Stairway calculations

[SR71B]

I am building a loft in my shop, and I need help analyzing the stairway.

I am going to make the stringers from steel channels then weld angle iron the the channel to support the tread plates. Do to space constraints, I do not want to attach the tread plates to the angle iron supports.

The questions is, how to calculate the loading on the angles. Do I just treat it as a simple 2d static problem and draw the shear and moments diagrams. Then calculate the bending stress with MC/I? And see which stress is the highest?

Or do I need to consider the uniform loading along the length of the angle?

Thanks

 

[SteelPE]

I don't see the difference between your first question and the second question.

While the ASIC does not cover stairs most people use that code for analysis purposes. It covers single angles in venting in chapter F. Calculate the load in the angle (bemding) then use the section to figure the required angle size.

 

[SR71B]

Thanks for the reply.

To make sure I have this correct. For yielding, I divide the Normal Load applied to single angle by omegaa (1.67). If the quotation is less than the value publish in Table 5-2 of the AISC Handbook I am good.

Plus some factor of safety,

 

[SR71B]

Ok - the above is incorrect. The value listed in the ASD chart under the P/omega header is the allowable max value.

The more I look at this isn't the angle(s) in flexure not tension?

 

[SteelPE]

I think you are doing this wrong, or I may have no idea what you are trying to do.

I assume your angle is in some sort of bending so I referred you to chapter F of the AISC specification. Now that I have my book in front of me, if your angle is in bending you would need to use section F10. If you angle is in compression you would need to use chapter E (probably E5). If you angles in in tension, chapter D and if your angle is in combined compression and bending, chapter H.

The tables you refer to are used to help you run your analysis. They were made based off the equations in the AISC specification and should only be used if you know what you are doing. From what I know, there are no tables in the 13th edition manual for angles in bending, so you must use section F10 of the AISC specification to calculate the bending capacities of angles.

 

[SR71B]

I have attached a sketch of the proposed stringers and angle tread plate supports.

http://files.engineering.com/getfil...5-deae-4ecb-88a2-e4b689cd20dc&file=stairs.pdf

 

[jayrod12]

from your sketch, if you're welding the top and bottom of the angle to the channel, then the only thing you need to check would be for the bending of the angle leg that is supporting the stair tread. I would think of it as a cantilever plate with a fixed end. Then if you want to check your welds then design the top weld for the tension to resist the moment about the bottom toe.

But I might not understand your question.

 

[hetgen]

Hi SR71B,

You can design the angle leg which support the tread as a cantilever plate loaded at its tip, you need to check for bending, shear and deflection.

Please also check the lateral stability of the stringers, if you are not fixing the tread plates with the stringer the effective buckling length of the stringer is critical.

Steel stairs are susceptible to vibration leading to discomfort, get you design reviewed by SE.

HTH

 

[SteelPE]

OK, so you are using the angle to rest the on. In this instance all you would need to do is check the outstanding leg of the angle for bending. I would use AISC section F11.

 

[SR71B]

Thanks to all. My original calculations were correct. Just worried there was some lurking structual steel loading case that I was not aware of.