The art of concrete detailing - stair question 1

[bbookz]

I'm reviewing a stair on grade design. It's an exterior stair built into a terraced slope. The stair has temp&shrinkage #4 reinforcement each way. The stair is fairly long maybe 60ft with four flights and three landings and is 6ft wide. They have it detailed with sloped side walls which project a couple feet above the stair.

Currently they have perpendicular walls at the top and bottom of each flight. Iso joints are shown all over the place - way too many in my opinion. They detailed it with an iso joint between the stair/slab and long side wall on either side -basically the stair floats between the two long walls. Additionally each landing has an iso joint between the upper and lower flights. Money is not really an issue so I'm not too concerned with over reinforcement, but I'm questioning all the joints - kind of a maintenance problem.

I'm suggesting they eliminate the walls at top of each flight so that you only have walls perpendicular to the side walls at the bottom of each flight with a landing and flight poured together. I'm cutting the perpendicular iso joints in half so there is only a joint the width of the stair in three locations located at the base of flights so a little heave doesn't cause a tripping hazard. Honestly I don't know if we need any iso joints but I do think the length of the pour should be broken up in a few locations with construction joints at least. I'm struggling with the iso joints they show between the stair/landings and the side walls. Every walkout type stair I've walked down the stair is poured tight to the wall. There isn't some messy joint filler/caulk at the interface. I don't think you can just pour tight to the wall because it would probably open a bit an get filled with dirt but maybe this isn't an issue since the shrinkage is only occurring the width of the stair so would be negligible in this direction. So in this instance if we don't have an iso joint I would lean towards having hooked dowels come out of the wall and tie into the slab so it can't pull away. My question is can you just pour tight to the wall without these dowels? Is an iso joint agains the wall following the up and down of the stairs and at landings like they've shown a good idea? Is the right way to detail this be to have dowels stick out of the wall - complicates formwork but keeps the joint from stair to wall tight.

Sorry for the super long question.

 

[BAretired]

A drawing might help.

BA

 

[bbookz]

See attached rough sketch of what I'm describing.

 

[jike]

I would also opt for half as many joints (about every 20 feet). I would also agree on eliminating the joints at the walls and instead dowel into them. Eliminate holes in forms by using threaded rebar inserts or by drilling and epoxying the dowels.

Another suggestion might be to eliminate the walls altogether (depending on soil conditions) and pour the stair slabs with short curbs on them.

 

[bbookz]

Jike, thanks for validating my thoughts

 

[JLNJ]

I have done these with the walls and not the footings with the walls doweled into the slab to prevent separation.

The walls provide a nice place to attach the handrail.