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I am not aware of any testing were a 4” steel block was added to a 32” concrete parapet to form a MASH TL-4 barrier (now 36” tall).  However, this concept has been proposed before within the MwRSF Pooled Fund.  In fact, as recently as 2017 a proposal to design and test such a barrier was on the ballot for project selection in our annual April meeting.  Unfortunately, it was not selected for funding (missed by a few votes). If Missouri is interested in this project, I encourage you to resubmit the project problem statement for consideration in next year’s pooled fund program via our website:  https://mwrsf.unl.edu/membersOnly.php .  The original problem statement can be found here (https://mwrsf.unl.edu/viewSubmittedProblem.php?id=184) if you want to copy and paste it into the submittal page.

A similar design was crash tested at TTI back in 2002, but it involved the steel tube raising the height of a 27” open concrete bridge rail to 30” inches to satisfy NCHRP Report 350  TL-3.  A link to this report is below:

https://static.tti.tamu.edu/tti.tamu.edu/documents/0-4138-3.pdf

Let me know if you have any further questions.

The 4” blockout proposed is casting concrete on top of existing 32” safety shape with some anchors to make overall height equal to 36” where the blockout is vertical on both sides. See attached. (I should have been more clear since the drawing has the words “steel tube” on it)

Essentially we would be attempting to change a 32” safety shape MASH TL-3 to a 36” safety shape MASH TL-4. Has a 36” safety shape been tested to MASH TL-4?

I am not aware of any testing where 4” was cast on top of a 32” barrier to make a 36” concrete barrier.  Further, the only concrete barrier shapes that I have seen tested to MASH TL-4 are single slopes and vertical barriers (not counting the failed 32” tall safety shapes that resulted in rollovers)

With regards to your question, there exists a open concrete bridge in the State of Nebraska, on highway 77 just south of Wahoo, where the bridge rail was constructed too low. In this case, a concrete cap was constructed on top of the rail to raise the effective height. In such cases, one really needs to have sufficient width to install vertical and longitudinal steel reinforcement to hold the concrete cap. One would likely need to rough up the top surface and/or apply a bonding agent to further enhance the integrity. Unfortunately, I also am not aware of any research or guidance on this topic. However, I am optimistic that it could work if sufficient top barrier width exists to install adequate vertical steel bars. Without research, we cannot answer what would define adequate and would need to use our best engineering judgment in the absence of research. Narrow top widths would pose the greatest concerns with implementing this retrofit.

There have been other testing where RC glare screens were added to single slope or NJ shape PCBs. However, the crash testing involved either large sedans or pickup trucks and not SUTs.

Please let me know if you have any further questions regarding the information above. I also apologize in my delay in responding.