Ibeam canopy - structural advice needed!

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Hi everyone,I have a friend who wants me to build a frame out of ibeam for a canopy in his backyard. Hes going to be building a wooden roof on top but wants the lolly columns and headers out of ibeam. The dimensions are 21' long x 15' wide and 8' high.  He wants four posts installed, one at each end.  So basically like a giant rectangle out of ibeam with 4 posts lagged into the concrete ground. Seems pretty straight forward in my mind. How would one calculate how much weight this span could hold? One with snow load, etc...What size beam would be enough? or not enough. Is a 21' span to much to go with no lolly in between? I was thinking 4" x 13lbs ibeam would be sufficient but I am no steel erector.Anyone with any advice would be great!
Reply:I would guess this is in New York so you have alot of snow load, plus some weight for the dead load of the roof system. You would have to figure what the combined weight is for the square footage of roof and base that on what ever deflection value you are trying to achieve when fully loaded. Where I work we span 25'-30' between column spacings without any problems with a W8x18, I don't think I would try this with a 4" deep beam. I think the snow load would deflect it too much, especially it being a open wall structure. You aren't getting any diaphragm from the wall system to support the rest of the structure. Is this going to be a gable or a single slope? What roof slope is it going to be? That will play into the equation as well, the greater the roof slope the better for strength. The flatter the roof the heavier the primary steel is.
Reply:You need to calculate the per foot loading of each beam.  Then download a program like beamboy to calculate the stress and deflection of the beam.  Usual deflection limits for a static loaded beam are around L/240, although I always use L/360.In this case I'd figure snow load + roof deck at 30# / sq ft.  Thats high but I like a safety factor.  Total load on this roof is now 9450# (21*15*30).  Each 21' beam is going to hold half of that which gives a beam loading of 225# per foot.  ((9450 / 2) / 21)Beamboy tells me that a 4" 13# beam supported on each end with this load would deflect 2.9" in the center.Using the guidelines above that would tell me this beam is not heavy enough.To get less than 1" of deflection you would need at least an 8" x 13" beamI AM NOT A PROFESSIONAL ENGINEER.  IF YOU USE ANY OF THE ADVICE I'VE GIVEN ABOVE YOUR STRUCTURE WILL UNDOUBTEDLY IMMEDIATELY COLLAPSE KILLING HUNDREDS OF PEOPLE INCLUDING NUNS AND CHILDREN CAUSING YOU TO BE SUED FOR BILLIONS OF DOLLARS.
Reply:Do not forget about wind load on a heavily loaded structure , are you in and area that gets sustained strong winds during the winter?  Always best to lay the liability off on and engineer if it is in the budget, if not , visit some existing similar structures.   Will the wooden part be flat or Gable with a good pitch?"Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:Originally Posted by kolotDo not forget about wind load on a heavily loaded structure , are you in and area that gets sustained strong winds during the winter?  Always best to lay the liability off on and engineer if it is in the budget, if not , visit some existing similar structures.   Will the wooden part be flat or Gable with a good pitch?
Reply:usen2 is right on the calcs, there are many apps for this now, but I think some residential roofs are designed at 40PSF which would make the 4" beam choice even worse. Ditto what Kalot said, I see many of those new bent pipe garages upside down after a wind, I don't know what the residential spec is for uplift load, but anchor down whatever it is, even if it's only 20PSF thats over 6000 lbs of uplift, Call the building inspector or an engineer and find out what a roofload in your area is suppoaed to be designed to, snow load may go 60PSF or higher. He may not have the uplift#.  4" might work with 2 more uprights or 1 more cross beam (perhaps as a ridge)Last edited by blackbart; 04-28-2013 at 12:56 PM.
Reply:Thanks for the responses. According to the town, there needs to be permits from an engineer in order to use steel. The customer opted not to do the job. Appricate all advice.
Reply:For future reference.The kind of calculations you need should be trivial for a P.E.   Whenever you deal with structures (I think there even was a post about someone building an overhead crane - to lift engines out etc.) spending a few dollars on a P.E. is well worth it.Where I live, there in an exemption from building permits for "pole barns".  Even so, I wouldn't put one up without an engineer's blessing (from pre-made plans or sign off on current design).BTW, all those "metal shed/building" companies should be able to design it for you (and probably ship all the materials to your site for less than you can get them elsewhere.... pre-painted to boot.  The should have a P.E. on staff or at least on call.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:Originally Posted by con_fuse9The kind of calculations you need should be trivial for a P.E.   Whenever you deal with structures (I think there even was a post about someone building an overhead crane - to lift engines out etc.) spending a few dollars on a P.E. is well worth it.
Reply:Like several other people have said, you need professional help. It won't cost much and you'll be able to sleep at night, even when a major storm is blowing thru or a mini micro burst hits the neighborhood.Your local building code probably agrees. Your liabilty exposure is pretty severe here, it's not a task for a couple welders standing around having a beer or three to figgure up. Welders weld, in structural applications engineers engineer. That's legal, and removes all liability from the guy with the stinger (as long as he welds to the specs). Small amount of money for a lifetime of "peace of mind".A bunch of guesses (educated, semi educated or not) on the internet just isn't a good thing here. Cheap, stamped drawings really are worth their weight in gold. Don't want to be involved when things come apart in a "100 year storm" on somebody's kids. No good for anybody, and when the lawsuits fly, they fly shotgun style and take large amounts of money. It's a case of "if you have to ask". Not to mention the moral aspect involved.JT