Laura Ierimonti

Effects of control-structure interaction in active mass driver systems with electric torsional servomotor for seismic applications

Active control systems are a viable solution to mitigate seismic effects in buildings. The actual response of structures equipped with active control devices is influenced by control-structure interaction (CSI) and actuation imperfection. This paper investigates both effects on the response and on closed-loop stability of a frame structure equipped with an Active Mass Driver with electric torsional servomotor. The closed-loop stability conditions are studied by investigation of the root-locus of the system and the effects of CSI and actuation imperfection are individually quantified. Results obtained under harmonic and seismic base excitations show that accounting for CSI leads to non-negligible variations in control performance, especially for large mass ratios, and that actuator’s dynamics significantly influence the system’s stability.

Exploiting multiple reference models for adaptive control of flexible structures

Flexible structures like tall buildings are often equipped with active control systems which allow the reduction of structural vibration induced by wind and earthquakes. Wind gusts and earthquakes are different in terms of intensity level, frequency and duration of the excitation. In particular, wind induced vibrations are usually moderate and require a continuously operating control system whose main goal is to provide occupants’ comfort in serviceability conditions. Conversely, earthquakes of significant intensity are rarely experienced by the structure and may produce structural damage that leads to deterioration in structural stiffness. The use of Model-Reference Adaptive Control (MRAC) has recently been considered for structural applications for its capability of dealing with systems’s uncertainties and time dependence of parameters. The adaptive controller has two loops: the inner loop consists of an ordinary feedback control process while the outer loop adjusts the controller parameters through an adaptation rule in order to minimize the difference between measured output and model output. In this paper the use of MRAC in conjunction with a Lyapunov-based adaptation rule is investigated for the response mitigation of a tall building equipped on top with an active device and subjected to both wind and seismic hazards. Since the required structural performances in case of wind and earthquake-excited vibrations are different, in order to optimize the control effectiveness, a modified MRAC algorithm based on multiple reference models (M-MRAC) is proposed in which the switch between the targets is performed based on the measured feedback information. The main advantage of the proposed methods is its capability of providing power saving and limitation of the peak control force. Parametric analyses allow to identify proper threshold levels for the switching condition and optimal reference models providing a compromise between safety and economy. Results of the numerical analyses on a benchmark tall building show the effectiveness of the control strategy for several loading conditions.

Multi-hazard loss analysis of tall buildings under wind and seismic loads

Abstract This paper presents a framework for life-cycle loss estimation for non-structural damage in tall buildings under wind and seismic loads. Life-cycle cost analysis is a useful design tool for decision- makers, aimed at predicting monetary losses over the lifetime of a structure, accounting for uncertainties involved in the problem definition. For tall buildings, sensitive to dynamic excitations like earthquake and wind, it can be particularly suitable to base design decisions not only on initial cost and performance but also on future repair expenses. The proposed approach harmonises the procedures for intervention costs evaluation of structures subjected to multiple-hazards, taking into account the peculiar differences of wind and earthquake, in terms of load characterisation, type and evolution of damage. Relative effect of the two hazards on damage to drift- and acceleration-sensitive non-structural elements are examined. The influence of uncertainty in structural damping is also taken into account. It is shown that, although it is commonly believed that the design of a given structure is usually dominated by either winds or earthquakes, when LCC-based design is performed, both winds and earthquakes may be important.

Active Base Isolation of Museum Artifacts under Seismic Excitation

ABSTRACT This article investigates the possibility of using active control devices for the seismic protection of museum artifacts subjected to sliding and rocking. An actively base isolated system is compared to a passively base isolated one constituted by a spring-dashpot system that can represent a simplified modeling of both a base isolator or a flexible case-supporting system. Results show that active base isolation has superior performance than the passive one for the seismic protection of museum’s artifacts. Moreover, due to their adaptability and robustness, active control devices can be adopted for different works of art in different site exposure conditions.