Ballasted track interaction effects in railway bridges with simply-supported spans composed by adjacent twin single-track decks

Abstract

This paper is devoted to track-bridge interaction phenomena in railway bridges of short simply-supported (SS) spans composed by ballasted tracks. These structures may experience high vertical acceleration levels under operating conditions. In particular, the coupling effect exerted by the ballast track shared by structural parts that are theoretically independent, such as consecutive simply-supported spans or twin adjacent single-track decks, is investigated. Experimental evidence shows that in these cases there may be an important vibration transmission from the loaded to the unloaded track, and that the interlocked ballast granules couple some of the lowest modes of vibration to an important extent. To this end a detailed three-dimensional (3D) Finite Element (FE) model of an existing bridge is implemented where the ballast in weakly connected regions is simulated as transversely isotropic material, in order to represent in a simplified manner the degraded state due to the relative motion between the disconnected structural parts. First, the bridge numerical model is updated from the ambient vibration response of the structure previously measured by the authors. Second, a sensitivity analysis is performed on the properties of the degraded ballast and their effect on the first five modes of vibration of the bridge is discussed. Finally, the response of the bridge under operating conditions is computed numerically, compared with the response measured experimentally in the time and frequency domains and conclusions are extracted regarding the model adequacy.

Experimental Validation of a Double-Deck Track-Bridge System under Railway Traffic

“…A significant improvement in the agreement between the results is notorious, showing that the numerical model with the proposed modification captures with more accuracy the actual behaviour of the bridge. This conclusion is evident not only by observing the responses, but also by looking into the nMAE indicator, which decreased to 14.6% (22.5% in the previous model) and 22.6% (33.8% in the previous model) with respect to the results obtained in the OT and RT, respectively. Finally, in the frequency domain, a better match between the amplitudes of the peaks has also been achieved, especially in the main peak related with the first mode of vibration of the bridge around 10 Hz.…”

“…The inclusion of the ballasted track in the numerical models of the bridges has several advantages. Particularly, it: (i) guarantees an efficient distribution of the trains' axleloads [17]; (ii) acts as a filter, removing the high-frequency content from the bridge's dynamic response [18]; (iii) considers the track-bridge composite effect due to the longitudinal shear stress transmission occurring between rails and bridge deck, through the ballast layer [19,20]; (iv) simulates the track continuity between neighbouring decks [21,22]; and (v) considers the damping mechanisms due to energy dissipation on the track components caused by structure-induced movements [23].…”

“…In addition, the ballast in the transverse joint between consecutive simply supported decks showed some localized degradation, although not as significantly as that verified in the longitudinal joint. A recent work developed by Sánchez-Quesada et al [22] demonstrated the relevance of the ballast degradation located on the longitudinal joint between two adjacent simply supported decks, each one carrying a single track, on the modal parameters of the bridge. The best adjustment between numerical and experimental frequencies and mode shapes occurred for a degradation scenario where the value of the deformability modulus of the ballast in the lateral direction was approximately 10% of the value in the vertical direction.…”

Ballast shear effects on the dynamic response of railway bridges

“…This fact has been verified by means of a modal analysis performed with a detailed 3D numerical model of an existing railway bridge implemented for this purpose in ANSYS(R)17.1. The model, similar than the one proposed in [30],…”

“…The maximum absolute vertical displacement of the rail in the same section is determined for forcing frequencies in the range f f ∈ [1,250] Hz in steps of ∆f f = 0.01 Hz. This wide frequency range has been chosen to properly capture at least the resonant response of the lowest structural modes in frequency order with high participation of the track, although European Standards [4] limit the maximum frequency of interest for the verification of the Serviceability Limit State for traffic safety up to the greater of (i) 30 Hz, (ii) 1.5 times the frequency of the fundamental mode of vibration or (iii) the frequency of the third one. The analysis is repeated for individual variations of the ballast vertical shear stiffness and damping of [0.0, 0.5, 1.0, 1.5, 2.0] × K w and [0.5, 1.0, 1.5, 2.0] × C w , being C w and K w the reference values of these parameters (see Table 3).…”