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The objective of this evaluation was to determine the effect of a horizontal tear on barrier crash performance (Figure 19). The approach was to subject a barrier test section with an arti- ficially introduced horizontal tear to a pendulum test. The per- formance of the barrier section with the flaw 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. 5.1 Method of Introducing the Damage A horizontal tear was simulated by cutting a longitudinal notch in the center of the upper protrusion of the w-beam using a reciprocating saw. Each end of the notch was cut into a âVâ shape to provide a stress concentrator similar to those observed in the field in a crash-induced horizontal tear. The location of the tear corresponded to the pendulum mass impact loca- tion, as this was believed to have the largest risk for rail rupture. The horizontal tear was a total of 306 mm (12 inches) long. The middle 204 mm (8 inches) of the tear was 13 mm wide (0.5 inches) with a 51 mm (2 inches) âVâ shaped taper on either end. 5.2 Results The horizontal tear damaged barrier in Test 07-3 contained the pendulum mass impacting at 29.3 km/hr (18.2 mph), which was calculated using the data from the high speed video footage. The maximum dynamic deflection of the test section was 579 mm (22.8 inches) at 130 ms after the initial impact, computed from the pendulum acceleration data. The maximum static crush at the center of the w-beam was 406 mm (16.0 inches). The damage at the impact location and individual post damages are shown in Figure 20. Both post-rail connections remained intact and there was 16 mm (0.63 inches) of relative movement between the two w-beams at the splice location. Figure 21 shows time sequential snapshots of Test 07-3 obtained from the high speed camera positioned overhead. In Test 02-1, the horizontal tear damaged barrier (overhead sequence not shown) was unable to contain the pendulum mass impacting at 31.2 km/hr (19.4 mph), which was calcu- lated using the data from the high speed overhead video. The deflection of the rail was 699 mm (27.5 inches) at 128 ms after the initial impact, which was just prior to penetration of the w-beam section. The barrier section failed at the splice due to C H A P T E R 5 Evaluation of Horizontal Tear Damage 28 Field Example Pendulum Test Setup Figure 19. Horizontal tear evaluated in pendulum tests.
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 21. Sequential overhead photographs for 29.3 km/hr pendulum impact of barrier with horizontal tear damage (Test 07-3). Figure 20. Test 07-3: detailed view of impact location (left), post damage at splice (center), and non-splice location (right). the splice bolts pulling through holes in the rail with none of the individual splice bolts fracturing. At both the splice and non-splice location, the post bolt pulled through the rail ele- ment. The splice failure and post damage is shown in Figure 22. 5.3 Recommendation Pendulum tests show that horizontal tears less than 306 mm (12 inches) in length and 13 mm (0.5 inches) in width do not significantly alter the performance of the barrier. In the 29.3 km/hr (18.2 mph) test, the damaged barrier was able to contain the impacting pendulum mass. In the higher speed 31.2 km/hr (19.4 mph) test, a splice failure was observed, although there was no evidence of rail rupture near the loca- tion of the horizontal tear. A pendulum test (18.2 mph impact speed) of a strong-post w-beam barrier section with a 12-inch horizontal (longitu- dinal) tear (0.5 inches wide) resulted in successful contain- ment of the pendulum mass. For this test, the horizontal tear was located at the impact location in the upper fold of the w-beam in order to represent a practical worst case. The performance of this damaged barrier section was virtually identical to that of the undamaged strong-post barrier section tested at the 17.5 mph impact speed. In a slightly higher speed 31.2 km/hr (19.4 mph) test, a splice failure was observed, although there was no evidence of rail rupture near the loca- tion of the horizontal tear. As a result, the research team has recommended that the repair threshold for horizontal tears be those exceeding a length of 12 inches and a width of 0.5 inches. The rationale for the width specification is that horizontal tears with suf- ficient width reduce the tensile capacity of the rail through a reduction in available cross-section area in the area of the tear. The research teamâs recommendation is that larger horizontal tears should be repaired with a medium priority (Exhibit 2.0). 29
30 Figure 22. Test 02-1: detailed view of splice failure (left), post damage at splice (center), and non-splice location (right). Damage Mode Repair Threshold Relative Priority Horizontal tears Horizontal (longitudinal) tears greater than 12 in. long or greater than 0.5 in. wide should be repaired with a medium priority. Note: for horizontal tears less than 12 in. in length or less than 0.5 in. in height, use the non-manufactured holes guidelines. Medium Exhibit 2.0. Recommendations for horizontal tear damage repair.
