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Title:Flexural behavior of prestressed concrete monoblock crossties
Author(s):Wolf, Henry E
Advisor(s):Edwards, John R.; Lange, David A.
Department / Program:Civil & Environmental Engineering
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Concrete Crosstie
Concrete Sleeper
Prestressed Concrete
Flexural Behavior
Bending Moments
Concrete Curl
Thermal Gradient
Abstract:As the use of concrete crossties increases for heavy-haul freight railroad lines in North America, it is becoming more critical to improve the understanding of their flexural behavior. This improved understanding can help to optimize current design and maintenance practices for concrete crossties, leading to longer service life, lower life cycle costs, and fewer in-service failures. Currently, center cracking is regarded as one of the most common concrete crosstie failure mechanisms in North America. Improving the understanding of crosstie flexure can help reduce the occurrences of center cracked crossties by ensuring designs are adequate for the field conditions that are encountered. Throughout the international railway community, many methods have been developed to analyze the flexural demand of concrete crossties. The current flexural analysis methodologies contained in American Railway Engineering and Maintenance-of-way Association (AREMA) Chapter 30, EuroNorm (EN) 13230, International Union of Railways (UIC) 713R, and Australian Standard (AS) 1085.14 are explained and compared. A linear-elastic crosstie analysis model was developed to perform a parametric study to determine the sensitivity of the crosstie to changes in ballast reaction along the crosstie. The results of this parametric study were compared to existing design recommendations to find allowable levels of ballast reaction that can occur beneath the crosstie before failure is expected. This model was also used to calculate theoretical bending moment values under ballast reactions measured in the field. Based on the results of these analyses, recommendations to improve current design and maintenance practices for prestressed concrete crossties are presented. To measure the bending moments and support conditions experienced in North American heavy-haul freight service, surface strain gauges were mounted to ten concrete crossties along a high-tonnage, heavy-haul North American freight railroad line. Data were collected from over 7,500 axles from fourteen train passes over three site visits in the spring. The variation of the measured bending moments were found to be non-normally distributed, with a negative skew, indicating a large number of high bending moments experienced by the crosstie. Although minor cracking was observed at the center of most crossties in this test section, measured bending moments and strains did not exceed the current industry standard design limits. Ballast support conditions were found to be a major source of variation in crosstie flexure and were found to be highly variable in both the longitudinal and transverse direction. Warping or curling due to temperature gradients is a well-documented behavior in concrete pavements, girders, and slab-track, but this behavior has not been documented in concrete crossties. Curling in concrete crossties was investigated using finite element modeling along with data obtained from laboratory and field experimentation. Curling was found to follow a direct relationship with thermal gradient. Both analytical and empirical methods were found for predicting curl based solely on temperature measurements. Finally, field experimentation was conducted on a North American heavy-haul freight railroad line to investigate the effect temperature-induced curl has on center negative bending moments. The results from data obtained during three separate site visits show a strong inverse relationship between temperature gradient and center negative bending moments.
Issue Date:2015-12-11
Rights Information:Copyright 2015 Henry Wolf
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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