Composites for Timber-Replacement Bearers in Railway Switches and Crossings
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infrastructures Review Composites for Timber-Replacement Bearers in Railway Switches and Crossings Sakdirat Kaewunruen 1,* ID , Ruilin You 2 ID and Makoto Ishida 3 1 School of Engineering, The University of Birmingham, Birmingham B15 2TT, UK 2 Railway Engineering Institute, China Academy of Railway Sciences, Beijing 100081, China; [email protected] 3 Railway Engineering Department, Nippon Koei, Tokyo 102-8539, Japan; [email protected] * Correspondence: [email protected]; Tel.: +44-(0)-1214-142-670 Received: 25 August 2017; Accepted: 6 October 2017; Published: 9 October 2017 Abstract: Recent developments in composite materials have resulted in their pilot adoption in railway industry, such as ‘fibre-reinforced foamed urethane (FFU)’, ‘geopolymer concrete’, ‘recycled polymer’, and ‘CarbonLoc composite’. Railway track support systems are critical for safe and reliable operations of railway tracks. There are two types of support structures, which can be designed to be either a slab or a cluster of discrete bearers or sleepers. The choice of turnout support system depends on asset management strategy of the rail operators or maintainers. The aim of this paper is to present the criteria, fundamental and multi-disciplinary issues for the design and practical selection of composite materials in railway turnout systems. As a case study, a full-scale trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, ‘fibre-reinforced foamed urethane (FFU)’ bearers, is presented. Influences of the composite bearers on track geometry (recorded by track inspection vehicle ‘AK Car’ and based on survey data), track settlement, track dynamics, and acoustic characteristics are highlighted in this paper. Comparative studies of composite materials for railway track applications are reviewed and presented in order to improve material design process. This state-of-the-art review paper will also focus on practicality and environmental risks of composite components in railway built environments. It embraces the requirement considerations of new materials for use as safety-critical track elements. Keywords: geopolymer concrete; recycled polymer; CarbonLoc composite; fibre-reinforced foamed urethane (FFU) bearers; turnout grillage; track geometry; stability; vibration; timber replacement 1. Introduction Railway urban turnout is a special track system used to divert a train from a particular direction or a particular track onto other directions or other tracks. It is a structural grillage system that consists of steel rails, points (or called ‘switches’), crossings (special track components), steel plates, rubber pads, insulators, fasteners, screw spikes, beam bearers (either timber, polymer, steel, or concrete), ballast, and formation, as shown in Figure1[ 1]. Traditional turnout structures were generally supported by timber bearers. The timber bearers allow the steelwork to be mounted directly on steel plates that are spiked or screwed into the bearers. Timber, steel, and concrete are common materials, which have had long history records of usage in tracks over a decade. Timber has an excellent damping coefficient, whilst concrete and steel tend to have almost no damping coefficient [2–5]. Concrete has proven to be an excellent counterpart to improve track and turnout stability—laterally, longitudinally, and vertically [6,7]. Recent studies also show that steel bearers perform well in a short term, but have higher turnout settlement and ballast breakage over the long term [8,9]. Infrastructures 2017, 2, 13; doi:10.3390/infrastructures2040013 www.mdpi.com/journal/infrastructures Infrastructures 2017, 2, 13 2 of 16 Infrastructures 2017, 2, 13 2 of 17 Switch/point Closure Rails Check Rail Check Rail Crossing Figure 1. Typical turnout geometry. Figure 1. Typical turnout geometry. This paper presents the criteria and fundamental of bearer design for a grillage turnout system. ThisThe materials’ paper presents characteristics the criteria are illustrated and fundamental to provide an of in-depth bearer design understanding for a grillage into the turnout static and system. The materials’dynamic performances characteristics of area turnout illustrated over toits providelife cycle, an as in-depth well as understandingthe potential benefits into the of staticnew and materials in reducing the depth of bearers while maintaining stability. It demonstrates a case study dynamic performances of a turnout over its life cycle, as well as the potential benefits of new materials of monitoring the static and dynamic in-situ performance of the alternative fibre-reinforced foamed in reducing the depth of bearers while maintaining stability. It demonstrates a case study of monitoring urethane (FFU) material as a like-for-like replacement of timber bearers. This study involves the the staticinspection, and dynamic turnout in-situsettlement performance monitoring, of geometry the alternative data analysis, fibre-reinforced train-track foamed interaction, urethane sound (FFU) materialpressure, as a like-for-likeand vibration replacement measurements of of timber the double bearers. slips, This and studybenchmarking involves with the inspection,other field data turnout settlement[10–13]. monitoring, geometry data analysis, train-track interaction, sound pressure, and vibration measurements of the double slips, and benchmarking with other field data [10–13]. 2. Materials and Methods 2. Materials and Methods It is well known that traditional turnout generally imparts high impact forces on to structural Itmembers is well knownbecause thatof its traditional blunt geometry turnout and generally mechanical imparts connections high impactbetween forces closure on rails to structural and membersswitch because rails (i.e., of heel-block its blunt geometryjoints). Although and mechanical a new method connections of geometrical between design closure has been rails adopted and switch for tangential turnouts, the transfer zone at a crossing nose in complex turnout system still imposes rails (i.e., heel-block joints). Although a new method of geometrical design has been adopted for high-frequency forces to track components. Under static and high-intensity impact loading tangential turnouts, the transfer zone at a crossing nose in complex turnout system still imposes conditions, timber bearers have a long proven record that they can provide firmed support to such high-frequencyturnouts. The forces structural to track timber components. bearers in Underturnout static systems and are high-intensity usually in Strength impact Group loading 1 [3] conditions, and timberthe bearers typical timber have a species long proven are tabulated record in that Table they 1. Based can provide on the strength, firmed supportTable 2 displays to such the turnouts. design The structuraldimensions timber of bearers timber inbearers turnout in a systems variety of are ra usuallyilway turnouts in Strength with Groupnominal 1 design [3] and spacing the typical of 600 timber speciesmm are (or tabulatedbetween 500 in mm Table and1. 700 Based mm) on [3]. the It is strength, important Table to note2 displaysthat timber the bearers design for dimensionssupporting of timberpoints bearers and incrossing a variety structures of railway may turnouts be designed with using nominal the beam design on spacing elastic foundation of 600 mm analysis (or between 500 mm(similar and to 700 traditional mm) [3]. railway It is important sleepers) tobut note one thatmust timber take into bearers account for additional supporting factors: points and crossing structures• Extra may length be designed of timber using bearers the beamin comparison on elastic with foundation standard analysissleepers; (similar to traditional railway sleepers)• Centrifugal but one must forces take through into account curved pairs additional of rails; factors: • Forces and bending moments induced from points, motors, and other signaling equipment; • Extra• Impact length forces of timber induced bearers by wheel-rail in comparison interaction; with standard sleepers; • Centrifugal• Mechanical forces rail throughjoints (maximum curved pairsspacing of of rails; bearers is 600 mm); • Forces and bending moments induced from points, motors, and other signaling equipment; • Impact forces induced by wheel-rail interaction; Infrastructures 2017, 2, 13 3 of 16 • Mechanical rail joints (maximum spacing of bearers is 600 mm); Infrastructures 2017, 2, 13 3 of 17 Table 1. Timber species for railway turnout applications [3]. Table 1. Timber species for railway turnout applications [3]. Group Common Name Scientific Name Group Common Name Scientific Name Ironbark Grey E. Siderophloia Ironbark Grey E. Siderophloia Ironbark Grey E Paniculata Ironbark Grey E Paniculata Ironbark Grey E Drepanophylla Ironbark RedIronbark (broad Grey leaved) E Drepanophylla E Fibrosa Group 1 Ironbark Red (broad leaved) E Fibrosa Group Ironbark1 Red (narrow leaved) E Creba IronbarkIronbark Red Red(narrow leaved) E Creba E Sideroxylon Gum SlatyIronbark or Box SlatyRed E Sideroxylon E Dawsonil GumBox Slaty White or Box Slaty E Dawsonil E Albens BoxBox Grey White E Albens E Microcarpa BoxBox Grey Grey E Microcarpa E Moluccana TallowBox wood Grey E Moluccana E Microcorys Group 2 GumTallow Grey wood E Microcorys E Punctata Group 2 GumGum Grey Grey E Punctata E Propinqua Gum ForestGum RedGrey E Propinqua E Tereticornis MahoganyGum Forest White Red E Tereticornis E Acmeniodies Mahogany White E Acmeniodies Table 2. Timber design for railway turnout applications [3].