Beveled Edge at Culvert Outlet Headwall 1

[calc junkie]

I noticed looking at ADOT's standard outlet concrete headwall details that they indicate a beveled edge. It struck me as odd, as in a culvert calculation there is no input for the bevel on the outlet, and I'm not sure that it would have any value at the outlet, but for construction it is more difficult to form. Can any of you comment on the value of having a beveled edge on the outlet of a culvert concrete headwall? (see drawing attached).

 

[BridgeSmith]

To which "bevel" were you referring? Is it the out of plumb on the end of the pipe, the sweptback wingwall, or something else?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

I think he's talking about the 3/4" chamfer requirement at edges of outlet walls. A common practice of protection?

 

[calc junkie]

I'm referring to the 6" x 6" bevel in the concrete beyond the pipe in the concrete detail on Detail D and Detail E for the outlet end. I noticed on a recent project that it wasn't the easiest thing for the contractor to form it that way, it has value for an entrance as it changes the entrance coefficient in the culvert calculation, but I'm not sure of the value at the outlet side of the culvert.

 

[BridgeSmith]

If it's the chamfer, yes, it's to prevent spalling of the concrete at the corners. That's a detail common to all of our concrete.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

And quite easy to form, construction-wise.

 

[calc junkie]

Not the 3/4" Chamfer, the 6" 45 degree bevel beyond the pipe on Details D and Detail E. I get it on the inlet, but do not understand its hydraulic value on the outlet.

 

[BridgeSmith]

Ah, that bevel. That would seem to be only needed for the bottom half, to allow water to drain away from the steel. However, the detailing to convey that intent was likely considered to be more trouble than it was worth.

It's hard for me to believe that an experienced contractor would have any difficulty forming or striking off to create that detail.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[r13]

I believe the bevel was resulted from hydraulic studies with flow channel partially/fully full, to improve flow efficiency.

 

[AS_PEng]

How big is your culvert? Culverts over a certain diametre may experience Hydraulic Uplift if and when the flow exceeds the culvert sofit. Concrete collars are placed at the inlet and/or outlet to provided extra weight to anchor down the culvert and prevent uplift.

 

[dhengr]

Calc junkie:
That’s actually a kinda nasty little detail. It is not just a straight piece of 6x6 cant strip, but rather part of the side of a large cone, with different circumferential lengths on the two edged, at the culvert surface and at the face of the conc. wall. And, I’ll bet that the finish ends up fairly ragged at the culvert outer surface, without a bunch of patching. I understand there is some hydraulic advantage to the shaped entrance, how do they form that without much complaining, and then have a problem on the exit end? It would be much easier to just let the culvert extend 2-3” beyond the face of the headwall on the exit end, and let er drip dry. It might be interesting to talk with some culvert people and ask how they usually handle that detail.