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).