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CONTENTS
Volume 14, Number 2, August 2014
 

Abstract
The purpose of this paper is to investigate the flexible structure of parabolic shell using photostrictive actuators. The analysis is made to know its dynamic behavior and light-induced control forces for coupled parabolic shell. The effects of an actuator location as well as membrane and bending components under the control action have been analyzed considering the approximate spherical model. The parabolic membrane shell accuracy is being mathematically approximated and validated comparing the light induced control forces using approximate equivalent spherical shell model. The parabolic shell with kapton smart material and photostrictive actuators has been used to formulate the governing equation in the transverse direction. The Kirchhoff-Love assumptions are used to obtain the governing equation of shell with actuator. The mechanical membrane forces and bending moments for parabolic thin shell with actuator is used to analyze the dynamic effect. The results show that membrane control action is much more significant than bending control action. Photostrictive actuators oriented along circumferential direction (actuator-2) can give better control effect than actuators placed along longitudinal direction (actuator-1). The slight difference is observed between spherical and parabolic shell for a surface with focal length to the diameter ratio of 1.00 or more than unity. Space applications often have the shape of parabolical shells or shell of revolution, due to their required focusing, aiming, or reflecting performance. The present approach is focused that photostrictive actuators can effectively control the vibration of parabolical membrane shell. Also, the actuator\'s location plays an important role in defining the control force.

Key Words
parabolic shells; spherical shell; actuators; membrane effect; bending effect

Address
S.C. Gajbhiye: Vishwavidyalaya Engineering College, Saguja Univeristy, Ambikapur, Chhattisgarh-497001, India
S.H. Upadhyay and S.P. Harsha: Indian Institute of Technology Roorkee, Uttarakhand-247667, India

Abstract
Damage detection is a challenging, complex, and at the same time very important research topic in civil engineering. Identifying the location and severity of damage in a structure, as well as the global effects of local damage on the performance of the structure are fundamental elements of damage detection algorithms. Local damage detection is essential for structural health monitoring since local damages can propagate and become detrimental to the functionality of the entire structure. Existing studies present several methods which utilize sensor data, and track global changes in the structure. The challenging issue for these methods is to be sensitive enough in identifying local damage. Autoregressive models with exogenous terms (ARX) are a popular class of modeling approaches which are the basis for a large group of local damage detection algorithms. This study presents an algorithm, called Influence-based Damage Detection Algorithm (IDDA), which is developed for identification of local damage based on regression of the vibration responses. The formulation of the algorithm and the post-processing statistical framework is presented and its performance is validated through implementation on an experimental beam-column connection which is instrumented by dense-clustered wired and wireless sensor networks. While implementing the algorithm, two different sensor networks with different sensing qualities are utilized and the results are compared. Based on the comparison of the results, the effect of sensor noise on the performance of the proposed algorithm is observed and discussed in this paper.

Key Words
structural health monitoring; localized damage detection; influence-based damage detection

Address
Siavash Dorvash, Shamim N. Pakzad and Elizabeth L. LaCrosse: Civil and Environmental Engineering, Lehigh University, Bethlehem, PA, USA

Abstract
The stochastic damage locating vector (SDLV) method has been studied extensively in recent years because of its potential to determine the location of damage in structures without the need for measuring the input excitation. The SDLV method has been shown to be a particularly useful tool for damage localization in steel truss bridges through numerical simulation and experimental validation. However, several issues still need clarification. For example, two methods have been suggested for determining the observation matrix C identified for the structural system; yet little guidance has been provided regarding the conditions under which the respective formulations should be used. Additionally, the specific layout of the sensors to achieve effective performance with the SDLV method and the associated relationship to the specific type of truss structure have yet to be explored. Moreover, how the location of truss members influences the damage localization results should be studied. In this paper, these three issues are first investigated through numerical simulation and subsequently the main results are validated experimentally. The results of this paper provide guidance on the effective use of the SDLV method.

Key Words
stochastic damage locating vector (SDLV) method; sensor layout; damage detection; steel-truss bridge; damage localization; structural health monitoring

Address
Yonghui An and Jinping Ou:Department of Civil Engineering, Dalian University of technology, Dalian, China
Jian Li: Department of Civil, Environmental, and Architectural Engineering, University of Kansas, Lawrence, KS, USA
B.F. Spencer Jr: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL, USA


Abstract
In this paper, a fuzzy inference system and an analytical hierarchy process-based online evaluation technique is developed to monitor the condition of the 32-km Donghai Bridge in Shanghai. The system has 478 sensors distributed along eight segments selected from the whole bridge. An online evaluation subsystem is realized, which uses raw data and extracted features or indices to give a set of hierarchically organized condition evaluations. The thresholds of each index were set to an initial value obtained from a structure damage and performance evolution analysis of the bridge. After one year of baseline monitoring, the initial threshold system was updated from the collected data. The results show that the techniques described are valid and reliable. The online method fulfills long-term infrastructure health monitoring requirements for the Donghai Bridge.

Key Words
health monitoring; Donghai Bridge; online evaluation; analytical hierarchy process; fuzzy inference system

Address
Danhui Dan:Department of Bridge Engineering, Tongji University, Shanghai 200092, China
Limin Sun:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Zhifang Yang: Shanghai Municipal Engineering Research Institute (SHMERI), China
Daqi Xie :Donghai Bridge Management Ltd., China

Abstract
The objective of this study is to improve the survivability and reliability of the FBG sensor network in the structural health monitoring (SHM) system. Therefore, a model reconstruction soft computing recognition algorithm based on support vector regression (SVR) is proposed to achieve the high reliability of the FBG sensor network, and the grid search algorithm is used to optimize the parameters of SVR model. Furthermore, in order to demonstrate the effectiveness of the proposed model reconstruction algorithm, a SHM system based on an eight-point fiber Bragg grating (FBG) sensor network is designed to monitor the foreign-object low velocity impact of a CFRP composite plate. Simultaneously, some sensors data are neglected to simulate different kinds of FBG sensor network failure modes, the predicting results are compared with non-reconstruction for the same failure mode. The comparative results indicate that the performance of the model reconstruction recognition algorithm based on SVR has more excellence than that of non-reconstruction, and the model reconstruction algorithm almost keeps the consistent predicting accuracy when no sensor, one sensor and two sensors are invalid in the FBG sensor network, thus the reliability is improved when there are FBG sensors are invalid in the structural health monitoring system.

Key Words
health monitoring; low velocity impact; fiber bragg grating; support vector regression; sensor network; reliability

Address
Xiaoli Zhang: College of Physics and Electronic Engineering, Xinyang Normal University, 237# Chang\'an Road, Xinyang 464000, People\'s Republic of China
Dakai Liang, Jie Zeng and Jiyun Lu: The State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, 29# Yu Dao Street, Nanjing 210016, People\'s Republic of China

Abstract
One of the most important requirements in the evaluation of existing structural systems and ensuring a safe performance during their service life is damage assessment. Damage can be defined as a weakening of the structure that adversely affects its current or future performance which may cause undesirable displacements, stresses or vibrations to the structure. The mass and stiffness of a structure will change due to the damage, which in turn changes the measured dynamic response of the system. Damage detection can increase safety, reduce maintenance costs and increase serviceability of the structures. Artificial Neural Networks (ANNs) are simplified models of the human brain and evolved as one of the most useful mathematical concepts used in almost all branches of science and engineering. ANNs have been applied increasingly due to its powerful computational and excellent pattern recognition ability for detecting damage in structural engineering. This paper presents and reviews the technical literature for past two decades on structural damage detection using ANNs with modal parameters such as natural frequencies and mode shapes as inputs.

Key Words
Artificial Neural Networks (ANNs); Finite Element Analysis (FEA); Back Propagation Neural Network (BPNN); Multi-Layer Perceptron (MLP)

Address
S.J.S. Hakim and H. Abdul Razak: StrucHMRS Group, Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Abstract
In this research, an internal model based method is proposed to estimate the structural displacements and velocities under ambient excitation using only acceleration measurements. The structural response is assumed to be within the linear range. The excitation is assumed to be with zero mean and relatively broad bandwidth such that at least one of the fundamental modes of the structure is excited and dominates in the response. Using the structural modal parameters and partial knowledge of the bandwidth of the excitation, the internal models of the structure and the excitation can be respectively established, which can be used to form an autonomous state-space representation of the system. It is shown that structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations only. Reliable estimates of structural displacements and velocities are obtained using the standard Kalman filtering technique. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulations on an eight-story lumped mass model and experimental data of a three-story frame excited by the ground accelerations of actual earthquake records.

Key Words
structural health monitoring; modal decomposition; observer design; internal model

Address
T.W. Ma, M. Bell and N.S. Xu: Department of Civil and Environmental Engineering, University of Hawaii, Mānoa, Honolulu, HI, USA
W. Lu :Department of Civil and Environmental Engineering, University of Hawaii, Mānoa, Honolulu, HI, USA;
Department of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzen,
Guangzhou, China


Abstract
With more and more built long-term structural health monitoring (SHM) systems, it has been considered to apply monitored data to learn the reliability of bridges. In this paper, based on a long-term SHM system, especially in which the sensors were embedded from the beginning of the construction of the bridge, a method to calculate the localized reliability around an embedded sensor is recommended and implemented. In the reliability analysis, the probability distribution of loading can be the statistics of stress transferred from the monitored strain which covered the effects of both the live and dead loads directly, and it means that the mean value and deviation of loads are fully derived from the monitored data. The probability distribution of resistance may be the statistics of strength of the material of the bridge accordingly. With five years\' monitored strains, the localized reliabilities around the monitoring sensors of a bridge were computed by the method. Further, the monitored stresses are classified into two time segments in one year period to count the loading probability distribution according to the local climate conditions, which helps us to learn the reliability in different time segments and their evolvement trends. The results show that reliabilities and their evolvement trends in different parts of the bridge are different though they are all reliable yet. The method recommended in this paper is feasible to learn the localized reliabilities revealed from monitored data of a long-term SHM system of bridges, which would help bridge engineers and managers to decide a bridge inspection or maintenance strategy.

Key Words
bridges; localized reliability; long-term health monitoring system; strain preprocessing; statistics

Address
Zejia Liu, Yinghua Li, Liqun Tang, Yiping Liu, Zhenyu Jiang and Daining Fang:School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, China. 510640

Abstract
The present paper develops piezo-thermo-elastic analysis of a thick spherical shell for generalized functionally graded piezoelectric material. The assumed structure is loaded under thermal, electrical and mechanical loads. The mechanical, thermal and electrical properties are graded along the radial direction based on a power function with three different non homogenous indexes. Primarily, the non homogenous heat transfer equation is solved by applying the general boundary conditions, individually. Substitution of stress, strain, electrical displacement and material properties in equilibrium and Maxwell equations present two non homogenous differential equation of order two. The main objective of the present study is to improve the relations between mechanical and electrical loads in hollow spherical shells especially for functionally graded piezoelectric materials. The obtained results can evaluate the effect of every non homogenous parameter on the mechanical and electrical components.

Key Words
piezoelectric; thick hollow spherical shell; functionally graded piezoelectric material; non homogenous

Address
M. Arefi: Department of Solid Mechanics, Faculty of Mechanical engineering, University of Kashan,
Kashan 87317-51167, Iran
M.J. Khoshgoftar: Mechanical Engineering, Tarbiat Modares University, Jalal Ale Ahmad Highway, P.O. Box, 14115-111,
Tehran, Iran


Abstract
Conventional cantilevered piezoelectric energy harvesters (PEHs) are usually fabricated with continuous electrode configuration (CEC), which suffers from the electrical cancellation at higher vibration modes. Though previous research pointed out that the segmented electrode configuration (SEC) can address this issue, a comprehensive evaluation of the PEH with SEC has yet been reported. With the consideration of delivering power to a common load, the AC outputs from all segmented electrode pairs should be rectified to DC outputs separately. In such case, theoretical formulation for power estimation becomes challenging. This paper proposes a method based on equivalent circuit model (ECM) and circuit simulation to evaluate the performance of the PEH with SEC. First, the parameters of the multi-mode ECM are identified from theoretical analysis. The ECM is then established in SPICE software and validated by the theoretical model and finite element method (FEM) with resistive loads. Subsequently, the optimal performances with SEC and CEC are compared considering the practical DC interface circuit. A comprehensive evaluation of the advantageous performance with SEC is provided for the first time. The results demonstrate the feasibility of using SEC as a simple and effective means to improve the performance of a cantilevered PEH at a higher mode.

Key Words
piezoelectric cantilever; energy harvesting; segmented electrode configuration; equivalent circuit model; circuit simulation

Address
Hongyan Wang: State Key Laboratory of Robotics and System, Harbin Institute of Technology, No.2 Yikuang Street, Nangang District, Harbin, Heilongjiang, China;
College of Computer and Control Engineering, Qiqihar University, No.42 Wenhua Street, Qiqihar, Heilongjiang, China
Lihua Tang:School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798;
Department of Mechanical Engineering, University of Auckland, 20 Symonds Street, Auckland 1010, New Zealand
Xiaobiao Shan and Tao Xie:State Key Laboratory of Robotics and System, Harbin Institute of Technology, No.2 Yikuang Street, Nangang District, Harbin, Heilongjiang, China
Yaowen Yang: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798


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