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64 Figure 79. Simulation results with asperity spacing of 203 mm for a 45-degree asperity angle. damage is reduced. This effect is illustrated by the vertical fail- vehicle remained upright during and after the collision period. ure line in Figure 79 and is similar to the one observed for The longitudinal occupant impact velocity and ridedown 90-degree asperities where greater asperity depths can be accelerations were within acceptable limits of NCHRP Re- achieved for asperity widths of 30 mm and less (see Figure 66). port 350. Maximum OCD was 260 mm in the left firewall area. The first and second asperity spacings after impact point showed CRASH TEST 7 (474630-7) some scraping near edges but were intact after the test. The Even though only six tests were budgeted for the project, third through fifth asperity spacings were gouged but intact the method of construction used to fabricate the barriers after the test (see Figure 81). The crash test did not meet the resulted in a cost savings. With the approval of the project evaluation criteria presented in NCHRP Report 350 due to panel, an additional crash test was conducted. This test was excessive OCD. used to help verify the failure threshold of asperities with larger asperity spacing. The asperity configuration evaluated in Test 7 is given below. Test 7: d = 51 mm, W = 559 mm, Ws = 203 mm, = 45 degrees (pickup truck impact) The New Jersey concrete safety shape barrier evaluated in the seventh test had asperities that were 559 mm wide and 51 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 203 mm. A photograph of the barrier before the test is shown in Figure 80. The barrier was impacted by a 2,099-kg pickup truck at an angle of 25 degrees and a speed of 100.3 km/h. The barrier contained and redirected the pickup truck. The vehicle did not penetrate, underride, or override the installation. The Figure 80. Setup for Crash Test 7.

OCR for page 64
65 OCD confirms that the originally developed energy thresholds are valid for wider asperity spacings (Ws). In conclusion, it was noted that snagging severity may be reduced below levels expected for rigid asperities when an asperity spacing of 25 mm is used. This is because the narrow concrete regions between asperities tend to shear off during impact. As the asperity spacing increases, the width of the concrete region between asperities increases. When this con- crete region between asperities becomes sufficiently wide, the concrete is not completely sheared off. However, even though these concrete regions remain intact, the increased asperity spacing offsets (and in fact reduces) any increase in the over- all snagging severity. In fact, the severity associated with the larger asperity spacing is actually reduced, even though the Figure 81. Barrier damage for Crash Test 7. concrete spalling is significantly reduced. As a last step in formulating the final design guidelines, all of the available crash test data were evaluated and used to make As can be seen from Figure 79, the asperity configuration adjustments to the preliminary guidelines developed through tested in Test 7 was at the failure line established through simulation. The details of these adjustments are presented in the simulation. The fact that the crash test failed due to excessive next chapter along with the final design guidelines.