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Steel Posts in the Bridge Transition Section

Question
State IA
Description Text

We received a call from a contractor asking if they could
use a longer 6’9”  for posts 8-13 in that attached modified road
standard.  This would keep the same length of embedment but would allow
the top of the post to be flush with the blockout.   It sounds like
they are having trouble getting the post installed correctly with the method
they typically use.  The other reason they sighted, for the longer posts,
is that the dies their manufacture have need 7 inches at the top of the post to
punch the holes.  The shorter posts shown are requiring custom punching of
the posts and driving costs up.  Do you see an issue with allowing the
post to be 3 inches longer?   They are waiting to order some posts,
so a quick response would be greatly appreciated. 

Keywords
  • Approach Guardrail Transitions
Other Keywords none
Date August 6, 2015
Attachment Steel Posts in the Bridge Transition Section.jpg


Response
Response

Brian:

 

I have reviewed our prior research studies that pertain to this issue. These include:

 

System No. 1 - ITNJ Test Series – nested thrie-beam AGT with steel posts on ¼-spacing near buttress end

Report can be accessed at:

http://mwrsf.unl.edu/reportresult.php?reportId=61&search-textbox=transition

Test ITNJ-2 on an improved design consisted of successful 2000P pickup truck test at TL-3 impact conditions. The six ¼-spaced posts were installed with a 49” embedment depth and a 2” recess for top of post below top of 31” tall thrie beam rail. The distance between the buttress end and the center of the first post was 11.5”. The top of posts were recessed 2” in this stiffer transition region due to concerns for engine hood and quarter panel contact and snag that may lead to instabilities and even rollover. This snag behavior was observed and deemed a contributing factor in the rollover of a pickup truck in a R&D study performed on a Missouri transition system. See System No. 2 discussion below. This testing was performed under NCHRP Report No. 350.

 

System No. 2 – MTSS Test Series – dual 10-gauge thrie-beam median AGT with steel posts on ¼-spacing near buttress end

Report can be accessed at:

http://mwrsf.unl.edu/reportresult.php?reportId=84&search-textbox=transition

Test MTSS-2 on a modified design consisted of successful 2000P pickup truck test at TL-3 impact conditions. The six ¼-spaced posts were installed with a 43” embedment depth and a 2” recess for top of post below top of 31” tall thrie beam rail. The distance between the buttress end and the center of the first post was 11.5”. Following the first failed test, the top of posts were recessed 2” in this stiffer transition region due to engine hood and/or quarter panel contact and snag on top of the median posts and on the upper sloped end of concrete buttress. This testing was performed under NCHRP Report No. 350.

 

System No. 3 – Test 2214T-1 – nested thrie-beam AGT with steel posts on ¼-spacing near buttress end

Report can be accessed at:

http://mwrsf.unl.edu/reportresult.php?reportId=148&search-textbox=transition

Test 2214T-1 consisted of same system evaluated under System No. 1 above and included a successful 2270P pickup truck test at TL-3 impact conditions. The six ¼-spaced posts were installed with a 49” embedment depth and a 2” recess for top of post below top of 31” tall thrie beam rail. The distance between the buttress end and the center of the first post was 11.5”. The top of posts were recessed 2” in this stiffer transition region due to concerns for engine hood and quarter panel contact and snag that may lead to instabilities and even rollover. This testing was performed under MASH.

 

System No. 4 – nested thrie-beam AGT to T131RC using steel posts on ¼-post spacing [no recessed posts]

Report can be accessed at:

http://tti.tamu.edu/publications/catalog/record/?id=38552

Two tests - 2270P and 1100C - were successfully run under MASH TL-3. The six ¼-spaced posts were 7-ft long but did not utilize a recessed top of posts relative to the top of the rail. As such, this testing may suggest that the recessed region may not be needed under MASH.

 

 

**At this time, I have requested two other crash test reports from TTI. I want to review these tests and determine whether those successful thrie beam AGT systems utilized recessed tops for posts relative to top of rail. I should have those reports by next week. In closing, I believe that there is strong potential for the tops of closely-spaced, steel transition posts to incorporate the same height as the blockouts under MASH testing. However, I want more evidence from a few more cases for confirmation, and then I will get back to you with an updated response.

 

Thanks again and feel free to contact me with any additional questions or comments!

Date August 7, 2015


Response
Response

Hi Ron,

 

Sorry for the delay in getting you this information.  It is amazing how quickly things get buried these days.  I appreciate the reminder. J

 

The first test was run under NCHRP Report 350.  It did not have a curb, and the end shoe was rotated into the slope of the concrete bridge rail parapet to which it was attached.  The link to the report for this test is:

 

http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/4564-1.pdf

 

The second test was run under MASH.  It also did not have a curb.  However, in this case, a special adaptor block was fabricated for use under the end shoe to keep the thrie beam rail in a vertical plane throughout its length.  The link to the report for this test is:

 

http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/9-1002-12-3.pdf

 

Please let me know if you have any questions or need any additional information.   We can forward video, etc. as needed.

 

Best regards,

 

Roger

Date August 27, 2015


Response
Response I believe that the recess may not be needed based on System No. 4 noted below. Thus, an increase in post length without the use of top recess may seem reasonable.

I agree that you could move forward with the longer post that no longer includes a recessed top region.

Date September 9, 2015


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