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Utah Guardrail Bridge Rail Need

Question
State UT
Description Text I am in hopes you have seen something similar to this in the past. This is a very old structure. See photos below. I made a site visit and was hoping to be able to remove the railing and railroad tie material and use a 25 foot guardrail span. From the first CRT post location on each side of the structure would require a 28 foot span. The speed limit is 45 mph. Would the additional 3 feet span be an issue?

Other than that I do not see an option because of the width of the structure. With very narrow shoulder and 10 feet lane width there is no room to move the face of barrier towards the edge of travel lane. Mounting hardware to the deck is not an option due to how it is constructed. The steel beam is located just over 2 feet in from edge of deck.

Span it with high tension cable?

Basically a new structure needs to be constructed but money is not available to do so at this time so a best that we can do method is what we are stuck with at this time.
Keywords
  • Bridge Rails
Other Keywords none
Date October 19, 2016
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Response
Response

What is under the timber curb rail and how thick? Do you have any views from back side or in ravine?

I assume that there is an RC deck with asphalt wearing surface. You note that the timber elements do not rest on either but instead only the corrugated lower formwork?

Date October 20, 2016


Response
Response Unfortunately, I do not have additional photos.  The timber curb is sitting directly on top of the Corrugated medal sheeting.  If needed I could have additional photos taken.  I have also put in a request for structure drawings with our Structures folks.

Yes the timber sits on the corrugated lower form work. The outer beam runs just under the white shoulder line.

Date October 21, 2016


Response
Response

A few years ago, Wyoming had a rural timber bridge that needed a retrofit rail as the bridge was not slated for replacement for a long time. We helped guide them on a few options. I think that they worked out a way to install weak-post MGS bridge rail by attaching sockets to structural tube that replaced a timber curb rail. The tubes supported sockets and attached to outer timber beam. The tubes attached across the road using long HS rods through tubes to bear against thick asphalt roadway. Yes, cuts were made into road to allow for placement of rods. Your challenge is that the outer stringer beam in inset from outer deck. If the weak-post, MGS bridge rail is used, one must find a way to anchor the tube sockets that support posts. The tube sockets must be effectively rigid. The MGS bridge rail would be best option if you can figure out how to anchor sockets.

 

You mentioned the Long-Span MGS as did a few of my colleagues. That system met TL-3 at 25 ft but had one of two tests fail at 31.25 ft. We all agree that it would be better at TL-2 but have no proof for a 28-ft span for success.

 

Thus, these two potential directions may be your options for now using best engineering judgement. Let me know if you have any further questions.

Date October 22, 2016
Attachment WY Timber Bridge Guardrail Retrofit.pdf


Response
Response

Would there be any negative effects if we stiffen the long span with nested rail on the MGS system?

Date October 23, 2016


Response
Response

We used nesting in the NCHRP 350 version of the 25-ft long long-span system. The nested rail was 100 ft long and hade some guidelines on position and overall system length. We provided this guidance on our Pooled Fund Consulting website. In terms of a 28-ft long-span system at TL-2, it may be beneficial and conservative to use the 100-ft of rail nesting with MGS. Of course, there is no certainty with this deviation as we did not test with MGS on a 28-ft span.

Date October 24, 2016


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