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Phase I Ponderosa Pine Round Post Equivalency Study

REPORT NUMBER

TRP-03-287-13

AUTHORS

Ronald Faller, Scott Rosenbaugh, Karla Lechtenberg, Brad Winkelbauer, Craig Price

PUBLICATION DATE

2013-11-22

ABSTRACT

The primary research objective was to determine the appropriate size and embedment depth of a round Ponderosa Pine (PP) post for serving as a surrogate for the standard 6-in. x 8-in. x 64-in. (152-mm x 203-mm x 1,626-mm) Southern Yellow Pine (SYP) post used in Arizona Department of Transportation (AzDOT) guardrail systems. A total of seventeen dynamic component tests were performed. Three baseline tests were conducted on 6-in. x 8-in. x 72-in. (152-mm x 203-mm x 1,829-mm) SYP posts with a 43¼-in. (1,099-mm) embedment depth for comparison with standard U.S. guardrail systems in a follow-on Phase II continuation effort. Three baseline tests were conducted on the standard 6-in. x 8-in. (152-mm x 203-mm) AzDOT SYP post at an embedment depth of 35 in. (889 mm). Eleven tests were conducted on round PP posts. The first three PP tests were conducted with a 37-in. (940-mm) embedment depth, and the remaining eight tests used a 35-in. (889-mm) embedment depth. The posts were fabricated with various targeted diameters: 8¼ in. (210 mm), 8½ in. (216 mm), and 8¾ in. (222 mm). The posts were embedded in a highly-compacted, coarse, crushed limestone material. For each test, acceleration data was used to determine the force vs. deflection and energy vs. deflection characteristics of the post-soil behavior. Post-soil interaction forces and energy dissipation characteristics of the PP posts were compared to those behaviors obtained for the SYP posts. From these comparisons, an 8½-in. (216-mm) diameter by 64-in. (1,626-mm) long graded PP post with an embedment depth of 35 in. (889 mm) provided similar post-soil behavior to that obtained for 6-in. x 8-in. x 64-in. (152-mm x 203-mm x 1,626-mm) SYP rectangular posts used by the AzDOT. Therefore, the AzDOT standard G4(2W) W-beam guardrail system would be expected to provide acceptable safety performance when configured with round PP posts with a minimum ground line diameter of 8½ in. (216 mm) as well as the current rectangular SYP posts.

KEYWORDS

Highway Safety, Roadside Safety, Guardrail, MGS, Dynamic Test, Bogie, Wood Post, Round Post, Southern Yellow Pine, Ponderosa Pine, and Equivalency

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