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CONTENTS
Volume 14, Number 4, October 2014
 

Abstract
The rocking pier system (RPS) allows the columns to rock on beam or foundation surfaces during the attacks of a strong earthquake. Literatures have proved that seismic energy dissipated by the RPS through the column impact is limited. To enhance the energy dissipation capacity of a RPS bridge substructure, frictional hinge dampers (FHDs) were installed and evaluated by shaking table tests. The supplemental FHDs consist of two brass plates sandwiched by three steel plates. The strategy of self-centering design is to isolate the seismic energy by RPS at the columns and then dissipate the energy by FHDs at the bridge deck. Component tests of FHD were first conducted to verify the friction coefficient and dynamic characteristic of the FHDs. In total, 32 shaking table tests were conducted to investigate parameters such as wave forms of the earthquake (El Centro 1940 and Kobe 1995) and normal forces applied on the friction dampers. An analytical model was also proposed to compare with the tested damping of the bridge sub-structure with or without FHDs.

Key Words
rocking; self-centering; bridge structure; damping ratio; frictional hinge damper

Address
Chin-Tung Cheng and Fu-Lin Chen: Department of Construction Engineering, National Kaohsiung First University of Science & Technology, No. 1, University Road, Yenchao, Kaohsiung 824, Taiwan

Abstract
The combined use of smart materials, complementing each others\' characteristics and resulting in devices with optimised features, is providing new solutions in many industries. The use of ingenious combinations of smart materials has led to improvements in actuation speed and force, signal-to-noise ratio, sensor precision and unique capabilities such as self-sensing self-healing systems and energy autonomy. This may all give rise to a revival for numerous families of smart materials, for which application proposals had already reached a stationary situation. It may also provide the boost needed for the definitive industrial success of many others. This study focuses on reviewing the proposals, preliminary studies and success cases related to combining smart materials to obtain multifunctional, improved systems. It also examines the most outstanding applications and fields for the combined use of these smart materials. We will also discuss related study areas which warrant further research for the development of novel approaches for demanding applications.

Key Words
smart materials; intelligent systems; sensors and actuators; energy harvesting; self sensing materials and structures; self-healing materials and structures; autonomous systems

Address
A. Díaz Lantada, P. Lafont Morgado, J.M. Munoz-Guijosa,
J.L. Muñoz Sanz, J. Echávarri Otero, E. Chacón Tanarro and E. De la Guerra Ochoa: Machine Engineering Research Group - Higher Technical School of Industrial Engineering
Universidad Politécnica de Madrid, c/ José Gutiérrez Abascal n 2, 28006 Madrid, Spain

Abstract
This paper proposes a new design of shape memory alloy (SMA) wire actuated gripper for open mode operation. SMA can generate smooth muscle movements during actuation which make them potentially good contenders in designing grippers. The principle of the shape memory alloy gripper is to convert the linear displacement of the SMA wire actuator into the angular displacement of the gripping jaw. Steady state analysis is performed to design the wire diameter of the bias spring for a known SMA wire. The gripper is designed to open about an angle of 22.5 when actuated using pulsating electric current from a constant current source. The safe operating power range of the gripper is determined and verified theoretically. Experimental evaluation for the uncontrolled gripper showed a rotation of 19.97. Forced cooling techniques were employed to speed up the cooling process. The gripper is simple and robust in design (single movable jaw), easy to fabricate, low cost, and exhibits wide handling capabilities like longer object handling time and handling wide sizes of objects with minimum utilization of power since power is required only to grasp and release operations.

Key Words
actuator; shape memory alloy (SMA); gripper; forced air cooling; response time

Address
S. Krishna Chaitanya: Vignan\'s University, Vadlamudi 522213, India
K. Dhanalakshmi: National Institute of Technology, Tiruchirappalli 620015, India

Abstract
The model of unit dynamic reliability of repairable k/n (G) system with unit strength degradation under repeated random shocks has been developed according to the stress-strength interference theory. The unit failure number is obtained based on the unit failure probability which can be computed from the unit dynamic reliability. Then, the transfer probability function of the repairable k/n (G) system is given by its Markov property. Once the transfer probability function has been obtained, the probability density matrix and the steady-state probabilities of the system can be retrieved. Finally, the dynamic reliability of the repairable k/n (G) system is obtained by solving the differential equations. It is illustrated that the proposed method is practicable, feasible and gives reasonable prediction which conforms to the engineering practice.

Key Words
random shocks; repairable; k/n (G) system; dynamic; reliability

Address
Yongfeng Fang and Wenliang Tao: School of Mechanical Engineering, Bijie University, Bijie 551700, China
Kong Fah Tee: Department of Civil Engineering, University of Greenwich, Kent, ME4 4TB, U.K.

Abstract
Damage detection methods based on modal analysis have been widely studied in recent years. However the calculation of mode shapes in real structures can be time consuming and often requires dedicated software programmes. In the present paper the combined application of proper orthogonal decomposition and gapped smoothing method to structural damage detection is presented. The first is used to calculate the dynamic shapes of a damaged structural element using only the time response of the system while the second is used to derive a reference baseline to which compare the data coming from the damaged structure. Experimental verification is provided for a beam case while numerical analyses are conducted on plates. The introduction of a stiffener on a plate is investigated and a method to distinguish its influence from that of a defect is presented. Results highlight that the derivatives of the proper orthogonal modes are more effective damage indices than the modes themselves and that they can be used in damage detection when only data from the damaged structure are available. Furthermore the stiffened plate case shows how the simple use of the curvature is not sufficient when analysing complex components. The combined application of the two techniques provides a possible improvement in damage detection of typical aeronautical structures.

Key Words
damage detection; POD; GSM; stiffened panel; threshold approach

Address
M. Thiene and U. Galvanetto:Department of Industrial Engineering, University of Padova, via Marzolo 9, 35131 Padova, Italy;
Centre for Space Studies and Activities G. Colombo, University of Padova, via Venezia 15, 35131 Padova, Italy
C. Surace: Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, corso Duca degli Abruzzi 24 – 10129 Turin, Italy


Abstract
This study aims to investigate the relationship between structural damage and sensitivity indices using the Hilbert-Huang transform (HHT) method. Two damage detection indices are proposed: the ratio of bandwidth (RB), and the ratio of effective stiffness (RES). The nonlinear four bays multiple degree of freedom models with various predominant frequencies are constructed using the SAP2000 program. Adjusted PGA earthquake data (Japan 311, Chi-Chi 921) are used as the excitations. Next, the damage detection indices obtained using the HHT and the fast Fourier transform (FFT) methods are evaluated based on the acceleration responses of the structures to earthquakes. Simulation results indicate that, the column of the 1st floor is the first yielding position and the RB value is changed when the RES<90% in all cases. Moreover, the RB value of the 1st floor changes more sensitive than those from the top floor. In addition, when the structural response is nonlinear (i.e., RES<100%), the RB and the RES curves indicate the incremental change in the HHT spectra. However, the same phenomenon can be found from FFT spectra only when the stiffness reduction is large enough. Therefore, the RB estimated from the smoothed HHT spectra is an effective and sensitive index for detecting structural damage.

Key Words
HHT; damage detection index; effective stiffness; sensitivity

Address
Wen-Ko Hsu and Dung-Jiang Chiou:Research Center for Hazard Mitigation and Prevention, National Central University, Jhung-li, Taoyuan County, Taiwan, R.O.C.
Cheng-Wu Chen: Department of Maritime Information and Technology, National Kaohsiung Marine University,
Kaohsiung 80543, Taiwan, R.O.C.;
Faculty of Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Ming-Yi Liu: Department of Civil Engineering, Chung Yuan University, Jhung-li, Taoyuan County, Taiwan, R.O.C.
Wei-Ling Chiang and Pei-Chiung Huang: Department of Civil Engineering, National Central University, Jhung-li, Taoyuan County, Taiwan, R.O.C.



Abstract
The energy constraint is still a common issue for the practical application of wireless sensors, since they are usually powered by batteries which limit their lifetime. In this paper, a practical compound energy efficiency strategy is proposed and realized in the implementation of a real time wireless sensor platform. The platform is intended for wireless structural monitoring applications and consists of three parts, wireless sensing unit, base station and data acquisition and configuration software running in a computer within the Matlab environment. The high energy efficiency of the wireless sensor platform is achieved by a proposed adaptive radio transmission power control algorithm, and some straightforward methods, including adopting low power ICs and high efficient power management circuits, low duty cycle radio polling and switching off radio between two adjacent data packets\' transmission. The adaptive transmission power control algorithm is based on the statistical average of the path loss estimations using a moving average filter. The algorithm is implemented in the wireless node and relies on the received signal strength feedback piggybacked in the ACK packet from the base station node to estimate the path loss. Therefore, it does not need any control packet overheads. Several experiments are carried out to investigate the link quality of radio channels, validate and evaluate the proposed adaptive transmission power control algorithm, including static and dynamic experiments.

Key Words
wireless data acquisition; real time wireless sensor; energy efficiency; low duty cycle polling; adaptive transmission power control; path loss estimation

Address
ZhiCong Chen: Institute of Micro-Nano devices & Solar Cells, College of Physics and Information Engineering, Fuzhou University, Fuzhou 350108, China;
Department of Civil Engineering and Architecture, University of Pavia, Pavia 27100, Italy


Abstract
This paper presents the design, modelling and, simulation and experimental results of a shape memory alloy (SMA) actuator based critical motion control application. Dynamic performance of SMA and its ability in replacing servo motor is studied for which the famous open loop unstable balancing ball and beam system direct driven by antagonistic SMA is designed and developed. Simulation uses the mathematical model of ball and beam structure derived from the first principles and model estimated for the SMA actuator by system identification. A PID based cascade control system consisting of two loops is designed and control of ball trajectory for various target positions with settling time as control parameter is verified experimentally. The results demonstrate the performance of SMA for a complicated i.e., under actuated, highly nonlinear unstable system, and thereby it\'s dynamic behaviour. Control strategies bring out the effectiveness of the actuator and its possible application to much more complex applications such as in aerospace control and robotics.

Key Words
shape memory alloy; ball and beam system; dynamic behaviour; PID control; system identification

Address
S. Sunjai Nakshatharan, K. Dhanalakshmi and D. Josephine Selvarani Ruth: Department of Instrumentation and Control Engineering, National Institute of Technology, Tiruchirappalli, India

Abstract
The study is aimed at investigating the feasibility of a high TRL solution for a wing flap segment characterized by morphable camber airfoil and properly tailored to be implemented on a real-scale regional transportation aircraft. On the base of specific aerodynamic requirements in terms of target airfoil shapes and related external loads, the structural layout of the device was preliminarily defined. Advanced FE analyses were then carried out in order to properly size the load-carrying structure and the embedded actuation system. A full scale limited span prototype was finally manufactured and tested to: • demonstrate the morphing capability of the conceived structural layout; • demonstrate the capability of the morphing structure to withstand static loads representative of the limit aerodynamic pressures expected in service; • characterize the dynamic behavior of the morphing structure through the identification of the most significant normal modes. Obtained results showed high correlation levels with respect to numerical expectations thus proving the compliance of the device with the design requirements as well as the goodness of modeling approaches implemented during the design phase.

Key Words
smart structure; morphing; camber variation; wing flap; regional aircraft; FE simulations; experimental tests

Address
Rosario Pecora, Francesco Amoroso and Gianluca Amendola:Department of Aerospace Engineering, University of Naples \"Federico II\", Via Claudio, 21 -80125- Napoli, Italy
Antonio Concilio: Smart Structures Laboratory, Italian Aerospace Research Center (C.I.R.A. S.c.p.A.), Via Maiorise -81043-Capua (CE), Italy

Abstract
The strain data acquired from structural health monitoring (SHM) systems play an important role in the state monitoring and damage identification of bridges. Due to the environmental complexity of civil structures, a better understanding of the actual strain data will help filling the gap between theoretical/laboratorial results and practical application. In the study, the multi-scale features of strain response are first revealed after abundant investigations on the actual data from two typical long-span bridges. Results show that, strain types at the three typical temporal scales of 105, 102 and 100 sec are caused by temperature change, trains and heavy trucks, and have their respective cut-off frequency in the order of 10-2, 10-1 and 100 Hz. Multi-resolution analysis and wavelet shrinkage are applied for separating and extracting these strain types. During the above process, two methods for determining thresholds are introduced. The excellent ability of wavelet transform on simultaneously time-frequency analysis leads to an effective information extraction. After extraction, the strain data will be compressed at an attractive ratio. This research may contribute to a further understanding of actual strain data of long-span bridges; also, the proposed extracting methodology is applicable on actual SHM systems.

Key Words
health monitoring; bridges; strain; information extraction; multi-scale; wavelet

Address
Baijian Wu, Zhaoxia Li and Ying Wang: Department of Engineering Mechanics, Southeast University, Nanjing 210096, China
Tommy H.T. Chan: School of Civil Engineering and Built Environment, Science and Engineering Faculty,
Queensland University of Technology, Queensland, Australia


Abstract
The indirect displacement estimation using acceleration and strain (IDEAS) method is extended to various types of beam structures beyond the previous validation on the prismatic or near-prismatic beams. By fusing different types of responses, the IDEAS method is able to estimate displacements containing pseudo-static components with high frequency noise to be significantly reduced. However, the concerns to the IDEAS method come from possible disagreement of the assumed sinusoidal mode shapes to the actual mode shapes, which allows the IDEAS method to be valid only for simply-supported prismatic beams and limits its applicability to real world problems. In this paper, the extension of the IDEAS method to the general types of beams is investigated by the mathematical formulation of the modal mapping matrix only for the monitored substructure, so-called monitoring span. The formulation particularly considers continuous and wide beams to extend the IDEAS method to general beam structures that reflect many real bridges. Numerical simulations using four types of beams with various irregularities are presented to show the effectiveness and accuracy of the IDEAS method in estimating displacements.

Key Words
displacement; acceleration; strain; data fusion; beam structure

Address
Soojin Cho, Sung-Han Sim and Junhwa Lee: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea
Jong-Woong Park: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana 61801, IL, USA

Abstract
Monitoring surface cracks is important to ensure the health of concrete structures. However, traditional visual inspection to monitor the concrete cracks has disadvantages such as subjective inspection nature, associated time and cost, and possible danger to inspectors. To alter the visual inspection, a complete procedure for automated crack assessment based on adaptive digital image processing has been proposed in this study. Crack objects are extracted from the images using the subtraction with median filter and the local binarization using the Niblack\' s method. To adaptively determine the optimal window sizes for the median filter and the Niblack\' s method without distortion of crack object, an optimal filter size index (OFSI) is proposed. From the extracted crack objects using the optimal size of window, the crack objects are decomposed to the crack skeletons and edges, and the crack width is calculated using 4-connected normal line according to the orientation of the local skeleton line. For an image, a crack width nephogram is obtained to have an intuitive view of the crack distribution. The proposed procedure is verified from a test on a concrete reaction wall with various types of cracks. From the crack images with different crack widths and patterns, the widths of cracks in the order of submillimeters are calculated with high accuracy.

Key Words
crack width; digital image processing; adaptive image processing; window size; median filter

Address
Yufei Liu and Jiansheng Fan:Key Laboratory of Civil Engineering Safety and Durability of Ministry of Education,
Department of Civil Engineering, Tsinghua University, Beijing 100084, China
Soojin Cho: chool of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology,
Ulsan 689-798, KoreaBillie F. Spencer, Jr.: epartment of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,
Urbana, IL 61801, USA





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