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Rigid Barrier Height Transitions

Question
State IA
Description Text I am aware of recommendations that changes in the top height of rigid barriers occur at a rate of 8:1 or 10:1. These rates are not always practical, however, and in some cases the use of a more aggressive taper rate may be necessary. Could you please provide a recommendation for the maximum allowable taper rate for height transitions of rigid barriers? Also, would this recommendation vary depending on the degree of change in height? For example, couldn't a more aggressive taper rate be tolerated for minor height differences (say 4 inches or less) compared to the taper rate for major height differences (12 inches or more)?
Keywords
  • Bridge Rails
  • Permanent Concrete Barriers
Other Keywords none
Date April 2, 2013


Response
Response

We have used more aggressive slopes for vertical height transitions in the past. Recent testing of the median transition from free-standing TCB to a 42" tall single slope barrier used a sloped, steel cap to transition between the 32" tall PCB segments and the 42" tall single slope barrier.

That steel cap was constructed with a 5:1 flare. It performed well under crash testing. Based on the performance of the this 5:1 flared cap, it would seem reasonable to use slopes as high as 5:1 when transitioning from 32" tall b! arriers up to higher heights. We could not recommend the use of these higher flares for shorter barrier heights below 32" as the potential for the vehicle to climb the flared section may increase if the starting height of the flare is lower.
Date May 15, 2013


Response
Response Thanks.  Could you provide a recommendation for maximum vertical flare rate for rigid barriers with heights ranging from 27 to 32 inches?
Date May 15, 2013


Response
Response

Before addressing the 27"-32" height transition, we should be clear about the guidance for the 5:1 slope. The 5:1 height transition slope that we tested with the PCB transition used a steel cap to create the vertical transition flare. There is some concern that using concrete to create the 5:1 flare may increase friction and or gouging of vehicle components in the flared region. Thus, the 5:1 is an aggressive approach with some co! ncerns for its use. 

 

For your 27" to 32" transition, the recommendation would still be the 8:1 slope. We would recommend this based on the concerns noted above regarding the difference in the slope materials. In addition, as noted in the first response, we would not want to go to steeper slopes for barrier heights below 32" on the low side due to concerns for increased vehicle exposure to the slope and climb.

Date May 15, 2013


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