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School of Civil and Environmental Engineering
Ph.D. Thesis Defense Announcement
Assessment of Guardrail Systems in Stiff Ground Layers via Continuum and Discrete Simulation Approaches
By
Esmaeel Bakhtiary
Advisors:
Dr. Lauren K. Stewart
Committee Members:
Dr. Donald W. White (CEE, Co-Advisor), Dr. David W. Scott (CEE), Dr. David Frost (CEE), Dr. Min Zhou (ME)
Date & Time: Thursday, July 19th, 3:00pm
Location: Mason Building Room 3132
Assessment of Guardrail Systems in Stiff Ground Layers via Continuum and Discrete Simulation Approaches
Mow strips are asphalt or concrete layers, which are used as vegetation barriers around guardrail posts in the
design of roadside safety structures. Asphalt mow strips have historically been modeled as a rigid layer in
simulations. This assumption often results in unrealistic ground level restraint of the guardrail post. Recent
experiments conducted in a parallel research effort have shown that asphalt rupture and other material behavior
should be considered in the analysis of the response of guardrail posts embedded in mow strips.
This study provides an accurate and efficient approach for simulating the guardrail system and investigates the
effect of asphalt material properties and mow strip geometry on the guardrail system performance. Simplified
analytical solutions are constructed to obtain the lateral capacity of posts embedded in asphalt mow strips. These
solutions are further enhanced by combining finite element simulations and regression analysis to provide predictive
equations for lateral strength and stiffness of asphalt mow strips. The predictive equations are utilized to construct
force-displacement curves (p-y curves) for asphalt layers with various rear distances and material properties. The p-y
curves are employed to efficiently model asphalt mow strips using nonlinear uncoupled springs. Moreover, several
mow strip designs with various thicknesses, rear distances behind the posts, and asphalt pre-cuts are investigated to
provide recommendations for retrofit techniques and new construction.
The recommended retrofit and new construction techniques are evaluated with static and dynamic numerical
simulations of guardrail posts embedded in asphalt mow strips, and full-scale crash simulations of the guardrail
systems are performed. The results are compared with available data from experiments and material tests. The
simulation results for guardrail posts are used to evaluate the level of restraint provided by the asphalt mow strips.
Thereafter, full-scale crash simulation results are evaluated using guidelines in the Manual for Assessing Safety
Hardware (MASH).
