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Preface Dynamic Interaction Analysis of Coupled Train-bridge System Vibration Testing as a Tool for Tuning & Validating Train-bridge Interaction Models Dynamics of High-speed Railway Bridges: Methods & Design Issues Dynamic Responses of a Simply-supported Beam Subjected to Various Moving Loads Efficient Models for Train-bridge Interaction Strategies for Modeling Train-bridge Lateral Dynamic Interaction Dynamic Responses of Long-span Bridges under Wind Action & Their Influences on Running Safety of Train Vehicles.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
This paper discusses two very relevant practical issues in the application of vibration-based health monitoring to civil engineering structures: the excitation source and the effect of temperature. The idea of vibration-based damage detection is to measure dynamic characteristics such as eigenfrequencies, damping ratios and mode shapes on a regular basis. The state, and eventually degradation, of the structure is reflected in the evolution of these characteristics. Unfortunately, it is not only the health of a structure that influences its measurable dynamics, but also the applied excitation and the changing temperature are important factors and may erode the damage detection potential. In the first part, the results of different excitation types are compared: band-limited noise generated by shakers, an impact from a drop weight and ambient sources such as wind and traffic. In the second part, the undeniable effect of temperature on measured eigenfrequencies is demonstrated and a methodology is proposed to distinguish these temperature effects from real damage events. The method could be validated on a unique data set from a bridge that was artificially damaged after a one-year monitoring period.
© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. The hybrid deterministic - statistical energy analysis method is a versatile framework for vibro-acoustic analysis. Stiff system components are modelled deterministically, while the wave fields in flexible components are modelled as diffuse. In this paper, the hybrid method is extended such that the ensemble mean and variance of the band-averaged system response can be computed. The variance represents the uncertainty that is due to the assumption of a diffuse field in the flexible components of the hybrid system. After generalizing the diffuse field reciprocity relationship, explicit expressions are derived for the cross-frequency and band-averaged variance of the vibrational energies in the diffuse components and the cross spectrum of the response of the deterministic components. These expressions are extensively validated against detailed Monte Carlo analyses of coupled plate systems in which diffuse fields are simulated by randomly distributing small point masses across the flexible components, and good agreement is found.
When predicting the radiation of structure-borne sound into a room, it is often assumed that the generated sound field is diffuse. A diffuse field is by definition a random field, composed of a large number of statistically independent plane waves, the spatial phase of which is uniformly distributed and independent from the amplitude. It may represent the sound field of a conceptual ensemble of rooms with the same modal density and total absorption, but otherwise any possible arrangement of boundaries and small objects that scatter incoming sound waves. Adopting a diffuse field model therefore inherently implies that uncertainty due to random wave scattering is present in the computed results. This uncertainty can be large, especially at low frequencies. In this work, practical formulas are derived for computing not only the mean, but also the variance of energetic level quantities, such as the band-integrated spatially averaged sound pressure level, in a diffuse sound field caused by a mechanically excited structure. The obtained expressions are first verified in a simulation study, and then experimentally validated for a point-loaded bare plate and a rib-stiffened plate. It is found that both the average sound pressure level and its standard deviation can be well predicted. Knowledge of this standard deviation then allows the analyst to estimate, for example, by how much the spatially averaged sound pressure level in one particular room can deviate from the ensemble averaged result, and this for any frequency band.
Vibration monitoring is a useful evaluation tool in the development of a non-destructive damage-identification technique, and relies on the fact that occurrence of damage in a structural system leads to changes in its dynamic properties. It can give global information of a structure, and the location of the damage has not to be known in advance. The damage-identification technique is based on the observed shifts in eigenfrequencies and modeshapes and relate the dynamic characteristics to a damage pattern of the structure. The presented technique makes use of the calculation of modal bending moments and curvatures to derive the bending stiffness at each location. The basic assumption is that damage can be directly related to a decrease of stiffness in the structure. Damage-assessment techniques are validated on the progressively damaged prestressed concrete bridge Z24 in Switzerland, tested in the framework of the Brite Euram project SIMCES. A series of full modal surveys are carried out on the bridge before and after applying a number of damage scenarios.
When the vibration of a structure is considerably magnified by resonance effects, adding of damping is an effective method to reduce the level of vibration. Viscoelastic materials are generally used as an instrument to increase the amount of damping in the structure. The constrained-layer damping (CLD) method involves sandwiching a viscoelastic damping medium between two outer layers. The most important parameters which influence the dynamic behavior of a CLD system are the geometrical dimensions and the frequency dependent material properties of the viscoelastic material. Therefore, a direct solution of the equation of motion in the frequency domain seems to be the only valid solution technique. However, this method has to be rejected from a computational point of view when dealing with large structures. The mode superposition method is a powerful solution method to characterize the dynamic response of a large structure. The two basic assumptions to apply this method are that the material properties are constant and that the damping is proportional which is not the case for a CLD system. In the paper, four different solution techniques based on the solution of a (non- linear) eigenvalue problem are presented to predict the dynamic behavior of a simple supported sandwich layer system due to a uniform base excitation. The damping ratio of each eigenmode is calculated by the Modal Strain Energy method. Each proposed technique is validated in terms of accuracy and computational effort.
