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Bob: For Report 350 TL-3 transitions from freestanding PCB on asphalt (2” min) to bolted PCB on concrete, we have specified the Kansas PCB and pinned transition according to details in TRP-03-180-06 (9 steel pins on traffic side over 5 PCBs and nested 12ga thrie beams on front and back at connection to permanent or bolted PCB – Figure 38 on page 63).

We currently need a transition from freestanding PCB on concrete to bolted PCB on concrete, and would appreciate clarification with respect to statements on page 91 of report regarding asphalt and bolt-through concrete tie-down systems are believed to possess similar lateral restraint and thus can be interchanged in the transition design as needed. Would it be acceptable to drill through 8” to 9” thick concrete pavement on the transition and use 9 standard 1-1/2” dia x 38-1/2” long A36 steel pins that are normally used for asphalt as we can’t use the 1-1/8” dia A307 threaded rod?

There are a couple of options here. First, I should note that the free-standing PCB to concrete bolted PCB transition for roadside applications has not yet been evaluated to MASH. The median transition was however evaluated to MASH. Both the median and roadside designs were evaluated with the asphalt pins. The roadside and median transitions use similar pin configurations, but the median transition was designed for attachment to taller, concrete median barriers and used pins on both sides of the system. Pins were applied to the both sides of the median transition to prevent the potential for impacting a the barrier in a region that only has pins on the backside of the PCB. Previous research at MwRSF and CALTRANS has suggested that pins on only the backside of the PCBs can promote tipping of the barrier which can increased vehicle climb and instability.  

Additionally, you are correct that we have noted in past PCB transition reports that the bolt and pin tie-downs would have similar barrier restraint and that either could be used in the transition.

Previously, we have been asked about installing the 1.5” diameter pins through concrete pavement with an asphalt overlay. At that time, we noted that it was believed that the asphalt pin tie-down could be used with concrete pavement with an asphalt overlay. This would be stiffer that what we originally tested, but we think it is was a viable option. The pins should not fracture, but would tend to bend and pull up. We believed that they will constrain the barriers.

Your request is somewhat similar in that you are installing the pins through 8”-9” of concrete with no overlay. I think that this would fall somewhere between the stiffness of the asphalt pin and bolted anchorages. I would recommend that the drill holes be only 1/16" to 1/8" larger than the pin diameter. This would be a maximum bit size of 1.625". The hole in the pavement needs to be kept as small as possible to make the pin engage as soon as possible during the impact. For installation, it may be easier to set the barriers down and then drill through the existing holes in the barrier as guides to make sure the pins will fit.

A potentially better option would be to use the bolted option with shorter epoxy rod embedment. We recently re-evaluated the bolted tie-down for the F-shape barrier as part of MASH Implementation updates. In this MASH testing, we used 1 1/8” dia. A307 threaded rods similar to the previous NCHRP 350 testing, but we only embedded the rods 5 ¼” into the concrete. This test met MASH TL-3 criteria, but the report is not completed. System drawings are attached. Use of this reduced embedment anchor rod would probably be the best option for you in the transition when installed on a 8”-9” thick concrete pavement.

While reviewing this issue, we also reviewed TRP-03-208-10 which has a MASH TL-3 transition from freestanding PCB on asphalt (3” min) to bolted PCB on concrete. We noticed a similar statement on page 109 regarding asphalt pin and bolt-through tie-down systems are believed to possess similar lateral restraint and can thus be interchanged in the transition design as needed. As asked in previous paragraph, would it be acceptable to drill through the concrete and use the steel pins normally used for asphalt.

The same logic would apply here. The asphalt pins could potentially be used, but the minimal embedment anchors that were recently MASH tested would likely be a better solution.

With respect to the MASH TL-3 transition from freestanding PCB to permanent concrete median barrier, for transitions to bolted or permanent concrete roadside barrier (such as on a bridge with traffic on one side only), are the steel pins needed on both sides of the PCB (9 x 2 = 18 pins over four PCBs) when traffic is on one side only?

If you have traffic on one side only, then the backside pins are not likely needed. As noted above, they are there to provide to prevent barrier tipping during reverse direction traffic impacts. I believe that the stiffness transition from free-standing to fixed barrier would be adequate with only the frontside pins. You would want to follow the snag reduction guidance for PCB alignment with the concrete median barrier and the use of the upper steel cap if the concrete median barrier has increased height.