Free standing stair

[slickdeals]

Folks:
I am in the process of analyzing/designing my first floating stair and could use your inputs/wisdom as I try to understand behavior.

My starting point is a cantilevered truss frame with tension (top flight) and compression (bottom flight). Then the flights get separated by a distance to create the stair.

Before I try to model it or get "fancy", I want to really understand the working of it. See attached cartoon sketch for what I think are the various forces/moments that act on it. Chances are that I am missing some more.

I would appreciate if you could share your insights from previous similar stairs you designed and suggest ways to analyze/detail it.

 

[Ron]

Slickdeals...I agree that you'll have a torsion component in the center of the landing, producing shear, but I do not believe all of that is resolved from the stringer vertical loads. You will still have a moment at the stringer-landing interface, due at least to the loading on the landing.

I do not agree that the landing acts as a support.

 

[slickdeals]

Ron,
Yes, you are right. There will be moments at the interface of landing/flight.

What would be the best way to approach this? It is a concrete stair.

 

[ToadJones]

I supposed one way to look at it might be to first envision the loads and forces as if the top flight and bottom flight were lined up; then determine what forces arise from shifting them.

The top and bottom landings will certainly have a bending component that will make its way into the top and bottom stringers.

Should be an easy model to make.

 

[paddingtongreen]

I would rotate the picture with the supports at the bottom to make the structure look more familiar. I would provide temp supports at the four corners of the landing and rough out the magnitudes, these reactions will give you a picture on the forces driving the landing, shear, torsional shear etc. I would think of the stairs as having stringers and the landing as having beams lining up with the stair stringers.

This behavior should give you a better understanding of how to model the real structure.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[dik]

Pretty much the approach I used for the stair at the Cornwall Centre in Regina (prior to PC's and common FEA programs)... you're on the right track. I treated the supports as pinned at the top and bottom with fairy substntial horizontal loads transferred to the floor plates. The interior stringers were a couple of feet apart and the entire stair was fairly massive concrete.

Good Luck and nice to see this type of work happening...

Dik

 

[dik]

Forgot to add... post a pix when it's done...

Dik

 

[hokie66]

I've always been able to convince the architect to put the post in.

 

[DST148]

slickdeals: I would start with an assumption of a three-hinged frame(arch). I would lump the entire load on the two flights and the the mid-landing at the crown including a moment at the crown to account for the cantilevered mid-landing.So instead of zero moment at the crown, there would be moment at the crown. Then start with the actual modeling using any available software.

 

[DST148]

slickdeals: I am sorry. My last post was misleading. What I wanted to convey was .....
A four member rigid frame with pinned supports (some thing similar to a gable frame) with a point load and a moment at the ridge. To further simplify, it could be two member rigid frame(arch) with pinned supports with a point load and a moment at the ridge(crown).

 

[slickdeals]

@DST148,
Personally, I think the key to making this work is to ensure the transfer of forces through the landing.

In this case, the 2 members (stringers) are not in the same plane, but offset from each other forcing the landing to the "link" between the two.

 

[dik]

YOu are on the correct path, I think... The horiz beam at the stringer/landing take the torsion and shear from the stringers... and the 'teeter-totter' motion is resisted at the ends by the outer stringers and spandrel/guard at the landing. I'm not an expert... only done two of these in concrete, one large one and one smaller one.

Dik

 

[DST148]

@slickdeals - Your approach is right. I was just trying to simplify the actual three-dimensional structure into a plane frame as a starting point.

 

[BAretired]

I designed one of those for the first phase of NAIT (Northern Alberta Institute of Technology) in about 1960. It is still standing.

There are some references on the Internet. Here is one link:

http://books.google.ca/books/about/Staircases.html?id=fy-CNhhoAIMC&redir_esc=y

You can get more by Googling "free standing concrete stairway".


BA

 

[msquared48]

Should be no problem to model in 3D, definitely with fixed connections at the wall, or whatever the supports are.

Looks like a two beer stair system to me.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[SteelPE]

How about this link:

http://jce-ieb.org.bd/pdfdown/ce290102.pdf

 

[dik]

Merry Christmas and all the best in the upcoming New Years...

Dik, Wanda and Family

 

[mbullism]

A little late, I guess...I did one of these in HSS stringers and pan infill a while back (RISA)...As I recall, one the biggest difficulties was accounting for the relative displacements floor to floor due to deflections, and not necessarily direct loading. Mine was elevated slab to slab on grade...ended up with a "substantial" spandrel at the top to help reduce it...