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Transition from single slope to F-shape barrier

Question
State IA
Description Text

I am working on a new standard.  The need for this standard came from the transition from F-shape to single slope as our standard shape.  This new standard is a transition from 44” single slope to an existing 44” F-shape.  I was hoping you could review this standard and provide your thoughts.



 



A couple of discussion points that have come up:




  • Field bending of the horizontal

  • Connection between existing barrier and new barrier.  Dowls vs. chipping away concrete and lapping with existing rebar.



 



Please review and provide comments.



 



MASH
TL-4

Permanent Concrete Barriers


Transition and Attachment Structures

Date June 28, 2022
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Attachment BA-111.pdf
Response
Response
(active)

Overall,  this detail looks pretty good.  We have been recommending a minimum lateral taper of 10:1 for concrete barrier shape changes.  Your 4-ft long transition section satisfies this criteria as the two barrier sections are similar in width.

 

  • From what I have heard during discussions with various DOTs, field bending of longitudinal rebar is pretty common for shape transitions.  Even if the longitudinal bars are pre-bent to approximately the correct shape, there always seems to be small tweaks necessary to fit right within the rebar cage. I do not think this is a problem.
  • Chipping away concrete to lap with the rebar in the existing barrier would likely result in a stronger barrier connection.  However, using a doweled joint similar to the one you are showing is common and has been successfully crash tested in multiple barrier segments. In fact, MwRSF has recently crash tested a similar joint detail on multiple of Hawaii DOT’s concrete bridge rails to Mash TL-3.  Thus, I don’t see an issue with using a doweled joint. I do recommend increasing the length of the dowel bars.  The tested Hawaii barriers used 2-ft long bars with a corresponding 12-in. embedment in each barrier.  This increases concrete breakout shear strength and typically results in the dowel extending through 2 transverse stirrups (additional strength and robustness).

 

 

Let me know if you have any further questions.


Date June 30, 2022
Previous Views (57) Favorites (0)