Diogo Ribeiro

Finite-element model calibration of a railway vehicle based on experimental modal parameters

This article describes the experimental calibration of a three-dimensional numerical model of an Alfa Pendular train vehicle based on modal parameters. The dynamic tests of the carbody and bogie of the vehicle allowed the determination of the frequencies and modal configurations of 13 vibration modes, by applying the data-driven stochastic subspace identification method. In addition, a dynamic characterisation test of the passenger-seat system was also conducted. The calibration of the model was performed using a submodelling/multistep approach involving two phases, the first one focused on the calibration of the model of the bogie under test conditions and the second one focused on the calibration of the complete model of the vehicle. The calibration was performed through an iterative method based on a genetic algorithm and allowed to obtain optimal values of 17 parameters of the numerical model. For the pairing of the vibration modes, real and complex, a recent technique was used based on the calculation of the modal strain energy. The stability of a significant number of parameters considering different initial populations demonstrated the robustness of the algorithm. The comparison of experimental and numerical responses before and after calibration revealed significant improvements in the numerical model and a very good correlation between the responses obtained with the calibrated model and the experimental responses.

Hybrid Fiber-Optic/Electrical Measurement System for Characterization of Railway Traffic and Its Effects on a Short Span Bridge

The characterization of traffic effects on a short span railway bridge in Northern Portugal with a new hybrid platform that allows the simultaneous assessment of signals generated by a sensing network composed of both electrical and fiber Bragg grating-based sensors was demonstrated. A commercial fiber-optic-based train characterization system using a bridge weight-in-motion algorithm was also developed and tested. By using only three fiber Bragg grating sensors the system allows on-motion determination of train speed and weight distribution.

Updating and validation of the dynamic model of a railway viaduct with precast deck

This study describes the calibration and experimental validation of the dynamic model of a railway viaduct with precast deck. Global modal parameters of the structure and local modal parameters of the upper slab of the deck are identified based on a dynamic test. The calibration of the numerical model is done using a genetic algorithm that allows obtaining optimal values of 11 parameters of the numerical model. The inclusion of local modal parameters proved to be crucial, as various parameters of the numerical model do not have significant influence on global modal parameters. Mode pairing between numerical and experimental vibration modes is performed using a recent technique based on modal strain energy. The experimental validation of the calibrated numerical model is done by the comparison between numerical responses and experimental responses obtained in a dynamic test under railway traffic. This dynamic test shows the existence of a nonlinear behaviour of the viaducts supports. There is an excellent correlation between numerical and experimental responses for different train speeds with the adjustment of the longitudinal supports stiffness of the calibrated model.

Dynamic Response of a Railway Bridge to Heavy Axle-Load Trains Considering Vehicle–Bridge Interaction

Railway bridges can be particularly sensitive to dynamic effects induced by trains owing to the resonance phenomena originated by periodic loading associated with the passage of regularly spaced tr...

Impact of track irregularities and damping on the fatigue damage of a railway bridge deck slab

Abstract The structural response of reinforced concrete slabs in railway bridges is strongly influenced by local dynamic effects and, therefore, detailed calculations of internal forces have to be performed for a realistic fatigue assessment. In this context, this paper discusses the influence of track irregularities and modal damping coefficients in the dynamic response and fatigue behaviour of a railway bridge deck slab. For that purpose, track irregularities were measured (at different instants of time) and damping coefficients were determined based on acceleration records for passing trains in a real bridge. The bridge behaviour was calculated using a train–bridge interaction methodology, considering calibrated numerical models of the viaduct and the train. The fatigue damage was quantified through the linear damage accumulation method. This methodology allowed to understand the way track irregularities and damping coefficients affect the magnitude of applied bending moments and fatigue damage in the slab.

CALIBRATION OF THE NUMERICAL MODEL OF A STAND IN DRAGÃO STADIUM BASED ON GENETIC ALGORITHMS

This paper is focused on the experimental calibration of the numerical model of a stand in Dragão stadium based in genetic algorithms. A finite element numerical model of a group of seating deck units including the connections between them and the connections with the stands, was developed. Also a dynamic test was performed in the South stand in order to characterize the local dynamic properties of a group of seating deck units, particularly its natural frequencies, modal configurations and damping coefficients. The experimental calibration of the numerical model was performed using an iterative method based on a genetic algorithm. The stability of a significant number of parameters, considering different initial populations, proved the robustness of the adopted algorithm in the scope of the optimization of the numerical model. Also the calibration results demonstrate a very good agreement between numerical and experimental modal responses and a significant improvement of the numerical model before calibration.

Calibration of Dynamic Models of Railway Bridges Based on Genetic Algorithms

This chapter presents the main experimental calibration methodologies of finite element numerical models, with particular focus on methodologies based on modal parameters. In this context, the computational implementation of an iterative method based on a genetic algorithm is described. The iterative method involves the resolution of an optimization problem, which involves the minimization of an objective function by varying a set of preselected model parameters. The objective function includes residuals associated to natural frequencies and mode shapes. The proposed methodology is applied to the calibration of the dynamic models of two railway bridges, Sao Lourenco bridge and Alverca viaduct, both located in the northern line of the Portuguese railways in recently upgraded track sections. The calibration results demonstrate a very good agreement between numerical and experimental modal responses and a significant improvement of the numerical models before calibration. Also the stability of a significant number of parameters, considering different initial populations, proved the robustness of the genetic algorithm in the scope of the optimization of the numerical models. The updated numerical models were validated based on dynamic tests under railway traffic. The results showed an excellent agreement between numerical and experimental responses in terms of displacements and accelerations of the bridges’ decks.

Experimental Validation of a Numerical Model for the Dynamic Analysis of a Bowstring Arch Railway Bridge

This paper will focus on the development and experimental validation of a numerical model for the dynamic analysis of the Sao Lourenco railway bridge. The bridge is used for railroad traffic and is located at the Northern line of the Portuguese railways. The bridge is a bowstring arch bridge that consists of two half-decks with a 42m span and each span carries a single track. Each deck consists of a 40 cm thick prestressed concrete slab suspended by two lateral arches. The suspension is performed by means of metallic hangers and diagonals in the proximity of the support blocks of the arches. The paper shows how the numerical model involves the modeling of the bridge, the train and their dynamic interaction.

Characterization of railway traffic and its effects on a short span bridge by using a hybrid fibre optic/electrical measurement system

The characterization of traffic effects on a short span railway bridge in Northern Portugal with a new hybrid platform that allows the simultaneous assessment of signals generated by a sensing network composed of both electrical and fibre Bragg grating based sensors was demonstrated. A Bridge Weight-in-Motion algorithm was also developed, which allows on-motion determination of train speed and weight distribution with only three fibre Bragg grating sensors.