Steel Stairs With Perforated Metal Guards

[spats]

I am designing exterior steel stair guardrail where the infill panels are perforated metal, as specified by the architect. The attached file shows a typical infill panel. By code, the infill for a guardrail needs to resist 50 lbs. applied to a 1' square area. Being exterior, wind load should probably also enter the conversation. Calculations are required for the shop drawing submittal. Question is, how the heck do you calculate such a thing short of a finite element analysis? In some respect, the whole thing could go into some sort of catenary suspension. How would you handle this? It's not going anywhere if it "fails", and I'm not doing finite element analysis.

 

[spats]

Forgot the attachment...

 

[jayrod12]

Is there a known amount of perforations? say 50% or something like that?

I would be designing for the entire wind load (it's likely higher than the 50 lbs in 1 sq ft) as if unperforated, but only using 50% of the unperforated capacity.

The pattern shown seems fairly symmetrical so I would think that the stresses would reasonably transfer around the openings to the available metal.

 

[BUGGAR]

Is there sufficient quantity to justify a test? You could test the first panel at the fabricator's shop with sandbags.

Or is this still in the design phase? If design phase, make this element design-build and pass the buck.

 

[sbisteel]

The industrial perforators association has some really good technical info on their website, including modified yield strengths and youngs modulus based on perforation patterns. Basically analyze as a solid plate, but modified for the open areas.

http://www.iperf.org/perforating/knowledge-center/

 

[spats]

Cool beans sbisteel! I've already determined it will work for the 50 lbs. on 1' square, but I doubt it will meet wind loads... that check is next. I might have to tell that it doesn't meet wind load. The technical literature you referred me to has some verbage about reduced pressure due to the perforations, but gives no technical data.

 

[sbisteel]

Yeah, that is a tough call to make. I've only dealt with these panels indoors, so I've never had to justify wind pressures. I might fiddle around with ASCE7's treatment of "lattice frameworks" which are based on open area ratios, but I would think the manufacturer would have the ability to just increase the sheet thickness to something that works for the load you're looking at.

 

[spats]

I'm using 11 gauge and the heaviest in the pattern and material I'm looking for is 10 gauge, which would increase bending capacity by about 26%. This is still probably not enough to make wind work. Trying to span both ways for these parallelogram shapes would be an analysis nightmare.

 

[SAIL3]

As the OP mentioned..checking a continous strip(even if it is on a diagonal) as a catenary would give a conservative upper bound value...just make sure of a good connection of the panel to the supporting frame....if that does not get you there, then, a practical approach ,as suggested by BUGGAR, would be to test a panel...