Pilaster: Column vs. Beam?

[Archie264]

I'm interested in the case where a pilaster is stiffening a free-standing exterior masonry wall, i.e., a "garden wall". The vertical load is only the pilaster's self weight. As I read the commentary in ACI 530-08, Sect. 2.1.7, it states that "Pilasters...can serve one of several purposes..." I infer from that that it may be treated as either a beam or a column (or a beam-column) depending on the application.

So...

1. May it be treated as simply a cantilever beam carrying the wind load when there's no significant vertical forces? It makes a difference in the minimum steel required.

...and...

2. Regardless of (1), how would you esteemed colleagues handle it?

Thanks.

 

[hokie66]

It is a beam.

 

[KootK]

X2 for beam.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Chalk another one up for beam.

It would be a beam column if it supported anything besides it's own self weight vertically.

Is it that large of a difference in steel? Don't forget that you can reduce your minimum steel for a column to 0.5% if you are stressed to less than 1/2 of the factored capacity.

That tightens the gap on the minimum steel argument.

I would likely put that much reinforcing in it. So I guess my answer could be, I'd analyze it as a beam, but I'd provide minimum column reinforcement. That way when they go to add something crazy to it I know there's capacity there. 4-15m verticals give you a 16x16 pilaster, seems reasonable to me.

 

[Archie264]

Thanks, all. It seemed like a beam to me too but I was going through an approval agency's criteria and they required that all pilasters had at least the minimum column steel, so stated. Maybe they're a step ahead of things, a la Jayrod's recommendation? Or maybe that's their version of a safety factor? Who knows? In any case, thanks.

 

[WiSEiwish]

Take a look at the NCMA Tek 17-4B. It offers design information and some tables for masonry pilasters.

 

[Archie264]

Thanks! Excellent resource.