Click for next page ( 34


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 33
33 CHAPTER 7 Evaluation of Twisted Blockout Damage The objective of this evaluation was to determine the effect of shows time sequential snapshots of Test 03-8 obtained from twisted blockouts on barrier crash performance by pendulum the overhead high speed camera. testing (Figure 26). The performance of the barrier section with The posts experienced similar damage to that in previous twisted blockouts was compared to the performance of a sim- tests that contained the pendulum. The post at the splice loca- ilar barrier section without this flaw. The pendulum test setup tion experienced more torsion than the non-splice post and is described in an earlier chapter on the research approach. In had some minor cracking at the flange. The post at the splice this case, the routed wooden blockout at the splice was installed remained connected to the rail while the post-rail bolt at rotated about the post-rail bolt. The blockout was rotated the non-splice location pulled out of the slot in the rail. There approximately 45 degrees with respect to the vertical in all tests. 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 7.1 Results with approximately 19 mm (0.75 inches) of relative motion In Test 03-8, the twisted blockout damaged barrier con- between the w-beam sections. No tears developed in the guard- tained the pendulum mass impacting at 31.2 km/hr (19.4 mph). rail and no bolts failed. The analogous 3-cable test (not shown), The impact velocity was calculated using the data from the Test 02-2, also contained the pendulum mass with very sim- pendulum-mounted accelerometers. Based on the analysis ilar impact performance. of the high-speed overhead video, the maximum dynamic deflection was 691 mm (27.2 inches) at 131 ms after the ini- 7.2 Recommendation tial impact. The maximum static crush at the center of the w-beam was 356 mm (14 inches). The overall damage and the The performance of the barrier section with this damage was post damage due to impact are shown in Figure 27. Figure 28 indistinguishable from that of the undamaged barrier section Field Example Pendulum Test Setup Figure 26. Twisted blockout evaluated in pendulum tests.

OCR for page 33
34 Figure 27. Test 03-8: Overall damage (left) and post damage at splice (center) and non-splice location (right). 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 (45 degrees relative to the ver- tical position) at the splice location successfully contained the pendulum mass. 0.035 s 0.070 s 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 0.105 s 0.140 s 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. 0.175 s 0.210 s Exhibit 4.0. Recommendation for twisted blockout damage repair. Damage Mode Repair Threshold Relative Priority Twisted blockouts Any misaligned, top edge Low of block 6 in. or more from bottom edge 0.245 s 0.280 s Note: Repairs of twisted Figure 28. Sequential overhead photographs blockouts are relatively for barrier with a twisted blockout, Test 03-8 quick and inexpensive. (31.2 km/hr).