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I was in Virginia a week ago and saw the Bullnose Thrie Beam in
While I have seen several in medians, this was the first time I
Attached are some pictures from Google of the location.
Are the Midwest states doing this design in gores.
Any pointers for this application, concerns?
What are your thoughts?
|Date||August 17, 2015|
Thanks for the information. I want to give some background. As you know, MwRSF developed and tested this system in the late 90s. At that time, we tested a narrow system with parallel sides and requested eligibility of two wider alternatives with parallel sides to accommodate different median/hazard widths. During the review process, Dick Powers suggested an alternative design that included non-parallel sides (i.e, the back-side rail flaring away from the front rail that runs parallel with the traveled way. As such, the FHWA letter included an alternative layout that included Dick’s suggested variation that is similar to the front of the system contained in your photographs.
Again, the as-tested configuration utilized parallel sides. The as-tested design could be used to shield the hazards shown therein and would result in shallower impact angles along the sides of the bullnose. The currently-depicted dual flares would seem to potentially increase approach angles for 1 or both sides.
In such scenarios, I would always prefer to use the bullnose in a parallel configuration if site conditions allow. However, the Power’s alternative may allow for a flared version to be used in these settings when traffic is on both sides. One potential item to consider is the effect of flare angle on sides and resulting increased I.S. Historically speaking, there has not been considerable crash testing performed on crashworthy systems that are now installed with the maximum allowable flare angle provided in the AASHTO RDG for highway and WZ applications. We performed some testing on a flared MGS many years ago. However, PCBs/TCBs and some other devices may not always have had the allowable flare built into the testing program on the front end. That topic may be something to reconsider moving forward under MASH.
I have also copied Bob on this reply as he was largely responsible for the original bullnose system. He has fielded the majority of the bullnose implementation questions and may be able to provide additional input into this special scenario. Please let me know if you have any questions regarding the information provided thus far. Thanks!
|Date||August 17, 2015|
Ron made most of the good points on the bullnose in gore areas, but I have a couple more.
As Ron noted, there are concerns with flaring the bullnose sides on a couple of levels. First, is the increased IS issue Ron noted below. Second, is that we don’t want the flaring of the bullnose to negatively affect the capture and energy absorption of the system. Thus we have typically not recommended flaring of the bullnose prior to post no. 5 on each side. Dick Powers did approve a flared version as noted below, but that was intended for medians and not necessarily gore areas where the traffic on both sides of the bullnose is in the same direction.
Also because the system in this application would have traffic in the same direction on both sides, the guardrail splicing would be different than a median bullnose installation in that the overlap of the splice on the left side of the system would be reversed.
We have addressed this issue in the past through our Pooled Fund Consulting efforts and I have attached those responses as well for you to review as they contain some additional thoughts.
As Ron noted, if you have any questions, let us know.
|Date||August 18, 2015|
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