Criteria for Restoration of Longitudinal Barriers, Phase II (2021) / Chapter Skim
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255 CHAPTER 10 – COMBINATION DAMAGE MODE OF RAIL DEFLECTION AND RAIL-POST CONNECTION FOR THE G4(2W) In this chapter guardrail deflection in combination with rail-to-post connection strength are evaluated using finite element analysis to quantify their effects on the crash performance of the G4(2W)
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256 alternative reference system was used for labeling the posts within the impact region of the guardrail. This section of posts was labeled A through G, with Post A being the first post upstream of the impact point, as illustrated in Figure 203.
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257 Table 62. Summary of results for the low-severity impact analyses.
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258 considered "medium." Thus, this damage mode was relatively significant for many of these cases. The permanent longitudinal deflection of the rail element at the upstream anchor ranged from 0.6 inch for the 30 mph case to just over 1 inch for the 40 mph case.
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259 Figure 205. Extent of damage resulting from impact on G4(2W)
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260 Figure 206. Initial conditions used in evaluating effects of low-level guardrail deflection on the performance of the G4(2W)
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261 Table 63. Summary of barrier damage resulting from analysis of high-speed impact into the G4(2W)
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262 Figure 207. Summary of barrier damage resulting from analysis of high-speed impact into the G4(2W)
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263 The movement of the anchors and the maximum tensile forces in the rail tended to increase as the severity of the pre-existing crash-induced rail deflections increased. The anchor deflections also tended to be higher for cases involving Impact Point 1, which was in part attributed to the fact that Impact Point 1 was closer to the downstream end-terminal (e.g., tensile force in rail were distributed to fewer upstream posts for IP01 cases)
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264 Table 64. Summary of occupant risk measures from analysis of high-speed impact into the G4(2W)
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265 Figure 210. Summary of occupant impact velocity (OIV)
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266 Figure 212. Summary of 50-ms average acceleration from analysis of high-speed impact into the G4(2W)
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267 The maximum lateral deflections of the rail increased, The tensile load in the rail increased, The deflection of the upstream anchor increased, The post-bolt connection at w-beam splice locations allowed greater post deflections before releasing, The post-bolt connection at non-splice locations released consistently regardless of pre-damage deflections, Potential for splice rupture increased, Occupant ridedown accelerations in the longitudinal direction increased (primarily due to increased wheel snag on posts) , and All other occupant risk measures were less affected.
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268 distance, (2) the post buckling at the groundline, and (3)
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269 Figure 215. Results of Test 404201-1 illustrating brittle fracture of wood posts due to tensile forces in the w-beam rail.[Bullard00]
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270 Table 65. Recommendations for post and rail deflection damage.
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