Structural Control and Health Monitoring

Beskhyroun, Sherif; Oshima, Toshiyuki; Mikami, Shuichi

doi: 10.1002/stc.316pmid: N/A

A wavelet‐based technique is proposed for structural damage detection and health monitoring. In this technique, characteristics of representative vibration signals under the wavelet transformation are examined for damage identification. The proposed method is based on only the output data without the need for measuring the excitation forces, any modal identification or numerical models. The method is described theoretically and verified both experimentally and numerically using a railway steel bridge. The applicability of utilizing piezoelectric actuators for exciting large structures such as steel bridges is also investigated in this paper. Several damage scenarios were introduced to the test structure by removing bolts from some stiffeners located on the web of the main girder. Similar damage scenarios were introduced to the finite element model of the test structure. The results indicate that the current approach can identify the location of small damage effectively. The proposed method combined with the use of piezoelectric actuators is shown to be very suitable for continuous health monitoring of steel bridges. Copyright © 2009 John Wiley & Sons, Ltd.

Li, Hui; Li, Shunlong; Ou, Jinping; Li, Hongwei

doi: 10.1002/stc.319pmid: N/A

Numerous investigations have indicated that structural modal parameters are significantly impacted by varying environmental and operational conditions. This phenomenon will cause confusion when conducting modal‐based damage detection and model updating. This paper investigates the dependency of modal frequencies, modal shapes and the associated damping ratios on temperature and wind velocity. The nonlinear principal component analysis (NLPCA) is first employed as a signal pre‐processing tool to distinguish temperature and wind effects on structural modal parameters from other environmental factors. The pre‐processed dataset by NLPCA implies the relationship between modal parameters and temperature as well as wind velocity. Consequently, the artificial neural network (ANN) technique is employed to model the relationship between the pre‐processed modal parameters and environmental factors. Numerical results indicate that pre‐processed modal parameters by NLPCA can retain the most features of original signals. Furthermore, the pre‐processed modal frequency and damping ratios are dramatically affected by temperature and wind velocity. The ANN regression models have good capacities for mapping relationship of environmental factors and modal frequency, damping ratios. However, environmental effects on the entire modal shapes are insignificant. Copyright © 2009 John Wiley & Sons, Ltd.

Agranovich, G.; Ribakov, Y.

doi: 10.1002/stc.329pmid: N/A

Using supplemental active and semi‐active dampers is known as an efficient way for improving structural response to earthquakes. An actual problem that should be solved by the engineer is how many dampers should be used and what is their optimal location yielding the desired structural response by minimum cost. The last one usually depends on the price of a damping unit and its connection to the frame, number of damping units and energy required for activation of the control system in order to realize the optimal control algorithm. In this paper, the following heuristic solution of this problem is proposed. This solution is based on the well‐known LQG design of active dampers. It is first assumed that the LQG controlled dampers are located at each floor. Energy, dissipated in the dampers at each floor, is obtained and most effective dampers' locations are selected according to maximum contribution to the total energy dissipation. A procedure for realization of this idea is proposed. Effectiveness of the proposed method is demonstrated in a numerical example. It shows a promising way for effective improvement of structural seismic response by a limited set of damping units. Copyright © 2009 John Wiley & Sons, Ltd.

Chang, Min‐Li; Lin, Chi‐Chang; Ueng, Jin‐Min; Hsieh, Kai‐Hsiang; Wang, Jer‐Fu

doi: 10.1002/stc.330pmid: N/A

This paper deals with the optimum design of a tuned mass damper (TMD) for the mitigation of machine‐induced vertical vibration of structures. Theoretically, a TMD without damping tuning to the machine operating frequency will make optimum control performance. Considering zero damping is impossible, a new field‐based design procedure and an adjustable vertically moving TMD (VTMD) are proposed. The VTMD is composed of variable mass blocks and changeable springs. A prototype of the VTMD was fabricated and tested on a simply supported beam and a reinforced‐concrete floor of a school building. Both experimental results confirmed the control effectiveness and usefulness of the VTMD. In the beam test, more than 90% reduction in accelerations was observed. In the floor test, 41–56% acceleration reduction can be achieved even though the mass ratio of TMD to structure is very small. Copyright © 2009 John Wiley & Sons, Ltd.

Zhang, Chunwei; Li, Luyu; Ou, Jinping

doi: 10.1002/stc.331pmid: N/A

This paper discusses the development of non‐linear differential equation modeling and characteristic analysis of control force for motion control of suspended structures, and proposes an innovative passive control system for suppressing swinging motion of similar structures. Based on the classical Lagrangian principle, the system EOM can be established with respect to two basic motion modes: planar motion and swinging motion. The analytical results indicate that different control systems should be considered owing to the diverse motion characteristics of the suspended system. Furthermore, theoretical results show that the tuned mass damper (subsequently abbreviated as TMD) cannot be used for swinging motion control, due to the coupling effect between linear stroke of TMD mass and angular velocity of suspended structure. Then, based on thorough numerical analysis, the concept of tuned rotary inertia damper (subsequently abbreviated as TRID) control system is proposed, and the differential equations of motion, denoting the motion law of the whole system, are studied. In addition, optimization issues of TRID control are equivalent to the classical optimization problem of TMD control. At last, conclusions were extended to vibration or motion control of typical civil engineering structures, such as high‐rising tower structures with prior bending deformation characteristics and long‐span bridges with rotation vibration characteristics. Once the structural motion or vibration is similar to the single pendulum or inverted pendulum, the planar TMD control system will lose its effectiveness and the innovative TRID system should be considered for suppressing swinging motion of such structures. Copyright © 2009 John Wiley & Sons, Ltd.

Renzi, Emanuele; De Angelis, Maurizio

doi: 10.1002/stc.338pmid: N/A

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.