ABSTRACT
The structural response of reinforced concrete slabs in railway viaducts is strongly influenced by local effects and, therefore, detailed analysis methodologies are required for a proper quantification of the internal forces and stress values due to train passages. The existence of track irregularities is an important source of excitation for both the vehicle and the structure, leading to a considerable amplification of these values. This amplification can lead to excessive bridge vibrations and increased fatigue damage. Reinforced concrete (RC) deck slabs in railway bridges and viaducts can be particularly sensitive to fatigue, depending on the structure and track geometry, and also on traffic and temperature loading, among other factors.
In this context, the influence of track irregularities in the global and local responses of a railway viaduct with a precast deck is evaluated in the present work, based on the case of the Alverca railway viaduct, located in the northern line of the Portuguese railways. Figure 1 shows a perspective view of the current zone of the viaduct. Alverca railway viaduct. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig132_1.jpg"/>
The dynamic responses are obtained based on threedimensional finite-element numerical models of the viaduct and trains and using a train-bridge interaction methodology, including track irregularities. The numerical analyses were performed considering the passage of a freight train and the Alfa Pendular passengers train for different speeds, and two distinct sections of the deck were analysed: the upper slab, particularly sensitive to local movements, and the intersection between the lower slab and the girder web (where the global movements of the structure are dominant).
By analysing the structure response for increasing train speeds, it was concluded that the irregularities effect is prevalent for higher train speeds (Figure 2). The comparison of the structure responses, in terms of vertical acceleration time records and corresponding auto-spectra, considering or not the irregularities, revealed that the structure is particularly sensitive to track irregularities with small wavelengths (especially lower than 3 m). This is because the frequency of the action resulting from such wavelengths coincides with certain natural frequencies of the structure. For higher train speeds, the frequency of that action tends to increase and thereby contributes to the excitation of vibration modes with higher natural frequencies, normally associated to a local behaviour of the structure. The analysis of the consequences of track irregularities, for different structure elements and for different train types, revealed considerable differences which are discussed in the paper. Maximum acceleration for the girder (mid-span cross-section) for the passage of AP train. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig132_2.tif"/>
