Concrete cantilever (“how’s it hangin’)
epoxybreath
| Posted in Construction Techniques on
I have to pour a small 4 inch slab to support a vertical wheelchair lift adjacent to a porch. Part of the slab will extend over a basement window well. Can I support the slab over that area with a steel angle. Should the angle be attached to the front of the house? (I tend to think not) Does the angle have to be supported from below where it hangs out over the window well.
( about 24 inches by 12 inches out of a 5 by 5 slab). Also should th plywood used for the bottom of this “form” be removed after the concrete sets? Thanks for the responses
Replies
Thanks Pete,
Got to go over the window well because there are no other viable options. Lift has to be adjacent to porch. he only other real option is to make the porch larger, but then we might as well go back to building a ramp 32' long with 2 landings etc. Filling in the window well gets you into the whole ventilation thing in the bathroom that it opens into etc. Appreciate the feedback.
I'd use 3/8" rebar at 6" centers both ways, placed 1" from the bottom of the concrete over the whole slab.
In addition, over the area of the cantilever, and extending at least 6" beyond it, I'd put 3/8" size rebar at 6" centers both ways but 1" down from the top of the concrete, to cope with shear forces.
Edited 3/28/2002 3:36:04 AM ET by IanG
Thanks much Ian, Sounds like a plan.
Hi Ian,
Do you have either real or rule-of-thumb numbers for the load that the #3 bar can support in this configuration? Just curious. And under what conditions would you up it to #4 bar?
We have a 10' x 8' cantilever of 8" concrete, and the engineer speced 17 #6 bar 1" from the top. Cantilevers fascinate me.
Thanks. Jim
Sounds like rule of thumb over engineering. I have a crazy idea, why not hire an engineer?...that's not a mistake, it's rustic
Sorry I haven't answered before -- Man, these posts disappear fast!!
I couldn't find the US equivalent of UK rebar (Mesh) so 3/8" is an over-design but with so small a slab the additional cost is peanuts.
The top mesh for shear is over-kill, but again, peanuts in cost and I'm bearing in mind it is DIY.
IMHO, hiring an engineer for the slab as described WOULD be overkill.
What did he allow for shear at the bearing point? -- just curious.
You mean what were his calculations and design criteria? I dunno. Sorry. I just followed the directions he gave.