Precast Spire

[ztengguy]

I am designing a precast spire, a cantilevered concrete piece about 24' from a structural steel base. Based on it being a architectural piece, I dont want to classify as a column, thus having the 1% steel based on gross area. I have designed as a cantilevered beam, and provided min steel based on a beam.
What would you guys do?

 

[hokie66]

I agree that it is a beam. Is mimimum steel enough?

 

[ztengguy]

No, but I didnt want to provide 1% either, its short, and thick at the base, 2'9"x1'8" at the base, so 6.6sq in of steel based on 1%.

 

[hokie66]

Well, 6.6 in^2 is not very much, in my opinion. Remember, as a beam resisting wind and earthquake forces, the load can be in any direction, so the reinforcement must be as required to resist bending in all those directions. How is the precast section connected to the base?

 

[dhengr]

Out of curiosity, why are you using such a heavy building material in such a precarious position, particularly if you have to deal with EQ’s? I agree with Hokie and the rebar should be mostly near the outer surfaces and corners, with fully enclosed ties. And, I too, wonder how you are going to attach the spire to the primary structure and make this connection area water tight. Would lighter materials such as fiberglass or a covered steel frame be any easier to deal with?

 

[shobroco]

I'm going to sound really dumb but why isn't it square? A 24' spire 33" square at the base is pretty easy to do in concrete but the 21" dimension is odd. It doesn't make it that tough; utility poles are smaller, it's just odd. The easiest way to deal with it is to ignore the extra concrete & assume 21" square at the base.