Date of this Version
Throughout the United States, various approach guardrail transition systems are routinely implemented by State Highway Departments to connect standard strong-post, W-beam guardrail systems to the blunt end of concrete bridge rails and roadside median barriers. When installed correctly, approach guardrail transitions shield the hazardous exposed ends of rigid parapets as well as significantly reduce the propensity for wheel snag and vehicle pocketing throughout the transition region. Unfortunately, approach guardrail transitions that are installed in the field may not always resemble that of the as-tested configuration, thus reducing the desired lateral stiffness and strength of the transition system. A recent survey of approach guardrail transition systems in use along highways and roadways in the State of Wisconsin determined that many of the transition systems were installed in the manner which substantially deviated from the as-tested design details. These deviations included missing transition posts, transition posts installed on fill slopes, insufficient soil backfill/grading behind transition posts, wood posts installed in asphalt surfacing, and the presence of drainage structures (i.e., lateral curbs) below the rail. These deviations in approach guardrail transition installations were examined using a combination of prior research results, engineering experience, an extensive BARRIER VII computer simulation effort, and a total of eight dynamic component tests on wood posts embedded in soil with varying terrain and foundation conditions. This investigation was performed to evaluate whether the noted design deviations excessively degraded barrier performance for two commonly-used approach guardrail transition systems in the State of Wisconsin. When design deficiencies were determined based on computer simulations, dynamic component testing, and estimated critical limits, several design modifications were developed for use in retrofitting existing transition systems to resolve such deficiencies.
Advisor: Ronald K. Faller