Maurizio De Angelis

ABSTRACT This paper presents the results of shaking table tests on adjacent structures controlled by passive and semi-active MR dampers. The aim was to demonstrate experimentally the effectiveness of passive and semi-active strategies in reducing structural vibrations due to seismic excitation. The physical model at issue was represented by two adjacent steel structures, respectively of 4 and 2 levels, connected at the second level by a MR damper. When the device operated in semi-active mode, an ON–OFF control algorithm, derived by the Lyapunov stability theory, was implemented and experimentally validated. Since the experimentation concerned adjacent structures, two control objectives have been reached: global and selective protection. In case of global protection, the attention was focused on protecting both structures, whereas, in case of selective protection, the attention was focused on protecting only one structure. For each objective the effectiveness of passive control has been compared with the situation of no control and then the effectiveness of semi-active control has been compared with the passive one. The quantities directly compared have been: measured displacements, accelerations and force–displacement of the MR damper, moreover some global response quantities have been estimated from experimental measures, which are the base share force and the base bending moment, the input energy and the energy dissipated by the device. In order to evaluate the effectiveness of the control action in both passive and semi-active case, an energy index EDI, previously defined and already often applied numerically, has been utilized. The aspects investigated in the experimentation have been: the implementation and validation of the control algorithm for selective and global protection, the MR damper input voltage influence, the kind of seismic input and its intensity.

ABSTRACT Inter-story isolation, an effective strategy for mitigating the seismic risk of both new and existing buildings, has gained more and more interest in recent years as alternative to base isolation, whenever the latter results to be impractical, technically difficult or uneconomic. As suggested by the name, the technique consists in inserting flexible isolators at floor levels other than the base along the height of a multi-story building, thus realizing a non-conventional Tuned Mass Damper (TMD). Consistent with this, an optimal design methodology is developed in the present paper with the objective of achieving the global protection of both the structural portions separated by the inter-story isolation system, that is, the lower portion (below the isolation system) and the isolated upper portion (above the isolation system). The optimization procedure is formulated on the basis of an energy performance criterion that consists in maximizing the ratio between the energy dissipated in the isolation system and the input energy globally transferred to the entire structure. Numerical simulations, performed under natural accelerograms with different frequency content and considering increasing isolation levels along the height of a reference frame structure, are used to investigate the seismic performance of the optimized inter-story isolation systems. Copyright © 2015 John Wiley & Sons, Ltd.

SUMMARY. Presented herein is an exploratory study on the seismic effectiveness of a Tuned Mass Damper (TMD) with high mass ratio. Optimal design of the device is developed by minimizing the displacement response of the structure to be protected. The study ...

SUMMARY The introduction of passive dissipative devices between two adjacent structures has been shown to be a viable method to protect both structures from seismic excitation. In this paper a shaking table experimentation is presented, which refers to a coupled ...

SUMMARY In this paper a particular ON-OFF type of Semi-Active control of the seismic response of braced frames is considered, in which the braces are connected to the frame by special elements, which are activated or deactivated at different times, in order to obtain ...

ABSTRACT The purpose of this paper is to discuss a methodology for determining some modal parameters (frequencies, damping ratios, and seismic eigenvectors) and, under certain hypotheses, the physical matrices of a general structure with proportional damping and subjected to seismic loads. The procedure is based on a time-domain state space formulation from which the modal parameters, including the seismic eigenvectors, and the complex eigenvectors of the system can be derived also in the case of a limited set of instrumentations. The conditions to normalize the eigenvectors are then illustrated and, finally, applied to derive the second-order matrices of the system. The proposed procedure is applied to some numerical examples also in the case of noise-polluted measurements and to an experimental investigation performed on a four-story steel frame subjected to earthquake excitations. An optimization procedure to improve the prediction of the first-order modal parameters of the system is also discussed and experimentally proved.

ABSTRACT 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.

ABSTRACT The present work refers to steel frame structures in industrial plants. A passive isolation system for seismic protection of a considerable equipment, already present on a frame support structure and rigidly constrained to it, is investigated through both numerical simulations (1+1 DOF system) and shaking table tests on a 1:5 scale two-story steel frame structure. The equipment (e.g. a pipeline, a compressor unit, ...) is modelled as a rigid mass. The optimal design is determined by minimizing the dynamic response of the isolated mass. In order to ensure strenght and serviceability, the response of the frame is also monitored.

ABSTRACT In the present paper, a linear model for multi-degree-of-freedom systems with rate-independent damping is proposed to the purposes of dynamic response prediction and identification. A viscoelastic model with memory, equivalent to the ideal hysteretic model as for the energy dissipation properties, but causal and physically consistent in both the time and the frequency domain, is developed by adopting the Maxwell–Wiechert kernel function and by requiring the loss modulus to be substantially independent of frequency in a specified range of interest. The finite element model of the equivalent viscoelastic system is constructed and its equations of motion are shown to be uncoupled, in terms of modal coordinates, by the real-valued eigenvectors of the conservative system. An augmented state-space formulation, which encompasses, besides the customary displacements and velocites, a number of internal variables devoted to represent the viscoelastic memory, is then provided for the sake of system identification. Mechanical and modal properties of the equivalent viscoelastic model are finally illustrated by means of numerical examples.

ABSTRACT The semi-active (SA) control techniques appear a realistic way to adopt active control in structural engineering. This paper reports an exploratory study on SA continuous control, where the mechanical parameters of the devices may continuously assume any value between the given limits.First, a Lyapounov-based control strategy for SA continuous control is proposed and studied for base-excited structures. The obtained continuous control process is initially applied to a seismic-excited single-DOF structure with a variable stiffness device, in order to study the dynamics of the controlled system and the optimal configuration of the algorithm. Successively, the optimized control strategy is applied to single-DOF structures with more realistic SA elasto-plastic devices, and the performances of SA continuous control are compared with the ones of passive and SA ON–OFF control cases. Finally, the obtained results are verified and confirmed in the application to a 4-storey Multi-DOF-framed structure, equipped with continuously variable SA magnetorheological dampers.The study shows the applicability and the possible advantages of the proposed control case, also in comparison with passive and SA ON–OFF cases. Generally it may be stated that the best performances in terms of structural displacements may be obtained by using ON–OFF SA control. Differently, continuous SA control significantly reduces the absolute accelerations and the total forces transmitted to the structures. Copyright © 2009 John Wiley & Sons, Ltd.

ABSTRACT In this paper, a new methodology is proposed to identify modal and physical parameters of linear non-viscously damped multi-degree-of-freedom systems using recorded time-histories of their dynamic response. The methodology is based on the identification of a symmetric state-space realization of the system, whose modal parameters (spectral and modal matrices) are subsequently used to determine the physical parameters (mass, stiffness and damping matrices) of the model in second-order form. The state-space formulation, well known in the literature for systems with viscous damping, is extended to systems with non-viscous damping through the use of additional internal variables, devoted to represent the dependence of the dissipative forces on the past history of generalized velocities. The methodology is validated by means of numerical simulations aiming at assessing its accuracy and the errors possibly due to incomplete experimental data. Considering that the general non-viscous model is able to represent also the viscous damping behaviour as a special case of memoryless damping, applications are eventually provided to investigate the applicability of the proposed methodology to the identification of both proportional and non-proportional viscously damped systems.

... of implementations, both linear and nonlinear, in available literature and applications [3]. The principle of operation consists in ... 2.2. Seismic excitation model and system response ... to find the optimal value, while the damping ratio 2 resulted from the complex modal analysis of the ...