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NJ Safety Shape Median Barrier Curb

Question
State NJ
Description Text

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.

The current hardware guide details basically contain the 1995 version. Both versions state:

AS PAGE 2 OF 4 OF THE FIGURE STATES UNDER "INTENDED USE", SECOND PARAGRAPH, THE "10 FT LONG, 10 INCH DEEP REINFORCED ANCHOR FOOTING SHOWN SHOULD BE PROVIDED AT BOTH ENDS TO PROPERLY SECURE THE BARRIER. OTHER COMMON METHODS OF SUPPORTING THIS BARRIER INCLUDE SETTING THE BARRIER IN A CONTINUOUS KEYED FOUNDATION OR DOWELING THE BARRIER TO A FOUNDATION."

Based on the hardware guide language above, I interpret that to mean that each state will design the footing for the SGM11a-b. Only one version is shown in the highway guide. I looked at the entire length of Federal acceptance letters on the web ( http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/listing.cfm?code=long) and have not found any federal acceptance letters concerning other footing designs for the SGM11a-b. These letters go back to 5/31/1985. If crash testing of the various state footing designs were required, why are there no acceptance letters for the different footing types the hardware guide referred to?

Another reason why I believe we do not need crash tests and acceptance letters for footing design is the same reason for the Transpo Breaksafe Sign Support System. The Breaksafe was crash tested and approved for the Breaksafe base and parts. Transpo told us that the footing design is up to each state. Each state did not have to get their footing designs crash tested and approved.

The SGM11a-b has no reinforcement except for some rebars near the top to prevent large pieces of barrier breaking off and falling into the traveled way in a severe collision. I believe the barrier reinforcement criteria you referred to in the LRFD specs in Chapter 13 are for bridge parapets, not median barrier.

I will basically give this info above to the Feds in NJ and hope that they agree with me that NJ's 9" deep continuous keyed foundation does not have to be crash tested and approved. If so, where are the other approved foundations that the hardware guide referred to? Also as you have stated, approval letters began from 1985 on. Since the original NJ barrier was crash tested prior to 1985, no approval letters exist.

Keywords
  • Permanent Concrete Barriers
Other Keywords none
Date January 17, 2014
Attachment sgm11a-b_4.pdf


Response
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


Response
Response

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
Attachment barrier curb_2014012310212300.PDF
Attachment ConcreteBarrierResearch_2014012314131800.PDF


Response
Response

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


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