We have construction asking questions about guardrail layout. Daniel is out of the office this week, so I wanted to run this by you for a second opinion.
On the approach end of a bridge we have curb & gutter, storm sewer intakes, longitudinal storm sewer pipe, light poles and steep foreslope.
The consultant has proposed that we push the guardrail in so that the face of the guardrail in in front of the gutter and the post is behind the curb. This is to miss the longitudinal storm sewer pipe. Then use a long span system over the intakes.
My thought is to agree with the consultant’s approach with modifications to they proposal. From the pictures it does not appear that crash history is an issue. This in on an on-ramp so set back from the through lane. We are providing more protection then is currently there. With how tight this site is I am not seeing many other options.
My proposal would be to move the guardrail forward as proposed. Our design manual does not recommend the face of the guardrail being in front of the gutter, but we do allow this on our bridge approaches. Then use a long-span to gap the post at the intakes but require the w-beam to be nested because there is a curb. Finally, to grind the curb (at least in the area of the end terminal, maybe the entire length) so that it is more of a sloped curb instead of a standard 6” curb.
Could you please review and let me know what your opinion is?
Questions;
Can we use W6x9 steel posts on the long-span system?
Should we grind the curb for the entire length?
Thank you,
Comments below in red.
The placement of the face of the rail in front of the curb should not be an issue. We used to use this type of placement as the standard for guardrail as it allowed the vehicle to interlock with the rail element prior to engaging the curb. The post itself is pretty close to the pipe and may contact it to some degree if the system is impacted. Due to the depth of the pipe, I don’t believe this will be a big issue for the post itself, but there may be potential to damage the pipe.
The use of the long span to span the inlets is acceptable as well. Note that for a single omitted post (12.5’ span) we have tested an omitted post system with nested rail that did not require the use of the CRT posts adjacent to the unsupported span. See report linked here.
https://mwrsf.unl.edu/researchhub/files/Report395/TRP-03-433-21.pdf
https://mwrsf.unl.edu/researchhub/files/Report357/TRP-03-393-19.pdf
I would agree with that assessment.
In terms of the end terminal, we have done some limited research with curbs in the pooled fund. We have run two critical tests on terminals with 4” wedge curbs adjacent to the terminal without issues. While this is not the full matrix and the testing was only conducted with the MSKT, it does indicate the potential for terminals to perform acceptably with shorter sloped curbs. As such, we would likely recommend removal of the curb entirely adjacent to the terminal or grinding it down to 4” or less.
The long span system requires the use of CRT posts for the first 3 posts on either side of the unsupported span. The exception is for the single omitted post option noted above.
See comments above on curbs. Grinding the curb down for the entire length of the terminal is the most conservative approach. However, if that is prohibitive, the recent curb and terminal testing we did provides some justification for the use of 4” wedge curbs.
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