Maurizio De Angelis

Optimal Semi-active Control and Non-linear Dynamic Response of Variable Stiffness Structures

In this paper we study the semi-active control of structural systems by means of variable stiffness devices, and the resulting non-linear dynamics of the controlled system. In particular, the study is applied to base-excited single-degree-of-freedom systems, controlled by variable ON–OFF elastic devices and subjected to simple motion conditions: free vibrations following initial conditions and stationary response to harmonic input. A performance index, which, in the case of base-excited structures, assumes an original dual formulation following the relative or absolute approaches, has been proposed for instantaneous optimal control. The study includes both the optimal control design and the observation of the resulting non-linear dynamics of the controlled system. The dynamic behavior of the controlled non-linear system is studied with respect to the parameters which characterize the algorithms, the control device, and the input. In this way, also by means of significant (and original) analytical solutions of the equations of motion, the optimal formulation of the algorithms, some particular behaviors of the controlled systems, and the performances of the control approach are shown and explained for the different control strategies.

A Darwinian evolution of electrical power systems design for preventing seismic risks in sensitive buildings

Seismic events cause serious problems to the electrical supply continuity in sensitive structures. The design of electrical and mechanical power systems can apply a “Darwinian” approach in sizing the components and in drawing the layout for minimizing the seismic stresses during an earthquake. This kind of evolution has to aim in preventing more than protecting damages to systems operability. All the components should have adequate ratings and be installed in a proper manner to provide a reliable and safe electrical system after or during earthquake. The electrical engineer and mechanical engineer should work closely with the structural engineer. The paper suggests a comparison among different international approaches in simplified evaluation of the seismic forces to assist the design electrical engineers and highlights the need that the constructors of equipment essential to the service continuity, as transformers, switchboards, generator sets, uninterruptible power supplies, motors driving critical loads, have to promote certified tests of their seismic behavior and to make available their basic seismic parameters.

Criteria for the Definition of the Equipment Seismic Levels: Comparisons Between USA and European Codes

In spite of the names of “building attachments” and “secondary elements” usually given to nonstructural components and equipment, they are far from being secondary in importance. In the worst case of critical facilities, the failure of equipment strongly impacts on the postearthquake functionality, causing the loss of essential services or businesses. Such considerations highlight the need for a seismic qualification of equipment as the essential means to demonstrate its adequacy to perform the required function during the expected earthquake event. In this paper, the authors deal with a new approach to the problem of seismic qualification, in which the seismic demand posed to the component is defined in terms of equipment seismic levels (ESLs), whereas its inherent seismic capacity is classified in terms of equipment qualification categories. The determination of the ESL, which is the subject of this paper, has to satisfy the requirements prescribed by the codes for the seismic design of equipment. A comparative study of the current seismic codes in the USA and in Europe is hence carried out in order to critically assess their provisions and to develop a methodology that can be implemented straightforwardly also by designers not having expertise in the field of earthquake engineering.

Modal Model Identification with Unknown Nonstationary Base Motion

Techniques developed for structural identification are typically devoted to obtaining a model, parametrical or not, on the basis of information on the structural response and on the forcing action, both assumed as known from experimental tests. In many situations, however, it may be necessary, or simply useful, to refer only to the measured response. In this paper we describe the theoretical aspects of a technique we have recently developed to identify the modal model in the frequency domain when the input is unknown. To simplify, we refer to unknown nonstationary base motion, but many of our conclusions can be extended to different situations. We show that, from a theoretical point of view, the identification problem has a unique solution, for this kind of input, when at least three time histories are known, and this circumstance had never been pointed out before. Because the theoretical analysis furnishes only necessary conditions for the existence of a unique solution, an extensive numerical analysis is reported in the second part of the paper, which also shows the sensitivity of the identification procedure.

Seismic Qualification Categories (EQC) of electrical equipment

The electrical equipment especially in critical facilities needs a seismic qualification and so the relative standard to define essential requirements to harmonize prescriptive protocols which ensure: - a minimum accepted level of integrity for the service continuity, - equipment tested in conventional configurations with benefits for all the stakeholders. Indeed, if design, installation and operation follow harmonized standards, they benefit from a presumption of conformity that avoid liability for improperly designed and installed systems. A main objective pursued by this paper consists in fostering the definition of a seismic qualification of electrical equipment. The suggested approach can address the concept of a need for varying degrees of safety on equipment and define Equipment Seismic Levels (ESL) and Equipment Qualification Categories (EQC) of their earthquake inherent resistance. It can be recognized that it should be beneficial to identify and mark all equipments according their inherent seismic risk.

Criteria for the definition of the Equipment Seismic Levels (ESL): Comparisons between USA and European codes

In spite of the names of “building attachments” and “secondary elements” usually given to nonstructural components and equipment, they are far from being secondary in importance. In the worst case of critical facilities, the failure of equipment strongly impacts on the post-earthquake functionality, causing the loss of essential services or businesses. Such considerations highlight the need for a seismic qualification of equipment as the essential means to demonstrate its adequacy to perform the required function during the expected earthquake event. In the present paper, the authors deal with a new approach to the problem of seismic qualification, in which the seismic demand posed to the component is defined in terms of Equipment Seismic Levels (ESL), while its inherent seismic capacity is classified in terms of Equipment Qualification Categories (EQC). The determination of the ESL, subject of this work, has to satisfy the requirements prescribed by the codes for the seismic design of equipment. A comparative study of the current seismic codes in USA and in Europe is hence carried out, in order to critically assess their provisions and to develop a methodology that can be implemented straightforwardly also by designers not having expertise in the field of earthquake engineering.

Impaired flow-mediated dilation in hospitalized patients with community-acquired pneumonia

BACKGROUND Community-acquired pneumonia (CAP) is complicated by cardiovascular events as myocardial infarction and stroke but the underlying mechanism is still unclear. We hypothesized that endothelial dysfunction may be implicated and that endotoxemia may have a role. METHODS Fifty patients with CAP and 50 controls were enrolled. At admission and at discharge, flow-mediated dilation (FMD), serum levels of endotoxins and oxidative stress, as assessed by serum levels of nitrite/nitrate (NOx) and isoprostanes, were studied. RESULTS At admission, a significant difference between patients with CAP and controls was observed for FMD (2.1±0.3 vs 4.0±0.3%, p<0.001), serum endotoxins (157.8±7.6 vs 33.1±4.8pg/ml), serum isoprostanes (341±14 vs 286±10 pM, p=0.009) and NOx (24.3±1.1 vs 29.7±2.2μM). Simple linear correlation analysis showed that serum endotoxins significantly correlated with Pneumonia Severity Index score (Rs=0.386, p=0.006). Compared to baseline, at discharge CAP patients showed a significant increase of FMD and NOx (from 2.1±0.3 to 4.6±0.4%, p<0.001 and from 24.3±1.1 to 31.1±1.5μM, p<0.001, respectively) and a significant decrease of serum endotoxins and isoprostanes (from 157.8±7.6 to 55.5±2.3pg/ml, p<0.001, and from 341±14 to 312±14 pM, p<0.001, respectively). Conversely, no changes for FMD, NOx, serum endotoxins and isoprostanes were observed in controls between baseline and discharge. Changes of FMD significantly correlated with changes of serum endotoxins (Rs=-0.315; p=0.001). CONCLUSIONS The study provides the first evidence that CAP is characterized by impaired FMD with a mechanism potentially involving endotoxin production and oxidative stress.

Equipment Isolation Systems by Means of Semi Active Control Devices

In this paper the isolation of a single equipment by means of a semi active control device item is investigated. The configuration of ground-mounted equipment, that is an equipment directly mounted on the ground, is studied, and a single horizontal component of ground acceleration is assumed as base excitation, having considered the sliding response of the equipment among the possible response modes. A numerical study on a single-DOF structural model equipped with a continuously variable elastic device subjected to harmonic input is discussed. The proposed control algorithm is based on semi active continuous control. The performances of the isolated equipment are compared with those of the corresponding case having assumed the semi active device operating in ON-OFF mode and conventional passive control, in order to investigate the applicability of a semi active continuous control law for the reduction of the dynamic response of structural base-excited systems.

Identification of Modal Parameters with Unknown Input

The techniques developed for structural identification are typically devoted to obtain a structural model on the base of information on the response and on the forcing action. In many situations, however, it can be necessary to refer only to the measured responses. In this paper we describe the theoretical and computational aspects of a technique we have recently developed to identify the modal model in the frequency domain when the input is unknown. We show that this identification problem has an unique solution when at least three responses are known. Anyway, when one of the modal parameters is known, the other ones can be obtained on the base of two responses only. Numerical applications are carried out on plane framed structures ranging from three to eight stories. The modal model may also be incomplete, including only the lowest modes. The results obtained are satisfactory in most cases.

Vibration Analysis and Models of Adjacent Structures Controlled by Magnetorheological Dampers

This paper deals with the vibration analysis of adjacent structures controlled by a magnetorheological (MR) damper and with the discussion of a numerical procedure for identification and definition of a reliable finite element model. The paper describes an extensive experimental campaign investigating the dynamic response, through shaking table tests, of a tridimensional four-story structure and a two-story structure connected by an MR device. Several base excitations and intensity levels are considered. The structures were tested in nonconnected and connected configuration, with the MR damper operating in passive or semiactive mode. Moreover, the paper illustrates a procedure for the structural identification and the definition of a reliable numerical model valid for adjacent structures connected by MR dampers. The procedure is applied in the original nonconnected configuration, which represents a linear system, and then in the connected configuration, which represents a nonlinear system due to the MR damper. In the end, the updated finite element model is reliable and suitable for all the considered configurations and the mass, damping, and stiffness matrices are derived. The experimental and numerical responses are compared and the results confirm the effectiveness of the identification procedure and the validation of the finite element model.