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We are making some corrections to the above referenced detail. Some questions came up when we were comparing WisDOT's detail with the recommended details from MwRSF Research Report No. TRP-03-134-03 "Evaluation of a Tie-Down System for the Redesigned F-Shape Concrete Temporary Barrier", dated August 22, 2003, and with the SDD's from IA, KS, MN, and MO.
* KS, MN, and MO show an optional 3/8" hole and retainer bolt at the
bottom of the CONNECTION PIN. MO requires the use of a retainer bolt on transition sections. IA shows a 5/8" hole with 1/2"x10" retainer bolt, which they require for connections with 2-loop barriers (their old design). Fig. 3 on p.15 of the MwRSF report shows the CONNECTION PIN without a hole.
Did MwRSF consider using a retainer bolt?
* Under RECOMMENDATIONS on p.59 of the MwRSF report it says that
"...this tie-down system is not recommended for use on a bridge deck with an asphalt overlay."
What is recommended for bridge decks with asphalt overlays?
* On p.12 of the MwRSF report it says that "... each anchor bolt was
epoxied into the concrete to an embedment depth of approximately 305 mm (12in.)... "
Is this the recommended minimum embedment length?
* Fig. 36 on p.62 of the MwRSF report shows a 1-1/4" x 40" steel stake
for staking down a barrier on asphalt pavementIs there an ASTM spec for this stake?
|Date||February 14, 2006|
It appears that you have performed a significant review of barrier design standards for the surrounding State DOT's who presently use the design noted above. One additional State that has prepared excellent design details using this barrier is the State of Florida. I highly recommend that you review their details since I believe that they are accessible on line. If they are not, please call Mr. Charles Boyd for additional information and using the contact information provided below. I have also attached a draft FL DOT file for your review and comment.
(1) With regard to your first question, you are correct that MwRSF, in cooperation with several Midwestern States, modified the original temporary barrier details after the first section was developed in the 1995-1997 time period. One change that you had noted was the omission of the retainer bolt and horizontal hole in the vertical drop pin in conjunction with a modified loop configuration. This overall change was made after it had been demonstrated that the Oregon temporary concrete barrier could meet the TL-3 impact safety standards without the use of a retainer bolt but with a pin and loop detail that placed the upper and lower pin locations in double shear. Therefore, a decision was made to leave out the retainer bolt for pin and loop connections that incorporated a double shear loading condition for the pin.
(2) The tie-down system described in the referenced report was intended for use on reinforced concrete bridge decks that did not include asphalt overlays. With overlays in place, the loaded barrier may allow the vertical anchor bolts to plow through the asphalt roadway material instead of being restrained by the rigid concrete deck, thus resulting in a longer moment arm and increased bending moment for the bolt region found at the asphalt-concrete interface. This change in loading and capacity may potentially decrease the safety performance of the existing, crashworthy tied-down barrier design. As such, we can not at this time recommend using this detail on bridge decks that contain an asphalt overlay. Although it may be possible that this design, or one very similar to it, may provide acceptable performance, we believe that future research is needed to investigate and evaluate various temporary tied-down barrier systems for this special application. Finally, we are not aware of any other temporary barrier solutions for bridge decks with asphalt overlays.
(3) For crash testing purposes, the vertical anchor rods were epoxied into a thick, un-reinforced concrete tarmac using a 12-in. embedment depth. For actual bridge applications, the vertical anchor rods or bolts also could be installed using either of two different methods: (a) rods epoxied into the bridge deck using acceptable anchoring methods that develop the ultimate strength of the rod or (b) rods installed using a through-bolt system that anchors the rods on the underside of the deck. To the best of my recollection, both Kansas and Florida have provided specifications for these alternative anchoring options within their standard plans. If desirable, I will try to obtain a summary of this prior correspondence between MwRSF and selected DOT's and forward it to your attention.
(4) After completing the MwRSF report noted above as well as the draft detail shown on page 62, MwRSF embarked on a new research project to develop a staked, tie-down system for use on roadway shoulders configured with a thin asphalt layer. This research study was funded by the States of Florida and Kansas. The results of this study led to a pinned through asphalt and roadside fill, tied-down barrier system as well as a transition between free-standing TBR's and rigid concrete barriers using this asphalt pinned system. Details of this research was presented at the 2006 Annual Meeting of the Transportation Research Board last month. I will attach an electronic copy of this paper within this email. In addition, if you would like to obtain additional information on these two systems, please let me know so that I can forward to you that information, CAD details, and test documentation (i.e., photographs and videos). Please note that a research report should also be available sometime this spring.
|Date||February 15, 2006|
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