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FLDOT Median Barrier

Question
State FL
Description Text Please take a look at the lightly reinforced concrete median barrier shown in the attached PDF file. Have you ever seen anything like this one? What test level criteria do you think this would meet?


It is difficult to determine from the drawing, but there are three #4 longitudinal bars (one near the top and two near the bottom) shown in "Section A", which is most likely intended to resist lifting and handling stresses. Since the drawing is not to scale, the aspect ratio of the elevation view may be misleading. There are only four anchors per unit (anchors paired transversely, then spaced at +/- 10.5' o.c. longitudinally). Would this affect your opinion?
Keywords
  • Permanent Concrete Barriers
Other Keywords none
Date June 11, 2010
Attachment Scan001.pdf


Response
Response

I have looked over the median barrier detail you sent and I have some concerns with it.

 

  1. The barrier has no longitudinal steel that I can identify. As such, I the capacity of the barrier sections are very limited and you could expect a large amount of fracture and cracking in any impact.
  2. It appears that the barrier sections are in segments with no connection between them. This has been show to be very detrimental to impact performance. When the a vehicle impacts one segment, you get a large shear displacement of the unconnected segment relative to the next segment downstream. This leads to snag on the downstream barrier which can cause excessive decelerations and vehicle instability. In addition, the lack of continuity between barrier segments increases the load on any one section that is impacted. Thus, with the lack of reinforcement in this barrier, you can expect an even higher level of barrier fracture and damage.
  3. The anchorage capacity used for the sections is difficult to judge. The anchors do not appear to have a lot of capacity, but they are closely spaced. However, these anchors will do very little to address the two points above.

 

I see the longitudinal steel now. This is still a very low amount of reinforcement for a TL-3 barrier and I would still expect the damage to the concrete sections to be very high. I can only see two anchor per unit, and they appear to be 1' apart longitudinally. Additional anchorage may help on some level, but the if the barrier is constrained more rigidly, the loads in the sections will increase. Thus, the lack of reinforcement becomes a more significant issue. For example, we tested the F-shape PCB section in as similar bolted down configuration at TL-3 with the 2000P vehicle , we observed cracking and fracture of the barrier section completely through the mid span of the barrier. Subsequent testing of the F-shape barrier with the 2270P vehicle has shown similar levels of damage in less constrained configurations. This PCB section has much more reinforcement and an joint connection to help distribute loads and it appears to be at or near its peak capacity. Thus I would assume that this section will not fare as well.

 

The concerns for lack of connection and continuity still hold true regardless. Thus, I would still be skeptical of the barriers TL-3 performance, but there may be potential for TL-2.

 

I have not seen a detail like this before. I would not expect this system to pass TL-3 of NCHRP 350 or MASH. There may be some chance of it passing at TL-2, but more analysis would been needed.

Date June 14, 2010


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