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Development and Evaluation of Weak-Post W-Beam Guardrail in Mow Strips

REPORT NUMBER

TRP-03-322-15

AUTHORS

Scott Rosenbaugh, Ronald Faller, Karla Lechtenberg (Polivka), James Holloway

PUBLICATION DATE

2015-10-01

ABSTRACT

The objective of this study was to adapt and evaluate a weak-post, W-beam guardrail system for use within mow strips and other pavements. The weak-post guardrail system was originally designed as the MGS bridge rail and has also been adapted for use on culverts. It was envisioned that the weak-post design would absorb the impact forces and prevent damage to the mow strips, thereby minimizing maintenance and repair costs. Evaluation of the weak posts in mow strips began with three rounds of dynamic bogie testing. Round 1 of bogie testing showed that 4-in. (102-mm) thick concrete would sustain only minor spalling from impacts to the posts. However, the posts would push through 4-in. and 6-in. (102-mm and 152-mm) thick asphalt mow strips. During Round 2, 24-in. (610-mm) long, 4-in. x 4-in. (102-mm x 102- mm) sockets with 10-in. x 9-in (254-mm x 229-mm) shear plates were utilized to better distribute the impact load to the asphalt pavement and prevent damage. However, Round 3 of bogie testing consisted of dual-post impacts, and the asphalt suffered from shear block fracture between the two 24-in. (610-mm) sockets and the back edge of the mow strip. A dual-post test within a 4-in. (102-mm) thick concrete pad showed only minor spalling. A full-scale MASH 3-11 test was conducted on the weak-post guardrail system installed within an asphalt mow strip. Due to the Round 3 testing results, the asphalt thickness was increased to 6 in. (152 mm), and the socket depth was increased to 30 in. (762 mm). The 2270P pickup was contained and safely redirected, and all MASH safety criteria were satisfied. Unfortunately, the asphalt fractured, and a 2½-in. (64-mm) wide crack ran from socket to socket throughout the impact region of the system. Therefore, the weak-post guardrail system was crashworthy, but would require repairs in its current configuration. The system could also be installed in a concrete mow strip to prevent pavement damage.