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|Description Text||We have a situtation where our Traffic Program set up to use our old portable concrete barrier (details attached)on a bridge deck over Interstate 80 placed 6 inches from the edge. The installation is in a workzone while the bridge deck is reconstructed. The speed will be posted at 30 mph and due to geometry it is unlikely the speeds would be much higher. The barrier would not meet NCHRP 350 for TL-3 as it only uses a single loop on each side of the barrier, top and bottom. However, it is likely to be a TL-2 barrier. The question is, for this situation, does it need to be pinned to the deck? If so, is there another solution such as the New York design with box beam mounted on the back of the barrier?|
|Date||May 21, 2013|
In the past, MwRSF estimated deflections for the F-shape PCB at a speed of 36 mph and an angle of 27.1 degrees when impacted with the 2000P vehicle. This analysis produced a estimated deflection of 24 in. Based on this, it would seem reasonable to assume that the NJ barrier in question would have similar deflections if impacted at 30 mph. Thus, there is a potential for the cg of the barrier segments to extend over the edge of the bridge deck. This suggests that the barrier segments would require some form of constraint to retain the barrier sections on the deck edge at a spacing of 6 in.
The box beam system that was tested with the New York NJ TCB section was successful in reducing deflections. MASH testing of the NY NJ TCB showed dynamic deflection of 40.3 in. for the free-standing barrier and dynamic deflection of 30.9 in. for the barrier with box beam across the back side. However, it should be noted that the test NY NJ barrier system used a I-beam connection with little to no gap between barrier segments and a 20-ft segment length. In addition, the test NY system pinned/anchored the ends of the barrier system, which further reduced system deflections. Thus, using the box beam to stiffen your system should reduce deflections, but it is difficult to be confident that the deflection reduction would be similar to the tested system due to the barrier differences.
Determination of more accurate deflections and the ability to retain barriers on the deck would likely require analysis and simulation. Thus, the best recommendation for this situation would be to anchor the barrier segments. If the NJ shape you are using does not have pockets for anchor pins, one could use the steel strap tied-down that was tested with the F-shape barrier. This would likely reduced deflections and would help maintain barriers on the bridge deck during an impact event. It uses drop in or mechanical concrete anchors rather than through bolting and should be installable with the loops on you barrier system at TL-2. One item to note is that this system requires a constraint bolt through the base of the pin to prevent it from pulling through the loops under loading.
We have also developed and tested a preliminary version of an unanchored, reduced deflection retrofit for Wisconsin. This system would likely work as well, but would need to be adapted over to work with a NJ shape rather than an F-shape. It would cost significantly more to install than the steel strap tie-down.
We can provide details for either system.
Please contact me with further questions.
|Date||May 21, 2013|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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