Unusual Guardrail In-fill - Residential

[XR250]

I have been asked to evaluate some guardrail in-fill to determine if it meets the 50 PSF IRC requirement. The infill is 4" O.C. horizontal 1/4x1 1/2" flat bar (1 1/2" horizontal). spanning 4 ft between 4x4 treated posts.
Realistically, I know this will work fine but...

1) Seems like evaluating the 1/4" compression flange of the flat bar as un-braced over 4 ft. will be tough. Especially as any realistic load on it will be de-stabilizing.
Regardless, even if it is unstable, it will just end up acting as a catenary between posts so who cares?

2) Will the baby's head spread these apart? I can tighten up the spacing if needed.

 

[XR250]

The arch. has decided to move a different direction but this would be an interesting discussion regardless.

 

[jayrod12]

Our guardrails are required to be non-climbable. It sounds like they wanted to make a ladder.

That part being said, a quick back of napkin calc shows that a 1/4" flat bar should be good with those proportions. I get that works out to around 3.2 ksi bending stress, I can't imagine the unbraced length being that punishing on the allowable bending stress. Around here, even flat bar is 44 ksi yield.

 

[DanKile]

The wind load would be not a problem. The kid or kid at heart will try and climb up infill like that. The bars would be bent after that.

 

[dik]

Use Roarc for strength determination. I occasionally encounter this type of construction, but the BARs are vertical. The small BAR stock will likely deform plastically with time due to the limited thickness of the BAR.

 

[XR250]

The wind load would be not a problem. The kid or kid at heart will try and climb up infill like that. The bars would be bent after that.

Agreed. I don't think the code requirement of 50 psf is for wind - rather to keep someone from falling through it who has enough velocity.
It is a dumb design IMHO. Although, once kids try to climb a cable rail, it is usually loose after that.