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Would you like responses based on MASH testing when available? Or, do you only want responses based on NCHRP Report 350 testing?

Both MASH and NCHRP will be important to us.  For now especially, a response based on NCHRP 350.  We have a contractor which will have to stage another section of a project in March, that would entail several of the below scenarios.  Currently, we have NCHRP 350 barrier in place.  I know March seems a long time, but the sub-contractor is wanting to provide a cost for the installation to us. 

Side note:  We are very interested in the MASH testing of our Iowa style barrier because we have so many contractors who have invested in that type of barrier.  Thank you for all the help you provide us. 

I do a lot of the research related to PCBs here at MwRSF, so I will try to respond to your question to Ron.

First, anchoring of PCBs depends on the barrier system being used because every PCB anchorage cannot necessarily be used with any PCB design. I noted in the email that you mentioned you were using the Iowa PCB design. The PCB design that we have developed anchorages for is a version of the original Iowa F-shape PCB that has been modified over time. The current iteration that has been used in our MASH testing is attached. We would recommend that your barrier be similar to this in order to employ the anchorages we are discussing. Note that this is details for NDOT’s version of the barrier with slightly different draining/lifting slots. The MASH TL-3 free-standing barrier report can be found at this link - https://mwrsf.unl.edu/researchhub/files/Report150/TRP-03-174-06.pdf

Second, we have developed several anchorage methods for this F-shape PCB.

1. A concrete anchorage that uses through bolts or epoxy threaded rod anchors. This system has been tested to both NCHRP 350 and MASH.
2. An asphalt pin anchorage. This system met NCHRP 350, but recently failed when tested to MASH TL-3. We are working on revising and retesting this system.
3. A steel strap anchorage. This system has only been tested to NCHRP 350.

Currently the only system we can recommend for median installations is the steel strap tie-down. The asphalt pin and concrete bolted options were designed and tested only for anchorage on the traffic side face. Application of these options to two-way traffic installations has not been recommended in the past due to the need to place anchors on both sides of the barrier system. There are concerns that anchors on the backside of the barrier can create a rotation point when impacted and that may cause increased vertical barrier rotation and potential vehicle instability.

Now to your 4 questions below.

1. The  roadways have two 12-ft lanes and at least 2-feet of shoulder between the lane line and barrier.  Do you have to pin the barrier or can you leave the barrier free standing?
1. Under NCHPR 350 MwRSF did an analysis on the F-shape PCB to account for more typical and slightly less severe impact conditions than we test to under TL-3 conditions. For this study, we analyzed the deflection of the F-shape PCB under the 85 percentile speed and 85% angle impact conditions and determined the barrier deflection under those reduced impact conditions.  Based on that study under NCHRP 350, we concluded that when the barrier is used in a free standing mode, immediately adjacent to the edge of a bridge deck, the design deflection limit should be the distance that the barrier was deflected during full-scale crash testing, 1.15 m (45.3 in.). For all other applications, the design deflection limit should be set at 600 mm (2 ft). This distance corresponds to the distance that the Iowa temporary barrier could be expected to deflect under the 85th percentile impact for passenger cars and light trucks. We also noted in that report, “When used to separate traffic, barrier deflections up to 600 mm (2 ft) would not cause a significant problem for opposing traffic. Even in narrow construction zones, traffic lanes of less than 3-m (10-ft) wide are rare, and a 600-mm (2-ft) lateral barrier displacement would not intrude significantly into the paths of oncoming traffic. Although larger deflections could begin to intrude into the normal paths of 2 oncoming traffic, the risk of an accident involving opposing traffic is still relatively low. Even when a vehicle in the opposing lane strikes a deflected barrier, the impact angle associated with any resulting crash would be expected to be extremely low. For this situation, the consequences of exceeding the deflection limit are not catastrophic.” Thus, this would suggest that for NCHRP 350, we would allow this configuration without anchoring.
2. https://mwrsf.unl.edu/researchhub/files/Report243/TRP-03-113-03%20(revised).pdf
3. It should be noted that this would not hold true under MASH as the expected deflections for that PCB effectively double. We did a similar analysis under MASH (https://mwrsf.unl.edu/researchhub/files/Report331/TRP-03-337-17.pdf), but the 85 percentile impact condition deflections were 68” rather than 24. At this level the intrusion into adjacent lanes may be too high to ignore.
2. The roadways have two 12-ft lanes but the lane line is less than  6-inches from the barrier.  Do you have to pin the barrier or can leave the barrier free standing?  Would you pin only one side or both?
1. Due to the limited space, one would generally need to anchor the barrier in this situation to prevent excessive intrusion into adjacent lanes. However, we do not currently have a pinning solution for this situation as noted above. The asphalt pin and the concrete anchorage have not been evaluated in a median configuration to either NCHRP 350 or MASH and concerns exist as noted above.
2. The steel strap anchorage deflection was approximately 33” under NCHRP 350 TL-3 which would suggest intrusion into adjacent lanes. We
3. However, we have previously argued that limited intrusion into opposing lanes may not be a major issue under NCHRP 350 as noted in TRP-03-113-03 above. Thus, under NCHRP 350, one may consider not pinning or anchoring in this situation.  Under MASH TL-3, this would not be recommended.
3. The roadways have three 10-ft lanes but the lane line is less than 6-inches from the barrier.  Do you have to pin the barrier or can leave the barrier free standing?  Would you pin only one side or both?
1. See no. 2.
4. The roadways have two 12-ft lanes but at least 2-feet of shoulder on one side of the barrier.  The other side of the barrier roadway has two 10-ft lanes but the lane line is about 6-inches from the barrier.  Do you have to pin the barrier or can leave the barrier free standing?  Would you pin only one side or both?
1. See no. 2.
2. You may want to consider placement of the barrier midway between the opposing lanes.

Let me know if you have further questions or concerns.

Thanks