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CONTENTS
Volume 17, Number 5, May 2016
 

Abstract
Recently, number of smart material are investigated and widely used in civil construction and other industries. Present study investigates the application of smart semi-active piezoelectric friction damper (PFD) made with piezoelectric material for the seismic control of the horizontally curved bridge isolated with lead rubber bearing (LRB). The main aim of the study is to investigate the effectiveness of hybrid system and to find out the optimum parameters of PFD for seismic control of the curved bridge. The selected curved bridge is a continuous three-span concrete box girder supported on pier and rigid abutment. The PFD is located between the deck and abutments or piers in chord and radial directions. The bridge is excited with four different earthquake ground motions with all three components (i.e. two horizontal and a vertical) having different characteristics. It is observed that the use of semi-active PFD with LRB is quite effective in controlling the response of the curved bridge as compared with passive system. The incorporation of the smart damper requiring small amount of energy in addition with an isolation system can be used for effective control the curved bridge against the dynamic loading.

Key Words
seismic isolation; PFD; LRB; curved bridge; seismic analysis

Address
N.P. Kataria and R.S. Jangid: Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai - 400 076, India

Abstract
This study investigates the optimum design parameters of a superelastic friction base isolator (S-FBI) system through a multi-objective genetic algorithm to improve the performance of isolated buildings against near-fault earthquakes. The S-FBI system consists of a flat steel-PTFE sliding bearing and superelastic NiTi shape memory alloy (SMA) cables. Sliding bearing limits the transfer of shear across the isolation interface and provides damping from sliding friction. SMA cables provide restoring force capability to the isolation system together with additional damping characteristics. A three-story building is modeled with S-FBI isolation system. Multiple-objective numerical optimization that simultaneously minimizes isolation-level displacements and superstructure response is carried out with a genetic algorithm in order to optimize S-FBI system. Nonlinear time history analyses of the building with optimal S-FBI system are performed. A set of 20 near-fault ground motion records are used in numerical simulations. Results show that S-FBI system successfully control response of the buildings against near-fault earthquakes without sacrificing in isolation efficacy and producing large isolation-level deformations.

Key Words
shape memory alloys; base isolation; near-fault earthquake; seismic control; friction

Address
Osman E. Ozbulut and Baikuntha Silwal: Department of Civil and Environmental Engineering, University of Virginia, Charlottesville, VA, USA 22904-1000


Abstract
This paper is focused on stiffness ratio effect and a new method to specify the best pattern of piezoelectric patches placement around a hole in a plate under tension to reduce the stress concentration factor. To investigate the stiffness ratio effect, some different values greater and less than unity are considered. Then a python code is developed by using particle swarm optimization algorithm to specify the best locations of piezoelectric actuators around the hole for each stiffness ratio. The results show that, there is a line called \"reference line\" for each plate with a hole under tension, which can guide the location of actuator patches in plate to have the maximum stress concentration reduction. The reference line also specifies that actuators should be located horizontally or vertically. This reference line is located at an angle of about 65 degrees from the stress line in plate. Finally two experimental tests for two different locations of the patches with various voltages are carried out for validation of the results.

Key Words
reference line; pattern recognition; piezoelectric actuator; stress concentration; plate under tension

Address
Javad Jafari Fesharaki: Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Sa\'id Golabi: Department of Mechanical Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran

Abstract
An ongoing research project is devoted to the design and implementation of a satellite based asset tracking for supporting emergency management in crisis operations. Due to the emergency environment, one has to rely on a low power consumption wireless communication. Therefore, the communication hardware and software must be designed to match requirements, which can only be foreseen at the level of more or less likely scenarios. The latter aspect suggests a deep use of a simulator (instead of a real network of sensors) to cover extreme situations. The former power consumption remark suggests the use of a minimal computer (Raspberry Pi) as data collector.

Key Words
critical asset tracking; crisis operation; GNSS sensor; wireless sensor network; ZigBee

Address
Sara Casciati: Department of Civil Engineering and Architecture, DICAr, University of Catania at Siracusa,
Piazza Federico di Svevia 1, Siracusa 96100, Italy
Zhi Cong Chen: Institute of Micro/Nano Devices and Solar Cell, College of Physics and Information Engineering,
Fuzhou University, QiShan Campus, Fuzhou 350108, China
Lucia Faravelli and Michele Vece: Department of Civil Engineering and Architecture, DICAr, University of Pavia, Via Ferrata 3, Pavia 27100, Italy



Abstract
This paper addresses the free and transient responses of a SDOF linear complex stiffness system by making use of the Hilbert transform and the convolution integral. Because the second-order differential equation of motion having the complex stiffness give rise to the conjugate complex eigen values, its time-domain analysis using the standard time integration scheme suffers from the numerical instability and divergence. In order to overcome this problem, the transient response of the linear complex stiffness system is obtained by the convolution integral of a green function which corresponds to the unit-impulse free vibration response of the complex system. The damped free vibration of the complex system is theoretically derived by making use of the state-space formulation and the Hilbert transform. The convolution integral is implemented by piecewise-linearly interpolating the external force and by superimposing the transient responses of discretized piecewise impulse forces. The numerical experiments are carried out to verify the proposed time-domain analysis method, and the correlation between the real and imaginary parts in the free and transient responses is also investigated.

Key Words
linear complex stiffness system; free and transient responses; time domain analysis; Hilbert transform; state-space formulation; convolution integral

Address
S.H. Bae and W.B. Jeong: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea
J.R. Cho: Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 339-701, Korea

Abstract
This work presents a methodology to distribute piezoelectric material for structural vibration active control. The objective is to design controlled structures with actuators which maximizes the system controllability. A topology optimization was formulated in order to distribute two material phases in the domain: a passive linear elastic material and an active linear piezoelectric material. The objective is the maximization of the smallest eigenvalue of the system controllability Gramian. Analytical sensitivities for the finite element model are derived for the objective functions and constraints. Results and comparisons with previous works are presented for the vibration control of a two-dimensional short beam.

Key Words
piezoelectric actuators; controllability Gramian; topology optimization

Address
Juliano F. Gonçalves and Jun S.O. Fonseca: Department of Mechanical Engineering, Federal University of Rio Grande do Sul, R: Sarmento Leite 425, CEP 90050-170, Porto Alegre, Brazil
Otávio A.A. Silveira: Department of Civil Engineering, Federal University of Santa Catarina, R: João Pio Duarte da Silva 205, CEP 88040-970, Florianópolis, Brazil


Abstract
A non-contact, in-situ and non-invasive technique for health monitoring of submerged fiber reinforced polymers (FRP) laminates has been developed using ultrasonic guided waves. A pair of mobile transducers at specific angles of incidence to the submerged FRP specimen was used to excite Lamb wave modes. Lamb wave modes were used for comprehensive inspection of various types of manufacturing defects like air gaps and missing epoxy, introduced during manufacturing of FRP using Vacuum Assisted Resin Infusion Molding (VARIM). Further service induced damages like notches and surface defects were also studied and evaluated using guided waves. Quantitative evaluation of transmitted ultrasonic signal in defect ridden FRPs vis-à-vis healthy signal has been used to relate the extent of damage in FRPs. The developed technique has the potential to develop into a quick, real time health monitoring tool for judging the service worthiness of FRPs.

Key Words
fiber reinforced polymer composites; guided waves; damage localizations; structural health monitoring; lamb waves; VARIM; defects

Address
Mohit Garg and Sandeep Sharma: Department of Mechanical Engineering, Thapar University, Patiala, Punjab, India
Shruti Sharma: Department of Civil Engineering, Thapar University, Patiala, Punjab, India
Rajeev Mehta: Department of Chemical Engineering, Thapar University, Patiala, Punjab, India

Abstract
In this paper, the activities carried out within the EU funded Clean Sky Joint Technology Initiative (JTI GRA) Project and aimed at developing a morphing flap, are illustrated. The reference device is a regional aircraft single slotted flap, enhanced with deforming capabilities to obtain improved hyper-lift performance. The design started with the identification of the internal architecture, intended to allow camber variations. A concentrated-hinge architecture was selected, for its ability to fit different curvatures and for the possibility of easily realizing an \"armadillo-like\" configuration, then avoiding the use of a complicate deformable skin. The flap layout is made of segmented ribs, elastically hinged each other and span-wise connected by conventional spars. Relative rotations of the rib elements are forced by SMA structural actuators, i.e., cooperating in the external loads absorption. Super-elastic SMA are used to make up recovery elastic elements, necessary to regain the original shape after activation. These further elements in turn contribute to the overall flap rigidity. After assessing the hinge number and the size of the SMA active and passive elements, the advanced design phase was dealt with. It was aimed at solving manufacturing issues and producing the executive drawings. The realized demonstrator was finally tested in lab conditions to prove its functionality in terms of whether target shape actuation or attained shape preservation under loads. On the basis of the numerical results and the experimental outcomes, precious hints were obtained for further developments of the concept.

Key Words
shape memory alloys; smart structures; morphing; flap

Address
Salvatore Ameduri and Antonio Concilio: Department of Adaptive Structures, Centro Italiano Ricerche Aerospaziali,
Via Maiorise, 81043, Capua (CE), Italy
Rosario Pecora: Department of Aerospace Engineering, Università degli Studi di Napoli \"Federico II\", Via Claudio, 21, 80125, Napoli, Italy
Dimitrios Karagiannis: INASCO Hellas Co, Napoleontos Zerva 18, 16675, Glifada, Greece


Abstract
In the present study, for first time the size dependent vibration behavior of a rotating functionally graded (FG) Timoshenko nanobeam based on Eringen\'s nonlocal theory is investigated. It is assumed that the physical and mechanical properties of the FG nanobeam are varying along the thickness based on a power law equation. The governing equations are determined using Hamilton\'s principle and the generalized differential quadrature method (GDQM) is used to obtain the results for cantilever boundary conditions. The accuracy and validity of the results are shown through several numerical examples. In order to display the influence of size effect on first three natural frequencies due to change of some important nanobeam parameters such as material length scale, angular velocity and gradient index of FG material, several diagrams and tables are presented. The results of this article can be used in designing and optimizing elastic and rotary type nano-electro-mechanical systems (NEMS) like nano-motors and nano-robots including rotating parts.

Key Words
bending vibration; Eringen\'s nonlocal theory; rotary functionally graded nanobeam; Timoshenko beam theory

Address
Farzad Ebrahimi and Navvab Shafiei: Department of Mechanical Engineering, Faculty of Engineering,Imam Khomeini International University, Qazvin, Iran


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