Date of Award

2017

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Dimitris Rizos

Abstract

Concrete ties have become a promising alternative to timber ties for freight lines with increased curvature, high annual traffic, and large axle loads. They are also widely adopted in passenger lines. High strength (HS) concrete is the material of choice in the fabrication of prestressed concrete railroad ties. The higher strength of the concrete is directly related to higher values of the Elastic Modulus, thus increasing the rigidity of the material. The combination of increased strength, rigidity, and the material brittleness may lead to the development of high amplitude stresses with high gradients, which appears to be a common underlying cause of premature cracking and deterioration observed in some concrete ties. Realizing the current issues associated with the performance of concrete ties and recalling the findings of an almost fifteenyear-old research conducted at the University of South Carolina (USC), a hypothesis was formulated that there is a potential benefit in introducing weathered granite aggregates into mix designs for railroad concrete ties. A high strength, yet lower rigidity, concrete will reduce the amplitude of the stress field and equally important, will regularize the stress field providing for a smoother load distribution that will diffuse stress concentrations. Consequently, the High Strength Reduced Modulus (HSRM) concrete improves the cracking resistance and fatigue performance, thus extending the life of the tie. A comprehensive research program has been conducted at USC to identify the benefits of using HSRM in concrete ties. The research is based on experimental investigations and computer simulations at the material, component and structural member levels. This work presents the details of the computer simulation studies that were conducted as part of the project. Three-dimensional nonlinear finite element (FE) models have been developed for the HSRM and the “standard” concrete ties . Nonlinear material models based on damaged plasticity are implemented. The steel-concrete bond interface is also modeled and discussed. Validation of these models is conducted through comparisons with laboratory testing of prototype and standard ties, and it has shown excellent accuracy. Subsequently, a series of parametric studies related to varying support conditions in tangent and curved track have been conducted. These studies showed that the HSRM concrete tie outperformed the standard concrete tie in all of the benchmark tests by better distributing its stresses and delaying the initiation of cracks. The analysis results are discussed and future recommendations presented.

Rights

© 2017, Adam I. Zeitouni

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