Stair Stringer Beam Uplift Reaction 7

[struggle67]

Hi Everyone,

It is my first-time designing stair stringer beams. My model is as shown below. I have upward reactions at the bottom supports and downward reactions at the top supports. At first, I thought that something is wrong with my model so I sent my model to the software support team. They told me that my model is correct and the uplift reactions at the bottom supports are due to the slanting profile of the stringer beam.

I always thought that stair design is similar to one-span simply support design. Why are the reactions uplift? How do I analyze/derive to get those uplift forces? Can't figure out. And the bending moment at the centre of the stringer beam is also zero.

Thanks.

 

[Celt83]

This Thread may also be relevant: Link

For a stair like this make sure you are also checking vibration.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[Brad805]

Having designed these I would be careful about the SLS state. Cranked stringers can be quite flexible, and if you do not have sufficient mass your stair can be uncomfortable to walk on. While I agree with steve about assumptions, you need to look carefully at your anchor points before selecting pin/pin.

 

[KootK]

Any thoughts?

I think that's a very cool way to demonstrate / validate the point.

 

[struggle67]

MIStructE_MIE

Thanks for spending time to do the model and sharing.

so the bottom defies physics and floats 8.8mm up in the air...which I don't believe is realistic. If it is, then I'm going to make a fortune showing this trick off at Hogwarts school of magic. Any thoughts?

Before you convince people and make a fortune, you easily convinced me not to go for that haha If I were to convince people of this flying ladder I wouldn't even know where to start and they will think I am crazy.