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Our district staff would like to install a modified version of the South Dakota snow gate (See attached "SD Snow Gate.pdf" and "TRP-03-44-94.pdf"). However, they are proposing some modifications to the base:
1. They would like to use a screw-in Chance Lighting Foundation (See attached "11242ng4 Model (1).pdf").
2. They would like to use the Transpo Pole-Safe " Model 4100 frangible bolts. (See attached "Pole-Safe 4100 Details.pdf" and "Pole-Safe Skirt Details.pdf").
They have some other thoughts regarding signing and lighting attachments as well as an alternate method of storing the gate in its road open condition. I will pass along information for those items as I receive it, but they would like to begin installing the foundation next Monday.
Would you please review the attached "SD_SnowGate_Mod.pdf" and verify that these modifications will not affect the crashworthiness of the system? Please comment also on the grading as shown. (Sorry for the short notice).
Let me know if you have any questions.
We received the below response from Transpo. Do you have any comments on the information they've provided?
"The original model PoleSafe 201 had a tensile strength of 24 kips and the new 4100 has a tensile strength of 49.8 kips. Both models had a restrained shear strength of 5.5 kips. With this said what it means is that the new PoleSafe couplings are twice as strong in tension and have the same breakaway strength as the 201 couplings. The new couplings should actually perform better than the old 201 couplings in that they will be able to support the gate in the open position with much less stress on the couplings.
|Other Keywords||Snow Gates|
|Date||November 3, 2010|
|Attachment||11242ng4 Model (1).pdf|
|Attachment||Pole-Safe 4100 Details.pdf|
|Attachment||Pole-Safe Skirt Details.pdf|
|Attachment||SD Snow Gate.pdf|
I have reviewed your proposed changes to the snow gate design. The changes you propose create two main issues with respect to the performance of the snow gate.
It appears that Transpo has stated that the Polesafe 4100 and 201 models have equivalent breakaway loads. Thus, it would be acceptable to use the 4100 model in your modified design. The only way to further evaluate this would be to compare the velocity change for tests of short, heavy poles from testing of both the 201 and 4100 couplers.
The use of the 10:1 grading shown is not a cause for serious concern in our eyes.
|Date||November 8, 2010|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
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