Concrete Stairs
Concrete Stairs
(OP)
At the risk of asking a vague, open ended question, does anyone have any basic information they'd like to share about C.I.P. exterior concrete stairs?.. I guess I will elaborate.
Doing a small (but wide) set for an existing building - landing is a suspended slab which is being removed and replaced with area beneath backfilled and ex. foundation walls to remain with a new SOG poured for landing. Question about stairs is about typical reinforcing, nosing, forming:
How is distribution steel requirement met in treads, risers? Are the bars (say, #5 @ 12" o.c. EW) 3" clear of sloped backfill going to help control shrinkage cracking at the surface? That reinforcing may be enough for the cross sectional area, but given the geometry will it really help limit crack widths at the surface? Climate is very cold, local Pg is 80 psf so there will be a lot of chloride exposure from deicing.
The existing set has deteriorated so badly there is a wood overbuilt set (and even that has been there over a decade). Want to get this one right.
For a very wide set can riser form boards simply be "braced" off each other and cleats at the bottom with 2x lumber perpendicular to forms? Otherwise, even with a stiff mix, they would bow badly I would imagine. On that note, will a 3" slump work? (to pour, not asking for a mix design). Are they typically vibrated? It would seem necessary to avoid honeycomb, but puts more stress on a potentially weak form frame.
I don't see the need to reinforce aside for temperature and shrinkage, although there is an obvious shear-plane. I doubt a pedestrian could cause a failure. Is this pretty typical?
Doing a small (but wide) set for an existing building - landing is a suspended slab which is being removed and replaced with area beneath backfilled and ex. foundation walls to remain with a new SOG poured for landing. Question about stairs is about typical reinforcing, nosing, forming:
How is distribution steel requirement met in treads, risers? Are the bars (say, #5 @ 12" o.c. EW) 3" clear of sloped backfill going to help control shrinkage cracking at the surface? That reinforcing may be enough for the cross sectional area, but given the geometry will it really help limit crack widths at the surface? Climate is very cold, local Pg is 80 psf so there will be a lot of chloride exposure from deicing.
The existing set has deteriorated so badly there is a wood overbuilt set (and even that has been there over a decade). Want to get this one right.
For a very wide set can riser form boards simply be "braced" off each other and cleats at the bottom with 2x lumber perpendicular to forms? Otherwise, even with a stiff mix, they would bow badly I would imagine. On that note, will a 3" slump work? (to pour, not asking for a mix design). Are they typically vibrated? It would seem necessary to avoid honeycomb, but puts more stress on a potentially weak form frame.
I don't see the need to reinforce aside for temperature and shrinkage, although there is an obvious shear-plane. I doubt a pedestrian could cause a failure. Is this pretty typical?






RE: Concrete Stairs
RE: Concrete Stairs
http://www.FerrellEngineering.com
RE: Concrete Stairs
Once you have stripped the walls proceeed to backfill. If there are many stairs, some contractors may opt to place a mud mat to be able to retain the backfill material better. (Usually its just some left over concrete from some other side of the job). To form the risers, rip 2X8 down to the riser height, make sure you chamfer the form as it makes finishing a lot easier. If your stair are wide, like 10' then nail a 2X12 following the slope of the stairs on each side of the wall. Layout the stairs on these outer 2X12's...nail your rises to the 2X12. Now to brace the middle of the riser lay oa 2X8, 2X6 or even 2X10 down the slope of the risers. This should catch the corner of every riser if they stairs were laid out correctly. Then just nail cleats down from 2X8, 2X6, or 2X10.
Oil forms well and place concrete from the bottom up. Vibrate as needed, but make sure to hit face of forms with hammer. Dont forget to drop in the nosing bars as required too. Then wait for the concrete to set up some and proceed strip the forms and finish the riser portion of the concrete.
As far as design goes, I have seen some engineers from up north design the slabs as suspended slab, requiring us to use corrugated decking to span between walls, and leave a 6" air space. But in our area, between backfilling with a pourous material, and doweling into the walls should suffice to prevent any frost heave.
I would use epoxy bars, and make sure the platform and treaders have pitch.
RE: Concrete Stairs
If chlorides are applied by the owner, you might look into a corrosion inhibitor (see DCI Inhibitor here: DCI Link
Also, some have used silica fume to densify the concrete and reduce water infiltration (water carrying the chlorides to the rebar).
RE: Concrete Stairs
RE: Concrete Stairs
Doka1- great explanation of forming.
I will specify epoxy bar. I will also use a tight mix design, and may specify a coating or corrosion-inhibiting add mix.
JAE - I am not sure whether or not the local batch plant can get silica fume. I will look into it.
I attached a PDF of how I think the stairs should connect to the existing foundation wall (stone masonry). Existing space is being backfilled. I think it makes sense to overpour the slab to form the first riser and tread. No visible joint and there is a "grade beam" or "cap" the whole perimeter of the ex. wall so I'm not worried about additional restraint on the slab.
Not sure why it didn't come out black and white -sorry. There will be fill below stairs.
RE: Concrete Stairs
RE: Concrete Stairs
Has anyone used these with success or failure?
RE: Concrete Stairs
Change the step dimensions. Carry your tape measure around and check various stairs. You won't find 6x12. These are too shallow and too long.
As far as nosing I have mixed feelings. You are probably better off creating a notch for it and adding it afterward. Look at brass or CopperNickle. I wouldn't expect Al or stainless to stand up in this application.
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Plymouth Tube
RE: Concrete Stairs
6/12 is architects call, not mine, and I agree.
Not sure how much I like a post installed nosing though... Create notch with wood chamfer strip and tapcon in?
RE: Concrete Stairs
RE: Concrete Stairs
RE: Concrete Stairs
RE: Concrete Stairs
No, I did mean actual 6/12 stairs. The nosing doesn't count. I thought we were talking about entrance stairs. There are a variety of treatments for the treads to make them look good and be slip resistant.
RE: Concrete Stairs
RE: Concrete Stairs
RE: Concrete Stairs