|Logged in as: Public User|
Sending this question to you since your name is on the paper...
Based on the June 18, 2003 research report, Deflection Limits for Temporary Concrete Barriers, Ohio has followed a 2' offset general standard.
However, we have an upcoming project on our Cleveland Innerbelt bridge on I-90 (main freeway through downtown), that has some additional criteria/concerns:
Temporary Concrete Barrier will be separating 6 lanes of opposing traffic: 2 Eastbound, 4 Westbound. 50mph. This phase of traffic will be on a new bridge deck, waiting for a 2nd bridge to be constructed for the traffic in the opposite direction.
Project duration may be DECADES depending on funding for the 2nd bridge. Thus we are facing a potential semi-permanent installation using temporary barrier.
The discussion is whether or not to anchor the temporary barrier. Obviously, the bridge guys would prefer not to put anchor holes in their brand new deck.
· Your report based on Iowa's Temp Concrete Barrier...Roadside Design Guide indicates NCHRP 350 deflection 45"; while Ohio's barrier deflected 66" when tested.
· Another point in the report, bottom of page 1 "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." I interpret this to mean that even if the path of oncoming traffic is reduced (temporarily until the barrier is moved back) to as little as 8' wide, the risk of an accident from opposing traffic is still low. Was that the intention?
· Another point to consider is the length of temporary barrier on the bridge " approx. 4200 feet has quite a bit more mass holding it in place as compared to the couple hundred ft test section. Yet with 4 lanes of westbound traffic, we anticipate the potential for increased impact angles
· Cross section sketch of barrier placement attached
Based on all of that, would you advise to anchor the barrier in order to limit deflection during the duration of the project? Any other points to consider?
|Date||February 14, 2012|
|Attachment||Ohio pcb schem.jpg|
Will you be using the Iowa Temp Barriers with the 45" of deflection or Ohio's with the 66" of deflection?
|Date||February 15, 2012|
We are using Ohio barrier, 66" deflection.
|Date||February 16, 2012|
First, we want to caution you on using the Ohio PCB in a permanent application. Recall, PCB's should only be used in short-term temporary applications. If you are looking at the project duration being DECADES, we would recommend placing a permanent barrier especially since it is separating 2-way traffic with lane width reductions. Recall, the more exposure you have the more permanent the barrier should be.
If the PCB's will only be used for a short-term duration, we ran a primitive set of calculations to help us get a hand on the deflections that may be encountered by the Ohio PCB at 50 mph. Free-standing PCB (Iowa/Kansas) impacted at 62 mph deflected 45". From the reference report (Deflection Limits for Temporary Concrete Barriers), at 36 mph free-standing PCB (Iowa/Kansas) was predicted to deflect 24". Therefore, at a 42% speed reduction there was an approximate 47% deflection reduction. For simplicity sake (and erring conservatively), we can say it is a 1 to 1 reduction. With the Ohio PCB when impacted at 62 mph in the free-standing configuration, it deflected 66". Therefore, at 50 mph (approximately 19% reduction) we can estimate the deflection of the free-standing Ohio PCB to be approximately 54" (4.5'). From your sketch of the barrier placement, this would mean there would be a potential for 1' of intrusion into the lane adjacent to the 3.5' temporary shoulder (2 lane side) and 2' of intrusion into the lane adjacent to the 2.5' temporary shoulder (4 lane side).
From this and if it will only be a short-term application, we recommend centering the free-standing PCB in the "median". Thus, you would have 3' temporary shoulders. Which would mean that the potential intrusion into either direction of traffic would be 18". In addition, we also recommend using lots of speed signs and even reduce the speed if possible.
Note the 4200' length of the temporary barriers on the bridge will have minimal effects (if any) on the deflection the system could sustain. When the Iowa/Kansa PCB was tested in a free-standing configuration with a length of 200', the longitudinal movement of the system was only an inch or so.
In addition, since the application you are using the Ohio PCB is a median application, we have concerns with anchoring the Ohio barrier. I am attaching the email correspondence that Bob Bielenberg had with Michael Bline in July 2009 in regards to tied-down Ohio PCB and the recommendations. A brief summary:
(1) Backside anchors cause concern since testing had not been conducted on tied-down PCB with anchors on both sides
(2) Ohio PCB anchorage insufficient to develop full strength of the threaded rods
(3) Ohio PCB anchor pockets reinforcement insufficient to develop full strength of the threaded rods.
(4) JJ-Hooks connection torsional rigidity is not sufficient for tied-down applications.
Please let me know if you have further comments or concerns.
|Date||February 17, 2012|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
The information contained on the Midwest Roadside Safety Facility (MwRSF) website is subject to change without prior notice. The University of Nebraska and the MwRSF is not responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the use or misuse of or reliance upon any such content, goods, or services available on this site.