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Illinois DOT is revising our attached Sand Module Impact Attenuators (TL-3 and TL-2) arrays, and we are wondering if MwRSF can look at the attached Standards and provide us recommendation for both to meet MASH.

• Test Level 3 Array, we have made some changes based on the two MASH proprietary designs (TL-3 Energite III Sand Barrel Array and Big Sandy MASH).


• Test Level 2 Array, we have not made any changes yet to our current design.

Thanks,

I ran a quick analysis on both the TL-3 and TL-2 the sand barrel arrays you provided. Details are attached. When we analyzed the array, we basically have three criteria. First, the vehicle must drop its velocity below 10 mph by the end of the array. Second, the calculated OIV must be below 40 ft/s. Third, the calculated average deceleration must remain below 12 g’s. The average acceleration does not capture peaks in the acceleration like an actual impact event, so the acceleration threshold is lowered from 20 g’s to 12 g’s. This is consistent with section 8.4.3 in the RDG. Our analysis is just a more advanced version of that procedure.

MASH has 5 tests for a no-redirective crash cushion like sand barrels. I did not analyze the 3-45 test for the 1500A sedan based on the successful analysis of the 1100C and 2270 P vehicles. I can if you like. I also did not analyze test nos. 3-42 and 3-43, which are angled impacts on the nose of the system. For your array with a single barrel in front, these are non-issues.

I analyzed your proposed TL-3 array for end on impacts with an 1100C vehicle and 2270P vehicle at 62 mph. In both impacts, the TL-3 array worked well for tests 3-40 and 3-41.

I also conducted analysis of impact on the side of the system. I did both test no. 3-44, the coffin corner impact, and a 1100C impact on the side of the system. The 3-44 test is only with the 2270P vehicle in MASH. Note that the 1100C impact on the side of the system is not a MASH requirement, but I do look at it for completeness. I should also note that these side impact analyses are not typically conducted on inertial barriers. The procedures used by the manufacturers and the RDG have not typically looked at oblique impacts.

The 3-44 test analysis performed marginally. No issues with acceleration or OIV, but I should note that the vehicle velocity was not below 10 mph at the end of the array ( it was 15.7 mph). This is slightly higher than the threshold. However, I looked at the two barrel systems that have MASH letters. Both of these systems have similar mass in the barrels impacted in the 3-44 coffin corner impact. As such, we would expect similar velocity drops and final velocity at the end of the array in those systems and they both met MASH. As such, I would believe that your array could potentially work as well for TL-3 impact conditions. The 1100C impact analysis showed an issue with high ORA values when impacting the heavier barrels midway down the array. Again, this is just for your knowledge. It is not a required MASH test.  

The TL-2 analysis was similar. The 2-40 and 2-41 tests looked good. The 2-44 test has a final velocity of 12.02 mph, which was just above the 10 mph target limit. The TL-2 array did not have any issues with the 1100C side impact.

All of the analysis is in the attached zip file. If you need more information or want to discuss, let me know.

For learning purpose, I have the following questions:

• It is observed in each spreadsheet that OIV is increased in each sand barrel, following the Impact Order. However, I am not sure how this OIV value is selected. For example, TL-3 1100C_3-40, the OIV is taken on the third sand barrel impact order, likewise TL-3 2270P_3-44 the OIV is taken at the 5^th Impact Order.
• For the TL-3_1100C_Side Impact in case it is desired to lower the ORA values, lighter barrels (let’s say 700 lbs.) should be placed on rows 7 and 8, next to barrel weights 1400 lbs. and 2100 lbs., respectively, in each side?

Thanks again,

Responses below.

1. The OIV column in the analysis is compiling the relative velocity of the simulated occupant in the flail space analysis. As the vehicle decelerates, that number increases. The OIV used for occupant risk analysis is taken from that velocity when the simulated occupant makes contact with the boundary of the occupant compartment. It is a measure of how fast the occupant is moving relative to the interior of the vehicle when he impacts the interior. For this analysis, the occupant must move 0.6 m prior to impacting the interior. The time of that impact is indicated as t* in the analysis sheets. The analysis then calculates the velocity at the time of impact as the OIV. That value is highlighted in green in the cells (or red if it exceeds the MASH limits). It is also provided in a table of output. Details on the basics of the flail space model calculations are provided in the appendix of MASH.
2. Addressing the 1100C side impact under TL-3 conditions would take some additional consideration. You are correct that using lighter barrels in the back half of the barrel array would assist in the side impact. However, it may cause adverse effects for the other impact conditions. Thus, one would need to check the other impacts with any changes that were made. That said, you basic premise has merit.

One more quick comment that I forgot to mention that is pretty relevant. The side impact in MASH – test 3-44 – does not require the test result to meet OIV and ORA requirements. I believe this was a caveat included to ensure that sand barrels would still be an option for DOTs when MASH was adopted. As such, systems have been tested to MASH and observed ORA’s around 30 g’s in the 3-44 test and still been given approval letters.

Thanks!