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56 Table 22. Comparison of missing post ported span are presented. Maximum rail deflection, maximum model results with UNL long-span crash rail tension, and vehicle exit speed increased as the number of test OLS2. missing posts increased. All occupant injury metrics, i.e., occu- OLS Crash OLS2 pant ridedown acceleration and occupant impact velocities, Test Simulation were well below the NCHRP Report 350 limits. Impact Conditions Speed (kph) 102.7 102.7 Angle (deg) 24.5 24.5 11.4 Discussion Exit Conditions Speed (kph) 66.2 55.0 For all simulations, there was a large increase in dynamic Angle (deg) 16.7 16.3 Occupant deflection for each post that was removed from the system. Impact Velocity X 6.7 8.6 The maximum dynamic deflection contours are shown in (m/s) Impact Velocity Y 5.0 -6.3 Figure 49. For most of the simulations, the maximum deflec- (m/s) tion typically occurs around 0.2 seconds after impact. At this Ridedown X (G) 6.4 -14.0 time, the vehicle was just beginning to redirect due to contact Ridedown Y (G) 8.3 14.6 50 ms Average X (G) NR -9.1 with the rails. As would be expected, the dynamic deflection 50 ms Average Y (G) NR 8.6 increased as more posts were removed from the system. For 50 ms Average Z (G) NR -4.9 Guardrail Deflections the simulation with three missing posts, the guardrail deflec- Dynamic (m) 1.3 1.0 tion exceeded that of the OLS validation simulation, which Static (m) 1.0 0.7 was also missing three posts. However, the OLS test made use Vehicle Rotations Max Roll (deg) Rolled 14.3 of nested guardrail to reduce the deflection, so this was not Max Pitch (deg) NR -15.5 unexpected. The static deflection varied greatly between Max Yaw (deg) NR -43.5 simulations. This was partly due to twisting in the rails, but also because of the manner in which the vehicle exited the dynamic deflection increased by a little over 50 percent. All guardrail. For the simulations with one and two posts miss- occupant injury metrics, i.e., occupant ridedown acceleration ing, the snagging of the vehicle tires on the posts caused the and occupant impact velocities, were well below the NCHRP vehicle to slide away from the rails. In the simulations with Report 350 limits. undamaged and 3 posts missing, the vehicle remained in con- In Table 24, the results for the missing post simulations for tact with the rails longer which caused the damage contour to which the point of impact was the beginning of the unsup- smooth out more. Table 23. Results for missing post simulations with mid-span impacts. Undamaged 1 Post 2 Posts 3 Posts Missing Missing Missing Impact Conditions Speed (kph) 100 100 100 100 Angle (deg) 25 25 25 25 Exit Conditions Speed (kph) 53 60 47 32 Angle (deg) 14.5 20.9 29.4 13.3 Occupant Impact Velocity X (m/s) 7.51 7.55 6.81 7.63 Impact Velocity Y (m/s) 5.54 5.56 3.65 3.56 Ridedown X (G) -11.77 -9.50 -13.98 -12.88 Ridedown Y (G) -12.27 -9.02 -9.87 -9.71 50 ms Average X (G) -6.68 -6.67 -8.11 -8.52 50 ms Average Y (G) -6.82 -6.10 -7.00 -6.44 50 ms Average Z (G) -3.85 4.29 -3.18 -6.73 Guardrail Deflections Dynamic (m) 0.69 0.86 0.97 1.05 Static (m) 0.55 0.71 0.78 0.60 Vehicle Rotations Max Roll (deg) -14.4 -15.4 -13.2 -19.4 Max Pitch (deg) -9.9 -44.6 -17.8 -23.4 Max Yaw (deg) 40.3 44 78.8 40 Max Rail Tension 237.4 267.5 299.8 352.8

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57 Table 24. Results for missing post simulations with beginning of span impacts. Undamaged 1 Post 2 Posts 3 Posts Missing Missing Missing Impact Conditions Speed (kph) 100 100 100 100 Angle (deg) 25 25 25 25 Exit Conditions Speed (kph) 53 39 57 63 Angle (deg) 14.5 -11.5 11.4 15.3 Occupant Impact Velocity X (m/s) 7.51 8.88 7.53 6.51 Impact Velocity Y (m/s) 5.54 5.81 5.75 5.48 Ridedown X (G) -11.77 -9.10 -12.13 -10.22 Ridedown Y (G) -12.27 -10.08 -8.89 -10.30 50 ms Average X (G) -6.68 -7.93 -6.37 -6.32 50 ms Average Y (G) -6.82 -6.76 -6.75 -7.27 50 ms Average Z (G) -3.85 -4.82 3.21 1.71 Guardrail Deflections Dynamic (m) 0.69 0.78 0.89 1.00 Static (m) 0.55 0.51 0.68 0.70 Vehicle Rotations Max Roll (deg) -14.4 -7.6 -7.8 -6.5 Max Pitch (deg) -9.9 -7.6 -6.9 2 Max Yaw (deg) 40.3 23.8 37 40 Max Rail Tension (kN) 237.4 268.4 286.2 336.7 Because of the coarse sampling, the damage contours shown which covers the full area of contact. In all of the curves, the in Figure 49 do not always show the same maximums that were peak was formed around the corner of the vehicle, with rela- recorded in Tables 23 and 24. However, the contours are use- tively smooth leading and trailing edges created by the vehicle's ful for observing the shape of the guardrail during the time of front and side, respectively. The difference in the locations of maximum deflection. The contours shown all begin at that the peak deflections was due to changes in the impact point same point, starting at post 9. The deflection was sampled relative to the reference post. roughly every 953 mm (3.1 feet) until post 21 was reached. Figure 50 shows the vehicle velocity for each simulation. All The total length sampled was just under 23 meters (75.5 feet) velocities were reported in the vehicle local coordinate system. 1 post missing, beginning of span impact (t = 0.7s) 1 post missing, mid-span impact (t = 0.7s) 2 posts missing, beginning of span impact (t = 0.7s) 2 posts missing, mid-span impact (t = 0.7s) 3 posts missing, beginning of span impact (t = 0.7s) 3 posts missing, mid-span impact (t = 0.7s) Figure 48. Post-impact behavior of the vehicle for missing post simulations.

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58 1200 1200 1100 Undamaged 1100 Undamaged 1 Post Missing 1 Post Missing 1000 1000 2 Posts Missing 2 Posts Missing 900 3 Posts Missing 900 3 Posts Missing Deflection (mm) Deflection (mm) 800 800 700 700 600 600 500 500 400 400 300 300 200 200 100 100 0 0 -5000 0 5000 10000 15000 20000 -5000 0 5000 10000 15000 20000 Position Relative to Impact Point (mm) Position Relative to Impact Point (mm) Figure 49. Maximum dynamic deflection contours; impacts at the beginning of the unsupported span (left) and the middle of the unsupported span (right). Many of the vehicles showed decreases in velocity due to fric- To explore the possible causes of this difference, the distance tion after exiting the guardrail. All exit velocities were recorded between the vehicle's point of impact and the first downstream at 700 ms as a common reference velocity. Although this did post was examined. For mid-span impacts, the distances to the not eliminate any loss in speed due to friction, this approach next post were 1.9, 2.86, and 3.8 meters (6.2, 9.4, and 12.5 feet) ensured that the measurements were consistent across all the for 1, 2, and 3 posts missing, respectively. For the beginning of simulations. The magnitude of the Y and Z velocity compo- span impacts, the same distances were 3.8, 5.7, and 7.6 meters nents tended to be the highest for the simulations where there (12.5, 18.7, and 24.9 feet). The two simulations where the vehi- was a short distance between the point of impact and the first cle was 3.8 meters (6.2 feet) from the next post resulted in the downstream post. This was attributed to the front left tire snag- two lowest exit velocities, whereas the exit speed for the vehi- ging on the downstream posts. cle increased as the distance either increased or decreased. This For simulations where the impact point was at the beginning behavior was attributed to the existence of a critical impact of the unsupported span, the exit speed of the vehicle increased point for which the chance of the vehicle snagging on the posts as the number of posts removed from the system was increased. was maximized. The most likely explanation for this was that the increased dis- tance to the next post in the guardrail prevented severe wheel 11.4.1 Evaluation of Rail Rupture Potential snagging from occurring. By contrast, for the three simulations were the impact point was at the middle of the unsupported Rail rupture is a great concern for guardrails with long span the exit speed decreased as more posts were removed. stretches of unsupported rail. Ruptures are occasionally ob- 100 100 90 90 80 80 70 70 Total Velocity (kph) Total Velocity (kph) 60 60 50 50 40 40 30 30 Undamaged Undamaged 20 1 Post Missing 20 1 Post Missing 2 Posts Missing 2 Posts Missing 10 10 3 Posts Missing 3 Posts Missing 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (s) Time (s) Figure 50. Vehicle velocity at center of gravity. Velocity for impacts at the beginning of the unsupported span (left) and the middle (right).