Concrete Stair Reinf Detailing 1

[bookowski]

Anyone care to opine on how a concrete stair as shown in attached sketch should be detailed in relation to slab into stair bars. Assume slabs are poured first so bars (or dwls) are left for the stair. I'm not concerned with the reinforcing in the guts of the stair, just how the slab top & bottom bars should relate to the stair top/bottom, i.e. at upper landing should slab bottom bars extend and bend down into top of stair slab and slab top bars into bottom of stair slab, or vice versa, or add a 3rd layer of dowels to complete the crossing etc Thanks.

 

[KootK]

Details like those shown below are common in my area. I worry about the halving joints unless there's enough depth available to make a go if it as a corbel. We usually only do that at precast stairs. In practice these details usually end up being a jumble of rebar at more or less mid depth.

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.

 

[bookowski]

Thanks. That is essentially identical to my typical detail (except I have the key/corbel and I have longer bar extensions). I got a rejection from a building official that the bottom stair bars are not lapped. He wanted the top slab bars lapped with bottom stair bars, after pointing out some possible deficiencies in this he wanted a 3rd set of dowels, from top of slab crossing down into bottom of stair - certainly wouldn't hurt but it's getting crowded in there. Was just wondering if my typical detail was off but seems like it's typical/consistent.

Stair sidetrack (I'm on a stair kick), do you guys do scissor stairs in ca and if so how are you supporting your dividing wall?

 

[TehMightyEngineer]

I see a lot of joints like these in precast stairs. KootK's details are similar to how we typically will setup the rebar. Shear on the supporting key will be something to check but we can often satisfy the requirements through plain concrete strength or shear friction.

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

http://www.americanconcrete.com

 

[KootK]

Stair sidetrack (I'm on a stair kick), do you guys do scissor stairs in ca and if so how are you supporting your dividing wall?

Is this a trick question? Support the divider from whatever horizontal thing is at the bottom of the shaft??

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.

 

[Teguci]

How about reinforcing like this? Contractor only needs to place hairpins to cross the construction joint, and the construction joint is very close to where the stair starts and stops. A bit of unusual bending, but may be worth it. I detailed it as a simple span with minimal top embedment. Any thoughts?

Bookowski - are you talking about laterally bracing a stair end wall that is discontinuous from the diaphragm? Had a problem like that where one of the shearwalls I needed for the stair tower was the end wall for the stairs. I wound up designing the stairs to take torsional loading. Lots of fun designing - hate to be the builder - don't do this.

 

[bookowski]

Interesting detail!

No, I was talking about a beam (or lack of) between two adjacent stairs. We have 'scissor' stairs here, basically like two corkscrews around each other. They are fire separated, typically by an 8" cmu wall. So it's two stair openings side by side with a wall between. It is common practice here to make this middle beam the same thickness as the slab, so typically it's an 8" x 8" 'beam' that supports that CMU. While I was on my stair kick I was just wondering if this happens elsewhere. It's a really crap detail that makes your stomach churn but since that's what everyone has been doing it's a real arm twist to say it's not ok.

 

[KootK]

Ah yes, now I remember your strange divider beam (Link). I've been fortunate to have not yet encountered that in practice. Although, clearly, they seem to work.

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.

 

[rapt]

Teguci

You would have to use increased radius bends for the bottom steel and I doubt that you have sufficient development for the top steel.

 

[bookowski]

kootk - FYI here is a pic of the weirdo stair divider beam detail in practice.

 

[KootK]

Sweet... I've been dying to get a peak at one of these. Extra questionable given the QC issues that I imagine go hand in hand with such a confined put space all busied up with those little stirrups. No judgement implied of course. It is what it is and seems to work. Will there eventually be dowels into the block or is just a friction connection? The block comes up hard to the bottom, right? No gap?

I wonder if there might be an opportunity to come up with an appealing precast alternative. prestress it with some little wires and drop it in there somehow. Maybe TME could help out with that if we cut him in on the patent.



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.

 

[bookowski]

Definitely seems sketchy but it's baked into standard practice here so hard to argue it doesn't work. Not a hard connection, the top of cmu/b.o.beam detail is something like a pta 422 anchor or similar. Dowels up - just to add to the congestion.