He also wants a second story on it but he is doing it on a budget so we were thinking 7" x 2" joists at 12" centres for the ceiling/floor joists. I was just wondering what size of a beam we would need running down the middle to support it all? i was thinking of 12" osb i-beam with 3 laminates. Would two of these, side by side in the middle, stretching along a 16' span, be enough to support that second floor without the need for a pillar in the middle, or would a pillar be required? There may be upwards of ten people up there and we want to make sure everything is as safe as possible. I was going to put a pillar in the middle to be sure but if  two 3 ply 12" osb i-beams would be enough on their own then freeing up that space would be great. I could figure it out if it was a steel or aluminum ibeam but im stumped when it comes to osb.

Thanks!

Edited October 4, 2020 by GloriainX
typo

[Mr Punter]

For that size of 2 storey building you should get it properly designed and specified.  They should also be able to make it as cost effective as possible.

[PeterW]

47x220 C24 at 400mm centres will just do that span but will have some deflection in it. Reduce to 300mm centres and you may get away with 47x195 C24 but again, it will flex. 
 

If you went to an I-joist then a JJI195C at 300mm centres would work with hangers but centre deflection would be 10mm so not sure if that would be acceptable. 
 

 

 

[GloriainX]

7 minutes ago, PeterW said:

47x220 C24 at 400mm centres will just do that span but will have some deflection in it. Reduce to 300mm centres and you may get away with 47x195 C24 but again, it will flex. 
 

If you went to an I-joist then a JJI195C at 300mm centres would work with hangers but centre deflection would be 10mm so not sure if that would be acceptable. 
 

 

 

Thanks Peter for all that information, much appreciate it! So if we use 47x220's (its C16 min unfortunately, no C24 avail) at 300mm centers over a 15'3" (not 16', sorry) span that will be more than enough would you say without the need for any supporting beams, for a live load of 40psf? It would not cost much more than the 175mm (there are no 195's available here or I-joists, we were gonna make our own for the beams..) so considering how much extra the supporting beams woulda cost it would probably work out cheaper using the 220's without a  big beam encroaching down from the already pretty low ceiling (7ft).

If that kind of structure will take 40psf live load then we are singin. (can't find a span calculator that will use 9", just 8" or 10" so if anyone can weigh in to confirm the 220's (9") will achieve 40psf live load at that span please feel free to chime in.

[PeterW]

Question - imperial units, are you not in the UK..?

 

C16 would mean that at 400mm centres you would need a 47x220 for that span, assuming a live load of 1.5kN/m2. That’s only 32 psf, so reducing the spacing to 300mm then you arguably gain a small amount of strength which would allow you to use a 47x195. 
 

If it was me - and the timber was easily obtainable - I would sister and bolt every 4th pair of joists to make a 94x195 at 300 centres, that would be a very rigid beam.  

[GloriainX]

On 05/10/2020 at 08:16, PeterW said:

Question - imperial units, are you not in the UK..?

 

C16 would mean that at 400mm centres you would need a 47x220 for that span, assuming a live load of 1.5kN/m2. That’s only 32 psf, so reducing the spacing to 300mm then you arguably gain a small amount of strength which would allow you to use a 47x195. 
 

If it was me - and the timber was easily obtainable - I would sister and bolt every 4th pair of joists to make a 94x195 at 300 centres, that would be a very rigid beam.  

Thanks Peter. I'm in Ireland and grew up using imperial so nowadays i used a combination of both, eh imperietric? So they ended up going with I believe 220mm x 44mm at 300mm centres so that should about bring us up to 40psf im guessing?

Do you mean by sister and bolt, to double up every fourth joist while maintaining 300mm centres? Would that be perhaps overkill if they are using 220's at 300 centres? 

Cheers for your input.

Edited October 12, 2020 by GloriainX

[PeterW]

Hi - yes I meant if 195 was being used I would make every 4th joist a pair of 47 x 195 bolted together. 
 

I’m assuming they have or are putting plenty of noggins between the joists ..?? It will stop any desire to twist. 

[GloriainX]

13 hours ago, PeterW said:

Hi - yes I meant if 195 was being used I would make every 4th joist a pair of 47 x 195 bolted together. 
 

I’m assuming they have or are putting plenty of noggins between the joists ..?? It will stop any desire to twist. 

On the 16' span I told them to put 3 lines of bridging's, I'm guessing that will be enough? Some years of my life were spend in roofing so although I've got a general feel for what will be sufficient, I'm still no engineer, so its nice to have confirmation.