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ZOI

Question
State
Description Text

I was wondering if you'd be able to send me your report (Guidelines for  Attachments to Bridge Rails and Median Barriers: regarding the ZOI) for  consideration in my review of a recent submittal for a continuous CRB  median barrier that tapers up to cast-in-place 1350mm high (with a  vertical face) near the location of bridge piers behind the median. I am  no longer with Equilibrium and am now working on a major bridge project  reviewing engineer's submittals for a different project.

 

The divided highway is a 90 kM/hr high use one, and I have personally  never seen a Vertical face barrier of 1350 high with a 453 minimum  clearance (measured from traffic side to face of pier behind) ZOI behind  it (610 is noted as being preferred).

 

In general cases,  should the geometry of the vertical 1350 height face  beyond the physical obstructions and the taper zone back to the typical  CRB height be defined on drawings? Is 453mm an acceptable minimum ZOI?

 

If you can send the document by PDF, it'd be appreciated. Let me know if  you have any questions, or if the above is unclear.

Keywords
  • Temporary Barriers
Other Keywords none
Date April 21, 2010


Response
Response

I have enclosed a copy of the requested report. Please note that the ZOI information mostly pertained to test levels 3 and 4. Information for TL-5 was not determined nor provided therein. However, as barrier height is increased, the ZOI would decrease for TL-3 and 4 conditions.

 

Various height for rigid parapets have been used across the U.S. For TL-5 barriers, it is common to use 42" tall parapets. In addition, it is not uncommon for States to use 51 to 54" tall parapets when shielding objects or for additional glare screen protection.

Date April 27, 2010


Response
Response

My responses to your recent email are in red


Some questions related to ZOI and traffic barriers;

  1. Treatment of CRB placed up against MSE (concrete panel) walls parallel to traveled highways (I.e. Are barriers even needed, should the MSE wall be designed for Impact, or just be designed for repair, panel replacement)

**Does CRB stand for a permanent or temporary concrete barrier " either precast or cast-in-place? Regardless, MSE walls would not need to be shielded unless done so to: (1) prevent vehicular impacts into MSE walls located within clear zone if the crash results in serious safety risks to motorists; (2) prevent significant repair costs to MSE wall panels, if found to occur; or (3) prevent structural damage to highway/roadway infrastructure located above as well as to surrounding motorists
- adjacent and above.

**It should be noted that TTI researchers are currently conducting a research study pertaining to vehicular impact into MSE walls. I do not have any results from this study but would recommend that you contact Dr. Roger Bligh at TTI for further details.

  1. Some of our drawings show a 1.0m sliding distance for divided highway precast CRB's. If the sliding distance is reduced at overpass columns in the centre, should there be a transition detail from free to fixed? (Current details seem to show a rising of the height to vertical 1300mm high barriers).

**If temporary or portable concrete barrier are installed in a free-standing manner, then the location of discrete fixed objects on the back side could have serious consequences. Free-standing. portable concrete barriers move laterally when impacted. Vehicle redirection occurs as a result of the inertial resistance of the barrier, the axial tension developed throughout the long, inter-connected barrier system, and the friction developed between the barrier base and the support surface. If barrier movement is restricted at discrete locations, vehicle could pocket into the barrier, snag on barrier components, override the barrier, become unstable upon redirection, etc. Depending on the location of the fixed object, transitioning of the barrier system from free-standing to fixed may be required. Some barrier systems may have options for transitioning the lateral barrier stiffness, others may not.

**I am not sure how the rise in barrier height corresponds to the placement of hazards and free-standing and rigid barriers. Can you provide further details regarding the situation to which you refer?

  1. Do you have any information on the California 60G barrier Design, and what levels of Crash testing it meets (I.e. CAN/CSA-S6-06)?

**CALTRANS has conducted significant research on a family of single-slope concrete barriers. The research results from these crash testing programs are contained on two different locations of their website. Actual research reports and crash videos are available. I will ask that one of my colleagues sends to you the links if you are unable to locate them.

http://www.dot.ca.gov/research/researchreports/dri_reports.htm

http://www.dot.ca.gov/research/operations/roadsidesafety/index.htm

**Scott " do you have any additional information on the Type 60G barrier?

  1. Are you familiar with the ZOI TL-4 of 230mm from Keller, Sicking, Polivka, and Rohde, feb 26-2003 document: do any of your findings disagree with this?

**I do not understand your question. MwRSF prepared a TL-4 ZOI chart for concrete parapets based on a review of research findings available at that time. No new study has been performed to review and/or update the prior findings. As such, they stand as prepared until further research is funded.

  1. Is it normal practise to reduce shoulder widths at underpass column support locations on divided highways (>80kM/hr): what is the absolute unsafe minimum that should be accommodated in these types of situations.

**Unfortunately, I do not have an answer to this question and must defer to any guidance provided within the AASHTO document entitled, "A Policy on Geometric Design of Highways and Streets."

Date July 7, 2010


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