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CONTENTS
Volume 7, Number 2, February 17 2011
 

Abstract
As a testbed for various structural health monitoring (SHM) technologies, a super-tall structure – the 610 m-tall Guangzhou Television and Sightseeing Tower (GTST) in southern China – is currently under construction. This study aims to explore state-of-the-art wireless sensing technologies for monitoring the ambient vibration of such a super-tall structure during construction. The very nature of wireless sensing frees the system from the need for extensive cabling and renders the system suitable for use on construction sites where conditions continuously change. On the other hand, unique technical hurdles exist when deploying wireless sensors in real-life structural monitoring applications. For example, the low-frequency and lowamplitude ambient vibration of the GTST poses significant challenges to sensor signal conditioning and digitization. Reliable wireless transmission over long distances is another technical challenge when utilized in such a super-tall structure. In this study, wireless sensing measurements are conducted at multiple heights of the GTST tower. Data transmission between a wireless sensing device installed at the upper levels of the tower and a base station located at the ground level (a distance that exceeds 443 m) is implemented. To verify the quality of the wireless measurements, the wireless data is compared with data collected by a conventional cable-based monitoring system. This preliminary study demonstrates that wireless sensing technologies have the capability of monitoring the low-amplitude and low-frequency ambient vibration of a super-tall and slender structure like the GTST.

Key Words
wireless sensing; super-tall structure; ambient vibration; structural health monitoring (SHM); in-construction monitoring.

Address
Y.Q. Ni, B. Li and K.H. Lam :Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
D.P. Zhu and Y. Wang :School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA
J.P. Lynch :Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA
K.H. Law : Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA

Abstract
This paper is concerned with the trajectory tracking and vibration suppression of a single-link flexible arm by using piezoelectric materials. The dynamics of a single flexible arm with PZT patches as sensor and actuator is derived using extended Hamilton

Key Words
flexible arm; piezoelectric material; variable structure control; singular perturbation theory; vibration suppression.

Address
E. Mirzaee, M. Eghtesad and S.A. Fazelzadeh : Mechanical Engineering Department, Shiraz University, Shiraz, 71348-51154, I.R. Iran.

Abstract
This paper is aimed at presenting two methods on the basis of pattern search and genetic algorithms to detect and estimate damage in plates using the modal data of a damaged plate. The proposed methods determine the damages of plate structures using optimization of an objective function by pattern search and genetic algorithms. These methods have been applied to two numerical examples, namely fourfixed supported and cantilever plates with and without noise in the modal data and containing one or several damages. The obtained results clearly reveal that the proposed methods can be viewed as a powerful and reliable method for structural damage detection in plates using the modal data.

Key Words
damage detection; plate; pattern search algorithm; genetic algorithm; modal data.

Address
G. Ghodrati Amiri, S.A. Seyed Razzaghi and A. Bagheri :Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering,
Iran University of Science & Technology, PO Box 16765-163, Narmak, Tehran 16846, Iran.

Abstract
System identification is a fundamental step towards the application of structural health monitoring and damage detection techniques. On this respect, the development of evolved identification strategies is a priority for obtaining reliable and repeatable baseline modal parameters of an undamaged structure to be adopted as references for future structural health assessments. The paper presents the identification of the modal parameters of the Guangzhou New Television Tower, China, using a data-driven stochastic subspace identification (SSI-data) approach complemented with an appropriate automatic mode selection strategy which proved to be successful in previous literature studies. This well-known approach is based on a clustering technique which is adopted to discriminate structural modes from spurious noise ones. The method is applied to the acceleration measurements made available within the task I of the ANCRiSST benchmark problem, which cover 24 hours of continuous monitoring of the structural response under ambient excitation. These records are then subdivided into a convenient number of data sets and the variability of modal parameter estimates with ambient temperature and mean wind velocity are pointed out. Both 10 minutes and 1 hour long records are considered for this purpose. A comparison with finite element model predictions is finally carried out, using the structural matrices provided within the benchmark, in order to check that all the structural modes contained in the considered frequency interval are effectively identified via SSI-data.

Key Words
system identification; field measurements; stochastic subspace decomposition; environmental effects; finite element analysis.

Address
Lucia Faravelli : Department of Structural Mechanics, University of Pavia, Pavia, Italy.
Filippo Ubertini :Department of Civil and Environmental Engineering, University of Perugia, Perugia, Italy.
Clemente Fuggini :Research & Innovation Division, D

Abstract
The Subspace based System Identification Techniques (SSIT) have been very popular within the research circles in the last decade due to their proven superiority over the other existing system identification techniques. For operational (output only) modal analysis, the stochastic SSIT and for operational modal analysis in the presence of exogenous inputs, the combined deterministic stochastic SSIT have been used in the literature. This study compares the application of the two alternative techniques on a typical school building in Istanbul using 100 Monte Carlo simulations. The study clearly shows that the combined deterministic stochastic SSIT performs superior to the stochastic SSIT when the techniques are applied on noisy data from low to mid rise stiff structures.

Key Words
subspace based system identification; structural health monitoring; ambient vibration; operational modal analysis; buildings.

Address
Pelin Gundes Bakir ,Serhat Alkan : Department of Civil Engineering, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey.
Ender Mete Eksioglu :Department of Electronics and Communications Engineering, Istanbul Technical University,
Maslak, 34469, Istanbul, Turkey


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