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Snag Potential for Historic Concrete Railing with Recessed Panels

Question
State	IN
Description Text	INDOT is looking for guidance on evaluating the snag potential for recreating a historic concrete railing with recessed rectangular panels, see the attached PDF for details. Using the guidelines from NCHRP Report 554, the ¾” panel recess with 45 degree edge, shouldn’t pose a snag concern if the panel is 2 ft wide, see second second page of the attached PDF for the NCHRP Report 554 Figure 83. Two questions 1. Is there similar guidance that has been updated for MASH? If not, is this guidance still reasonable when evaluating snag potential under MASH? 2. When evaluating for snag, is the continuous projection at the top of the rail (highlighted yellow in the section and plan views of the attached PDF) cause for con concern? Per a previous conversation with Scott, we understand the standardized buttress would need to be modified to match to the historic rail section.

Question

State

Description Text

INDOT is looking for guidance on evaluating the snag potential for recreating a historic concrete railing with recessed rectangular panels, see the attached PDF for
details. Using the guidelines from NCHRP Report 554, the ¾” panel recess with 45 degree edge, shouldn’t pose a snag concern if the panel is 2 ft wide, see second
second page of the attached PDF for the NCHRP Report 554 Figure 83.

Two questions
1. Is there similar guidance that has been updated for MASH? If not, is this guidance still reasonable when evaluating snag potential under MASH?
2. When evaluating for snag, is the continuous projection at the top of the rail (highlighted yellow in the section and plan views of the attached PDF) cause for con
concern?

Per a previous conversation with Scott, we understand the standardized buttress would need to be modified to match to the historic rail section.

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Date July 8, 2019
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Attachment Snag Potential Question Details .pdf

Response
Response (active)	Hello, Responses below: 1. Is there similar guidance that has been updated for MASH? If not, is this guidance still reasonable when evaluating snag potential under MASH? NCHRP 554 has not be repeated for the MASH vehicles particularly with respect to the higher angle small car impact. That said, it is currently the best available guidance. We do have some recent crash testing that may shed light on the subject. We have recent tested a similar bridge rails for Hawaii that are 34" tall and 42" tall. The 34" tall barrier as very similar recessed panels to those shown in your system. However, Hawaii's system used slightly more conservative insets that were 1/2" deep and used a 1" long taper. The 34" tall Hawaii bridge rail passed MASH TL-3 in both test nos. 3-10 and 3-11. This would indicate that your system as shown with 1/2" depth recesses has a very high potential to meet MASH TL-3. https://unl.box.com/s/1dwfpuh3m8e6ro218xrkzwkggphiw7tz We are in the process of testing the 42" bridge rail system. That bride rail has smaller inset window asperities with the same 1/2" depth but the inset is achieved over a shorter 1/4" taper. This system has passed MASH 3-10 and is awaiting completion of MASH 3-11. https://unl.box.com/s/8j32bi02gz8eevq6gtn7mtzdg4k6cz4j TTI recently tested a concrete bridge rail with larger asperities, but it was only able to meet TL-2. Based on the OIV values recorded for the small car test, it is unlikely that it would have performed acceptably under TL-3 conditions. Thus, there is a limit to the depth and angle of the asperities. https://static.tti.tamu.edu/tti.tamu.edu/documents/0-6946-R2.pdf As such, the most up-to-date MASH data I have is that the 1/2 deep recesses are acceptable, but that does not mean that 3/4" would not work. We just don't have MASH testing to support it. 2. When evaluating for snag, is the continuous projection at the top of the rail (highlighted yellow in the section and plan views of the attached PDF) cause for con concern? We do not believe so.

Response

Response
(active)

Hello,

Responses below:

1. Is there similar guidance that has been updated for MASH? If not, is this guidance still reasonable when evaluating snag potential under MASH?

NCHRP 554 has not be repeated for the MASH vehicles particularly with respect to the higher angle small car impact. That said, it is currently the best available guidance.

We do have some recent crash testing that may shed light on the subject. We have recent tested a similar bridge rails for Hawaii that are 34" tall and 42" tall. The 34" tall barrier as very similar recessed panels to those shown in your system. However, Hawaii's system used slightly more conservative insets that were 1/2" deep and used a 1" long taper. The 34" tall Hawaii bridge rail passed MASH TL-3 in both test nos. 3-10 and 3-11. This would indicate that your system as shown with 1/2" depth recesses has a very high potential to meet MASH TL-3.

https://unl.box.com/s/1dwfpuh3m8e6ro218xrkzwkggphiw7tz

We are in the process of testing the 42" bridge rail system. That bride rail has smaller inset window asperities with the same 1/2" depth but the inset is achieved over a shorter 1/4" taper. This system has passed MASH 3-10 and is awaiting completion of MASH 3-11.

https://unl.box.com/s/8j32bi02gz8eevq6gtn7mtzdg4k6cz4j

TTI recently tested a concrete bridge rail with larger asperities, but it was only able to meet TL-2. Based on the OIV values recorded for the small car test, it is unlikely that it would have performed acceptably under TL-3 conditions. Thus, there is a limit to the depth and angle of the asperities.

https://static.tti.tamu.edu/tti.tamu.edu/documents/0-6946-R2.pdf

As such, the most up-to-date MASH data I have is that the 1/2 deep recesses are acceptable, but that does not mean that 3/4" would not work. We just don't have MASH testing to support it.

2. When evaluating for snag, is the continuous projection at the top of the rail (highlighted yellow in the section and plan views of the attached PDF) cause for con
concern?

We do not believe so.

Date July 30, 2019
Previous Views (175) Favorites (0)