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Question | |
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State | IA |
Description Text | I have two
1. 2. a. b.
Thanks in |
Keywords |
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Other Keywords | none |
Date | April 7, 2015 |
Attachment | eba401.pdf |
Attachment | TBR.pdf |
Response | |
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Response | Comments below.
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.
http://mwrsf-qa.unl.edu/view.php?id=636
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.
http://mwrsf.unl.edu/researchhub/files/Report133/TRP-03-180-06.pdf
http://mwrsf.unl.edu/researchhub/files/Report54/TRP-03-208-10.pdf
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 |
Contact Us: 130 Whittier Research Center 2200 Vine Street Lincoln, NE 68583-0853 (402) 472-0965 Email: mwrsf@unl.edu |
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