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39 C H A P T E R 9 Evaluation of Hole in Rail cessful containment of the pendulum mass. To represent worst case conditions, the hole was aligned with the impact loca- tion and in the upper fold of the w-beam section. Based on the results of the test, the performance of the hole-damaged rail section was virtually identical to that of the undamaged strong post barrier section tested at the 17.5 mph impact speed. As a result, the research team has recommended that the repair be initiated if the hole exceeds 1 inch in height. Note that the limit on size of a non-manufactured hole has been specified in the vertical, rather than the horizontal, direction because the vertical direction is perpendicular to predominant (tension) loads, and is thus more likely to cause failures. A medium priority was assigned to smaller holes in the rail because of the possibility that holes may serve as the initiation point for horizontal tearing on im- pact. The only exception would be if this hole was located near the splice as described below. Multiple holes in a rail section or holes with a diameter exceeding a height of 1 inch could lead to rail tearing as seen in the vertical tear pendulum tests. To avoid the possibility of catastrophic rail failure, these modes were assigned a high priority for repair. A special case was a hole of any size which intersects either the top or bottom edge of the rail. Because a hole which disrupts either the upper or lower surface of a rail has the characteristics of a vertical tear, this damage mode has the potential for the same catastrophic failure of the rail that was observed in the pendulum tests of vertical tears. This damage mode was given a high priority for repair (Exhibit 6.0). The objective of this evaluation was to determine the effect of a hole in a rail on barrier crash performance through pen- dulum testing (Figure 34). The performance of the barrier section with an artificially introduced hole was compared to the performance of a similar barrier section with no flaw. The pendulum test setup is described in an earlier chapter on the research approach. Test 07-2 investigated the performance of a two-post section of strong-post w-beam barrier with a 1.25-inch hole. For this test, a hole in the rail was simulated by drilling through the rail. The location of the hole corresponded to the pendulum mass impact location and was on the upper fold of the w-beam. 9.1 Results The barrier with a hole in the rail successfully contained the pendulum mass impacting at 18.2 mph. Based on an analysis of the overhead high-speed video data, the maximum dynamic deflection of the rail was 22 inches and occurred 120 ms after trigger. Based on an analysis of the overhead high speed video data, the maximum static deflection was 15.4 inches The rail was intact at the position of the hole (Figure 35). Figure 36 shows time sequential snapshots of the test obtained from the high speed camera positioned overhead. 9.2 Recommendation A pendulum test (18.2 mph impact speed) of a strong-post w-beam barrier with a 1.25-inch diameter hole resulted in suc-
Field Example Pendulum Test Setup Figure 34. Hole damage evaluated in pendulum tests. 40 Figure 35. Damage near a hole in Test 07-2.
41 0.02 s 0.06 s 0.10 s 0.14 s 0.18 s 0.22 s 0.26 s 0.30 s Figure 36. Sequential photographs for 1.25-inch hole damage (Test 07-2): overhead view. Damage Mode Repair Threshold Relative Priority More than 2 holes less than 1 in. in height in a 12.5-in. length of rail. Any holes greater than 1in. in height. Any hole which intersects either the top or bottom edge of the rail. High Non-Manufactured holes (such as crash-induced holes, lug-nut damage, or holes rusted-through the rail) 1 or 2 holes less than 1 in. in height in a 12.5-in length of rail. Medium Exhibit 6.0. Recommendations for hole in rail damage.
