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STH 78; additional guardrail over culvert question 5590-03-30

State WI
Description Text

Please review the text and
drawing and let me know if the proposed installation is acceptable.

Here is additional information
with a section view. 

Notice due to the elevation of the roadway with respect to the elevation
of the existing headwall a reinforced concrete section will be added to the
existing headwall in order to meet the 10:1 requirement for grading at the
guardrail.  We did a structural analysis to know that what we have shown
will work structurally to retain the earth that needs to be against it for
grading.   This will also allow us to extend the wings vertically to
better grade behind the posts and in which case the posts could be moved closer
to the edges of the box, if that will address some of the beam guard deflection
concerns.   If we meet the 15’ horizontal roadway clearance requirement,
 we still are not meeting typical criteria for placement of the headwall
behind the guardrail post installation.  For the installation to meet
current long span system guardrail installation requirements using the CRT
posts the horizontal clearance would only be 14’3” instead of 15’. 
Horizontal clearance is a controlling criteria.    We are asking
for an exception to the typical beam guard installation criteria to allow the
back of the post to be placed in the same plane as the headwall. 
  • Guardrail
Other Keywords Long Span
Date August 12, 2014
Attachment 5590-03-30.60 STH 78_Lafayette Co._Box Culvert STA 341+22 Updated 8-8-14....pdf


We have concerns that changing the offset of the posts relative to the headwall from the tested system may increase vehicle extent over the culvert and potential wheel snag on the culvert. In the detail shown, the culvert wingwalls appear to be perpendicular to the headwall, which would further increase the snag concerns.


Thus, we would not recommend the offset shown. 

Date August 13, 2014

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