Ricerc@Sapienza

An energy-based approach facilitates the explicit consideration of the damage associated with both maximum displacements and cumulative plastic deformations under earthquakes. For structural systems that can undergo pulse-like seismic ground motions close to causative faults, an energy-based approach is deemed especially appropriate with respect to well-established force-or displacement-based strategies.

The experimental dynamical response of three types of nonlinear hysteretic systems is identified employing phenomenological models togheter with the Differential Evolutionary algorithm. The mass–spring–damper system is characterized by hysteretic restoring forces provided by assemblies of shape memory and steel wire ropes subject to flexure or coupled states of tension and flexure. The energy dissipation due to phase transformations and inter-wire friction and the stretching-induced geometric nonlinearities give rise to different shapes of hysteresis cycles.

The problem of reducing the damage due to seismic loads in engineering structures by means of tuned mass dampers (TMDs) is addressed. Differently from previous studies focused on linear or geometrically nonlinear TMDs, the present work is concerned with a device that exhibits a hysteretic restoring force with pinching. A numerical TMD optimization is carried out so as to ensure optimal energy transfer from the main structure to the TMD for various seismic ground motion severities. The effectiveness of the vibration protection strategy is discussed for two different structural systems, i.e.

The seismic assessment of masonry buildings requires the definition of adequate models. Simplified approaches have well known positive outcomes, but the definition of their properties to describe all the complex phenomena in which structural elements are involved, especially when subjected to dynamic loading, is not an easy task. Masonry exhibits a strongly nonlinear behaviour under both static and dynamic loading and hysteretic nature of restoring forces should be considered.

This paper presents an enriched hysteresis model with damage relying on the Bouc-Wen formulation, in which a single scalar variable is introduced to reproduce effects of strength and stiffness degradation emerging for damaging materials. First, some acknowledged limits of the original Bouc-Wen model are discussed, focusing on its thermodynamic admissibility and compatibility with Drucker's plasticity postulate, and highlighting the effects of the parameters β and γ.

The dynamic behavior of a 2DOF system consisting of a primary structure and a hysteretic vibration
attachment is investigated. With respect to viscoelastic tuned mass damper, which works in internal resonance
condition (1:1), the systems with the nonlinear attachment can exhibit different internal resonance conditions
(n:1), with n>1. Such these conditions be met, hysteresis produces bifurcations and superabundant nonlinear
modes which are shown to be very effective in reducing the response of the primary structure