Fabio de Angelis

An efficient return mapping algorithm for elastoplasticity with exact closed form solution of the local constitutive problem

Purpose – The purpose of this paper is to present an efficient return mapping algorithm for elastoplastic constitutive problems of ductile metals with an exact closed form solution of the local constitutive problem in the small strain regime. A Newton Raphson iterative method is adopted for the solution of the boundary value problem. Design/methodology/approach – An efficient return mapping algorithm is illustrated which is based on an elastic predictor and a plastic corrector scheme resulting in an implicit and accurate numerical integration method. Nonlinear kinematic hardening rules and linear isotropic hardening rules are used to describe the components of the hardening variables. In the adopted algorithmic approach the solution of the local constitutive equations reduces to only one straightforward nonlinear scalar equation. Findings – The presented algorithmic scheme naturally leads to a particularly simple form of the nonlinear scalar equation which ultimately scales down to an algebraic (polynomia...

Dynamic Nonlinear Analysis of an Hybrid Base Isolation System with Viscous Dampers and Friction Sliders in Parallel

In the present work we have analyzed a particular base isolation system for the seismic protection of a multi-storey reinforced concrete (RC) building. The viscous dampers and friction sliders are the devices adopted in parallel for realizing the base isolation system. The base isolation structure has been designed and verified according to European seismic code EC8 and by considering for the friction sliders the influence of the sliding velocity on the value of the friction coefficient. A dynamic nonlinear analysis for a three-dimensional base isolated structure has been performed. Recorded accelerograms for bi-directional ground motions have been used which comply with the requirements imposed by EC8 for the representation of a seismic action in a time history analysis. In this paper a comparative analysis is presented between the base isolated structure with the described hybrid base isolation system and the traditional fixed base structure.

On the Influence of the Elastic Medium Stiffness in the Buckling Behavior of Compressed Beams on Elastic Foundation

In the present work the stability and buckling behavior of compressed beams on elastic foundation are analyzed. The influence of the elastic stiffness of the medium on the overall stability of the structural system is investigated. The analysis is performed via energetic methods. The buckling loads are evaluated as a function of the stiffness of the beam and the stiffness of the elastic medium. Considerations are illustrated on the influence of the elastic medium stiffness and on the effects of the ratio of the length of the beam and the characteristic half-wave on the stability of the structural system.

On the Stability of Discrete Models of Compressed Beams in Elastic Media

The equilibrium configurations of compressed elastic beams in an elastic medium are investigated. The analysis is performed on discrete models by means of a geometric non linear treatment. The effect of the elastic stiffness of the medium on the overall stability of the structural system is taken into account through a parameter which represents the ratio between the elastic medium stiffness and the beam stiffness. This parameter shows to have a great influence on the buckling and post-buckling behaviour of the structure.

A Novel Seismic Base Isolation System Consisting of a Lead Rubber Bearing in Series with a Friction Slider. Part I: Nonlinear Modeling of the System

In this paper a new seismic base isolator, called High Damping Hybrid Seismic Isolator (HDHSI), is proposed. It is obtained by the assembly in series of a Lead Rubber Bearing (LRB) and a Friction Slider (FS) with a high friction coefficient. The HDHSI device is in contrast with the Resilient-Friction Base Isolator (R-FBI) with the aim of optimizing the Electricité De France (EDF) system. The mathematical model of a structure base isolated by a HDHSI system is analyzed with a two Degree of Freedom System (2-DOF) in which the superstructure is assimilated to a rigid body. Nonlinear finite elements are adopted for modeling the HDHSI device. A dynamic nonlinear analysis is performed and the hysteretic cycles are derived and evaluated for the single components and for the innovative HDHSI device.

A Novel Seismic Base Isolation System Consisting of a Lead Rubber Bearing in Series with a Friction Slider. Part II: Application to a Multi-Storey RC Building and Comparison with Traditional Systems

In a parallel paper a new High Damping Hybrid Seismic Isolator (HDHSI) has been proposed and obtained by the assembly in series of a Lead Rubber Bearing (LRB) and a Friction Slider (FS) characterized by a high friction coefficient. In the present paper, within the context of seismic base isolation techniques for the earthquake resistance of Reinforced Concrete (RC) buildings, a multi-storey RC building is analyzed as base isolated by the seismic isolator HDHSI (High Damping Hybrid Seismic Isolator). The seismic response of this base isolated RC building is compared with the seismic response of the same structure isolated by a LRB (Lead Rubber Bearing) isolator. The analysis is developed by considering different seismic events in terms of intensity and in terms of frequency content with regard to a supervening collapse. The purpose of this comparative analysis is to highlight the features offered by the HDHSI system compared to the LRB system in the seismic protection of structures. Accordingly, a nonlinear dynamic analysis is performed for a RC structure base isolated by means of the proposed device. In the analysis anomalous seismic events are considered. They are the El Centro earthquake (N00W component, 1940) which is characterized by high intensity and the Erzincan earthquake (N90W component, 1992) which is characterized by anomalous frequency content. The comparison between the two base isolation systems is presented by analyzing the time history of the shear force and the time history of the displacement at the base of the superstructure. The benefits of the HDHSI system in conferring protection to the structure are shown to be significant even under extreme seismic events.

Characterization of an Autoclaved Aerated Concrete Building with Respect to a Similar Unreinforced Masonry Structure

In the present work some characteristical features of autoclaved aerated concrete structures are illustrated in the seismic and nonseismic design for residential and industrial buildings. Besides the properties of this material with regards to fire resistance and thermal and acoustical insulation, the use of autoclaved aerated concrete for engineering structures may have the advantage of a confined structure with reinforced concrete bond elements that are disposed horizontally and vertically. In the present work the dynamical behavior of a building prototype realized with autoclaved aerated concrete is analyzed, a finite element modelling of the structure has been calibrated according to an experimental modal analysis carried by loading the structure with a vibrodyne located on top of the building and by monitoring the building outputs due to horizontal harmonic forces. The finite element modelling of the dynamical behavior of the autoclaved aerated concrete structure has been compared with a similar tuff masonry building whose characteristical behavior has already been the object of experimental and numerical analysis in a previous work.

Hybrid Base Isolation System with Friction Sliders and Viscous Dampers in Parallel: Comparative Dynamic Nonlinear Analysis with Traditional Fixed Base Structure

In the present paper we have analyzed a multi-storey reinforced concrete (RC) building in presence of a hybrid seismic protection system for highlighting the limits of the conventional fixed base seismic design of structures. This hybrid seismic protection system is a passive structural control system that combines the Base Isolation System (BIS) and the Passive Supplemental Damping (PSD). The Viscous Dampers (VS) and Friction Sliders (FS) are the devices adopted in parallel for realizing the innovative base isolation system. The fixed base structure and the base isolated structure have been designed and verified according to the European seismic code EC8 and the European code for the design of concrete structures EC2. A three-dimensional dynamic nonlinear analysis for a base isolated structure has been performed adopting recorded accelerograms for the defined bi-directional ground motions according to the conditions imposed by EC8. The seismic isolation is a promising alternative for the earthquake resistant design of buildings and its peculiarity is that the base isolated buildings are designed such that the superstructure remains elastic and the nonlinearities are localized at the isolation level. In this paper a comparative analysis is presented between the base isolated structure, with the viscous dampers in parallel with friction sliders, and the traditional fixed-base structure.

Implications due to Different Loading Programs in Inelastic Materials

In the present paper the effects of different loading procedures on the response of rate-sensitive inelastic materials are analysed. The elasto/viscoplastic model problem is developed by taking advantage of the postulate of maximum dissipation in order to derive an associated formulation of the evolutive laws. A non-dimensional loading program parameter is introduced which accounts for the loading procedure and the intrinsic properties of the material. An appropriate solution method is applied and specific numerical examples are reported so that the implications due to different loading programs on the inelastic behaviour of rate-sensitive materials are suitably illustrated.

An Effective Computational Approach for the Numerical Simulation of Elasto-/Viscoplastic Solid Materials

The effects of different loading programs on the elasto-/viscoplastic behavior of rate-sensitive materials are analyzed with specific numerical examples. An appropriate solution scheme and a consistent tangent operator are applied which are capable of being adopted for general computational procedures. Numerical computations and results are reported which illustrate the rate-dependence of the elasto-/viscoplastic constitutive model in use. In the numerical analysis the loading is applied by increasing the pressure and accordingly a nondimensional loading program parameter is introduced. In the numerical results the significance of the loading program is thus emphasized with reference to the nonlinear response of the elasto-/viscoplastic material behavior of solids.The effects of different loading programs on the elasto-/viscoplastic behavior of rate-sensitive materials are analyzed with specific numerical examples. An appropriate solution scheme and a consistent tangent operator are applied which are capable of being adopted for general computational procedures. Numerical computations and results are reported which illustrate the rate-dependence of the elasto-/viscoplastic constitutive model in use. In the numerical analysis the loading is applied by increasing the pressure and accordingly a nondimensional loading program parameter is introduced. In the numerical results the significance of the loading program is thus emphasized with reference to the nonlinear response of the elasto-/viscoplastic material behavior of solids.