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Dear MwRSF,

Below is an email from one of our major project teams who are building some tunnels as we speak. They are having an issue with the stand pipes. Do you have any suggestions

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Subject: Mitchell Interchange Standpipe Protection

As discussed last week, the Mitchell Interchange Construction team is looking at options to enhance standpipe protection within Tunnel construction at the request of the City of Milwaukee Fire Department. MFD is requesting "the maximum, reasonable,
protection and/or isolation of the standpipe outlets from vehicular damage".

Currently the standpipe system has been protected with 7" (+/-) lateral offset to connection fittings in Tunnel 3. Tunnel 1 and 2 will have nearer to 10" of lateral offset to standpipe that is located about 18" above the top of barrier. Our construction team has dismissed the potential to change to vertical face barrier due to potential increased damage to vehicles involved in a crash.

Construction team has identified that we have met NFPA requirements:

9.3.3 " Fire department connections shall be protected from vehicular damage by means of bollards or other approved barriers.

9.4.3 " Hose connections shall be located so that they are conspicuous and convenient but still reasonably protected from damage by errant vehicles or vandals

Team has discussed locating bollard, or some physical protection on top of the barrier at the same offset as the standpipe fittings. You offered some hesitation with that alternative in our phone call last week, and also potential to look at other alternatives. Can you look into, and get me an assessment on physical protection alternatives " bollard and other?

Appreciate your help in advance.

We are unaware of any special protection barrier systems that have been designed and tested for use in shielding water values which extend off of the tunnel side walls and above the vehicular barriers. However, if safety treatment is desired, it would seem possible to design steel or reinforced concrete structures which anchor to the top of the concrete parapet and possibly to tunnel wall in order to prevent vehicle snag, and even occupant snag, on the pipe hardware.

If this barrier option is considered, then the upstream and downstream ends should be sloped to mitigate snag concerns as the additional protective barrier which falls within the zone of intrusion. As noted above, these systems could be attached to barrier or tunnel.

Alternatively, it may be reasonable to consider design changes to the pipe system, such as to recess more the structure (i.e., 2 outlets and handle for valve) within the tunnel side walls, thus greatly reducing concerns for vehicle snag, and even occupant snag, on the pipe structure.

Please let me know if you have any further questions or comments regarding the information provided above.

After looking at the standpipe issues further, we are concerned that the standpipe can be impacted based on the ZOI for the barrier in questions. In order to address this, I came up with the concept attached. It consists of telescoping tubes that shield the stand pipe. Access to the stand pipe would only require removing the drop pins and sliding the middle tube into the larger side tubes.

This design should protect the standpipe from interaction with impacting vehicles. I have not fleshed out the anchorage details yet, but I wanted to get some feedback from you on the concept.

Thanks

The fire department didn't like the standpipe design.   Construction team is asking if we could use the top portion of our combination rail design.  I've attached a link to the railing details.

<http://on.dot.wi.gov/dtid_bos/extranet/structures/LRFD/standards/3005.pdf>

I believe that the railing design shown can prevent interaction with the stand pipe as desired. However, we have seen potential for horizontal railings to promote vehicle instability when mounted on single slope barriers. In previous pedestrian rail testing on a 32" single slope, we found that the horizontal railings provided vertical restrain on the front corner of the vehicle which caused it to roll towards to the barrier and become unstable enough to rollover. Please refer to the attached report.

We would have concerns for the railing shown potentially affecting vehicle stability. I don't recall the speeds in this areas. Obviously, if the speed were limited to TL-2 type speeds, then the concern becomes much less.

This was the rationale behind the design we sent previously having a solid front face.