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Transition Connector Assembly Modifications

Question
State	IL
Description Text	This wedge plate design was developed a while back by Midwest when you guys tested it with Missouri’s single slope barrier under NCHRP 350. https://mwrsf.unl.edu/reportResult.php?reportId=84&search-textbox=thrie%20beam%20transition Please see the updated draft attached. We’re proposing to keep the same basic shape/dimensions but increase plate thicknesses and remove a few stiffeners. 1. Was the original wedge plate designed to break, crush or move in any way, or is it to remain rigid during an impact? 2. Our Bridge Office Fabrication Unit has had warping issues when galvanizing plates as thin as ¼”. The original design calls for 3/16” plates and ¼” stiffeners, but we’re proposing 3/8” for all. It would weigh approx. 90 lbs. We also believe there are too many small stiffeners which makes fabrication difficult. We’d like to remove all horizontal stiffeners along with two vertical stiffeners, and simply use four vertical S1 plates (3/8” thick) with continuous welds. Do you foresee any issues with our proposed design? 3. Do you think it will react the way it’s supposed to in a crash? 4. Do you foresee any liability issues with using our proposed design? Please let me know if you have any additional comments or questions. I’d really appreciate the feedback as soon as possible. Thank you in advance!

Question

State

Description Text

This wedge plate design was developed a while back by Midwest when you guys tested it with Missouri’s single slope barrier under NCHRP 350.
https://mwrsf.unl.edu/reportResult.php?reportId=84&search-textbox=thrie%20beam%20transition

Please see the updated draft attached. We’re proposing to keep the same basic shape/dimensions but increase plate thicknesses and remove a few
stiffeners.

1. Was the original wedge plate designed to break, crush or move in any way, or is it to remain rigid during an impact?
2. Our Bridge Office Fabrication Unit has had warping issues when galvanizing plates as thin as ¼”. The original design calls for 3/16” plates and ¼”
stiffeners, but we’re proposing 3/8” for all. It would weigh approx. 90 lbs. We also believe there are too many small stiffeners which makes fabrication
difficult. We’d like to remove all horizontal stiffeners along with two vertical stiffeners, and simply use four vertical S1 plates (3/8” thick) with continuous
welds. Do you foresee any issues with our proposed design?
3. Do you think it will react the way it’s supposed to in a crash?
4. Do you foresee any liability issues with using our proposed design?

Please let me know if you have any additional comments or questions. I’d really appreciate the feedback as soon as possible. Thank you in advance!

System Performance Evaluation

System Types
Approach Guardrail Transitions (AGTs)

Applications

System Features

Date August 14, 2019
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Attachment DRAFT Steel Connector Plate for TrafBarTermType6.pdf

Response
Response (active)	See below in for responses to individual questions: 1. The transition wedge connector was designed to remain rigid during impacts, keep the thrie beam vertical, and mitigate snag for reverse direction impacts. 2. Overall, I like the design you are proposing. The exterior dimensions remained the same while the thickness of the face plates (P1 and P2) was doubled and the thickness of the stiffeners was increased by 50%, which would offset much of the strength lost from eliminating horizontal stiffeners. I do have a couple comments on the design. First, I would recommend adding a single horizontal stiffener near mid-height on the downstream end of the assembly. This plate would preserve the strength of the P2 plate against crushing while also helping the P2 plate to maintain its shape and lay flush against the surface of the parapet (snag mitigation). Second, the vertical stiffeners were placed adjacent to the bolts on the downstream side to encourage shear loading of the bolts and prevent the bolts from being subjected to bending loads (which could cause premature failure. Thus, I recommend shifting two of the vertical stiffeners over to be adjacent to the downstream side of the bolt holes. I have sketched these modifications (in red) on top of the IL proposed drawing – see attachment. 3. I believe the proposed design (with the above modifications) has the strength to prevent crushing, and would transfer loads similarly to the original during impact events. However, the only way to be 100% sure would be to evaluate through full-scale crash testing. 4. I am nowhere near an expert in liability/legal aspects, so I can’t say that a lawsuit won’t ever happen. From an engineering point of view, I would feel pretty comfortable with this new design. That said, I highly recommend documenting the thought process for this new design including comments about the strength and function of the component and comparisons between the original and new designs in terms of geometry, strength, etc.

Response

Response
(active)

See below in for responses to individual questions:

1. The transition wedge connector was designed to remain rigid during impacts, keep the thrie beam vertical, and mitigate snag for reverse direction impacts.

2. Overall, I like the design you are proposing. The exterior dimensions remained the same while the thickness of the face plates (P1 and P2) was doubled and the thickness of the stiffeners was increased by 50%, which would offset much of the strength lost from eliminating horizontal stiffeners. I do have a couple comments on the design. First, I would recommend adding a single horizontal stiffener near mid-height on the downstream end of the assembly. This plate would preserve the strength of the P2 plate against crushing while also helping the P2 plate to maintain its shape and lay flush against the surface of the parapet (snag mitigation). Second, the vertical stiffeners were placed adjacent to the bolts on the downstream side to encourage shear loading of the bolts and prevent the bolts from being subjected to bending loads (which could cause premature failure. Thus, I recommend shifting two of the vertical stiffeners over to be adjacent to the downstream side of the bolt holes. I have sketched these modifications (in red) on top of the IL proposed drawing – see attachment.

3. I believe the proposed design (with the above modifications) has the strength to prevent crushing, and would transfer loads similarly to the original during impact events. However, the only way to be 100% sure would be to evaluate through full-scale crash testing.

4. I am nowhere near an expert in liability/legal aspects, so I can’t say that a lawsuit won’t ever happen. From an engineering point of view, I would feel pretty comfortable with this new design. That said, I highly recommend documenting the thought process for this new design including comments about the strength and function of the component and comparisons between the original and new designs in terms of geometry, strength, etc.

Date August 28, 2019
Previous Views (206) Favorites (0)

Attachment Sketch - transition connector modifications.jpg