Professor John D. Reid
Date of this Version
Bickhaus, R.F., Evaluation of Flared Approach Guardrail Transitions and MASH 2270P Ram Vehicle Model Improvements, M.S. Thesis, University of Nebraska-Lincoln, Lincoln, NE, 2021.
The objective of this research study was to use computer simulation to identify the critical flare rate for flaring approach guardrail transitions (AGTs) away from the primary roadway. AGTs installed with a flared configuration result in a length of need (LON) reduction as well as an increase in the clear zone area in front of the barrier, which would reduce both installation cost and crash frequency. The research focused on the determination of the maximum allowable flare rate that could safely be utilized with 31-in. (787-mm) tall thrie-beam AGTs without concrete curbs that utilize the Midwest Guardrail System (MGS) upstream of the transition. The research consisted of a literature review, development and validation of a tangent AGT LS-DYNA model, LS-DYNA simulation of multiple AGT flare rates from 10:1 to 25:1 with respect to the roadway, and the determination of the critical flare rate and critical impact points (CIPs) for full-scale testing.
The simulation study identified the 15:1 and 12.5:1 flare rates as the critical flare rates that exhibited significant LON reduction while maintaining acceptable Manual for Assessing Safety Hardware (MASH 2016) safety performance criteria. Further simulation identified CIPs. In comparisons between the critical flare rates at the CIPs, the 15:1 flare rate exhibited improved vehicle stability and occupant risk criteria and should have a greater potential to pass MASH criteria, compared to the 12.5:1 flare rate. As a result, with sponsor feedback, the 15:1 flare rate was selected as the critical flare rate for full-scale crash testing.
Following the completion of the flared AGT simulation study, several updates were made to the tire, suspension, and steering models on the 2018 Ram LS-DYNA vehicle model. The model tire, suspension, and steering updates were evaluated through curb traversal testing and compared to physical test results. While the updated vehicle model exhibited improved correlation with the physical test results, additional updates to the vehicle model are required to improve the simulated vehicle behavior.
Advisor: John D. Reid