He attached the lower portion of the tarp to two concrete masonry units (a/k/a cinder blocks) at each corner. A neighbor tied a tarp on his roof and down the front of his house just before a big storm expected to generate gusts upwards of 50 to 60 mph. If it was near me, I'd want to know which for sure. might fail, blow away and hit somebody in the next big storm. How many gusts of wind will load it similarly and beyond over the course of a year or several? How many times can you do that before it fails? I'll keep looking and if I find something I'll let you know. I can do it for wood using fiber bending strength and modulus of elasticity of any species of wood, but I never went so far as to learn it for light steel framing. I don't know enough engineering at this point to make substitutions of smaller dimensions on the tubing for thicker tubes (and I guess that's why they make us hire the engineers). That's the only substitution I can make for the C channel. All I can say for sure is that if you use a minimum 18 gauge, 5 1/2" x 1 5/8" rectangular tube spaced 16" on center for your rafters, they will safely hold a 40psf load distributed above it. I'm not an engineer so I can't really get much farther on this one. The latter will work better for me than C channel.Ģ圆 is the right timber, but I'm hoping to use RHS for a smaller profile. While I can get load specs for timber and C channel, I can't get anything for Rectangular Hollow Section. None that I know of have engineers on staff. Over here, lumber and steel suppliers are reluctant to give that sort of advice. Many will even FAX their stamped engineering report right to you to show the local building inspector. Many large metal suppliers and lumber yards have engineers on staff that can spec. Here, using anything else would require an engineer's stamp. Translating that, it's an 18 gauge true C channel (with lips that wrap around) at least 5 1/2" deep, 1 5/8" wide, with 1/2" lip. In the states, for the same design load conditions as described above, typical residential code requirements would call for a minimum of a 550S162-43 spaced 16" on center. You would need to check the design load criteria where you are for wind loads and snow loads (if it snows where you are).įor structural steel framing, a true "c" channel is commonly used. Under those design load conditions, typical building codes for residential construction in the states would allow 2圆 rafters (any commonly available lumber species, grade #1 or better) 16" on center. live load for a total design load of 40 lbs. "dead" load (what it is assumed to weigh) plus 30 lbs. Typical roof design loads would be 10 lbs. I'm assuming you have the span listed correctly. You can figure out the loading and use that to size the steel (with the help of a steel supplier).įor rafters, the span is the horizontal distance between the support points (not the slope distance). I don't have my handbook(s) handy for those light sections, but my guess (worth what you paid for it, this is not professional advise, objects in mirror may be bigger than they appear, flammable objects may be inflammable, etc, etc, etc) is 3x4 C-channel on 2 ft centers is in the ballpark of what you need. Have the steel yard give you a handbook with the section properties, etc on steel and also have them check their dat charts for what you want. It rusts.Ĭ-channel or c-purlins should be able to do what you want. Steel isn't bothered by termites, but it is bothered by water. Its failure mode(s) can be sudden and catastrophic, mainly because just a little twist and the angle leg is no longer perpendicular to the load and when that happens. I would say do NOT use angle iron for structural purposes. You could squeak by with 2圆 #2 19.2" O-C for a flat roof rafter and still meet code by me. A flat roof rafter to span 12 ft could be 2x8 #2 24" O-C and meet code by me. It depends a lot on what the loading is, what the geometry is, and what the building codes may require.ģ.5 m = ~ 12 ft, so general lumber span tables would say you need 2x12 #2 16" O-C or so for floor joists to span 12 feet.
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