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Low-tension cable barrier displacement over steep slopes in TRP-03-334-21

Question
State MN
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I am looking for clarification on how to interpret Table 7. Summary of LS-DYNA Simulation Data in TRP-03-334-21. I see that the values in the rightmost column, "Pickup CG Displacement past Slope Break Point" are equal to the Max Lateral Barrier Displacement minus the Barrier Offset. What does "CG" stand for here? I assumed center of gravity, but how would the center of gravity be at the outermost edge of the vehicle? That doesn't make any sense.



Figure 80 indicates that the configurations deemed to show promise for meeting MASH TL-3 are those where "c.g. Lateral Encroachment onto Slope" is 34 inches or less. It labels this region and having Two Wheels on Shoulder at Redirection. In this context "c.g." standing for center of gravity would make sense, since 34 inches seems like a plausible minimum dimension from the center of a MASH pickup to the inner side of its tires. However, the lateral encroachement values plotted onto this chart are the same as those from the rightmost column of Table 7, which I think actually correspond to the outer edge of the vehicle, not the center.



Is there an error in either Table 7 or Figure 80 or am I misinterpreting something?



MASH
Working Width and Zone of Intrusion
TL-3

Cable Barriers

Systems Adjacent to Slope


Date April 26, 2024
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Attachment Acceptable-Displacement-Over-Slope_Table-7.png Attachment Acceptable-Displacement-Over-Slope_Figure-80.png
Response
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Table 7 does have a typographcal error. The last column should be labeled "Pickup Displacement past Slope Break Point". It is not the CG displacment. 

 

For Figure 80, the chart should again read Lateral Encroachment onto Slope, no cg lateral encroachment onto the slope. The data was determined from the CG displacment of the truck, but the nomenclature is misleading. The shaded area on the lower section of the chart indicates simulations that kept the non-impact side wheels on the shoulder. Some simulations had high levels of roll. Thus, while their CG displacment and lateral extension onto the slope may have mathematically been consistent with the the no- impact wheels staying on the slope, several of those cases had vehicle roll sufficent to lift the wheels off the shoulder and indicated high levels of instability.

 

Thus, there are two typos in the figures that indicate CG, but the CG displacment was used to estimate the position relative to the slope break point. However, the data in Figure 80 indicates the correct simulation configurations with the potential to have stable redirection. 


Date May 6, 2024
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