CMU retaining wall with concrete steps

[StrEng007]

I have to put together a design for a pair of retaining walls (which I'm capable of) with concrete steps.

My issue is how to detail the interface between the top of wall and the cast-in-place step. The arch would like to achieve the side elevation as shown.

Does this involve raking a tie-beam along the top of wall, then doing a 2nd pour to achieve the steps? Or pouring the steps down onto the top of wall, so there is no joint at the perimeter and the 'interior' part of the step (as shown in the section view)?

Is there a better way to achieve this?

 

[hokie66]

Cast the stair slab over the wall. The stair soffit will match the slope. No joint. But I would form the slab soffit straight across, no need for fill between the walls. The only tricky job is the mason'a. He may want to saw the top to suit once the blocks are laid. The other way is to cut first, then lay.

 

[phamENG]

That is a lot of fill. You'd be better off with reinforced stairs and a lighter wall. I agree with hokie - cut the block and form a flat stair soffit.

 

[Brad805]

Your not saving any formwork with this design. You still need a lot of forms to create that stair. I could form up CIP walls and stair slab in the same time as this multiple trade solution. Why backfill? Seems pointless since footing seems to be below grade for frost cover.

 

[StrEng007]

The end of the stair landing will abut up to an existing building. I like the idea of using CIP stairs with forms but I'd still like to use the block walls. If the slab is formed up and cast onto the wall, isn't this a 'boxed in' sort of situation. Do you leave one wall open to pull the forms out?

Doing the entire thing out of CIP is also an option. However, I also have many linear feet of ramp to tackle which is also proposed to be backfilled CMU...

 

[Brad805]

If you run the walls up past the edge of the stairs they only need to put nosing boards on to cast the stairs. That assumes there is a reason for the fill (stair then essentially SOG). As detailed, you would need to attach side forms to the block to cast the stairs. If nobody cares about a bunch of screw holes in the block, maybe it is not a big amount of work, but they may end up adding walls given the size. It probably does not make a huge amount of difference. If you have a mason on site I get the reason to use masonry walls.

 

[StrEng007]

Can't run the walls past the stairs. The arch is adamant about having free edge slab appearance.

 

[Brad805]

Ok, I get it. I am growing tired of architects who never seem to care what something may cost the owner who probably just wants a damn stair they can walk up/down. I am arguing with one about a roof problem. His crap design will cost the owner 30% more in insulation for no good reason than they do not want to redo any of their model which is not very good wrt to this part.

 

[StrEng007]

Yeah, this is an interesting one. I keep going back to using backfill as a natural form, raking the top of the masonry wall and pouring the stair down on top of the wall.

While it's extra back fill, it avoids having to juggle form work when the intention is for this thing to get fully boxed in. I've been through all my archives to find examples of this. Interestingly enough, I can't seem to find anything.

 

[azcats]

You could span some metal deck between the walls to act as a permanent but sacrificial form and avoid the backfill. Or use geofoam for the backfill.

 

[jayrod12]

I've usually seen the formwork for the slab be abandoned in the closed in area. Often it's a steel angle bolted to the wall with sacrificial steel deck. Slab is reinforced such that the steel deck isn't required once cured.

The cost of a bit of angle and steel deck would likely be cheaper than the backfilling procedures. and then your wall isn't working as hard.

 

[Brad805]

The precast company we work with is doing a lot of precast stairs as field rates go up. We did all the stairs for two or three towers this year, and have even been asked to supply them for wood frame buildings a few times. Quick and easy, but you would have a joint between the stair and landing. You would be hard pressed to find a precaster to build that section in a single form.

 

[KootK]

My issue is how to detail the interface between the top of wall and the cast-in-place step. The arch would like to achieve the side elevation as shown.

I vote for all concrete but, if you're doing it as shown, leave some verts protruding from the top of the block and field bend them into the stair slab?

 

[Tomfh]

Cut your walls along the diagonal line, sit metal decking on the walls, spanning the gap, pour.