purlin sizes

[bdog]

You may remember my thread on I-beams. Well I got a good deal on a semi load of 2 3/8" pipe so my plans on constructing my shed have changed. Instead of trying to make it clear span i have set 16 pipes in the ground to support the structure. I have attached a horrible drawing of what my plan is.

Basically the shed will be 36' wide and 39' feet deep. The pitch is in the 36' direction. With the 16 posts I have set in the ground (black on the drawing) the longest span for the purlin will be 13'. I plan on putting the purlins that the R panels will screw (green on my drawing) to on 4' centers so there will be a purlin centered over the pipes then two suspened in between the pipes by the purlins running in the direction of the pitch (yellow on the drawing).

I am guessing 4" purlins for the green ones will be plenty but I am wondering about the yellow ones if they need to be larger.

 

[LD1]

BAD IDEA.

Hire yourself a PE for peice of mind because if I am reading your drawing correctly, you are grossly undersizing what you actually need.

The green purlins in your drawing you are wanting to use 2x4's on are spanning 13' on 4' centers correct???

This would cause your roof to sag and look horrible just under their own weight and the weight of the roof panels.:confused2:

I know you dont have much snow load if any down in texas, but it is still a good Idea for build for a 20PSF live load at a minimum IMO. It maybe just a little overkill, but will account for things like when thewind is blowing across the roof causing downforce (think of the rear wing on a racecar), or wanking on the roof, or a once in a lifetime snow, etc.

So with that in mind, in order to span that 13' on 4' centers would require at least a 2x10. (assuming we are talking white pine lumber. SYP is a litte stronger)

With these loads in mind, your beams (yellow in the drawing) are going to have to carry that point load @ 4' and @ 8'. The ones directally over the poles arent carrying any weight. It is being transfered right into the support. So with the 20psf load plus the weight of the 2x10's and roofing, you are going to be putting a load of ~550lbs on the beams everyplace a 2x10 purlin touches it. So on the outer two beams, that is a point load of 550lbs @ 4' and 550lbs @ 8'. Which would require a 2x12. The middle two beams, because the have a purlin from each side, this gets doubled. So you would need a double 2x12 on the middle ones.

And we havent even accounted for the load on your supports. Depending on how heavy the pipes are, I would be worrying about them buckling.

Again, it would be very wise on your part to consult an engineer in your area. He will be familiar with the building codes and what is acceptable live loads in your area. For a few hundred bucks, it will be money well spent to get it right instead of having the building collapse and have to do it all over again.

 

[jgrreed]

My gut feeling was also 'bad idea', but I didn't have the knowledge to back it.

Get an Engineer involved.

-Jer.

 

[beppington]

I wouldn't want all those pipes/ posts in the interior of the shed being in the way all the time, knowing it's pretty easy & not that expensive to design it without them. You just need roof trusses.

 

[LD1]

I wouldn't want all those pipes/ posts in the interior of the shed being in the way all the time, knowing it's pretty easy & not that expensive to design it without them. You just need roof trusses.

Exacally.

Is there a reason you havent considered a convention post framed building. 36' trusses shouldn't be that expensive. And @ 4' OC, you would only need 10 of them. When you factor what all the 2x12's are going to cost, and the 2x10 purlins, trusses might be cheaper in the long haul. I may be wrong because I haven't priced trusses in awhile but a standard 36' truss from a truss company shouldn't be more than 50-60 bucks.

And just setting posts around the perimiter instead of in the middle, you might just save enough on concrete to offset the cost of the treated posts.

Not to mention, how were you planning on attaching the lumber to the round steel pipes anyway???

I would exhaust all other building options before I went ahead with the method you are describing.

 

[crazyal]

I'm not sure how well this will work for you. If you want to use the pipe you may be better off welding them together to form a truss.

 

[beppington]

Not to mention, how were you planning on attaching the lumber to the round steel pipes anyway???

Would "probably" be OK to use those pipes around the exterior walls of the building, using u-bolts to secure lumber to them ... but this is unusual construction I'm not familiar with, & I'd probably want an engineer to actually tell me it's OK.

 

[bdog]

Sorry for the misunderstanding. There is no wood going to be in this structure. The 4" purlins are metal C purlins. I should have made that clear but I assumed since it was in the welding forum it would be assumed all metal.

I have a 50x50 shop that was engineered and they have 8" purlins on it on 5' centers spanning 25'. That is why I was thinking 4" spanning 12-13' would be ok but I don't know.

The pipes are already in the ground. It took 3 bags of mix each so roughly $150 in concrete. The pipes are heavy wall (.190). Very few sheds or shop buildings are build with wood around here. Everyone uses steel. Probably because the are no trees for miles and miles lol.

I wouldn't want all those pipes/ posts in the interior of the shed being in the way all the time, knowing it's pretty easy & not that expensive to design it without them. You just need roof trusses.

The sole purpose of the shed is to park three trailers in. Eash one will have a 12' "bay" to fit in. The poles will serve as guides so they are parked evenly. I have three other building for other purposes that are all clear span. This one is just to keep three trailers out of the weather.

 

[jgrreed]

I wouldn't want all those pipes/ posts in the interior of the shed being in the way all the time, knowing it's pretty easy & not that expensive to design it without them. You just need roof trusses.

Maybe he's planning an indoor maze??

-Jer.

 

[LD1]

Sorry for the misunderstanding. There is no wood going to be in this structure. The 4" purlins are metal C purlins. I should have made that clear but I assumed since it was in the welding forum it would be assumed all metal.

I have a 50x50 shop that was engineered and they have 8" purlins on it on 5' centers spanning 25'. That is why I was thinking 4" spanning 12-13' would be ok but I don't know.

The pipes are already in the ground. It took 3 bags of mix each so roughly $150 in concrete. The pipes are heavy wall (.190). Very few sheds or shop buildings are build with wood around here. Everyone uses steel. Probably because the are no trees for miles and miles


The sole purpose of the shed is to park three trailers in. Eash one will have a 12' "bay" to fit in. The poles will serve as guides so they are parked evenly. I have three other building for other purposes that are all clear span. This one is just to keep three trailers out of the weather.

What is going to be your material of choice for the "beams". The ones that span the 12' and carry the 13' purlins??

Are you going to use structural steel like c-channel or are you wanting to us a larger CEE type purlin like you are using for the purlins??