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I have two
|Date||April 7, 2015|
Let me know if you have further questions.
I have two questions regarding the attached Temporary Barrier Rail standard (BA-401) that I received from the field and would appreciate your assistance with.
1. On page 3 we show details of Strap and Stake Anchorages. We state a Strap Anchorage is only allowed on PCC and Bridge Decks and provide the anchor bolt dimensions in circle note 6, while the Stake Anchorage is allowed on Composite, HMA, and PCC. We have a contractor asking if they can use a Strap Anchor on a Composite (say 3” HMA overlay over original PCC) if they use a longer bolt to provide the required depth into the PCC as specified in circle note 6, in this example at least 3” longer. Thoughts on whether the longer bolt should provide the originally intended anchorage?
The use of the steel strap tie-down has been restricted to concrete pavements with overlays due to concerns that installation through asphalt will increase the bending loads on the bolt and the moment on the drop-in anchor that could reduce the capacity of the anchorage. Thus, we would not recommend using a longer bolt with the drop-in type anchor.
We looked into this issue and some potential alternatives previously for Missouri and did not come up with a solution.
2. Also on page 3 we have Table A Anchorage Requirements, which indicates to designers and contractors when TBR needs to be anchored. The question has come up as to how many sections upstream and potentially downstream of an obstacle need to be pinned as well. I’ve attached a mock situation to assist. Let’s assume the dropoff is sufficiently great, so the TBR needs to be pinned and only the minimum 6” offset is available. I’m taking the worst case blanket approach here but also realize that pinning an entire run of TBR for one small section with an obstacle is too conservative.
a. What distance should be pinned upstream of the obstacle if we assume there are at least eight sections of 12.5’ long unpinned TBR upstream of these potentially anchored sections to sufficiently redirect a vehicle per other guidance (TRP-03-209-09, page 6 for one)?
With respect to the upstream side, the length of anchored barrier on the upstream side would be based on your deflection to the hazard. It could be as simple as the anchored barrier only being needed directly in front of the hazard as that is where the deflection needs to be reduced. It should be noted that an approach transition is needed for the steel pin and bolt through tie-down options.
b. What distance should be pinned upstream if we have less than eight sections upstream?
I am not sure I follow. The pinned/anchored sections need to be directly in front of the reduced deflection area of the hazard. Then an stiffness transition must be placed on the upstream end as noted above. We would recommend 8 free-standing TCB segments on both the upstream side of the transition and following the downstream end of the pinned/anchored TCB’s. On the downstream side of the pinned/anchored TCB’s, a transition is not needed, but we still recommend that 8 free-standing barrier be used. This distance may be able to be shortened following ongoing research on TCB LON requirements being conducted through NDOR, but we are recommending a conservative approach for now.
Thanks in advance for your time and assistance.
|Date||April 13, 2015|
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