American Railway Engineering And Maintenance-of-Way Association Research Articles

Improving serviceability of concrete railroad ties using prestressed AFRP strands

Prestressing with steel strands has been a key aspect in providing the required strength and durability for railroad ties (sleepers) needed to resist the loads on heavy haul lines in many countries. In spite of their improved durability in contrast to timber ties, a major flaw seen with concrete ties is deterioration due to the environmental or fatigue loading. Another issue found in concrete ties, not found in timber, is the electrical conductivity. The objective of this research is to design and to evaluate a class of concrete railroad ties utilizing aramid fiber reinforced polymer (AFRP) strand as the prestressing material. AFRP prestressed ties were constructed and tested for serviceability and strength following the guidelines provided by the American Railway Engineering and Maintenance-of-way Association (AREMA). Results demonstrated that AFRP strands are a potential substitute for steel strands. Some detail improvements may be necessary to mitigate cracking, this can be achieved by using smaller diameter strands.

Shakedown Limits and Uses in Railroad Engineering

A Poisson’s ratio of 0.3 has usually been used for all grades of steel to estimate shakedown limits; however, high-strength steel, heat-treated pearlitic steel, work-hardened (strain-hardened) steel, and the newly developed bainitic steel show better response to deformation than standard carbon steel. The characteristics of these steels are to be considered. Elastic and plastic shakedown limits are expressed in terms of tensile and yield strength using the von Mises yield criterion and Hertz contact theory. Hence, shakedown limits can be computed and a diagram created for each steel. Different steels may thus be compared to facilitate selection of the appropriate steel grade. In this study, elastic and plastic shakedown limits were computed for three grades of American Railway Engineering and Maintenance-of-Way Association (AREMA) steel. The shakedown process was analyzed quantitatively for AREMA steels. Shakedown limits were related by the coefficient of friction, for which a desirable range was determined. The desirable minimum contact area from the wheel load and the tensile strength of the rail was formulated so the wheel-rail profile could be optimized. Finally, AREMA high-strength steel and DOBAIN steel were compared.

Switch angle design: Formulation, inferences, and uses

Jerk, lateral acceleration, and unbalanced superelevation are induced at the point of switch due to the combined effect of the switch angle and speed. Two sets of formula are derived to compute the values of jerk, lateral acceleration, and unbalanced superelevation due to the switch angle and speed separately. A sudden change in the direction of motion by the switch induces jerk which affects passenger comfort. The jerk due to the sudden change in the direction of motion is formulated in this paper by using the cubic spiral formula. It is demonstrated that the jerk at the point of switch has a positive (direct) relation with the speed and switch angle, but has a negative (inverse) relation with the pivot pitch. It is demonstrated that the switch angle should be optimized to reduce the lateral jerk. To capture the effect of the speed, the effective radius at the point of switch is formulated first and then formulas are derived for the jerk, lateral acceleration, and unbalanced superelevation at the point of switch due to speed. Finally, the aforementioned formulas are added to obtain the total values at the point of switch. The formulas are applied on American Railway Engineering and Maintenance-of-Way Association (AREMA) turnouts and validated by computer simulation using Vampire. These formulas would be helpful for the practicing designers and engineers.

Evaluation of Ballast Behavior under Different Tie Support Conditions using Discrete Element Modeling

This paper presents findings of a railroad ballast study using the discrete element method (DEM) focused on mesoscale performance modeling of ballast layer under different tie support conditions. The simulation assembles ballast gradation that met the requirements of both American Railway Engineering and Maintenance-of-Way Association (AREMA) No. 3 and No. 4A specifications with polyhedral particle shapes created similar to the field-collected ballast samples. A full-track model was generated as a basic model, on which five different support conditions were studied in the DEM simulation. Static rail seat loads of 10 kips (44.5 kN) were applied until the DEM model became stable. The pressure distribution along the tie-ballast interface predicted by DEM simulations was in good agreement with previously published results backcalculated from laboratory testing. Static rail seat loads of 20 kips (89 kN) were then applied in the calibrated DEM model to evaluate in-track performance. Results from the validated full-track DEM simulations indicated that only a small portion of ballast particles participated in load distribution under static loading. Particles on the shoulders and particles in the areas with poor support conditions often experience no or very low contact forces. Load transfer mechanisms investigated through a contact force network varied greatly among different support conditions: lack of rail seat support, full support, and lack of center support had wider force distribution angles than the high center binding and severe center binding conditions. The severe center binding scenario was found to be the most critical support condition in terms of causing the highest tie-ballast contact pressure exceeding 30% of the AREMA allowable pressure.

Laboratory Characterization of Structural Capacity of North American Heavy Haul Concrete Crossties

Over the past few decades, the use of concrete crossties in North America has increased as a high-performance alternative to timber crossties, especially in heavy-haul freight and higher speed rail corridors. To accommodate heavier axle-loads and prevent center cracking, railroads and suppliers have consistently increased the bending moment thresholds that a crosstie must withstand, leading to stiffer elements that may be more prone to brittle cracking. This paper attempts to characterize the structural capacity of the crosstie at two critical design locations, the center and the rail seat cross sections. Concrete crossties were subjected to four-point bending tests at both the center and rail seat, while recording corresponding deflections using protocols adapted from the American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual on Railway Engineering. Experimentation was performed on some of the most representative concrete crosstie designs that are currently installed in North America, with 70 individual crossties undergoing tests. The resulting load-deflection curves illustrate the variability of each crosstie’s response to load and characterize the flexural performance of the crossties. Results showed that North American crosstie designs frequently have significant reserve capacity and high stiffness. The results also indicate that even severely abraded crossties can have enough flexural capacity to withstand typical field loading conditions.

Compressive stress distribution in prestressed concrete and its effect on railroad crosstie design

Recently, track mileage with concrete crossties has been increasing throughout the world. In North America, for example, approximately 30 million crossties are currently in service on Class I freight railroads. It is essential to understand the concrete crosstie bearing capacity and flexure behavior for both design and safety purposes. The American Railway Engineering and Maintenance-of-Way Association (AREMA) Recommended Practices and Australian Standard’s (AS) current flexural design methodologies consider rail seat loads to be vertically transferred to the neutral axis. However, the International Union of Railways (UIC) assumes rail seat loads are distributed at a 45 degree angle to the neutral axis. This load distribution behavior is commonly seen in the design of concrete corbels and spread footings, but is not well documented in the design of concrete crossties, and different assumptions (i.e. in AREMA and UIC design methods) will result in different designs. Better understanding the load distribution in concrete crossties will help to improve the design of concrete crossties and optimize their performance. This study presents preliminary results from an on-going research project at the University of Illinois at Urbana-Champaign (UIUC) focused on concrete crosstie mechanical behavior. A parametric study using three-dimensional (3D) finite element modeling (FEM) was performed to investigate stress distribution below the rail seat and quantify the corresponding distribution angles in prestressed concrete crosstie under static wheel loading. Laboratory experiments were also performed and successfully validated the results obtained from the numerical simulations. The results from both numerical simulation and laboratory experiments indicate the stress distribution angle under rail seat is not constant which disagrees with the assumptions in UIC 713R. Moreover, the stress distribution angle under rail seat is found to be sensitive to crosstie support conditions, and its value follows a direct relationship with rail seat load magnitude. The findings from this study can help to optimize prestressed concrete crosstie bearing capacity design.

Effect of pre-drilling, loading rate and temperature variation on the behavior of railroad spikes used for high-density-polyethylene crossties

Railroad spikes represent a vital component of the rail track system, as they fasten the rail to the supporting crossties. Thus, it is important to understand its behavior and effect on the fastening assembly to mitigate any local failure, which, in turn, could lead to system deterioration or damage. Currently, alternative solutions to the traditional hardwood timber crossties are increasing being adopted by the railroad industry in the USA, with recycled plastic composite crossties being among the available alternatives. Their sustainably, environmental benefits, durability and ease of installation render them an attractive and competitive solution. Several research programs have studied this material and its fastening system in the past; however, additional research is required to fully understand the behavior of these materials and their interactions with the fastening system components. This paper presents an investigation that aims to understand and assess the performance of typical railroad spikes used for recycled high-density-polyethylene crossties. The study encompassed a comprehensive experimental investigation and analytical finite element modeling. The testing program evaluated railroad spikes using static testing methods recommended by the American Railway Engineering and Maintenance-of-Way Association (AREMA) manual. These tests addressed the rail spike pullout and lateral restraint for both screw and cut spikes. Finite element models were constructed and calibrated using the data obtained from the experimental program in order to extrapolate on the experimental results and predict the behavior of full-scale systems beyond the scale of the laboratory. The results observed in this study showed great promise, surpassing all the AREMA recommendations, which highlights the potential of these materials if properly optimized and engineered. Screw spikes exhibited a very good performance, surpassing the minimum recommendations by a significant margin (up to more than 200%) and are thus are highly recommended for future implementation.

“Critical particle size” and ballast gradation studied by Discrete Element Modeling

In this paper, a Discrete Element Modeling (DEM) approach is used to evaluate the impacts of gradation on both ballast void space and load carrying performances. All existing ballast gradations were first represented by a set of “characteristic gradation curves”. The effect of “characteristic gradations” on aggregate assembly volumetric properties is then studied by using DEM. It is found that ballast particles with size around half of the nominal maximum size are not favorable as they separate major particle contacts and introduce extra voids i.e. decrease the overall density of the ballast. To test the effect of this particle size on ballast load carrying capability full-scale ballast layers with common gradations listed in the American Railway Engineering and Maintenance-of-Way Association (AREMA) specifications for main line railroads are generated and tested in DEM. Also, the lab test for the modeling was conducted to verify the modeling results. Repeated train loading is applied to investigate the structural performances by means of comparing settlements occurred after certain volume of traffic. Introducing ballast particles with size finer than half of the nominal maximum size was again not favorable because it yields the maximum ballast settlement. This finding is believed to provide insight into optimizing ballast layer aggregate gradations for better railroad track performances.

Discussion of “Empirical Design Rules for Effective Utilization of Orthotropic Decks” by Roman Wolchuk

The author’s statement that there is no stress-strain proportionality of welded connections because there are residual stresses that are at the yield point at the weld toes or in the weld, and therefore that linear-elastic analysis is not applicable at such locations, is in error as worldwide research has shown in published experimental fatigue studies of welded steel details provided in detailed National Cooperative Highway Research Program (NCHRP) reports (Fisher et al. 1970, 1974; Keating and Fisher 1986) and several books (Fisher 1984; Barsom and Rolfe 2001; Maddox 1991; Fisher et al. 1998; Gurney 2006). These results are also incorporated into design specifications around the world (every edition of the AASHTO standards from 1974 to the current version (AASHTO 2002); every edition of the AASHTO LRFD bridge design specifications from 1994 to the current version (AASHTO 2012); every edition of the American Railway Engineering and Maintenance-of-Way Association (AREMA) specification from 1978 to the current version [AREMA 2014; British Standards Institution 1980; European Convention for Constructional Steelwork (ECCS) 1985; European Committee for Standardization (CEN) 2006; Japanese Society of Steel Construction 1993]). There is no cumulative plasticity at these welded details as the author implies in Fig. 3 of the paper; plasticity mostly occurs at gross section yielding. At the weld toe section, the residual stresses are in equilibrium on the cross section, and the surrounding material remains elastic under subsequent dead and live loads. The flowwithin the high tensile residual stress region at the weld toe is contained by the surrounding, primarily elastic, material, which prevents cumulative plasticity at these regions. This has been verified in the experimental and analytical studies cited previously. Accordingly, the nominal elastic stress in the gross section is used for fatigue design, without any explicit consideration for the local residual stresses, which are implicitly considered by experimentally obtained fatigue resistance curves. This approach to fatigue design has been accepted universally; the phenomenon of metal fatigue was formally acknowledged in the 1860s (Barsom and Rolfe 2001; Bannantine et al. 1990). Only loads that create yielding on the entire cross section, such as that which occurs in cyclic hysteresis loops (or gross section yielding), as applied in seismic loading, redistribute the residual stress states. This does not occur in the orthotropic deck, nor in other welded bridge elements,which are designed for nominal elastic stresses under service conditions. Measurements on full-scale orthotropic decks and other bridge members have verified this finding in the laboratory and in the field (Fisher 1984; Connor and Fisher 2000; Tsakopoulos and Fisher 2005a, b; Connor et al. 2003). These measurements have also verified the analytical evaluation of orthotropic decks (Fanjiang et al. 2004).

Influence of Size and Shape Properties of Railroad Ballast on Aggregate Packing

Railroad ballast is uniformly graded coarse aggregate placed between and immediately underneath the ties to provide drainage and structural support for the loading applied by trains. In the United States, several ballast gradation recommendations are suggested by the American Railway Engineering and Maintenance-of-Way Association (AREMA). Most of these recommended uniform gradations have somewhat wide ranges at their control sieves; this range often creates significantly different grain-size distributions within the same gradation band. In this analysis, AREMA No. 24 gradation was studied for controlled changes in grain-size distributions within its band. Gradations were created by using three control sieves within the AREMA No. 24 gradation band. In addition, to emphasize the significance of particle shape, three sets of particles having high-, medium-, and low-angularity indexes quantified by image analysis were also considered in the packing simulations carried out with an image-aided ballast aggregate assembly modeling approach with the discrete element method (DEM). The significance of passing each control sieve as well as the importance of particle angularity on number of contacts, coordination number (average number of contacts that one particle makes with its neighbors), and porosity was analyzed by using analyses of variance and regression in the DEM packing simulations. The results indicated that increasing the number of particles between ballast nominal maximum sieve size and its half size would increase the number of particle contacts created in the granular assembly. When the imaging-based angularity indexes of the aggregate particles increased, the number of contacts also increased to give a higher coordination number. The ballast DEM simulations proved to be a powerful tool to study and optimize ballast gradations.

The advancement of wire rope in movable bridges

The paper describes the recent developments made in the design and manufacturing of wire rope for specific uses as Counterweight and Operation ropes on vertical lift bridges. New wire rope materials and designs provide increased strengths and improved mechanical properties allowing designers and engineers to take full advantage of the material strengths available. These developments involve high tenacity synthetic materials protected by high strength corrosion resistant carbon steel wires. This provides a hybrid wire rope with a high strength to weight ratio, low torque, and excellent operating characteristics that can outperform any wire rope related product currently available on the market. The results are longer field service, increased corrosion protection, less maintenance, and smaller diameter wire ropes in service applications. All of these characteristics are beneficial to the owner/operator of the movable structure. The paper will discuss the mechanical properties and benefits of improved wire rope constructions verses those currently specified for use in the American Association of State Highway and Transportation Officials (AASHTO) Standard Specification for Movable Bridges and the American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual for Railway Engineering. The use of new technology in Vertical Lift Bridge applications is non-existent in the United States. The European community utilizes wire rope products as described above to transform movable structures into iconic bridges. AASHTO and AREMA have made recent progress in adopting new wire rope standards; however, the ever changing developments in wire rope will require more change over time.

Investigation of Longitudinal Forces in a Concrete Railroad Trestle

Transportation Technology Center, Inc., the University of Illinois, and the Burlington Northern Santa Fe (BNSF) Railway Company conducted tests on a long concrete trestle to quantify the longitudinal forces generated by a coal train with AC locomotives. Results support the American Railway Engineering and Maintenance of Way Association (AREMA) formula for forces due to traction. Testing determined the distribution of shear forces in bents and the equilibrium of the structure in conjunction with an analytical model of the bridge structure. Design longitudinal forces and stresses in piles were also evaluated. The primary observation was that a large amount of longitudinal force is transmitted to the trestle, but it is distributed to a large number of bents through many spans. Forces in individual bents are quite small as compared to the total applied force.

Increasing Speeds Through the Diverging Route of a Turnout Without Increasing Lead Length

Presented are the results of Phase I of an FRA-sponsored study on low-cost means to increase safe speeds through turnouts by way of a retrofit or upgrade. Turnout lead length and frog angle were considered fixed, eliminating costs in relocating the frog or switch points. After in-depth research and dynamic simulation testing, it was determined that the best approach was to optimize existing American Railway Engineering and Maintenance of Way Association (AREMA) turnout geometry. This required a new diverging switch rail and reshaping both the curved stock and closure rails. This low-cost modification applies to most existing turnouts and is expected to improve ride quality and decrease wear without detriment to current maintenance practices. The optimization of a conventional AREMA #20 turnout with straight switch points is discussed as an example. The best vehicle performance in simulations was achieved by a design having a very low entry angle. Vehicle behavior at a speed of 51 mph was significantly improved over the AREMA straight point design at its speed limit of 36 mph, as well as that of the AREMA curved point design at its limit of 50 mph. Also, simulated vehicle performance was nearly as good as for a #20 tangential turnout that has a 20 ft longer lead length. Finally, there was improved performance at speeds as high as 60 mph without exceeding any established safety limits. From these results, a turnout with the reshaped geometry has been constructed and is scheduled for installation on New Jersey Transit.

Computer-Aided Graphical Analysis of Bridges under Vehicular Loading

A computer-based, graphical approach is presented to construct the Influence Profile for determinate bridge structures that are subjected to multiple axle loads. An Influence Profile represents the variation of an internal or external force, or moment, at a specific location of a structure, under loading by an actual vehicle (e.g., American Association of State Highway and Transportation Officials (AASHTO) HS-20 truck, American Railway Engineering and Maintenance-of-Way Association (AREMA) Cooper E-80 train). The technique works by scaling the influence line ordinates by the individual axle weights of the vehicle, and by applying distance delays to account for the horizontal separation between axles. The scaled and shifted influence lines for individual axle loads are then superimposed graphically to obtain the effect of the entire vehicle. Beam and truss examples are given to illustrate the technique. A simple method is also presented for constructing influence profiles for compound systems, where the load is transferred through the deck and floor beams to the superstructure. Because of its graphical concept, the technique provides a practical approach for evaluating the force effects caused by an actual vehicular load; it is also well suited for teaching purposes.