We are tossing around an experimental idea of a living roof on top of three foot culvert ripped to be an arc. Our thought was to support them on a fifteen foot span, bolt them together to form concentric arcs, and put soil on top for a living roof. We were having difficulty coming up with a good way to determine the load allowed on these arcs. Any thoughts or input is greatly appreciated.
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Determining loads on 3 ft culvert cut in half to form an arc
- Thread starter HipNeck
- Start date
msquared48
Structural
Off hand, I can see a bunch of problems with that, but a cross section would give better information here. Could you please post one?
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
dicksewerrat
Civil/Environmental
Are you going to have 5 half tubes next to each other? Would be less wasteful to have 6 of them. Or some other arrangement? Will they be touching at the low point? Are you going to bolt each one down to your 'roof' truss?
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
- Thread starter
- #4
We are out in the field and away from the office for a while. The building would be 60' wide and 30' deep. The ripped culverts would run the 30' depth, have support on both ends and the middle and be bolted together to keep them from spreading. I hope that gives you a better visual.
dicksewerrat
Civil/Environmental
Since these pipes are placed under roads with only the soil around them to help withstand the loads , I don't see much in the way of problems with this arrangement. Remember to do a very good job of waterproofing the roof. Don't put more than a foot of soil above the high point of the culverts and mostly use the saturated weight of the soil for your loading design. How will you maintain this area? Will you need a fence/wall to protect people up there?
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
At the moment I haven't a cluae as to what is proposed. I have no idea how you "rip" a culvert, or what you could do to a culvert to form it into an arc.
All I can say is that designing a roof over a 30 foot span (or is it a 6o foot span?) carrying a soil load is not a trivial exercise.
Any chance of a clear detailed description of what is proposed, preferably with some sketches?
Doug Jenkins
Interactive Design Services
All I can say is that designing a roof over a 30 foot span (or is it a 6o foot span?) carrying a soil load is not a trivial exercise.
Any chance of a clear detailed description of what is proposed, preferably with some sketches?
Doug Jenkins
Interactive Design Services
A better visual (not more verbiage) would be a few sketches showing what you are thinking of trying to do. But, it sounds kinda fishy to me. It will probably be quite difficult to keep the bolted system from leaking, water and soil. While these 3' dia. corrugated culverts work fine when they are fully buried and supported by well compacted soil, they do not work as a beam member the way I am imagining you are trying to use them. Remember, most roof spanning systems have a continuous top and bottom flange element which makes the bending member work; t&b chords for trusses, t&b flange plates for WF’s or girders, etc. If your culvert sections are placed with the concave down, your top flange will be a corrugated arc of some width which will act like an accordion and easily compress and buckle. The two bottom flanges are thin, cut edges, likely with flame cutting notches, these will have very high tension stresses and will just stretch out, again like an accordion. The orientation with the concave up is no better as a bending member. Try this experiment; cut two 1' wide arcs x 2' long sections out of a piece of culvert, with the corrugations parallel to the 1' arc direction and perpendicular to the 2' length; compression test one of the pieces, compression load in the 2' length direction, and it will just crumple under fairly low load, and tension test the other and it will stretch inordinately under fairly load loading, just straightening out the corrugations. These sections are just not meant to be loaded that way. Exactly the way they would be expected to act, if half the culvert were used as a beam member.
At least I've got some idea how you form a culvert into an arc now! When I read culvert I think concrete box, not corrugated steel pipe.
I quite agree with your comments on trying to use half a corrugated steel pipe in longitudinal bending.
Doug Jenkins
Interactive Design Services
dicksewerrat
Civil/Environmental
I think what they are trying to do is place the half culverts on a flat roof, already designed for the culvert + soil + plant load to keep heating/cooling costs down. Or to grow veggies for lunch.
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
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