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|Description Text||I would appreciate any comments you have on the barrier transition drawing below. There is a need for Ohio to improve the way we are transition from PCB to rigid structures. I have included some pictures from construction projects in Ohio. We know that additional testing is needed but until then we would like to do the best we can. We took the results of the K barrier report and created layouts of our Jersey shaped PCB to different rigid structures. The anchor holes are 1.125" in diameter so we changed the soil anchors to 1" in diameter.|
|Date||August 31, 2010|
I have gone through the transition plans that you sent and I have a few concerns.
1. The overall layout of the transition looks acceptable based on the design that we have developed here using the F-shape barrier. However, the barrier alignment will need some adjustment for some of the installation cases you have shown. The approach transition design was tested with the 42-in. tall, CA single-slope median barrier because this barrier was identified as the most critical barrier design for the transition. However, there are other permanent concrete median barriers that can be attached to the approach transition as long as the following guidelines are applied.
a. If the permanent median barrier is 32-in. high, the sloped, steel transition cap is not required for the transition. For barriers with heights greater than 32-in. high, the steel transition cap if required. The cap design can be adjusted for different height and shape barriers as long as adjusted cap provides equivalent slope, permanent barrier coverage, barrier overlap, structural capacity, and anchorage as the original design.
b. Alignment of the temporary barrier system with the permanent barrier may also change when the transition is applied to different permanent barrier geometries, as shown in below. When attaching to a single-slope barrier profile, the slope break point between the toe of the barrier and the main face of the barrier should be aligned flush with the oncoming traffic side of the single-slope barrier. For safety shape barriers, the toe of the temporary barrier should be aligned flush with the toe of the oncoming traffic side of the median barrier. Vertical median barriers require that the toe of the temporary barrier segments on the reverse direction traffic side be aligned with the base of the permanent barrier on the reverse direction traffic side. These alignments will prevent vehicle snag for oncoming traffic on the permanent median barrier while preventing snag on the toe of the barrier for reverse direction impacts. (See Figure 1.jpg)
c. The thrie beam sections that span the gap between the end of the temporary barrier and the permanent median barrier should be used in all instances.
2. I would recommend that you check taper on the vertical transition section to higher median barriers. The system we tested used a vertical taper of 11.4 degrees. We would not recommend tapering to the taller barrier at a rate faster than that.
3. I have concerns with the size of the anchors used in the design. Asphalt pins in your system are much smaller than tested (1" diameter versus 1.5" diameter pins). This may cause significantly lower pin reaction forces and thus lower constrain of the barrier.
4. Similarly, the threaded rod anchors smaller shown in your details appear to be smaller diameter than the A307 threaded rod anchors we have used in the past, but they are listed as high strength. What specifically is high strength? These may be acceptable.
5. In reviewing your barrier details, it appears that the barrier reinforcement is insufficient around the pin or bolt pockets. The F-shape barrier we tested with had specific reinforcement loops for those areas. During testing, those loops have been shown to be the primary restraint that contains the pins. Without that reinforcement in place, I do not believe that the tie-down system will function.
6. The barrier you use appears to be a NJ shape barrier. We cannot recommend this barrier for use with the tie-down system without further testing. Testing of the tie-down and transition systems has shown that the sloped face and toe of the barrier can rotate back during impact causing vehicles to ride up the barrier and increase instability. We believe that the NJ shape will make this behavior worse with its higher toe section. As such, we would not recommend NJ shapes with the tie-down systems shown.
7. We also have concerns with JJ-hooks connections with a tie-down system. We would not recommend this connection for use in an anchored barrier system. The JJ-Hooks connection is fine for free-standing systems. However, to be safely used in an anchored barrier or approach transition, the barrier joints must have comparable or greater torsional rigidity about the longitudinal barrier axis when compared to that of the as-tested configuration. JJ Hooks connection is not similar in torsion to the Kansas barrier joint, and the JJ Hooks connection is also non-symmetric in that it has different capacities depending on the direction it is loaded.
There are certain barrier types out there that use cable loops or other types of connections such as JJ Hooks that have significantly different torsional capacity than the F-shape we were working with. Thus, we feel the need to warn that applying tie-down anchorages to a barrier with less torsionally stiff joints could promote vehicle instability through barrier rotation or snag.
|Date||September 9, 2010|
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