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I know from previous discussions that the system to anchor temporary barriers to a bridge deck is not to be used on decks with asphalt overlays.
Is there a minimum amount of asphalt that MwRSF would consider an acceptable (e.g. 1" or 2" of asphalt ) or does all asphalt need to be removed?
Would there be an issue of removing asphalt from just underneath the barrier (i.e. the driving lanes would still have asphalt), and anchoring in the barrier to the bridge deck? Essentially the barrier would be keyed into the asphalt.
I know that the limit of this height reduction would be around 3 inches. But, are there other concerns about limiting the height of the temporary barrier based on current crash testing?
|Other Keywords||overlays, bridges|
|Date||March 26, 2012|
|Response||The tie-down system 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.
Even with only 2" of cover, the capacity of the bolt will be overcome without approaching the impact loads we expect.
Cutting away the asphalt in this area is an interesting option, but it brings barrier height reduction into concern. I don't believe there has been any TL-3 testing of safety shape barriers under 32" in height. There have been some shorter vertical barriers tested, but the concern with barrier climb much less when compared to safety shapes. The concern that arises is that the reduced height of the barrier combined with the sloped face could lead to increased vehicle instability and the potential for override of the barrier. Thus, we cannot recommend using this option as it would effectively reduce the height of the barrier to a level where the safety performance of the system is not quantified.
Thus, we cannot recommend reduction of the asphalt depth or cutting away the asphalt as solutions for the use of the bolt-through tie-down on a concrete bridge deck with an overlay without further analysis or testing.
|Date||March 27, 2012|
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