Nebraska LTAP


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Ranjha, S.A., Bielenberg, R.W., Reid, J.D., and Faller, R.K. (2017). Increased Span Length for the MGS Long-Span Guardrail System Part III: Failure Analysis". NDOT Research Report TRP-03-362-17.


The objective of this research study was to review and analyze the system failure observed during crash testing of an increased span length for the MGS long-span guardrail system in test no. MGSLS-2. Test no. MGSLS-2 was a full-scale crash test conducted on the MGS long-span guardrail with a span length of 311⁄4 ft (9.5 m). This test utilized universal breakaway steel posts (UBSPs) adjacent to the long span in lieu of the controlled release terminal (CRT) wood posts used in previous long span systems.

An engineering analysis was undertaken to review the downstream end anchorage failure observed in test no. MGSLS-2. The analysis also compared critical aspects of the barrier performance with previous full-scale crash tests that had similar features or increased anchor loading. The results of this analysis and conclusions regarding potential causes of the anchor failure suggested that there was no identifiable root cause for anchor failure, but the pocketing and deflection suggest that the barrier system may have been pushed near its limits. It was noted that certain factors may have contributed to the anchor failure, including increased span length, location of the impact point, differences in the breakaway post behavior adjacent to the unsupported span, and natural variation in wood strength.

Following the analysis, several potential design modifications were noted for improving the barrier system and reducing the potential for end anchorage failure. However, it was noted that further analysis of these potential improvements, selection of a preferred design, and evaluation of the revised barrier system through full-scale crash tests will be required to fully evaluate the system to MASH TL-3 criteria.