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CONTENTS
Volume 8, Number 2, August 2011
 

Abstract
A new method for both local damage(s) identification and input excitation force identification of beam structures is presented using the dynamic response sensitivity-based finite element model updating method. The state-space approach is used to calculate both the structural dynamic responses and the responses sensitivities with respect to structural physical parameters such as elemental flexural rigidity and with respect to the force parameters as well. The sensitivities of displacement and acceleration responses with respect to structural physical parameters are calculated in time domain and compared to those by using Newmark method in the forward analysis. In the inverse analysis, both the input excitation force and the local damage are identified from only several acceleration measurements. Local damages and the input excitation force are identified in a gradient-based model updating method based on dynamic response sensitivity. Both computation simulations and the laboratory work illustrate the effectiveness and robustness of the proposed method.

Key Words
response sensitivity; time domain; damage detection; excitation force; state-space.

Address
Z.R. Lu, M. Huang and J.K. Liu : School of Engineering, Sun Yat-sen University, Guangzhou, P.R. China

Abstract
As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional leadrubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called

Key Words
displacement-based design; shape memory alloy; base isolation; self-centering seismic resisting system; highway bridges; nonlinear response spectra.

Address
Jin-long Liu : Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom,
Kowloon, Hong Kong, China , Institute of Engineering Mechanics, China Earthquake Administration, Harbin 150080, China
Songye Zhu : Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom,
Kowloon, Hong Kong, China
You-lin Xu : Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom,
Kowloon, Hong Kong, China
Yunfeng Zhang : Department of Civil and Environmental Engineering, University of Maryland, College Park, MD, USA

Abstract
A technique for damage localization and assessment based on measurements of both eigenvectors curvatures and eigenfrequencies is proposed. The procedure is based on two successive steps: a model independent localization, based on changes of modal curvatures, and the solution of a one-dimensional minimization problem to evaluate damage intensity. The observability properties of damage parameters is discussed and, accordingly, a suitable change of coordinates is introduced. The proposed technique is illustrated with reference to a cantilever Euler beam endowed with a set of piezoelectric transducers. To assess the robustness of the algorithm, a parametric study of the identification errors with respect to the number of transducers and to the number of considered modal quantities is carried out with both clean and noisecorrupted data.

Key Words
damage detection; structural health monitoring; frequency response function; piezoelectric sensors.

Address
Jacopo Ciambella, Fabrizio Vestroni and Stefano Vidoli : Dipartimento di Ingegneria Strutturale e Geotecnica, Universita di Roma

Abstract
This article describes the research work involving the implementation of an Active Bracing System aimed at the modification of the initial dynamics of a laboratorial building structure to a new desired dynamics. By means of an adequate control force it is possible to assign an entirely new dynamics to a system by moving its natural frequencies and damping ratios to different values with the purpose of achieving a better overall structural response to external loads. In Civil Engineering applications, the most common procedures for controlling vibrations in structures include changing natural frequencies in order to avoid resonance phenomena and increasing the damping ratios of the critical vibration modes. In this study, the actual implementation of an active system is demonstrated, which is able to perform such modifications in a wide frequency range; to this end, a plane frame physical model with 4 degrees-of-freedom is used. The Active Bracing System developed is actuated by a linear motor controlled by an algorithm based on pole assignment strategy. The efficiency of this control system is verified experimentally by analyzing the control effect obtained with the modification of the initial dynamic parameters of the plane frame and observing the subsequent structural response.

Key Words
vibration control; system dynamics; pole assignment; laboratorial structure; active control; active bracing system.

Address
C. Moutinho, A. Cunha and E. Caetano : Faculty of Engineering of University of Porto (FEUP), Portugal

Abstract
This paper presents novel research into the source localization of multiple impacts. Source localization technology for single impact loads in a plate structure has been used for health monitoring. Most of research on source localization has been focused only on the localization of single impacts. Overlapping of dispersive waves induced by multiple impacts and reflection of those waves from the edge of the plate make it difficult to localize the sources of multiple impacts using traditional source localization technology. The method solving the overlapping problem and the reflection problem is presented in the paper. The suggested method is based on pre-signal processing technology using band pass filter and optimal filter. Results from numerical simulation and from experimentation are presented, and these verify the capability of the proposed method.

Key Words
plate; piezoelectronic sensor; multiple sources localization; reflection; optimal filter.

Address
S.K. Lee, Y.S. Moon and J.H. Park : Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong,Nam-Gu, Incheon 402-751, Korea


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