Arched Concrete Beam

[spats]

Does anyone know how to design a CIP concrete beam that is arched at the bottom?

If the bottom steel is made to follow the shape of the arch (seems logical), and the bottom bars are in tension, the reinforcing would try to straighten. The ties would be the only thing keeping the bars from popping out of the bottom of the beam. What am I missing here? What is the proper reinforcing layout for this situation?

 

[ishvaaag]

1st forget it is to be a cast in place (postensioned?) beam and analyze where tension will appear. Then dispose prestress to exactly match the precise hypothesis you want. It may not require it the whole span or whatever. Then it may require dispose some otherwise uncommon straightening containment as you say or not, will depend on your design.

 

[BAretired]

Boundary conditions are important. Are the supports hinged, fixed or hinge/roller? If hinge/roller, you are correct. The bottom steel will tend to burst out of the concrete unless held in by ties. If hinge/hinge, the bottom bars may not be in tension, so I agree with ishvaaag that you must analyze the structure before worrying about steel popping out.

BA

 

[DWHA]

The arch must be either restrained at both ends. The only other option is for it to be a tied arch. Like BA said, boundry conditions are important.

 

[hokie66]

spats,

It all depends on the geometry and the support conditions, as others have said. But if it is a simple span, I would tend to make the main bottom bars straight, with smaller supplemental bars following the curve.