Resources for turns in CIP RC Stairs

[Lomarandil]

I'm curious if any of you have resources or references for designing RC stairways. Particularly those with turns at an unsupported or partially supported landing?

I imagine many of these are done in practice using FEA, but that doesn't help me a lot with the detailing, which is my real time-sink. How are you all working those out?


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The name is a long story -- just call me Lo.

 

[Agent666]

I'd say strut and tie is used more commonly. For the opening corner case there is a diagonal tension across the joint that needs to be reinforced. Around these parts people us the attached paper which includes formulae for assessing the diagonal reinforcement requirement. This is undertaken on the basis of using all of the longitudinal reinforcement capacity to determine the maximum diagonal tie requirements.

 

[Lomarandil]

Thanks Agent! That's very good information, and something I hadn't considered.

In my case though, I (was) more specifically concerned about changes in direction in plan view. Do you also check that using S&T?

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The name is a long story -- just call me Lo.

 

[Agent666]

Looks like I completely misinterpreted the original question!

Never designed a stair that turns in plan, but dealing with the torsion would be paramount. Therefore likely you would get a good idea of performance/response resorting to a model with shell elements or equivalent. Secondly I'd look at some way of adding support even if it was separating the flights at the turn and cantilevering past the point of support, or having one flight supported on the other to eliminate 5he continuity. Coming up with some simplified arrangement is bound to make the detailing easier and the design time shorter.

 

[KootK]

There's not much out there that I'm aware of. What I know of is shown below. I find that:

1) The stair itself rarely requires special detailing. It's mostly about the landing.

2) There's so much variation in the morphology of these things that it's usually a custom design.

Particularly those with turns at an unsupported or partially supported landing?

3) The difference between unsupported and partially supported will be huge.

4) Your best bet might be to post your next few hear and let us vet your detailing for you.

 

[Agent666]

Don't forget about allowing for interstorey drifts either, this may dictate some break and support of the stair.

I've seen one steel framed stair like KootK posted without intermediate landing support in a low seismic zone (up to 0.3g) which the company I used to work for peer reviewed here in NZ. The design was as I understand it the equivalent of a 'small PhD' to justify it worked for the seismic drifts in each direction. Would be far harder in concrete I would imagine (more likely impossible and undesirable as would act as a prop bracing the building depending on the main structural system). So basically if you want to do something unique/difficult you really have to look at it in an appropriate level of detail with an appropriate fee (which might be means for trying to justify a move to something more conventional that can be designed and detailed in an efficient manner), clients like saving money and a post under a stair that is effectively dead space anyway may not worry them (sometimes architect can be too precious about stuff that no one will appreciate).