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MASH Bridge Rail Modifications

Question
State IA
Description Text I was asked by our Bridge Engineer, how much we can change an existing MASH tested TL-4 bridge barrier rail.

For example, we will probably use stainless steel in our bridge rails instead of epoxy. Would this constitute a big enough change that needs testing under MASH?


We also have a MASH TL-5 tested median barrier (see below left), if I use the face shape on a bridge (half section below right), with the same steel area per foot, would we have to get it crash tested?


Thanks for your help. This MASH stuff is a little confusing.
Keywords
  • Bridge Rails
  • Permanent Concrete Barriers
Other Keywords none
Date February 22, 2018
Attachment TL-5.png
Attachment TL-5-2.png


Response
Response

Hi Stuart

 

Responses below.

 _________________________________________________________________________________________________

 

I was asked by our Bridge Engineer, how much we can change an existing MASH tested TL-4 bridge barrier rail.

 

For example, we will probably use stainless steel in our bridge rails instead of epoxy. Would this constitute a big enough change that needs testing under MASH?

 

I don’t see an issue with changing to stainless steel reinforcement as long as a couple conditions are met. First, you would want to ensure that the stainless steel has a similar grade (yield, UTS, elongation) to the A615 Grade 60 rebar typically used. Second, it would be a good idea to verify that the stainless steel rebar has similar lap and development lengths as the standard rebar. It is likely similar, but worth checking. If you can verify those points, I don’t see any big issues with changing the rebar from the current A615 spec in terms of crashworthiness of the rail.

 

We also have a MASH TL-5 tested median barrier (see below left), if I use the face shape on a bridge (half section below right), with the same steel area per foot, would we have to get it crash tested?

 

Because you are changing the width of the barrier, you would have to check more than just steel area per foot. The width of the barrier will affect  the overall capacity and the anchorage of the barrier. Thus, we would expect the narrower section to potentially need more reinforcement and different anchorage configuration. That said, we believe that you could do that type of analysis with yield line theory to develop an equivalent configuration, and that should not require additional crash testing. Single slope barriers and vertical barriers have previously been tested to MASH with the passenger vehicles. You have not changed the basic barrier geometry and have slightly widened the top of the barrier, so the redirection of the TL-5 tractor trailer would be acceptable. Capacity is the only real issue and that can be confirmed with yield line theory.

 

Thanks for your help. This MASH stuff is a little confusing.

 

Yes. Yes it is. We are happy to help.

 

Date February 23, 2018


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