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TCB/Guardrail Transition

Question
State IL
Description Text

We are evaluating a proposal submitted by one of our
District offices regarding placement of temporary concrete barrier (TCB) across
and on both ends of a bridge deck. We have some questions about options for
transitioning the TCB once it leaves the bridge deck.



1.      
Section B-B in the attachment complies with
internal guidance to provide 2.0’ between the back of TCB and the curb on the
bridge deck. This scenario could be for freestanding TCB, or at most, short
pins (approximately 4.5” embedment into the bridge deck) could be provided.



2.      
Section A-A does not comply with internal
guidance since we indicate that the face of the TCB should be between 2” and 1’
from the face of the guardrail; and the underlying surface on which the TCB
rests needs to be paved and in the same plane extending to the face of the
guardrail.



We feel that the TCB could be shortened by using a taper of
not steeper than 1:12 once the installation is off of the bridge deck. At that
point a section or two could be placed parallel to the guardrail and the end
units could be anchored to the underlying paved shoulder using anchor pins in
all six holes. Placement of a Test Level 3 (the posted speed on the roadway is
55 mph) temporary narrow, redirective impact attenuator would be required at
both ends.



A.     
Are there any transition devices available that would
allow another option for realigning the guardrail to attach to the TCB on both
ends? We could anchor the end unit of the TCB into the underlying paved
shoulder (or we could anchor multiple units, provided that they are not on the
bridge deck, since our Bureau of Bridges and Structures does not allow
anchoring on bridge decks). Such an arrangement would not require temporary
impact attenuators on both ends; however, we are unaware of potential
performance issues for TL 3 connecting guardrail to TCB.



B.     
Are there other options that we might consider?

Any thoughts or guidance that you could provide would be appreciated.



Keywords
  • Approach Guardrail Transitions
  • Guardrail
  • Temporary Barriers
Other Keywords none
Date May 5, 2015
Attachment Street View, IL 170 over RR.pdf
Attachment SAFETY ENGINEERING.pdf


Response
Response We have reviewed you detail for the temporary barrier installation on bridges and believe that it is acceptable based on current safety practices. 

The overlap of the PCB on the guardrail and the shielding of the end of the PCB with an attenuation system is currently about all that can be done for this type of installation. There currently is no tested and approved transition between TCB and guardrail. However, we currently have research underway with NDOR to address exactly this situation. The system was designed in the report below and the testing of the system is scheduled for this summer. If all goes well, the system should be sent in for FHWA eligibility before the end of 2015. 

http://mwrsf.unl.edu/researchhub/files/Report299/TRP-03-300-14.pdf 

The only other comment we would have is that the 2 ft offset between the bridge rail curb and the back of the barrier may need to be increased. The concern is that the motion of the TCB's during impact may cause them to strike the curb and rotate back about the rear corner of the barrier. If this happens, the propensity for vehicle climb and instability can increase. Increasing the offset another foot to 3 ft or using the steel strap tie-down system for the F-shape TCB (or other tie-down systems) could help alleviate that concern. The steel strap tie-down uses less embedment and should restrain deflections sufficiently. 

http://mwrsf.unl.edu/researchhub/files/Report219/TRP-03-115-02.pdf 

Thanks 
Date May 29, 2015


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