Masonry Stairs/Buttress

[XR250]

I have residential basement storage area under a porch where the foundation wall has failed (buckled inwards) behind some existing masonry stairs. I am assuming the the existing stair footing does not extend to basement level and, as such, added sufficient surcharge to the soil to fail the wall. My idea is to construct a new set of stairs with a foundation that extends to basement level. The masonry platform would serve as a portion of the basement wall and the stairs would serve as the remainder. The stairs are 11 ft. wide.
Questions...

1) Does anyone have a better solution. (the owner wants masonry stairs)
2) How would you reinforce the platform - other than ladder wire? I am assuming hollow CMU. Seems there is enough mass here to prevent sliding and overturning.

Thanks!

 

[BAretired]

What is a masonry stair? Eleven feet seems unusually wide for a residential stair. A plan view and cross section might be helpful.

BA

 

[XR250]

BA,

These are the stairs for the entry porch. Would be constructed of brick over CMU.
They are 11 ft. wide x about 5'-4". What you are seeing is the cross section.

 

[BAretired]

XR250,
I am not seeing a cross section of the stair treads. I gather that the treads are 11' long, but it's not clear how bricks over CMU are able to span 11' without some sort of structural support underneath.

You could build a network of masonry beams, but they would need to be reinforced with something a little more robust than ladder wire.

A better idea would be to provide a stepped concrete slab spanning 4'-0" clear between walls. If the owner wants a masonry stair, the brick cladding could be added on top.

BA

 

[KootK]

More than one way to skin that cat but this is one viable option I think. I'm assuming no lateral restraint from the floor deck because that seems to be what you're suggesting (overturning). As for better ideas, I'd need more info:

1) Is there really to be no reliable lateral restraint at the top of this thing?

2) Will you demo the wall, shore the floor, and construct all of this in place of the wall?

3) Could the wall be reinforced on the inside with the usual array of vertical steel posts spanning SOG to floor deck behind the wall?

 

[XR250]

@BA,

The area below the stirs is intended to be a solid masonry mass 5'4" x 11'-0" x 5'-4" tall on one big footing. The stairs would not have to span.
They would be continuously supported by the CMU below.

1) Is there really to be no reliable lateral restraint at the top of this thing?

2) Will you demo the wall, shore the floor, and construct all of this in place of the wall?

3) Could the wall be reinforced on the inside with the usual array of vertical steel posts spanning SOG to floor deck behind the wall?

There is reliable restraint.

Here are the factors at play....
1) The existing masonry wall behind the existing stairs is too beat up for me to consider repairing it. The homeowner would prefer it be replaced. Yes, the floor would be temporarily shored.
2) The homeowner wants a large masonry entry stair.
3) In my experience when constructing masonry stairs adjacent to a basement, it is best to extend the foundation down to basement level.
4) We don't want a crawlspace under the stairs as that adds other confounding issues such as moisture management thru the stairs and access thru the basement.
5) The homeowner wants to dig up the entire area around this porch/basement to re-waterproof
6) There is no reason why I couldn't simply replace that section of foundation wall and then build the stairs mass in front of it.

Either way, I would like some guidance on if it there is any practical reason to reinforce a large rectangular cube of masonry. The numbers do not require it.
Does your drawing assume that a slab or other structural element would be placed on top of the wing walls to act as a platform to construct the stairs?

Thanks

 

[XR250]

Ahh, if I used the wing walls per KootK and placed a slab on top as a base for the stairs, I would not have to have a crawlspace - it could just have backfill beneath. I'll get up with the contractor and see what is cheaper/easier for him.

 

[KootK]

There is reliable restraint.

The area below the stirs is intended to be a solid masonry mass

I would like some guidance on if it there is any practical reason to reinforce a large rectangular cube of masonry.

I get it now, thanks. I do not see a need to reinforce the blob given that you're just using it to eliminate the surcharge on the wall due to the weight of the stair.

Does your drawing assume that a slab or other structural element would be placed on top of the wing walls to act as a platform to construct the stairs?

Either that or that the stair would be grade supported by backfill placed within the "bucket". Like BAretired, masonry stairs are fancy new technology for me. I believe you that they exist but am just now figuring out how they are constructed.

 

[JAE]

I would construct a structural slab just below the lowest riser - capable of supporting your "mass" of masonry steps.

The top of the slab would slope downward, away from the house.
The top of the slab would be waterproofed with a membrane and protection board on top.
The mass masonry could then be stacked up as needed.
Being outdoors, I'd be worried that the masonry would collect water and, if in a cold climate, freeze and damage the masonry - thus probably need to fully grout all this masonry.
(lots of weight for sure).

 

[BAretired]

You could use a closed box with footing on the bottom, slab on top and four masonry walls. Below grade, masonry to be fully grouted. The cavity below the slab could remain open or could be filled with granular fill but in either case, connected through the wall to the weeping tile outside.

BA

 

[XR250]

Thanks for everyone's responses.
Contractor likes the wing walls with a structural slab on top.
I was just considering how to waterproof it. Thanks for the advice - JAE.