Active Control

ACTIVE CONTROL OF CIVIL STRUCTURES: THEORETICAL EXPERIMENTAL STUDY
Frbdkric Bossens*, AndrQ Preumont’ Michel Aup&in**, Claude Dumoulin** Georges Magonette***, Francesco Marazzi***
* Active Structures Laboratory, Universite Libre de Bruxelles, 1050 Brussels, BELGIUM

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** Bouygues Travaux Publics, 78065 St Quentin en Yvelines Cedex. FRANCE *** EC, Joint Research Centre. Safety inStructural Mechanics, ELSA Lab.,21 020 Ispra, ITALY

ABSTRACT
An active tendon control system for civil engineering cablesupported structures is proposed. The technique is based on a tendon actuator collocated with a force sensor. A largescale mock-up using industrial components has been built and widely tested. The test-bed is a model of cable-stayed bridge during its construction phase, equipped withhydraulic actuators on the two longest stay-cables. The results of several damping experiences are presented; they clearly demonstrate the efficiency of the active damping system. The proposed technology is directly applicable to real structures by scaling up the devices.

future long bridges. An innovative way to reduce the vibrations of the structure is the application of an active dampingstrategy. The aim of the active control system is to upgrade the structural damping of the complete structure and consequently to mitigate the induced vibrations of both the cables and the cable-supported structure. The methodology is based on an active tendon including an actuator collocated with a force sensor. The active damping is driven by the displacement control of the cable anchor point [2,13, 151. This strategy has already been successfully applied for several laboratory-scale demonstrators: more details are presented in [4. 51. Hereafter we present recent experimental results obtained on a unique large-scale mock-up: it consists in a 30-m long cable-stayed bridge, whose longest cables are equipped with hydraulic actuators. This paper is a follow-up to previous documents wherepreliminary results of this project were presented [7, 10, 11, 12, 31. It is organized as follows: section 2 summarizes shortly the control strategy for active damping of cable structures; section 3 describes the largescale test-bench at JRC Ispra; the experimental testing campaign is presented in section 4 and the results are analyzed in section 5. Section 6 gives some concluding remarks. Thisresearch project, funded by the EC, is a partnership between universities and industries [I]. It aims to demonstrate the feasibility of active damping in the field of civil engineering.

NOMENCLATURE u gr, g T W 4 s Qi
Wi

actuator displacement physical controller gain reduced controller gain dynamic tension in the active cable mechanical power active cable stiffness Laplace variable naturalfrequencies natural frequencies damping ratio with active cables without active cables

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1. INTRODUCTION
Cable supported structures and particularly long-span suspension or cable-stayed bridges are among the most important engineering structures of the last decades. The structural damping of such slender structures is usually lower than one percent and large vibrations are often observed. Thisjustifies the development of new damping strategies for

2. CONTROL STRATEGY 2.1 Active control system
The aim of the active control system is to upgrade the structural damping of the complete structure and therefore

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to mitigate the induced vibrations of both the cables and the cable-supported structure. The methodology is based on an active tendon including an actuator collocatedwith a force sensor. The control law is the so-called htegral Force Feedback (IFF). The basic principle of this active control is to force the dynamic tension of the cable to produce a work by moving an anchorage according to the variation of the tension measured at the same anchorage. The advantages of this technique are summarized hereafter: . No knowledge of the state of the structure is...