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33 The objective of this evaluation was to determine the effect of twisted blockouts on barrier crash performance by pendulum testing (Figure 26). The performance of the barrier section with twisted blockouts was compared to the performance of a sim- ilar barrier section without this flaw. The pendulum test setup is described in an earlier chapter on the research approach. In this case, the routed wooden blockout at the splice was installed rotated about the post-rail bolt. The blockout was rotated approximately 45 degrees with respect to the vertical in all tests. 7.1 Results In Test 03-8, the twisted blockout damaged barrier con- tained the pendulum mass impacting at 31.2 km/hr (19.4 mph). The impact velocity was calculated using the data from the pendulum-mounted accelerometers. Based on the analysis of the high-speed overhead video, the maximum dynamic deflection was 691 mm (27.2 inches) at 131 ms after the ini- tial impact. The maximum static crush at the center of the w-beam was 356 mm (14 inches). The overall damage and the post damage due to impact are shown in Figure 27. Figure 28 shows time sequential snapshots of Test 03-8 obtained from the overhead high speed camera. The posts experienced similar damage to that in previous tests that contained the pendulum. The post at the splice loca- tion experienced more torsion than the non-splice post and had some minor cracking at the flange. The post at the splice remained connected to the rail while the post-rail bolt at the non-splice location pulled out of the slot in the rail. There were no failures in the anchor cables in this test, and there was no separation of the cable from the swage portion of the anchor cable assembly. Splice separation was similar to previous tests with approximately 19 mm (0.75 inches) of relative motion between the w-beam sections. No tears developed in the guard- rail and no bolts failed. The analogous 3-cable test (not shown), Test 02-2, also contained the pendulum mass with very sim- ilar impact performance. 7.2 Recommendation The performance of the barrier section with this damage was indistinguishable from that of the undamaged barrier section C H A P T E R 7 Evaluation of Twisted Blockout Damage Field Example Pendulum Test Setup Figure 26. Twisted blockout evaluated in pendulum tests.
in two higher speed tests conducted. This suggests that this damage mode has little effect on the structural adequacy of the barrier. A pendulum test of a strong-post w-beam barrier sec- tion with a twisted blockout (â¼45 degrees relative to the ver- tical position) at the splice location successfully contained the pendulum mass. The performance of this damaged barrier section was virtu- ally identical to that of the undamaged strong-post barrier sec- tion tested. As a result, the research team has recommended a repair threshold of one or more twisted blockouts. To be conservative, the twist threshold level for a misaligned block- out was set at 6 inches or more difference between the top and bottom edge of the blockout. This linear distance cor- responds to an angle of approximately 25 degrees relative to the vertical position, half the angle of the twisted blockout in the pendulum test. The priority assigned was low due to the indiscernible performance difference from the undamaged condition (Exhibit 4.0). The research team notes that the repair of twisted blockouts is relatively inexpensive, and there is lit- tle reason to delay this repair. 34 Figure 27. Test 03-8: Overall damage (left) and post damage at splice (center) and non-splice location (right). 0.035 s 0.070 s 0.105 s 0.140 s 0.175 s 0.210 s 0.245 s 0.280 s Figure 28. Sequential overhead photographs for barrier with a twisted blockout, Test 03-8 (31.2 km/hr). Damage Mode Repair Threshold Relative Priority Twisted blockouts Any misaligned, top edge of block 6 in. or more from bottom edge Note: Repairs of twisted blockouts are relatively quick and inexpensive. Low Exhibit 4.0. Recommendation for twisted blockout damage repair.
