|Logged in as: Public User|
Thanks you for returning my phone call. I think when I spoke to you this morning, you may have thought I was talking about the NJ safety shaped parapet. I was talking about the Safety Shape Median Barrier (Hardware Guide SGM11a-b), see attached detail. The last time it was approved was via the FHWA memorandum entitled Report 350 Nonproprietary Guardrails and Median Barriers dated Feb, 14, 2000, see attached memo. In this memo FHWA summarizes and describes all non-proprietary longitudinal roadside and median barriers that have met Report 350 requirements. Where applicable, the reference page number for each barrier included the 1995 AASHTO-AGC-ARTBA "Guide to Standardized Highway Barrier Hardware." As you can see on page 2, the 32" high safety shape barrier was approved for TL-4 and the reference page "SGM11a" is next to it. They deferred to the 1995 hardware guide details.
|Date||January 17, 2014|
|Response||I am not sure when the original version of this barrier was crash tested with the noted 10” footing. However, if you like, I can dig up some old testing references (possible from Southwest) to try to find the original tests. Just let me know if this would be of use to you. If so, it would also help to have a copy of your current state standard – reinforcement configurations for both interior and end sections. There have been a number of tests utilizing various anchorage designs. We would just need to find crash tests of a comparable barrier with a particular anchorage to justify the anchorage you desire.|
|Date||January 17, 2014|
Thank you very much for your help. The information contained in the on-line hardware guide pertaining to the footings for SGM11a-b appears to be the same info that was in the 1994/1995 published hardware guide. The 1995 hardware guide SGM11a-b (drawing dated 1994) and the current SGM11a-b (drawing dated 5/16/2005) site the same research references (March 1976 and May 1986). The 1986 reference mentions Dean Sicking. Our DOT library had a copy of the March 1976 reference which turned out to be FHWA-RD-77-3-4 dated June 1976 Final Report. The NJDOT ordered a hard copy of the May 1986 reference. The March 1976 (June 1976) reference contained info on the various footing designs for the 32" barrier. A Math model was developed to evaluate the Concrete Median Barrier (CMB) foundation restraint for stability. From this, they created Figures 52 and 53 which determines footing depth, dowel depth and keyed footings, see attached pages.
I also attached a pdf of NJDOT construction details CD-607-3 and 607-2.1
|Date||January 17, 2014|
A few comments as I have glanced through the figures you have provided
1. The original research report was from 1976, thus it predates even NCHRP 230 (which predated NCHRP 350). Therefore, the impact loads used to evaluate the barrier and anchorage options may be significantly lower than the impact loads to which barriers are evaluated under the current MASH standard, or even the old 350 standard. As such, any recommendations made from the report should be taken as absolute minimum requirements for strength.
2. The report’s recommendations for using asphalt keyways are for segment lengths of 30 ft. However, your construction details call for joints every 15 ft. Therefore, an asphalt keyway alone may not be enough to anchor the barrier.
3. The report’s recommendations for using dowels to anchor the barrier are to utilize a #8 bar every 18”. Your construction details call for the dowels to be spaced at 4 ft intervals. Again, using dowels alone may not be enough to anchor the barrier.
4. I don’t see a discussion within the report of the strength of the anchorage if both an asphalt keyway and dowels are utilized. Without conducting additional analysis or a crash test, it would be difficult to prove adequate anchorage compared to the original recommendations.
5. In terms of the Hardware Guide’s recommended minimum embedment depth of 10” for a footing within 10 ft of a discontinuity (end or open joint), your 9” deep footing is very near this mark, but still below the minimum requirement. I’m not sure where this requirement was established, but it may be hard to get around without a crash test proving a shallower embedment will suffice.
I am curious as to what FHWA will have to say about your request to utilize this anchorage scheme. We have been unsuccessful in requesting an approval letter for other concrete barrier systems in recent history based on anchorage details. One barrier in particular utilized an 18” x 18” footing reinforced with torsion and longitudinal steel to support an 8” wide vertical barrier. The system was even successfully crash tested to NCHRP 350, but FWHA still would not grant an approval letter. Please keep me posted on FHWA’s response to your request.
Let me know if you have additional questions.
|Date||January 23, 2014|
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.