Click for next page ( 22


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 21
21 3.5.1 Undamaged Barrier Full-Scale TTI Crash Test Simulation of 405421-1 TTI Crash Test Crash Test Validation The most crucial form of validation was the validation of LS-DYNA models of the coupled vehicle-longitudinal barrier systems. To validate the model, the research team constructed t = 0 ms t = 0 ms an LS-DYNA model of an NCHRP Report 350 crash test of the subject barrier under impact loading. The crash test that was selected for this purpose was a test performed by the TTI to demonstrate the crash performance of the modified G4 (1S) guardrail. The crash test was a success, with the vehicle being t = 120 ms t = 120 ms redirected away from the guardrail. The occupant impact velocity and ridedown acceleration were well below the rec- ommended values of 9 m/s (20.1 mph) and 15 G, respectively. The damage to the guardrail was considered to be moderate, t = 242 ms t = 240 ms with approximately 1 meter (3.3 feet) of dynamic deflection and 0.7 meters (2.3 feet) of static deflection recorded. Because this was a validation simulation, there was no need to induce any pre-existing damage in the guardrail. t = 359 ms t = 360 ms Thus, the finite element model of the vehicle and guardrail was unmodified. The finite element vehicle was given ini- tial conditions to match the test level 3 criteria i.e., an ini- tial velocity of 100 kph (62.1 mph) and an impact angle of 25 degrees. This varied slightly from the real test, for which t = 491 ms t = 490 ms the initial speed was 101.5 kph (63 mph) at 25.5 degrees. The model was run as is for 1,000 ms and compared to the documented crash test results. The crash test results were compared with the structural t = 691 ms t = 690 ms impact response of the simulated vehicle-barrier system. The Figure 13. Comparison of model was able to reproduce maximum dynamic and per- undamaged guardrail crash test manent rail deflection, vehicle exit conditions (exit speed and simulation. and angle of the test vehicle), and the occupant injury pa- rameter response (impact velocity and occupant ridedown acceleration as prescribed by NCHRP Report 350). Figure 13 3.5.3 Pendulum Component Test Validation shows the good qualitative comparison between the crash test Pendulum tests were conducted to provide additional vali- and simulation. Detailed validation results are contained in dation data for the finite element longitudinal barrier models. the appendices. Damaged two-post sections of barrier were impacted with a 2000 kg concrete impactor. The presumption is that if the finite 3.5.2 Damaged Barrier Full-Scale element model can replicate a pendulum test, this is a neces- Crash Test Validation sary (but not necessarily sufficient) test of a 100-foot long rail section. The models were able to reproduce barrier response This research program also conducted an NCHRP Report (maximum dynamic deflection and post position vs. time) 350-type crash test of a vehicle colliding with a damaged sec- and pendulum acceleration response. tion of strong-post w-beam barrier. In parallel, an LS-DYNA model of this scenario was constructed and executed. The 3.6 Extensions to Other Damage experimentally measured structural impact response of the Modes and Barrier Types vehicle/barrier was compared with the corresponding response from the simulation using the validation methodology used Comparison of the minor damage catalog in the appendices to validate the models against standard NCHRP Report 350 with the proposed repair guidelines also shows that it was not crash tests involving undamaged barrier sections. In each case, possible to test all proposed repair guidelines. However, the tests the finite element models were able to faithfully reproduce the and simulations that were conducted allow us to infer the per- corresponding impact experiment. formance of several other damage modes under crash loading.

OCR for page 21
22 The following paragraphs provide a summary of those dam- was expected to be similar to a rail hole or tear--a condi- age modes: tion which was evaluated. Rail Flattening (vertical dent)--The matrix evaluated Rotten Wood Posts/Blockouts--The proposed guide- length-wise flattening of the rail. This was observed to be lines recommended replacement of rotted wood posts or a more common occurrence than height-wise flattening blockouts. Although the research team did not simulate or vertical denting of rail. The research team's recom- or test this directly, the effect of a rotted post or blockout mendation was based upon the consensus of current state would be the same as a missing post or blockout--a con- guidelines. No simulations or tests were planned. dition which was evaluated. Missing or Loose Bolts--The guidelines proposed that Steel Post Torsion--The proposed guidelines recommend problems with bolts should be corrected. No simulations or repair of barrier systems with posts that have been severely tests were planned. twisted. Although the research team did not simulate or Weak Post W-Beam Systems--Weak post w-beam guide- test this directly, the effect of a severely twisted steel post lines were not evaluated independently of strong-post would be similar to a missing post--a condition which was w-beam guidelines. Crash tests have shown that a primary evaluated. failure mechanism of weak post w-beam barrier is rail rup- Any Structural Corrosion (hole or section loss)--The ture (Ray et al., 2001a; 2001b). The results of strong post proposed guidelines recommend repair of barrier systems pendulum tests of vertical tears, horizontal tears, and holes which have suffered structural corrosion as opposed to sur- were assumed to apply to weak post systems. Because of the face corrosion of the galvanizing treatment. Although the crucial function of the splice in weak-post systems, the pro- research team did not simulate or test the effect of structural posed guidelines do not allow any splice damage or absence corrosion directly, the response of a seriously corroded rail of splice bolts.