Design of holes and web openings in railway prestressed concrete sleepers

As the crosstie beam in railway track systems, the prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground. Their design takes into account static and dynamic loading conditions. It is evident that prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, there have always been many demands from rail engineers to improve serviceability and functionality of concrete sleepers. For example, signalling, fibre optic, equipment cables are often damaged either by ballast corners or by tamping machine. There has been a need to re-design concrete sleeper to cater cables internally so that they would not experience detrimental or harsh environments. Accordingly, this study will investigate the design criteria and effects of holes and web openings on structural capacity of concrete sleepers under rail loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The outcome of this study will enable the new design and calculation methods for prestressed concrete sleepers with holes and web opening that practically benefits civil, track and structural engineers in railway industry. INTRODUCTION Prestressing in railway concrete sleepers yields endurance property under high-cycle fatigue. In practice, track engineers need to generate holes or web openings in concrete sleepers to enable the accommodation of cables and signalling equipment. This study aims to provide a principle understanding of the structural capacity and energy toughness of prestressed concrete sleepers without and with holes and web openings. It will investigate the design criteria and effects of holes and web openings on structural capacity of concrete sleepers under rail loading. The modified compression field theory and finite element modelling for ultimate strength design of concrete sleepers will be highlighted in this study. In order to meet the objectives of this investigation, four approaches will be followed. Initial stages of the study involve a cross sectional analyses of concrete sleepers, which will be evaluated using, both modified compression field theory and finite element modelling. Then the analysis: the provisions of existing design guidelines will be used to calculate the capacity of the concrete sleepers. Next step involved lap testing where, five concrete sleepers obtained from our industry partner will be tested under a static bending load pattern. One sleeper will be a control sample, while the other four will be cored varying dimensions and locations. All sleepers will be subjected to static bending tests. The loaddeflection, stress-stress, and load-rotation curves will be plotted for comparison with analytical and numerical results. Finally the parametric studies using validated numerical model will be used to develop a practical design guideline for holes and web openings in railway concrete sleepers. This paper will present the design criteria and effects of holes and web openings on structural capacity of concrete sleepers under rail loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The effects of track environment including soft and hard tracks are also presented as to implement design guidance related to the ultimate limit state of concrete sleepers. The outcome of this study will enable the new design and calculation methods for prestressed concrete sleepers with holes and web opening that practically benefits civil, track and structural engineers in railway industry. CONCRETE SLEEPERS Sleepers are transverse beams laying on ballast and support. Wooden sleepers were utilized as a part of the past in light of the fact that timber was promptly accessible in the neighbourhood. Nevertheless, prestressed or reinforced concrete sleepers, and to a restricted degree steel sleepers, have been received in current railway tracks over the previous decades on account of their strength and long administration life [1-5]. Solid sleepers are depicted as either twin-square or mono-piece. Inside all these sorts, concrete sleepers are all the more generally utilized in light of the fact that they are not influenced all that much by either atmosphere or climate. Furthermore, it provides anchorage for the fastening system and limit longitudinal, parallel and vertical movement by implanting itself onto the substructures. Figure 1 below illustrates the two types of concrete sleepers [1-2]. Figure 1: Concrete sleepers (http://www.aboutcivil.org/types-of-railway-sleepers-advantages-disadvantages.html) CROSS SECTIONAL PROPERTIES All vital cross-sectional properties and measurements of the sleepers used in the investigation are represented below. These cross-sectional properties are used in order to calculate the moment of inertia, stress analysis of the rail seat utilizing the parallel axis theorem. Cross section 1 illustrates the sleeper with no web openings and cross section 2 illustrates a sleeper with a 50mm transverse hole. FLEXURAL CAPACITY The ultimate load capacity of the sleeper design will be resolved for comparative purposes. The nominal moment capacity will likewise show the real limit of the segment or potential store limit, which the section given is permissible to crack. Once separated into standard shapes the measurements are set into a spreadsheet, since this methodology will be rehashed for every segment and configuration cycle. However, the flexural calculations are done according to both ACI and Eurocode 2 [6]. A sample of the spreadsheet utilized for the estimation of cross-sectional properties is indicated in figure 2. a) Cross section 1Sleeper with no web opening b) Cross section 2 Sleeper with 50mm transverse hole Figure 2: Cross sections of concrete sleepers Figure 3: Cross sectional properties of concrete sleeper CROSS SECTION ANALYSIS: NO WEB OPENING A: American Concrete Institute (ACI) Method A.1) Calculation of ed,max (strain in concrete at furthest most layer of pre-stressing from extreme compression fiber at decompression condition) ed,max= fpe_RSAps Ec [ 1 Ac_RS + (dmax − yt_RS) 2