Optimization of the Auxiliary-Beam System in Railway Bridge Vibration Mitigation Using FEM Simulation and Genetic Algorithms

Abstract

In this paper, we present the optimization of a vibration mitigation system for railway bridges. These structures are subjected to significant moving loads, whose dynamic characteristics may produce resonance effects, compromising the integrity of the bridge and the security of the passengers if the speed or the load of the train is not controlled. The study focuses on the Auxiliary Beam system. It consists of a beam located under the bridge and connected to the slab by viscous dampers. The symmetry of the problem allowed for the use of a 2D Finite Element model of the system. This model was used together with a genetic algorithm in order to evaluate the behaviour of different candidates and to optimize the design parameters: the inertia of the beam and the damper coefficient. The goal of the optimization process is to minimize the acceleration of the bridge while adding the lightest mitigation system possible. The combination of a Finite Element Model and Genetic Algorithm helps to address the complex problem and to find an optimized set of structural parameters. The system finally shows good behaviour for optimal parameters. The Tuned Mass Damper (TMD) system is probably the most studied method for vibrational response reduction in bridges and buildings. Its popularity is due to its simplicity and cost-efficient implementation [8][9][10][11][12]. However, TMD systems are designed and tuned to a specific frequency value-typically, the first flexural mode of the structure. This may cause problems, since the added mass of different trains to the main structure modifies its natural frequencies.An alternative method for bridges is the Auxiliary Beam (AB) or double beam system [13][14][15][16]]. The AB system consists of an extra beam installed under the bridge deck, being both connected by a viscous damper; see Figure 1. The viscous damper of the system will dissipate part of the energy generated by the moving loads, reducing both the vertical acceleration and the displacement of the bridge. The tuning problem of TMDs is now avoided, since the viscous damper is capable of working properly in a wider range of frequencies. Also, this system is particularly interesting for the retrofitting of existing infrastructures, since it can be installed while the bridge is in use.