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We have a note on our current standard detail that requires the TCB to be anchored when the clear space behind the barrier is 2'-0" but no anchoring is required if that space exceeds two feet. In addition to the 2'-0" clear space, we also require that the drop-off exceed 2'-0" deep The decision for the 2' clear space and 2' drop-off was based on the fact that most locations where anchoring would be required are generally old bridge decks in 1st stage of construction. There is usually minimal space on these bridges. On some bridges we can't even get the 2 feet. The second reason was travel speed is usually reduced at these locations.
I have consulted a few other states and found a good number of them don't even anchor the TCB and those that require anchoring, have no definite minimum distance requirement.
What in your judgement would be the appropriate clear space given the
facts I mentioned above.
|Date||August 13, 2004|
I believe that you recommendations for anchoring of temporary concrete barrier are acceptable assuming you are refering to the F-shape temporary barrier design developed here at MwRSF. As stated in the report I gave you previously, the F-shape PCB can be safely used unanchored with 2' of clear space behind the barrier based on the 85th percentile impact. For distances less than this or installations with a sharp drop at the end of the clear space, an anchored PCB is more appropriate. This is basically agrees with what you have told me about the Wisconsin standard. Therefore, I would recommend that you stick with your currently guidelines for now.
The difference between our recomendation for the F-shape barrier as opposed to what some other states may recommend is likely due to the use of differenent PCB systems. Different PCB designs have vastly different deflections based on the type of section, the length of the section, and the connection between the barriers. North Carolina uses a 10' long NJ shape barrier with little reinforcement and a relatively weak connection when compared to the F-shape developed here. It will experience higher deflections than the F-shape and thus they have likely used more forgiving clear areas behind the barriers.
Hope this help you out. Let me know if you have more questions.
|Date||August 16, 2004|
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