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Dynamic Impact Testing of Wood Posts for the Midwest Guardrail System (MGS) Placed Adjacent to a 2H:1V Fill Slope

REPORT NUMBER

TRP-03-234-10

AUTHORS

Mary McGhee, Karla Lechtenberg, Bob Bielenberg, Ronald Faller, Dean Sicking, John Reid

PUBLICATION DATE

2010-12-16

ABSTRACT

A stiffened version of the Midwest Guardrail System (MGS) with steel posts has been developed for use adjacent to 2H:1V roadside slopes. However, many members of the Midwest States Pooled Fund Program utilize wood posts. Therefore, it was requested to determine a wood post alternative to the steel posts utilized in the MGS adjacent to a 2H:1V slope. Dynamic impact testing was conducted on 6-in. x 8-in. (152-mm x 203-mm) wood posts and W6x9 (W152x13.4) steel posts with varying lengths and embedment depths when installed at the slope breakpoint of a 2H:1V slope. A total of seven bogie tests were performed - five tests on wood posts and two tests on steel posts. The posts were embedded in strong soil conforming to AASHTO Grade B for all tests. For each bogie test, acceleration data was used to determine the force vs. deflection and energy vs. deflection characteristics of the various post installations. Post-soil interaction forces and energy dissipation characteristics of the wood posts were compared to those for the steel posts used in the original design of the MGS adjacent to a 2H:1V slope. From these comparisons, a recommended post length was selected for the wood post alternative to the steel post in the MGS adjacent to a steep slope. A 7.5-ft (2.3-m) long, 6-in. x 8-in. (152-mm x 203-mm) wood post with a 58-in. (1,473-mm) embedment depth was found to provide the best possible performance and the closest correlation with the 9-ft (2.7-m) long, steel post. As such, this wood post was recommended as an alternative for the 9-ft (2.7-m) long, W6x9 (W152x13.4) steel post utilized in the MGS placed adjacent to a 2H:1V slope.

KEYWORDS

Highway Safety, Bogie Crash Test, Roadside Appurtenances, Compliance Test, MASH, Longitudinal Barrier, Guardrail, Midwest Guardrail System, Roadside Slopes, 2H:1V, Wood Post

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