Research interest: vision

 

Besides inside the structure, look around it.

 

Actions on civil structures have to be carefully modelled, because generally they are not deterministic quantities. Hence their design values come from statistic analysis, where the action is viewed as a random variable or a stochastic process. In other terms, the physical system that produce the action energy – the exciting system in the following – is not studied from a mechanical point of view. The universe of interest is than restricted to the civil structure and the action is treated as one of its boundary conditions. This approach is often justified by the fact that:

-          the energy source is far from the structure;

-          the characteristic length and/or time scales of the exciting system are very different from the ones of the civil structure;

-          the parameters of the exciting system governing laws are too many, randomly varying or simply unknown;

-          the knowledge of the mechanical behaviour of the exciting system is of scarce interest in the design process;

-          the exciting and structural systems can be assumed with good accuracy as uncoupled.

For instance, the study of the structural dynamic response to the earthquake or to the gusty wind generally falls under these conditions, so that the ground acceleration or the wind velocity can be described by their power spectral density, disregarding the mechanical behaviour of the systems which produce them.

 

In some other cases, the conditions stated above do not longer hold: the energy source is around the structure or even very close to it, the exciting and structural systems share common characteristic length and time scales, the knowledge of the exciting system can inspire new design solutions to suppress its energy or to mitigate its effects on structures, they are coupled in the sense that the response of the former is the excitation of the latter and vice versa.

Fluid-structure interaction belongs to this class of problems: for instance, most of the aerodynamic and aeroelastic phenomena in civil engineering but also sloshing problems for reservoirs or hydrodynamic problems for bridge piers. Other coupled system of interest for structural engineering refers to soil-structure interaction or crowd-structure interaction.

In these cases, it is recommended to characterise the mechanical behaviour of the exciting system, even if its modelling is far from an easy task and/or it cannot be ascribed to the solid mechanics, so that a multi-physics modelling and specific competences in both structural dynamics and other disciplines are required.

In situ measurements or laboratory tests, although possible and required for validation purposes, are difficult to be performed for such kind of coupled multiphysical phenomena. The computational approach can represents an effective complementary tool because similitude requirements are easy to be fulfilled and accurate parametrical studies can be performed in both physical or unphysical conditions in order to point out the role of a single design parameter on the overall mechanical response.

 

 


Last updated: 21 January 2009