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Temporary Barrier Transitions

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State	OH
Description Text	One of the issues I know ODOT is behind the curve on is PCB connected to permanent longitudinal barrier in construction zones. I have an opportunity now to solve a current problem for a designer, and then to set an ODOT standard for the future. This designer is proposing using the attached design in two MOT phases. Phase 1 involves a PCB flared through a removed section of guardrail with a w-beam attached. Phase 2 shows a PCB flush against a permanents concrete barrier. We need to have a connection that could meet 350. My proposed solution to Phase 1 would be to anchor the PCB in the last two sections (12.5' x 2 =25'), and to use a nested w-beam section connect the old and the new. I would not see much a snagging issue. But maybe a steel wedge should be used at mid-span of the rail element and fastened to the PCB. Your thoughts would be appreciated. For Phase 2, I have seen other designers use an impact attenuator at the end of the PCB and flush with the existing barrier. That would work, I assume. But I wonder if you have other ideas? We use NJ PCB and Single Slope for permanent. but this project will tie into existing NJ barrier. I could poll the states, but I think their designs are probably just jury-rigged designs like ours.

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State

Description Text

One of the issues I know ODOT is behind the curve on is PCB connected to permanent longitudinal barrier in construction zones. I have an opportunity now to solve a current problem for a designer, and then to set an ODOT standard for the future.

This designer is proposing using the attached design in two MOT phases. Phase 1 involves a PCB flared through a removed section of guardrail with a w-beam attached. Phase 2 shows a PCB flush against a permanents concrete barrier. We need to have a connection that could meet 350.

My proposed solution to Phase 1 would be to anchor the PCB in the last two sections (12.5' x 2 =25'), and to use a nested w-beam section connect the old and the new. I would not see much a snagging issue. But maybe a steel wedge should be used at mid-span of the rail element and fastened to the PCB. Your thoughts would be appreciated.

For Phase 2, I have seen other designers use an impact attenuator at the end of the PCB and flush with the existing barrier. That would work, I assume. But I wonder if you have other ideas?

We use NJ PCB and Single Slope for permanent. but this project will tie into existing NJ barrier.

I could poll the states, but I think their designs are probably just jury-rigged designs like ours.

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Date July 27, 2004
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Attachment PCB_Transition.png

Response
Response (active)	A couple of quick responses to you temporary barrier transitions questions. I see several problems when looking at your Phase 1 option. Transitioning from the PCB to the guardrail would prove difficult on many levels. First, there is not enough of a transition in the relative stiffness between the two systems. Your anchored PCB's would essentially be rigid, while your guardrail would be much more flexible. Thus, eventhough the potential for snagging in not great, there is still a significant potential for vehicle instability. In order to make that concept function, significant work would need to be done to transition between the stiffness of the flexible rail and the stiff PCB's. You nested W-beam section is a start, but I don't believe it is sufficient to insure vehicle stability. The second issue with the Phase 1 transition is the anchorage of the guardrail. I have not looked into it sufficiently yet, but I am not sure you can get the necessary anchorage out of the PCB's. Your Phase 2 option is closer to what we would recommend, but it would need to be modified as well. In order to alleviate snag concerns and stability problems, the guardrail section would need to approach the temporary barriers at a 15:1 flare at most. The would likely mean using a longer transition section of guardrail than you have drawn. In addition, a rubrail of some for would need to be installed below the regular rail, and special spacer blocks would have to be installed on at least 3'-1 1/2" spacing. I have attached a pdf of a presentation that we recently gave in Minnesota regarding this issue. It shows our current recommendation for attaching temporary barriers to rigid barriers. It consists of using tie-downs on the temporary barriers as the approach the rigid rail. Then a 10 gage thrie beam section with end shoes is used to bridge across the PCB and rigid barrier connection. For now, this is our best alternative. We are currently working on a project with the Florida DOT to further research this issue. Let me know if you have further questions/concerns. Thanks for the questions.

Response

Response
(active)

A couple of quick responses to you temporary barrier transitions questions.

I see several problems when looking at your Phase 1 option. Transitioning from the PCB to the guardrail would prove difficult on many levels. First, there is not enough of a transition in the relative stiffness between the two systems. Your anchored PCB's would essentially be rigid, while your guardrail would be much more flexible. Thus, eventhough the potential for snagging in not great, there is still a significant potential for vehicle instability. In order to make that concept function, significant work would need to be done to transition between the stiffness of the flexible rail and the stiff PCB's. You nested W-beam section is a start, but I don't believe it is sufficient to insure vehicle stability. The second issue with the Phase 1 transition is the anchorage of the guardrail. I have not looked into it sufficiently yet, but I am not sure you can get the necessary anchorage out of the PCB's.

Your Phase 2 option is closer to what we would recommend, but it would need to be modified as well. In order to alleviate snag concerns and stability problems, the guardrail section would need to approach the temporary barriers at a 15:1 flare at most. The would likely mean using a longer transition section of guardrail than you have drawn. In addition, a rubrail of some for would need to be installed below the regular rail, and special spacer blocks would have to be installed on at least 3'-1 1/2" spacing.

I have attached a pdf of a presentation that we recently gave in Minnesota regarding this issue. It shows our current recommendation for attaching temporary barriers to rigid barriers. It consists of using tie-downs on the temporary barriers as the approach the rigid rail. Then a 10 gage thrie beam section with end shoes is used to bridge across the PCB and rigid barrier connection. For now, this is our best alternative. We are currently working on a project with the Florida DOT to further research this issue.

Let me know if you have further questions/concerns. Thanks for the questions.

Date July 27, 2004
Previous Views (30) Favorites (0)

Attachment ODOT Barrier Connected to Rigid Hazard (same as MNDOT Design Prob #2).pdf