sharp upstand

[chekre]

hi,

the attached is a section of a parapet having a sharp shape in reinforced concrete.
Since this shape, whether it will be cast in situ or precast, I am afraid that one of the aggregates will settle at the top of the parapet and we wont get the desired shape.
In addition, the reinforcement can not extend all the way and there will be a part which will be unreinforced.

Any thoughts regarding the above and if it can be constructed ?

Thank you

 

[dhengr]

Chekre:
Form the top 6-8" out of some sheet metal, any shape and color you want, but call it a parapet cap. Put drip edges on it front and back, with a locking attachment (riglet) on the front (outside) and a screwed or bolted attachment on the back. Maybe as part of your roofing system as it moves from the slab, and up the sloped wall to its upper fixings and flashings.

 

[chekre]

thank u dhengr.
However, the architect wants it as a fair faced element so it must be a reinforced concrete element.

 

[structSU10]

the durability of concrete coming to a sharp point is... bad. It will chip and crack and look awful in no time, as you allude to in your original post. What dhengr said, basically this element needs to be from a sheet metal to get that kind of profile such that it won't 'degrade' aesthetically. It may be possible to clad on a fiber concrete panels to create that profile, but it will likely need some sort of metal backup near the point to achieve that.

 

[KootK]

Agree with dhengr and structSU10. Your architect doesn't understand the nature of the material that he's trying to work with. Once you explain the likely outcomes of the sharp upstand, it's hard to imagine that he/she wouldn't come around.

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.

 

[dhengr]

Chekre:
Architects want all kinds of stupid things, without giving their practicality much thought. Then, when things go wrong they conveniently forget that you told them such-n-such wouldn’t work. And, it’s all your fault, again. You could form the top 6-8" of the conc. horiz., with eased edges, and they would still look the same from the street, as the sharp edge. And, they would be possible to build, reinforce and maintain. He can probably have an all conc. surface, or he can have the sharp edge, but not very practically both.

 

[hokie66]

Agree with everyone else. It can't be constructed in reinforced concrete. Perhaps in some composite material, but not concrete as we know it.

 

[TLHS]

You might be able to do it if you precast it, include a reinforcing material and then sawcut the sharp shape into it. It's dumb and expensive, though, and even if you keep it from breaking, the tip will slowly erode.

 

[Trenno]

One simple phone call to the architect...

 

[jayrod12]

The pre-casters around here would likely provide an steel embed to create the sharp corner. They wouldn't trust the durability of concrete alone.