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VDOT Standard MGS Details

Question
State VA
Description Text

We are moving forward with the 31” MSG for our MASH
compliant w-beam system; however, we wanted to get MwRSF to vet the
details.  Please review and let me know if you have any concerns /
comments.  Note that there are slight dimension differences in the
trailing end terminal due to the transition from centered holes in the wood
posts vs. offset holes in the steel post.  In addition, we will be
creating the special applications at a later date.



 



Thanks for your assistance.



 

Keywords
  • Guardrail
Other Keywords none
Date December 7, 2016
Attachment VDOT MGS System.pdf


Response
Response

I cannot technically “vet” your plans, but we are happy to review them and provide comments.

 

I have attached an edited version of the pdf with some comments. Please let me know if you have any questions or concerns.

 

Date December 8, 2016
Attachment VDOT MGS System_MwRSF Edits.pdf


Response
Response

Bob:

 

Thanks for reviewing our standard details!  I have a few comments on your evaluation:

 

Standard 506.__ (Tangent End Terminal)

 

I am not clear on your comment.  The transition that we mention is a height transition only (31”  to 27 ¾”) not a stiffness transition.  It will be used to go from a 31” terminal to 27 ¾” w-beam.  We will update our bridge rail transition once that project is complete.

 

We will have a full 50’ for the terminal and then beyond that, we will start our height transition.             

 

Standard 506.__ (Transition from MGS 31” to GR-2 27 ¾” height)

 

This detail was based on the Washington DOT and Caltrans design.  The height transition would probably begin at the off-post splice since there is a little flexibility there. 

  

Thanks

Date December 9, 2016


Response
Response

Hi Chuck.

 

Replies below in red….

 

 

From: Patterson, Charles W., P.E. (VDOT) [mailto:Chuck.Patterson@vdot.virginia.gov]
Sent: Friday, December 09, 2016 9:33 AM
To: Robert Bielenberg <rbielenberg2@unl.edu>
Subject: RE: VDOT Standard Details

 

Bob:

 

Thanks for reviewing our standard details!  I have a few comments on your evaluation:

 

Standard 506.__ (Tangent End Terminal)

 

I am not clear on your comment.  The transition that we mention is a height transition only (31”  to 27 ¾”) not a stiffness transition.  It will be used to go from a 31” terminal to 27 ¾” w-beam.  We will update our bridge rail transition once that project is complete.

 

We will have a full 50’ for the terminal and then beyond that, we will start our height transition.            

 

If you are referring to the height transition, that should be fine. I read it as the start of attachment to an approach guardrail transition to a bridge.

 

 

Standard 506.__ (Transition from MGS 31” to GR-2 27 ¾” height)

 

This detail was based on the Washington DOT and Caltrans design.  The height transition would probably begin at the off-post splice since there is a little flexibility there. 

 

I understand. We have typically not recommended the splice in the height transition area, but we cannot say that it will not function that way. We liked the idea of keeping the splice relocation and post spacing outside of an area where the rail is tapering vertically. Basically limiting alteration of the system to a single variation of the standard system at a time. Certainly the detail you have ma work as well. This was just what we have recommended.

 

Date December 10, 2016


Response
Response

One more quick question..  We are still working on our pieces / parts details for the MGS.  Can you address Mr. Cross’ question below?  This is in regards to a conflict at one or multiple posts.


Can you get an opinion on double 12” block out and a 4” with a 12” blockout.

Date December 11, 2016


Response
Response

We have looked at this issue previously with the state DOTs. I have placed a link to the response on the consulting site below. Let me know if you need anything else.

 

http://mwrsf-qa.unl.edu/view.php?id=267

 

In transitions, we have given slightly different guidance and have allowed more blockout depth. Let me know if you need that information as well.

 

Date December 12, 2016


Response
Response

Another small detail for clarification on the MGS…  When we are showing the height of the MGS in conjunction with curb AND gutter, should we extend the pavement height over for to account for the typical 2” drop (see attached detail) at the flow line of the gutter pan?  Otherwise the MGS will be 2” short in relation to the pavement.

 

It appears that most states take the dimension from the lowest point on the flow line but we want to get this right (the vehicle will not drop the 2” when impacting the curb / MGS
Date December 13, 2016
Attachment 201_03.pdf


Response
Response

This is a good question. Our recommendation would be to install the MGS relative to the edge of pavement rather than the flowline of the curb. When we tested the MGS we placed the height of the barrier relative to the tow of the curb. However, for the drop shown, that would effectively lower the barrier height from 31” to 29” relative to the roadway. We believe that the height of the MGS is an important feature with respect to its ability to be placed adjacent to an offset curb. As you noted, for high angle impacts, we would not expect much vehicle drop for higher angle impacts over the 2’ length shown. Thus, by setting the barrier height relative to the edge of the roadway, we maintain a barrier height similar to what has been tested.

 

If a low angle impact occurred which allowed the vehicle to drop 2”, the effective rail height of 33” relative to the flowline of the curb should not be an issue as we have successfully conducted 1100C tests on the MGS with barrier heights of 34” and 36”. The 2270P vehicle response is not expected to be adversely affected by the effective increase in rail height either.

 

Let me know if you need anything else.

 

Thanks 

Date December 15, 2016


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