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TBR deflection

State IA
Description Text

Good afternoon!


In preparation
for MASH deadlines, I’ve begun to review the history of NCHRP 350 guidance and
what has(n’t) been documented yet for MASH. One item that came up during review
of Deflection Limits for Temporary Concrete Barriers (http://mwrsf.unl.edu/researchhub/files/Report243/TRP-03-113-03%20(revised).pdf)
was the adjusted deflection using an 85th percentile impact. As I
understand, the full impact for NCHRP 350 was 45.3 inches (perhaps originating
in part from http://mwrsf.unl.edu/researchhub/files/Report158/TRP-03-64-96.pdf),
which we have rounded to 48 inches on our standard (Table A on page 3 of https://iowadot.gov/design/SRP/IndividualStandards/eba401.pdf),
and for less than severe drop-offs, an 85th percentile deflection of
24 inches was likely appropriate (page 14).


In reviewing
your recent Development of a Retrofit, Low-Deflection, Temporary Concrete
Barrier System
Table 1 on page 5 of the report suggests that expected deflection of the system
under full MASH conditions has increased to 79.6 inches but I couldn’t find a
similar statement regarding the 85th percentile for the non-steel
tube “prior” condition. Are you aware of what this recommendation is or will
this need to be a separate modeling project similar to NCHRP 350 efforts? As I
understand, with the steel tube system, full deflection is 40.7 inches (page
247) and the 85th percentile at 24 inches (page 248).


Thank you!

  • Temporary Barriers
Other Keywords none
Date May 17, 2017


Hi Khyle,


We just looked at this as part of an project for NDOR on reduced PCB system lengths. We estimated the MASH TL-3 85% impact severity deflection ay 68” for a system length of 16 barriers or more.


See the attached report.




Date May 18, 2017
Attachment PCB Deflection.png

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