A numerical study on the fatigue life design of concrete slabs for railway tracks Elisa Poveda, Rena C. Yu ⇑ , Juan C. Lancha, Gonzalo Ruiz E. T. S. de Ingenieros de Caminos, Canales y Puertos, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain article info Article history: Received 12 November 2014 Revised 7 May 2015 Accepted 17 June 2015 Keywords: Fatigue under compression Concrete slab track High-speed train Train load reconstruction abstract With the growing use of high-speed trains, non-ballasted tracks have become more popular compared to ballasted ones. However, the study on fatigue evaluation in concrete slabs under train load has been rather limited. This work presents a numerical study on the fatigue life design of concrete slabs for rail- way tracks. A finite element model for a three-slab track system is established for extracting the principal vibration modes and transient analysis under time-dependent loads. The fatigue evaluation procedure is first validated against full-scale experiments on slabs carried out in a three-point-bend load configuration under fatigue. Next, techniques in the context of digital signal processing, i.e., random phases combined with each constituent frequency amplitude to generate new load pulses, are employed to obtain the most unfavourable load scenario from numerous measured real-time train loads. A novel fatigue criterion which singles out the significance of stress amplitude (proper to concrete-like materials) is implemented to obtain the critical load direction. Fatigue damage under compression is evaluated under this most unfavourable load situation. Meanwhile, parametric analyses on material strength and slab geometry are carried out, recommendations for improved designs towards fatigue life are given accordingly. Even though the established procedure is demonstrated for fatigue under compression, damage evalua- tion based on the Model Code, extension to tension or mixed tension–compressive stress evaluations, as well as damage calculations with alternative criterions can be easily implemented. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Slab track, also called ballastless track, is a modern form of track construction which has been successfully used around the world for high speed lines, heavy rail, light rail and tram systems [1– 14]. Such a trend is mainly attributed to the fact that slab track sys- tems have numerous structural and operational advantages com- pared with the traditional ballasted track. For instance, the maintenance cost can be reduced up to 70–90% according to Esveld [2], the possibility of rail buckling is diminished due to the fixed track alignment, higher running speeds are achievable due to the greater lateral and longitudinal track stability [14]. An additional advantage of slab track systems in comparison with the ballasted ones, shown by Sheng et al. [9], is the reduced level of vibration in the presence of vertical track irregularities. Depending on the spectrum of the train load as well as the run- ning velocity, the dynamic response of a railway track can be sig- nificantly larger than its static counterpart. Furthermore, effects such as vertical track irregularities [9,15,16], temperature variations [17,18], or wheel-rail interaction, can all aggravate such a situation. Under such circumstances, a complete dynamic analy- sis of the slab structure is necessary in order to predict the service life of the constructed track. The dynamic response is, on the one hand, related to the vibration of the entire system (thus noise con- trol and passenger comfort); on the other hand, the fatigue damage within the slab resulted from repeated train load. Studies on the former are concentrated on the vehicle-track-subgrade coupling [19,20,13,7,18]. For example, Tanabe et al. [19] analysed the dynamic interaction between the Shinkansen train (through multi-body dynamics employing non-linear springs and dampers) and the railway structure (consist- ing of truss, beam, shell and solid elements). Steenbergen et al. [13] focused on the dynamic response of a slab track system to a running train axle in order to reduce the amplitudes of the slab vibration. By employing a beam on viscoelastic half-space subjected to a moving load, they determined the influence of slab stiffness, slab mass and soil improvement to reduce track deterioration. As regards the fatigue evaluation in concrete slab tracks, the studies have been rather scant. Even though the interest in the fati- gue of concrete began with the development of highway systems in the 1920s [21], fatigue evaluation and constitutive relations in http://dx.doi.org/10.1016/j.engstruct.2015.06.037 0141-0296/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 926 295 300x6313; fax: +34 926 295 391. E-mail address: rena@uclm.es (R.C. Yu). Engineering Structures 100 (2015) 455–467 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct