Criteria for Restoration of Longitudinal Barriers, Phase II (2021) / Chapter Skim
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340 CHAPTER 13 – ANCHOR STRENGTH QUANTIFIED IN TERMS OF ANCHOR DAMAGE In Chapter 9 the performance of the G4(2W) guardrail system was quantified in terms of anchor strength.
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341 physical testing, including: embedment depth of foundation tubes (i.e., stub height) ; missing or damaged groundline strut; slack anchor cable; and rotted/weakened posts.
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342 with significant mechanical advantage. Based on these difficulties, it was decided to use a more practical approach by performing a quasi-static test using a cable-and-winch system.
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343 Table 77. Test matrix for the anchor system damage study.
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344 Figure 288. Typical test set-up for measuring force-deflection response of the guardrail end-terminal anchor.
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345 Figure 290. Photo of the simulated terminal-head bracket mounted onto the end-post.
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346 Figure 292. Idler-pulley mount used to maintain vertical position of loading cable.
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347 Equipment and Instrumentation Force Transducer The load on the cable was measured using an Interface Model 1220 standard load cell, rated at 25-kip. With the 3:1 mechanical advantage of the cable-pulley system, the resulting load on the test article was thus three times greater than the load measured by the load cell.
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348 Figure 295. Video camera specifications and placement.
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349 Test Procedure A quasi-static displacement-time history was applied to the end of the w-beam rail of the end-terminal at a rate of approximately 0.5 – 1.4 in/sec. The test continued until there was a sudden decrease in resistance (e.g., failure of an end-terminal component)
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350 Figure 297. Force-displacement response of the anchor system measured at the load point on the end of the rail for undamaged end-terminal case.
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351 Figure 298. Sequential views of quasi-static test conducted for undamaged end-terminal case (Test 14011E)
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352 Table 78. Quasi-static test results for end-terminal damage modes (Table 1 of 2)
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353 Table 79. Quasi-static test results for end-terminal damage modes (Table 2 of 2)
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354 Missing or Non-Functioning Groundline Strut Pre-test and post-test photos of Test 14011D are shown in Figures 299 and 300, respectively. The data from the test were resampled to obtain the "approximate static" forcedeflection response, which is compared to that of the undamaged system in Figure 301.
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355 Figure 300. Post-test photo of Test 14001D (back view)
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356 Figure 302. Displacement and displacement rate vs.
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357 Figure 304. Procedure for measuring reduced embedment depth.
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358 measured during the test was 18.4 kips at 16 inches displacement. Post 1 foundation tube began to extract from the ground at a rail deflection of approximately 3 inches (based on assessment of real-time video and force-displacement data)
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359 Figure 306. Pre-test photo of Test 14001F for 4-inch reduced embedment case.
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360 Figure 308. Pre-test photo of Test 14001G for 8-inch reduced embedment case.
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361 Figure 310. Post-test photo of Test 14001F for 4-inch reduced embedment case.
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362 Figure 312. Post-test photo of Test 14001G for 8-inch reduced embedment case.
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363 Slack Anchor-Cable A total of four tests were performed to quantify the effects of slack in the anchor-cable on the force-deflection response of a standard anchor system. These tests included installations with 1, 2, 3 and 4 inches of slack in the anchor cable.
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364 Figure 315. Pre-test photo of Test 14001H for 1" slack-cable case.
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365 Figure 317. Pre-test photo of Test 14001K for 3" slack-cable case.
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366 Figure 319. Post-test photos of Test 14001H for 1" slack-cable case.
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367 Figure 322. Post-test photos of Test 14001J for 4" slack-cable case.
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368 undamaged system. Between 2-4 inches displacement the stiffness increased to 2.3 kips/in, compared to 4.5 kips/in for the undamaged system.
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369 Figure 324. Test 14001H showing continuing effectiveness of anchor after Post 2 fails.
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370 In NCHRP Report 656, Gabler et al. stated that when the stub height above ground level exceeds 4 inches (i.e., reduced embedment of 1 inch)
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371 Slack in Anchor Cable For the damage mode defined by slack in the anchor cable, the tests showed that the force-deflection response of the end-terminal was essentially unaffected for up to approximately 6 inches of rail deflection for cases where the initial slack in the cable was two inches or less. At 3 and 4 inches of slack, however, there was a significant drop in the force-deflection response.
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372 As a result of this study, the research team recommends that the repair threshold for the end-terminal for the G4(2W) be those in which the damage results in more than a 30% loss in anchor capacity relative to the baseline anchor strength.
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373 Table 80. Recommendations for end-terminal damage for the G4(2W)
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374 Crash Performance Evaluations o Future work should include analyses of the G4(2W) at impact points nearer to the anchor system.
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