Headwall+Guardrail to Box Culvert Connection
Headwall+Guardrail to Box Culvert Connection
(OP)
I've been tasked with designing a culvert headwall to box culvert connection. The headwall supports a traffic railing (guardrail) to be designed for TL-3 loads (54 kips over a 4 ft length of rail).
Designing the rebar to connect the headwall to the end of the box culvert is simple, I should have no trouble with that. Where I'm hesitant is the rebar in the culvert to take this load. I imagine that in addition to a tensile breakout of the culvert top slab there is going to be significant local bending in the top slab as well. Is there any design guides or reference documents anyone is aware of for this type of detail?
If not I suppose I can throw up a finite element model of this but that seems like overkill for this.
See attached sketch for details.
Designing the rebar to connect the headwall to the end of the box culvert is simple, I should have no trouble with that. Where I'm hesitant is the rebar in the culvert to take this load. I imagine that in addition to a tensile breakout of the culvert top slab there is going to be significant local bending in the top slab as well. Is there any design guides or reference documents anyone is aware of for this type of detail?
If not I suppose I can throw up a finite element model of this but that seems like overkill for this.
See attached sketch for details.
EIT with BS in Civil/Structural engineering.






RE: Headwall+Guardrail to Box Culvert Connection
RE: Headwall+Guardrail to Box Culvert Connection
EIT with BS in Civil/Structural engineering.
RE: Headwall+Guardrail to Box Culvert Connection
That report gave an equivalent "static" load that you can use instead of the dynamic load that AASHTO gives you. While this is not the exact situation that you are dealing with, you may be able to use it to form the basis for a more economical (and at the same time safe) design. Good luck.
RE: Headwall+Guardrail to Box Culvert Connection
EIT with BS in Civil/Structural engineering.
RE: Headwall+Guardrail to Box Culvert Connection
RE: Headwall+Guardrail to Box Culvert Connection
So, from that it seems that the dynamic load should be used (54 kips, see page 155, section 7.2.2) as I'm checking for rupture of the rebar in shear and tension.
Hmmmm, then again, after reading the conclusion (page 163) I see that they're finding that the barriers can indeed withstand either a 9.1 kip static load or a 47.2 kip dynamic load.
So, it seems that I should perform two design checks. One to check yielding of the rebar with a 10 kip load using the AASHTO phi factor of 0.85. The other check should be tensile rupture of the bars with a 54 kip load using the AASHTO phi factor of 1.0. (Both with an AASHTO load factor of 1.0 for the extreme event load combination.)
EIT with BS in Civil/Structural engineering.
RE: Headwall+Guardrail to Box Culvert Connection
FHWA has a page with links to most DOT's standard sheets: http:/
They also have a page with standard specifications.
Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/
RE: Headwall+Guardrail to Box Culvert Connection
Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/
RE: Headwall+Guardrail to Box Culvert Connection
RE: Headwall+Guardrail to Box Culvert Connection
In addition, the height of the headwall is significantly larger than the height used in the standard detail so I suspect that invalidates it.
Thanks for that website, though. That's extremely useful!
ztengguy: 8'-6". I would think that the headwall wouldn't see lateral flexure since we're transferring the shear into the top slab of the culvert. Thus, we just have to anchor the bars taking the shear load into the top slab far enough back to ensure that we don't pull off the end of the culvert top slab. The only way the headwall will be able to move is rotation around a longitudinal axis.
EIT with BS in Civil/Structural engineering.
RE: Headwall+Guardrail to Box Culvert Connection
EIT with BS in Civil/Structural engineering.
RE: Headwall+Guardrail to Box Culvert Connection
RE: Headwall+Guardrail to Box Culvert Connection
I agree, that would be more efficient.
EIT with BS in Civil/Structural engineering.