Donato Cancellara

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.

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.

Displacement Based Approach for the Seismic Retrofitting of a RC Existing Building Designed for only Gravitational Loads

The present paper deals with the evaluation of the level of seismic vulnerability of a Reinforced Concrete (RC) building by using a Displacement Based Approach (DBA), in the context of a performance methodology, and by adopting the N-2 method, according to Italian seismic code NTC 2008. The RC building is located in Southern Italy in an area classified as high seismicity zone and designed, in the past, only for gravitational loads. During the evaluation phase the effect of masonry infills is considered by modeling with a non linear analysis all the panels considered in effective interaction with the structural frame. It is highlighted that in the examined case the masonry infills determine a worsening of the seismic behavior of the existing structure. So that it is illusory that by neglecting these panels a general beneficial effect would be obtained. Moreover in such case the neglect of these panels would have guided to a retrofitting strategy which is completely different and would have not answered to the real needs of the structure. The correct evaluation of the seismic response is finalized to the seismic retrofitting by using a traditional strategy, designed through a displacement based approach, for reducing the displacement demand on the existing structure. The adopted retrofitting strategy is represented by steel braces with steel reinforcement elements for the columns. In the non linear model for these elements it has been considered their confinement action for the reinforced concrete columns. The vulnerability level of the structure and the Safety Factor (SF), defined as the ratio between the displacement capacity and the displacement demand, is calculated for the building before and after the seismic retrofitting.

Seismical Protection Properties of High Damping Rubber Bearing and Lead Rubber Bearing Base Isolation Systems for Multi-Storey RC Buildings

In the present paper two different base isolation systems, designed and verified according to the european seismic code (EC2 and EC8), are compared for evaluating the behaviour of a base isolated building, highly irregular in plan, in presence of a seismic excitation. The devices adopted for realizing the different base isolation systems are the High Damping Rubber Bearing (HDRB) and the Lead Rubber Bearing (LRB) both of them actuated in parallel with a Friction Slider (FS). A dynamic nonlinear analysis for a three-dimensional base isolated structure has been performed. Recorded accelerograms for bi-directional ground motions, compatible with the reference elastic response spectrum for each limit state have been used for a more realistic evaluation of the seismic response of the structure and a more realistic comparative analysis between the base isolated structure with the different considered base isolation systems and the traditional fixed base structure.

Constitutive Equations for a Model of Nonlocal Plasticity which Complies with a Nonlocal Maximum Plastic Dissipation Principle

In the present paper constitutive equations for a nonlocal plasticity model are presented. Elasticity is considered to be governed by local forces so that only the dissipation processes are adopted as nonlocal. Differing from other proposed models in which the isotropic hardening/softening variables are considered as nonlocal, in the present paper the nonlocality is extended in order to include the kinematic hardening behaviour as well, so that both types of hardening (kinematic and isotropic) are considered as nonlocal. The present formulation satisfies a variational condition representing nonlocal maximum plastic dissipation. The proposed constitutive formulation of nonlocal plasticity is thus equipped with a sound variational basis.