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Title:Quantification of prestressed concrete railway crosstie flexural response: Implications for mechanistic design
Author(s):Edwards, John Riley
Director of Research:Barkan, Christopher P.L.
Doctoral Committee Chair(s):Barkan, Christopher P.L.; Lange, David A.
Doctoral Committee Member(s):Tutumluer, Erol; Clarke, David B.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Railway, Crosstie, Sleeper, Flexural Strength, Bending, Center Negative, Rail Seat Positive, Support
Abstract:Concrete is the dominant crosstie material choice for demanding locations on heavy axle load (HAL) freight railroads with steep grades, sharp curves, and high annual gross tonnage. Concrete crossties are also used in rail transit applications where safety and reliability of infrastructure is at a premium and maintenance time is often limited. As such, development and implementation of a structural design method that enables optimization of crosstie design for varied applications and loading environments will reduce initial capital cost and recurring maintenance expense. Center flexural cracking is one of the most common factors limiting the service life of concrete crossties in North America, and rail seat cracking has been documented as a performance concern. Improving the understanding of crosstie flexure can help reduce the occurrences of cracked crossties by ensuring that designs conform to the field conditions in which they are used. To date, few methods have been proposed to accurately quantify the revenue service field bending moments of concrete crossties and their variability due to support conditions and other factors. This dissertation describes the development, deployment, and validation of a method to quantify crosstie bending moments using concrete surface strain gauges. Data collected using this method at field installations throughout the United States were used to investigate the effects of thermal gradient, axle load, axle location, support condition, and rail mode on crosstie bending moments. Results indicated that thermal gradient is significant and should be considered in crosstie flexural design, especially at the crosstie center. Additionally, crosstie support condition is the largest source of variability in crosstie bending moments and its effect is most pronounced on HAL freight railroads. The field results indicated the need for development and application of a probabilistic design method for the flexural capacity of concrete crossties. I developed a design process based on structural reliability analysis concepts whereby target values for reliability indices (β) for new designs are obtained and compared with existing designs for further design optimization. New (proposed) designs are more economical, having a center negative moment capacity reduction of 50% for heavy rail transit. For HAL freight, a reduction in rail seat bending capacity of approximately 40% is justified, reducing the size of the rail seat cross section by approximately the same magnitude. In most cases the proposed designs for both rail modes have fewer prestressing wires and a higher centroid of prestressing steel. In all cases the flexural capacities at the crosstie center and rail seat are better balanced from a structural reliability standpoint. The probabilistic method using structural reliability analysis fundamentals that is proposed and demonstrated in this dissertation constitutes a critical step in the development of mechanistic-empirical practices for the design of concrete crossties. Additionally, this framework for probabilistic design provides a foundation for the future application of mechanistic-empirical design practices to other railway track components.
Issue Date:2019-04-09
Rights Information:Copyright 2019 John Riley Edwards
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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