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Portable concrete barrier

Question
State ID
Description Text Hello, My name is Zach Cooper, I work for Knife River, a construction/materials company headquartered in Bismarck, ND. I work out of our Southern Idaho division, located in Boise, Idaho.

I received your contact information from a few gentlemen at the FHWA, but most directly from Mr. Artimovich, as noted in the email string below.

We have a contract with the State DOT here in Boise. The State has specified some Montana barrier, for scupper size, that we feel is not cost effective to make given the resources typical for Idaho. The quantity of barrier is relatively low, 6700 lf, and use on future projects is not highly likely.

We have proposed modifying standard barrier by increasing the scupper lengths to provide the same surface opening square footage that is provided by the Montana barrier. The state has denied this request based on NCHRP-350 compliance, stating, more or less, that modifications to the barrier would negate the existing NCHRP-350 testing that was done on the barrier and making it unsafe for use. The State left an opening saying that if NCHRP-350 compliance can be provided to substantiate our proposed modifications to barrier they will entertain the proposal.

The modification I am proposing is fairly straight forward, and by all accounts (all unofficially) the consensus is the modification would not change the “crashworthiness” of the barrier.

The proposed modification is as follows (drawing attached):

1. Typical 20’ Jersey style barrier, in this particular case the precast outfit is in Utah, so our hope is to use the Utah Standard BA 2A barrier. This barrier has 2 each, 2 ft long by 2” tall scupper openings, one on each half of the barrier, separated by 5’10”. That 5’10” separation is concrete.
2. The proposed modification is to block out that 5’10” span, connecting the two existing scuppers to make one large scupper measuring 9’10”.

Essentially, what I am trying to do is:

1. Get an engineering determination that states these proposed modifications are insignificant to the “crashworthiness” of the barrier.
2. Have that determination approved by the FHWA
3. Take a letter to the State DOT of Idaho, and hopefully have them approve the use of the modified barrier.

This seems all very doable to me, however time is a barrier. In order to have approval in time to actually make the barrier, this whole process would need to be wrapped up by February 17th, roughly.

I am hoping you can help me with step 1 of the 3 step plan, a sound engineering decision that that modifications do not change the integrity of the barrier enough to negate the existing NCHRP-350 rating of the barrier.

Please contact me and let me know your thoughts on the viability, cost and timing on this issue.

Thank you for your time.
Keywords
  • Temporary Barriers
Other Keywords none
Date February 10, 2014


Response
Response

Can you send to us full details of the crash tested design, including where the evaluation was performed, report, etc.? Once all of the information is acquired, I will see if one of our engineers can review the content. Thanks!

Date February 10, 2014


Response
Response Attached is the information I was able to obtain through various sources.

I was in a little error in my last information, our intent is to modify the Idaho barrier, not the Utah barrier.

So here is the list of the attachments.
1. July 17, 2000 letter. This is the letter from FHWA that approves the Idaho barrier, and it also has some test data (test 13-4300-001 & 002)
2. The current standard drawing for the Idaho barrier.
3. The submittal to the State requesting modification to the barrier. This includes some “conceptual” drawings of the proposed scuppers.

To be clear, our intent is to modify the 20’ Idaho barrier.

Hopefully this is enough information.

Your time is greatly appreciated.
Date February 11, 2014
Attachment G2A1_0613.pdf
Attachment July 17 2000 Letter.pdf
Attachment SUBMITTAL #4 - Barrier Modification Request.pdf


Response
Response We have reviewed the proposed details for revising the portable concrete barriers (PCBs) used by the Idaho Transportation Department. Several proposed modifications were provided.

First, you inquired as to whether the two proposed revisions would be acceptable for use with the free-standing option of Detail G-2-A-1, Sheet 1 of 2. A height change in the drainage slot from 2 in. to 2¼ in. was made. We do not believe that an increased height of ¼ in. would noticeably degrade the safety performance of Idaho’s free-standing PCB system that is configured with 20-ft long segments. Second, you inquired as to whether the drainage slots could be altered in the longitudinal direction. At the present, two 1-ft 11-5/8-in. long drainage slots are located near the one-third points along the segment. You inquired as to whether two 4-ft long slots could be used in lieu of the small slots but with an inner blocked region in excess of 26 in. long. At this time, we are not concerned with the length and position of the two drainage slots as prior testing has been conducted with an interior drainage slot of 4-ft long within a 10-ft PCB system for the Ohio Department of Transportation. The two drainage slots also maintains an inner support at the midpoint of the 20-ft long PCB. In addition, we do not believe that the use of two 4-ft long drainage slots would noticeably degrade the safety performance of Idaho’s free-standing PCB system that is configured with 20-ft long segments. Note that MwRSF’s guidance does not include tied-down applications.

Second, you again inquired as to whether the two proposed revisions would be acceptable for use with the free-standing option of Detail G-2-A-1, Sheet 2 of 2. A height change in the drainage slot from 2 in. to 2¼ in. was made. As stated above, we do not believe that an increased height of ¼ in. would noticeably degrade the safety performance of Idaho’s free-standing PCB system that is configured with 20-ft long segments. Second, you inquired as to whether the drainage slots could again be altered in the longitudinal direction but differently than noted above. At the present, two 1-ft 11-5/8-in. long drainage slots are located near the one-third points along the segment. You inquired as to whether one 8-ft long slot could be used in lieu of the two small slots. At this time, we do not have experience with using one very long slot in the inner region of 20-ft long PCBs. When PCBs are impacted in a free-standing configuration, several PCB segments are pushed backward, while the front base is lifted upward. As such, these shifted barrier segments often become supported by the backside toe or edge during the impact event. With an 8-ft long drainage slot in the inner region, the interior support (and backside edge support) would be removed in each segment, thus increasing the unsupported length of each tipped PCB. For the passing dynamic load on the front face of a tipped PCB, increased bending moments may be observed. Although this configuration may still provide adequate safety performance and not compromise barrier capacity, we do not have experience with using an 8-ft drainage slot even though additional steel reinforcement is provided above the drainage slots. As such, we have concerns regarding the use of a single 8-ft long drainage slot configuration within the Idaho Transportation Departments 20-ft long PCBs. It should be noted that full-scale crash testing and/or computer simulation modeling may later demonstrate that its use is acceptable. Note that MwRSF’s guidance does not include tied-down applications.

Third, you inquired as to whether the two proposed revisions would be acceptable for use with the free-standing option of Detail G-2-A-2, Sheet 1 of 2. A height change in the drainage slot from 2 in. to 2¼ in. was made. We do not believe that an increased height of ¼ in. would noticeably degrade the safety performance of Idaho’s free-standing PCB system that is configured with 10-ft long segments. Second, you inquired as to whether the drainage slots could be altered in the longitudinal direction. At the present, two 6-in. long drainage slots are located near the one-third points along the segment. You inquired as to whether one 3-ft 10-in. long slot could be used in lieu of the small slots in the 10-ft long PCBs. At this time, we are not concerned with the length and position of the single drainage slot as prior testing has been conducted with an interior drainage slot of 4-ft long within a 10-ft PCB system for the Ohio DOT. In addition, we do not believe that the use of a single 3-ft 10-in. long drainage slot would noticeably degrade the safety performance of Idaho’s free-standing PCB system that is configured with 10-ft long segments. Note that MwRSF’s guidance does not include tied-down applications.

Please let me know if you have any questions or comments regarding the information contained herein! We look forward to hearing from you on this matter in the near future. Thanks!

Date February 11, 2014


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