Cantilevered Concrete Wheel Chair Ramp Landing

[CBSE]

See attached. I haven't looked at a ramp in this manner before, but the architect is bound and determined to create a cantilevered landing for some stairs. It isn't shown in the detail, but the ramp would turn 180deg and continue up the opposite direction.

Anyone see any issues with this? Other than the potential for a nice crack above the CMU wall? The loads all calc out when I run the numbers.

 

[KootK]

Looks good to me. Beats having to do it without the wall, that's for sure. Obviously, some manner of positive attachment between the wall and slab would be a good idea.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

Cool. Yes, the wall rebar will extend into the slab with a standard 90deg hook. It was just a basic DD detail I threw together for the architect.

 

[TehMightyEngineer]

Might be a little hard to form up but certainly not impossible. We've done precast ramps setup like this before without issues, though we didn't cantilever the whole landing if I remember correctly. At 8 inches thick I doubt you'll have deflection issues but I'd check the cantilever just to be sure. #5 @ 4" seems reasonable and I doubt you'll get much cracking with that, especially if your rebar is a little over-designed.

I actually wouldn't worry about positive connection between the wall and ramp; assuming both are laterally supported elsewhere it might even be beneficial if thrust from the ramp and any thermal growth/shrinkage don't fully transfer to the wall.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[CBSE]

TehMightyEngineer: I hadn't thought about the thermal differences between the concrete and CMU...although small, it could have some effects. The Wall is braced by return CMU walls at each end and in the middle so the thrust is easily resolved.

 

[BAretired]

Your top bars should penetrate further into the slab. You should assume the cantilever has full live load and the slab has only dead load. You should not be reliant on tension in the concrete to balance the cantilever.

BA

 

[Teguci]

Great place to collect trash, house a family of beavers or a dry place for a vagrant. Structurally though, as BA noted, the top bars should extend about 8 ft on the ramp side.

 

[CBSE]

Thanksgiving the info. I spoke with the architect about the backspan area and convinced him they should just backfill the entire thing. Changed the embed length to 10ft.

 

[ACtrafficengr]

Can you calculate deflections enough to guarantee you'll meet ADA requirements at the joints? That's 0.25 inch max vertical rise, or 0.5 inch if chamfered at 1:2. If it's exterior and needs to be graded to drain, can you control the cross slope so it doesn't exceed 2%? I'd hate to see some martinet from DOJ make you tear it out and rebuild it because it just barely exceeds the maximums.

Since you're using inches instead of mm, I'm assuming this is in the US and subject to ADA.

 

[CBSE]

The calculated deflections are at .16 inches. I adjusted my landing length to 6'-0" to account for hand-rails and turning radius, etc.