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Advisory Committee Chair

Nasim Uddin

Advisory Committee Members

Ian Edward Hosch

Lee G Moradi

Document Type

Thesis

Date of Award

2015

Degree Name by School

Master of Science in Civil Engineering (MSCE) School of Engineering

Abstract

The American Association of State Highway and Transportation Officials (AASHTO) Bridge Specifications proposes “Yield Line Theory Analysis” in order to determine the structural capacity of concrete barriers based on their static strength. However, it appears that this method conservatively underestimates the structural capacity of concrete barriers to endure high vehicle impacts. Typically, this deficiency has been compensated for artificial reductions in bridge rail design loads used in the design code. Existing barrier design guidelines - static design methods incorporated into the AASHTO Bridge Specifications - are based upon National Cooperative Highway Research Program (NCHRP) Report 350. The Manual for Assessing Safety Hardware (MASH) guidelines propose higher impact angles, heavier trucks and higher impact speeds. The impact loads proposed by MASH appeared to be extremely high and were not approved by AASHTO’s T7 Committee on Guardrails and Bridge Rails. Therefore, it seems appropriate to modify the applied load to the barrier by using realistic dynamic impact, not only to meet the AASHTO design requirements but also to achieve a more reliable result. Barriers are designed to provide the maximum safety on highways, roads, and bridges. Unsymmetrical New Jersey - type concrete barriers have been designed to (1) minimize the damage to the vehicle caused by the crash via absorbed energy (2) keep the vehicle in line and not allow redirection to traffic flow, and (3) in the case of barriers installed on bridges, to not allow the vehicle to fall off the bridge, which would cause significant damage to traffic flow beneath. Hence, barriers not only have to be designed based on their strength capacity, but also need to satisfy all the industry criteria. Current New Jersey - type concrete barriers have been designed statically, only taking into consideration their strength capacity. Consequently, there is an opportunity to redesign this barrier using realistic dynamic simulations and analyses, by modeling the barrier and deck overhang from test level 1 through 6, in order to satisfy all criteria. The objective of this research is to perform analyses using the finite element method based upon the dynamic computer simulation (LS-DYNA) in order to propose five different types of concrete barriers that are different in thickness and geometry to the current New Jersey barrier with the aim of developing a more efficient design in terms of production cost and performance. The FEM simulation models are further verified using exiting dynamic field tests. This new proposed design will then be compared to the current New Jersey barrier in the interest of finding the best geometry that can provide the maximum safety. This comparison will also present both static design (AASHTO equivalent nominal resistance to transverse load measured at 54.0 kips) and dynamic design of the barrier (based on NCHRP 350 TL-4: NCAC single unit truck, with a velocity of 80 km/h and an angle of crash equal to 15 degrees).

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