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|Description Text||We are reviewing the options for connecting thrie beam to different types of barrier and it appears there are a few different designs that have been used. I have attached the 3 designs I have found and was wondering if any of the designs perform any better than another.
The TRP-03-175-06 version that was used in the 2006 crash tests looks like it was the latest version of the detail. We would like to use this design with both constant slope barrier and F shape barrier with some minor modifications to fit each barrier.
Do you see any issues with the 2006 design being used since the angled plate is shorter? Also would minor modifications to this design to fit specific barriers warrant further crash testing?
Any information or guidance you could provide would be appreciated.
|Date||March 22, 2018|
In the mid-1990s, we developed a MoDOT thrie beam median transition to a single-slope concrete median barrier. In the first crash test (MTSS-1) into design no. 1, several barrier behavior problems were observed, which contributed to a failed 2000P crash test. Following this test, several design modifications were incorporated, including a shortened steel thrie beam connector plate to allow thrie beam space to gradually deform backward at end of parapet, shortened blockout to allow lower thrie corrugation to deflect backward, flattened vertical slope for top of barrier at end, and tapered steel blocks and recessed posts at top to reduce vehicle snag.
For the re-test (MTSS-2) on design no. 2, the modified thrie beam median transition to single-slope barrier demonstrated improved safety performance. In your attached pdf, you will note that the steel apparatus was shortened from 50¼ in. to 40 in., and it did not extend to the end of the buttress.
In the mid-1990s, we developed an IaDOT thrie beam roadside transition to a New Jersey concrete roadside barrier under NCHRP Report No. 350 using four 2000P crash tests. Two unsuccessful and two successful crash tests were performed. Two tests with wood posts, and two tests with steel posts. The NJ Steel connector plate was approximately 32 in. long. Again, the end of the connector plate did not extend to the end of the buttress. The sloped end was 12 in. long versus the 20 in. long due to the narrower lateral top plate width over which to transition the sloped end.
In the mid-2000s, we retested the Iowa transition under MASH using a 2270P vehicle. The steel connector plate did not change from that used in the 350 testing program.
Lateral Slope Change
For the general configurations, the single-slope connector plate has a lateral slope of 3-13/16 over 20, or 1/5.25. The NJ connector plate has a lateral slope of 2-3/8 over 12, or 1/5.05. These two slopes are approximately equal. To provide similar behavior under reverse-direction crashes, we should maintain this slope or provide an even flatter lateral slope.
Note that we did not crash test the two parts in the reverse-direction. Minor changes may be acceptable. However, a much steeper slope may cause more concern for vehicle snagging on the end or too rapid of the change that may contribute to instability.
When we studied lateral slope changes on the face of concrete barriers with computer simulation, we iterated to a flatter slope. The more gentler slope consisted of a 1:10.
We completed another study involving a transition from MGS to F-shape PCBs in 2017. A W-beam steel connector plate was attached to PCBs and evaluated under MASH in two directions. For reverse-direction crashes with the 1100C vehicle, the connector plate had a lateral slope of 2-1/2 over 12, or 1/4.80. Again, the slope is close to 1/5 in combination with a PCB system that can translate under lateral loading.
Overall, I think that it may be best to try to maintain the lateral slope that has been used in prior steel connector plates. Of course, some minor deviation in lateral slope would seem to be reasonable. In fact, MoDOT has been developing some revised connector parts to aid in attachment to existing concrete buttresses. It may helpful to see where they wrapped up this work last month. Both Greg Sanders and Boyd Denison were working on this effort. A recent email with contact information is attached. Note that the details in that email may have changed after our conversations.
If we need to further discuss this topic in a conference call, please let me know. Thanks!
|Date||April 2, 2018|
|Attachment||Missouri Design Connector Plate.pdf|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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