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|Description Text||Mr. Bielenberg,
SCDOT historically used a device we referred to as “critical offset guardrail” often for bridge pier protection and in some cases adjacent to drop-offs when very limited shoulder space was available between the edge of travel and the hazard. We are looking for products that could be used to upgrade some of these sites that would fit within the same footprint and not introduce drainage changes that rigid barriers will introduce.
Critical offset consisted of Nested Thrie-Beam rail with W6x8.5 posts (6.5’ long) at 1’-6.75” post spacing with 8” deep composite offset blocks.
We will most likely be using rigid barriers for many of these conditions in future designs, but we hope to find a suitable tested product that can be used to retrofit existing sites.
Can you provide us with a list of semi-rigid or post and beam style devices that are MASH tested (or even available under NCHRP Report 350 testing) that meet Test Level 5 requirements? If you can provide links to reports or letters for these devices that would be very helpful.
If you are not aware of any products that meet test level 5 conditions, can you provide any recommendations for details appropriate to meet the requirements of Roadside Design Guide for Zone of Intrusion (page 5-34) and AASHTO LRFD Bridge Design Specification 3.6.5 and conditions outlined in SCDOT Bridge Design Memo DM0213.
Additionally, do you have thoughts on what conditions are appropriate for these barriers?
If site has lower ADT, lower speed, or lower truck traffic, would other barriers suffice?)
|Other Keywords||Pier Protection|
|Date||October 17, 2018|
I have some comments on your email.
First, with respect to thrie beam, no thrie beam system has met MASH TL-3 at this time. The original G9 thrie beam system was tested during NCHRP 22-14(3), but it resulted in rollover of the 2270P vehicle. We believe this was due to the blockout length and can be solved easily. This issue came up during the pooled fund meeting last year, but it did not move forward. SDDOT would like to evaluate thrie beam as well as thrie beam with curbs. Further reduction of deflection through reduced post spacing and nested could likely be achieved, but it would require additional analysis and testing.
We also plan to test modified thrie beam to MASH TL-3 for NJDOT and CALTRANS within the next week. This would be another thrie beam option.
Both the standard and modified thrie beam systems are NCHRP TL-3 system currently. Modified thrie beam was tested to NCHRP 350 TL-4 and may work under MASH TL-4, but it would need to be tested.
However, it appears that you are looking towards higher service level barrier to shield piers and abutments. The only beam and post type system I know of for this is the ArcelorMittal TL5 Steel Median Safety Barrier. For this system, passenger car deflections are low, but the TL-5 deflection are over 4’ and the working width is almost 5.5’.
There are several concrete barriers that could be used in this type of application that would meet TL-5 and limit working width, but it sounds like you are looking for something less costly. We can help with these if you are interested.
In terms of the warrants for bridge pier shielding, NCHRP 12-90 was conducted to deal specifically with this issue. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3170 The website states it is completed, but I have not seen and cannot locate the final report. You may want to contact Mac Ray at RoadSafe and see if he can get you the results of that study.
These issues may be something to consider for the upcoming Year 30 problem statements for the Midwest Pooled Fund. SCDOT can submit them if they would like to. I have SCDOT on the mailing list, but I am not sure if you get the problem statement submission information. I have forwarded it to you.
Let me know if that addresses your questions and if I can help you in any other way.
|Date||October 30, 2018|
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