Direct Ponding Analysis Using RISAfloor

[thoughtofthis]

So ponding analysis is covered in AISC K2 and SJI has a direct ponding analysis tool, but there are limitations to both. For instance, they're only applicable to rectangular bays with evenly spaced framing.

I understand that ponding stability is iterative for an exact solution, but why can't this be accomplished directly with a software like RISAfloor? Build a roof and set the deflection requirements to l/180 or whatever governs. Add a rain area load equal to the depth of the appropriate water head plus the l/180 deflection of the longest member in that bay. RISAfloor sizes the roof members to limit deflection to l/180 and checks the strength of the members.

For example, say you have a roof bay that is 30 by 30. The depth of water that can be impounded is 3 inches. l/180 at 30 ft is 2 inches. So input a rain area load of 62.4pcf*(3in + 2in / 12 in/ft)=26psf. Use the load combo D+(Lr, S, R).

 

[JoshPlumSE]

FWIW, AISC has moved the ponding provisions to Appendix 2.

I never personally looked at this when I worked for RISA, but I imagine it is possible. It's just a matter of priorities. If lots of users request this then it will become a priority.

 

[JoshPlumSE]

Caveat / Disclaimer: I worked for RISA for 16 years before they were acquired by Nemetschet. Now, I work for one of their competitors (CSI / SAP2000/ ETABS). So, please note that I am certainly not an unbiased source.

 

[DaveAtkins]

I agree with your approach, except you need to keep repeating until the deflection converges.

DaveAtkins

 

[Denial]

This is probably of academic interest only, and I have zero knowledge of RISA.

IF your software allows for elastic foundations AND IF it also allows for the elastic foundation constant (ie the "modulus of subgrade reaction") to be negative, then you can analyse ponding directly.[ ] However that is a small if followed by a very large one.