Mini-Symposium

A. Instability Phenomena in Materials and Structures

Static and dynamic instability analysis stand at the heart of structural and continuum mechanics. In spite of decades of research in this area, it continues to be a topic of interest in all engineering fields and new topics of research are constantly appearing in the literature. The aim of this mini-symposium is to gather specialists of different areas working on instability phenomena in materials and structures. Topics of interest include, but are not limited to, static and dynamic stability of bars, plates and shells, including elastic and non-elastic instability phenomena, stability design of steel and concrete structures, non-linear local and global bifurcations, problems of fracture and damage, instability phenomena in nano and micro structures, influence of bifurcations on the integrity of structural systems, random bifurcations, reduced-order modeling and its application in stability analysis and thermodynamic principles of stability of irreversible systems. Papers are solicited in all areas related to theoretical, computational and experimental aspects of the problem.

Symposium coordinators:

Raul Rosas e Silva
Paulo B. Gonçalves
Pontifical Catholic University, PUC-Rio

Carlos Eduardo Nigro Mazzilli
University of São Paulo, USP

Giuseppe Rega
University of Rome "La Sapienza"

Gláucio H. Paulino
University of Illinois at Urbana-Champaigne

 

INVITED LECTURE

CONTINUOUS AND DISCRETE TIME MODELS FOR THE PEDESTRIANS FOOTBRIDGES SYNCHRONIZATION

STEFANO LENCI
Università Politécnica delle Marche
Ancona, Italy

 

ABSTRACT. In this work a relatively novel instability phenomena of monodimensional structures is investigated in depth. We study the synchronization of the pedestrians motion with the lateral motion of slender footbridges, which attracted the attention of researchers mainly after the Millennium Bridge well known event. We consider two models to detect the phenomenon. A continuous-ti me bridge-pedestrians model initially developed by Strogatz and co-workers is improved to better understand some aspects of the underlying mechanical phenomena. We perform extensive parametric investi gations by means of systematic numerical simulations. This permits to highlight the parameters which mainly affect the trigger and the development of the phenomenon of synchronous lateral excitations, thus allowing a good understanding of the physical event and an evaluation of the engineering reliability of the model. Then, in order to obtain analytical instead of numerical predictions, a nonlinear discrete-ti me model based on stroboscopic Poincarè map is considered. It is able to provide a reliable value of the number of pedestrians which trigger the synchronization, thus predicting the onset of instability, which is also the onset of crowd synchronization. From a dynamical system point of view, the main result is that the model highlights how the phenomenon can be seen as a perturbation of a classical pitchfork bifurcation, which is then shown to be the underlying dynamical event.

Acknowledgement. This lecture was made possible through financial support from Pró-Reitoria de Pós-Graduação (PRPG/USP).