Piana, Gianfranco
Vibrations and Stability of Axially and Transversely Loaded Structures [Tesi di dottorato]
Politecnico di Torino, 2013
Modern lightweight and long-span structures are becoming increasingly slender and flexible thanks to continuous improvements in structural analysis techniques, construction methods, and the use of lighter and stronger materials. Modern airplanes, large roofs, and long-span bridges are just some examples of structures for which a design based on vibration and stability is of primary importance. The thesis aims to investigate into the interplay between vibration and stability phenomena in elastic structures. On the one hand, the concept of stability is intrinsically a dynamic one, and is in general more appropriate to investigate this phenomenon from a dynamic point of view. On the other hand, compressive or compressive-like loads, even if they do not lead to instability, affect the dynamic behaviour of the structure since they influence its natural vibration frequencies. Three application areas constitute the objective of the present research: • slender beams subjected to imposed displacements; • space truss models subjected to dead loads; • suspension bridges under aerodynamic loads. Stability and influence of the applied loads on the natural frequencies are studied using analytical, numerical, and experimental tools. The experimental tests were conducted at the Politecnico di Torino in cooperation with the Fluid Dynamics Unit of the National Institute of Metrological Research (INRIM). The fundamental frequency evolution in slender beams subjected to imposed displacements is analyzed through an experimental study. Different values of geometric imperfections as well as different constraint conditions are investigated, and the natural frequencies are obtained using several methods. The experimental study conducted in the present research leads to recognize two different phases in the bending frequency vs. axial load curves in case of displacement controlled condition, therefore showing a different behaviour with respect to the force controlled case. After, we show how the experimental results can be interpreted and reproduced through numerical simulations. The influence of dead loads on the natural frequencies of space truss models is investigated through a modal analysis with second-order effects. In particular, the effects of the direction and magnitude of the acting load are studied, leading to show an interesting aspect of the dynamic behaviour due to different effects of the geometric stiffness. In this case, numerical simulations are accompanied by some experiments. Finally, the effects of steady aerodynamic loads on stability and natural vibration frequencies of suspension bridge decks are analyzed by means of a simplified analytical model. The single (central) span suspension bridge model is considered, and the linearized integro-differential equations describing the flexural-torsional oscillations of the bridge deck are derived. In conclusion, some address on how this study might be integrated into the flutter analysis of long-span suspension bridges is provided. The quest for stronger, stiffer, and more lightweight structural systems is making the subject studied in this thesis increasingly important in practical applications in the areas of civil, mechanical, and aerospace engineering.
In relazione con http://porto.polito.it/2518986/
application/pdf
A. Carpinteri
R. Malvano
ICAR/08


Tesi di dottorato. | Lingua: en. | Paese: | BID: TD17056125