Criteria for Restoration of Longitudinal Barriers (2010) / Chapter Skim
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Pages 42-53
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From page 42... ...
The goal of this test was to observe the effect of the guardrail damage on the vehicle performance and to test the outcome as well as to provide additional data for the validation of the finite element models. The strong-post w-beam guardrail installed for the purpose of this two-part crash test was 162 feet (49.5 meters)
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From page 43... ...
at 25.5 degrees (NCHRP Report 350 Test 3-11 conditions)
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From page 44... ...
The guardrail deflection was far larger for the full-scale MGA test than for the typical TL-3 crash test into an undamaged guardrail. This difference was attributed to the difference in 44 0 ms 500 ms 100 ms 600 ms 200 ms 700 ms 300 ms 800 ms 400 ms 900 ms Figure 39.
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From page 45... ...
10.3 Evaluation Through Finite Element Modeling The crash tests show that 14 inches of lateral post and rail deflection is a damage level which requires repair. The level of damage below 14 inches of post/rail deflection which may be acceptable was investigated by finite element simulation.
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From page 46... ...
For this test, there was visually good agreement between the real crash test and the finite element model. The models were also compared by the NCHRP Report 350 criteria, as shown in Table 17.
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From page 47... ...
Validation of finite element simulations against second MGA crash test. Undamaged Model 3 in.
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From page 48... ...
The NCHRP Report 350 test criteria were almost entirely unchanged from the values recorded for the undamaged simulation. Between the undamaged and 6 inch rail only deflection simulation, the roll and pitch decreased by less than 4 degrees and the maximum dynamic deflection increased by less than 3 percent.
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From page 49... ...
Another possible outcome was reflected in the results of the MGA crash test. If an unseparated post was deflected backwards and 49 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 Time (s)
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conducted a study on rail rupture in crash tests which showed that rails can carry up to 92.2 kip (410 kN) 50 0 5 10 15 20 25 30 35 0 3 6 9 12 15 Prior Rail Deflection (in)
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From page 51... ...
10.5 Conclusions This study has examined the crash performance of strongpost w-beam guardrail with rail and post deflection from a previous impact. The MGA crash tests and finite element simulations of second impacts into damaged guardrails have shown that the combination of rail and post deflection can negatively affect the crash performance.
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From page 52... ...
The presence of any amount of deflection in the guardrail was found to increase the amount of maximum dynamic deflection, so repairs to guardrail with hazardous objects directly behind the guardrail should also be repaired as quickly as practical. Based on these initial simulations, a damage threshold of 6 inches of post and rail deflection has been set as the threshold for strong-post w-beam barrier repair.
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From page 53... ...
53 Damage Mode Repair Threshold Relative Priority One or more of the following thresholds: More than 9 inches of lateral deflection anywhere over a 25-ft length of rail. Top of rail height 2 or more inches lower than original top of rail height.
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