Federica Tubino

A turbulence model based on principal components

Literature on turbulence is very wide, providing several models for the power spectral density function of the single-point turbulence components, for the two-point coherence function of the same turbulence component and for the single-point coherence function of different turbulence components. On the other hand, no suitable and simple model seems to be available for representing the two-point coherence function of different turbulence components, in particular of the longitudinal and vertical turbulence components, which would be useful for modelling buffeting actions on bridges. The Proper Orthogonal Decomposition provides efficient tools to formulate a new model of the turbulence field based on principal components. Furthermore, it suggests physical principles and defines mathematical rules to establish an appropriate model of the two-point coherence function of the longitudinal and vertical components, completing the statistical model of turbulence. Embedded in a Monte Carlo framework, this new representation can be used to simulate multi-dimensional and multi-variate random turbulence fields.

Human-Induced Vibrations on Two Lively Footbridges in Milan

This article describes the results of extensive full-scale experiments carried out on two lively footbridges recently built in Milan, Italy. The objective of the study was to assess the dynamic characteristics of the bridges and the expected vibration level induced by pedestrians. A preliminary vibration analysis of the bridges revealed their potential sensitivity to human-induced vibrations in the vertical direction. Two sets of experiments were carried out, one before and one after the installation of tuned mass dampers. Furthermore, bridge vibrations during a marathon event were recorded and analyzed. Experimental and analytical results were compared for several loading scenarios.

Serviceability assessment of footbridges in unrestricted pedestrian traffic conditions

Abstract A critical analysis of the procedures available in the literature for the serviceability assessment of footbridges in unrestricted pedestrian traffic conditions is presented. Based on a full probabilistic model of the loading, Monte Carlo simulations are carried out and a critical discussion concerning the role of the statistical distribution of the random walking parameters on the footbridge dynamic response is provided. Furthermore, numerical results are compared with the ones obtained by simplified procedures. Finally, a graphical procedure is proposed which permits a simple evaluation of footbridge maximum acceleration as a function of the modal mass, damping ratio and expected average pedestrian flow.

Dynamic Approach to the Wind Loading of Structures: Alongwind, Crosswind and Torsional Response

This paper provides a general framework of the dynamic approach to the wind loading of structures, in particular of vertical structures such as buildings, towers and chimneys. The first part of the paper deals with the classical problems of the dynamic alongwind response and of the equivalent static forces, defining a chain of nondimensional coefficients, referred to as the gust factors, aimed at determining the maximum response for engineering applications to structural design. The second part of the paper generalises the above formulations and concepts to the crosswind and torsional response of structures due to gust buffeting; the focal problem of the vortex shedding is introduced but not developed in the due detail. The formulations and the applications discussed focuse on the analytical tools developed at the University of Genoa.

Wind - Induced Instability of Complex Lighting Poles and Antennas Masts: Static and Aeroelastic Experimental Study

In a previous paper authors studied the aeroelastic behavior of complex lighting poles and antennas masts by carrying out static sectional model tests, determining aerodynamic coefficients and using them in the framework of quasi-steady theory. This paper continues the above research by illustrating the results of aeroelastic sectional model tests aimed at verifying the precision and reliability of the previous approach. The aeroelastic experiments are conducted by increasing and decreasing the mean wind velocity in order to check the presence of hysteresis phenomena.

On the effect of mechanical non-linearities on vortex-induced lock-in vibrations

Vortex-induced vibrations at lock-in conditions are modeled through generalized van der Pol-Duffing oscillators endowed with frequency-dependent coefficients, taking inspiration from fluid-elastic models. Accordingly, it is found that the limit-cycle amplitude and the non-linear frequency are mutually dependent (feedback effect), differently from the classic oscillator behavior. Consequently, the mechanical non-linearities, which are often believed to be unimportant, do affect the amplitude of motion. Examples concerning an ideal one degree-of-freedom van der Pol-Duffing oscillator and a two degree-of-freedom model, coarsely representative of a tower building, confirm the importance of this approach also from a technical point of view. Thus, non-linear geometric terms and modal interaction (even in non-resonant cases) can lead to non-negligible modifications of purely aeroelastic problems.

A Critical Analysis of Simplified Procedures for Footbridges’ Serviceability Assessment

This paper provides a critical analysis of the procedures available in the literature for the serviceability assessment of footbridges in unrestricted pedestrian traffic condition. Based on a full probabilistic model of walking-induced forces, Monte Carlo simulations are carried out and the numerically obtained dynamic response is compared with the one provided by simplified procedures. Furthermore, a new technical procedure is proposed which permits a direct and simple evaluation of footbridge maximum acceleration as a function of the expected average pedestrian flow and the modal properties of the footbridge.