1,721,072 research outputs found
Numerical validation of the generalized equivalent spectral model through crowd dynamics simulations
No full textThis paper aims to provide a validation of the Generalized Equivalent Spectral Model of pedestrian-induced loading through numerical simulations of crowd dynamics. Pedestrian flows with varying density are numerically simulated based on the social force model. The instantaneous step frequency of each pedestrian is obtained from his instantaneous velocity. Results obtained from numerical simulations are statistically analyzed to obtain probability density functions of the step frequency. Then, each pedestrian is modelled as a moving harmonic load, whose trajectory and velocity are obtained from crowd simulations. The power spectral density function of the modal force obtained from numerical simulations is then compared with the analytical expression provided by the Generalized Equivalent Spectral Model. Possible modifications of the original formulation are analyzed, in order to fit numerical results
Dynamic characterization and vibration serviceability assessment of a historic suspension footbridge
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Aerodynamic admittance functions of bridge deck sections by CWE
No full textThe present paper analyses the capability of a modified indicial approach in determining the aerodynamic admittance functions of bluff bodies by means of Computational Wind Engineering simulations. The method is applied to a bridge deck section in order to pursue two main objectives. Firstly, the extension to bluff bodies of the aerodynamic admittance concept is discussed. Secondly, the sensitivity of the flow field around the section and of the aerodynamic admittance function to the incoming flow characteristics is analyzed. Computational results are compared with the experimental ones if the latter are available
Time varying mean extraction for stationary and nonstationary winds
No full textThis paper discusses different strategies for the extraction of the time-varying mean from wind speed time histories. Due to the advantage of allowing analytical evaluations, the attention is focused on kernel regression techniques, considering different weighting functions, namely a constant, a Gaussian and a cardinal sine weighting function. The problem is firstly treated analytically, and the frequency-domain properties of the filter associated to different kinds of weighting functions in the definition of the slowly varying mean through kernel regression are analysed. Then, different weighting functions are adopted for the analysis of digitally-simulated stationary wind speed time histories and for the time histories of thunderstorm outflows recorded by a tri-axial anemometer. The consequences of the adoption of different weighting functions on the harmonic content and statistical properties of turbulence are studied. The same features are found also for thunderstorm outflow records
Dynamic response of floors induced by a single walking pedestrian including walking path variability
No full textThis paper proposes a general non-dimensional closed-form solution to calculate the dynamic response of simply supported rectangular floors crossed by a single pedestrian schematized as a deterministic moving multi-harmonic load. The critical walking paths, which can provide the maximum vibration response, are identified and then a simplified approximated closed-form solution for the dynamic response due to a moving resonant harmonic load along the critical walking paths is proposed. Finally, the accuracy of simplified methods suggested by current guidelines is investigated by comparing the maximum non-dimensional acceleration response obtained from design guidelines with the corresponding value calculated by the analytical solution
Human-induced vibrations of floors: A probabilistic approach
No full textThe current design guidelines for assessing floor vibration performance rely on a simplified approach that considers a single pedestrian as a fixed load with multiple harmonic components applied to the anti-nodes of the floor mode shapes. However, these guidelines do not account for the influence of variability in the walking path on the dynamic response of floors. Moreover, the deterministic approaches used in these guidelines may yield unreliable estimates of vibration response due to the stochastic nature of pedestrian walking force. The aim of this paper is to investigate the dynamic response of floors under a single pedestrian walking load while considering the randomness of the walking path and the walking load itself. A probabilistic perspective is adopted to analyze the dynamic response under different random loading scenarios. Furthermore, the effectiveness of the current guidelines in predicting the dynamic response of floors is critically assessed.
The importance of incorporating probabilistic approaches is emphasized to achieve a more comprehensive understanding of the vibration serviceability of floors and to enhance design practices in this context
Experimental and Numerical Characterization of the Dynamic Behaviour of a Historic Suspension Footbridge
No full textThis paper investigates the dynamic characteristics and behavior of a historic suspension footbridge through experimental and numerical studies. Ambient vibration tests were performed on the footbridge to extract the modal parameters of the structure such as natural frequencies, damping ratios, and mode shapes. The modal properties were identified from ambient vibration tests adopting the Stochastic Subspace Identification (SSI) technique. The availability of a numerical model reproducing accurately the dynamic characteristics of the footbridge is essential to carry out numerical studies on the footbridge under different dynamic loading scenarios. Due to the lack of the original technical drawings of the footbridge, a geometrical survey was carried out in order to determine the geometric characteristics of the structural elements. Furthermore, the deformed configuration of the main cable under dead load was experimentally measured during the field survey. The results of field vibration tests were used to calibrate and validate the numerical model of the footbridge, e.g., boundary conditions, and initial cable tension. The present study reports the results of the geometrical survey, of the operational modal analysis, and of the numerical modeling of the footbridge. Moreover, the 3-D Finite Element Model of the footbridge and its calibration with respect to ambient vibration tests are reported. After calibration of the finite element model, a good agreement was observed between computed and measured natural frequencies and mode shapes
Interval serviceability assessment of footbridges
No full textThis paper studies serviceability assessment of footbridges through a non-deterministic approach. The parameters defining pedestrian-induced loading and the structural dynamic properties are characterized through possible ranges of variation. Starting from analytical expressions for the spectral moments of the structural response, the improved interval analysis is applied together with an optimization strategy that allows us to obtain the bounds of the standard deviation of the footbridge acceleration and of the mean value and cumulative distribution function of its maximum value. Based on this approach, a possible interval of variation of the structural response is evaluated, rather than a single deterministic value. Thus, an interval level of comfort can be defined
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