Keywords: railway bridges, numerical modelling, calibration, experimental validation, simulation for high speed traffic.

Trains travelling at high speed on bridges can induce significant dynamic effects as a result of resonance phenomena, which occur when the passage frequency of the axle, or axle groups, is equal to the natural frequency of vibration of the structure [1]. In this paper the dynamic behaviour of three different types of railway bridges, located in upgraded sections of the Portuguese railways, is investigated. The S. Lourenço Bridge is a bowstring arch consisting of two half-decks with 38.4 m span, each one carrying a single track. The Alverca viaduct has a deck with 47 spans made of simply supported prestressed concrete box girders, with spans between 16.5m and 21m. The Canelas Bridge has a deck with six simply supported spans of 12m. The deck is a composite steel-concrete structure composed of nine metal beams embedded in a concrete slab: the so-called "filler beam" structural solution. The analyses involved experimental studies using ambient vibration for the identification of the structural modal parameters: including frequencies, mode shapes, and damping ratios. The modal parameters constituted the basis for the calibration of the numerical models based on genetic algorithms. For the pairing of numerical and experimental vibration modes, a new technique based on the energy modal assurance criterion was successfully used. The genetic algorithms allowed the robust optimization of a significant number of parameters of the numerical models. To validate the numerical models, dynamic tests were performed with controlled rail traffic. The comparison of the dynamic responses in terms of displacements, accelerations and deformations of the bridge showed a very good agreement between numerical and experimental results. Based on the calibrated numerical models, dynamic analyses of the bridges for railway traffic at high speed were performed. The results of the simulations showed that very high dynamic amplifications occur because of resonance effects; and because of the impact induced by the rapid rate of loading arising from the speed of the trains crossing the bridges, which appeared at speeds higher than 250 km/h for the bridges in the study. These effects were shown to be dependent not only on the characteristics of the bridges, but also on the characteristics of the trains, thus confirming the requirement, to perform dynamic analyses which consider a wide range of high speed trains, as specified in the Eurocodes [2,3].

[1]

ERRI D214/RP9, "Railway bridges for speeds >200 km/h", European Rail Research Institute (ERRI), Final Report, Utrecht, The Netherlands, 2001.

[2]

EN1991-2, "Actions on Structures – Part 2: General Actions – Traffic loads on bridges", European Committee for Standardization (CEN), Brussels, Belgium, 2003.

[3]

EN1990-AnnexA2, "Basis of Structural Design – Annex A2: Applications for bridges (normative)", European Committee for Standardization (CEN), Brussels, Belgium, 2005.

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