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CONTENTS
Volume 7, Number 5, May 2011
 

Abstract
Large-scale earthquakes pose serious threats to infrastructure causing substantial damage and large residual deformations. Superelastic (SE) Shape-Memory-Alloys (SMAs) are unique alloys with the ability to undergo large deformations, but can recover its original shape upon stress removal. The purpose of this research is to exploit this characteristic of SMAs such that concrete Beam-Column Joints (BCJs) reinforced with SMA bars at the plastic hinge region experience reduced residual deformation at the end of earthquakes. Another objective is to evaluate the seismic performance of SMA Reinforced Concrete BCJs repaired with flowable Structural-Repair-Concrete (SRC). A

Key Words
beam-column joint; seismic; shape memory alloy; superelasticity; plastic hinge; repair; reversedcyclic loading.

Address
Moncef Nehdi and Maged A. Youssef: Department of Civil and Environmental Engineering, The University of Western Ontario,London, ON Canada, N6A 5B9
M. Shahria Alam : School of Engineering, The University of British Columbia, Kelowna, BC Canada, V1V1V7

Abstract
To assess the performance of a structure requires the measurement of global and relative displacements at critical points across the structure. They should be obtained in real time and in all weather condition. A Global Navigation Satellite System (GNSS) could satisfy the last two requirements. The American Global Position System (GPS) provides long term acquisitions with sampling rates sufficient to track the displacement of long period structures. The accuracy is of the order of sub centimetres. The steel building which hosts the authors

Key Words
global positioning systems; sensors; structural dynamics; structural identification; vibration.

Address
Fabio Casciati and Clemente Fuggini: Department of Structural Mechanics, University of Pavia, via Ferrata 1, 27100, Pavia, Italy

Abstract
Piezo-based active structural health monitoring (SHM) requires amplifiers specifically designed for capacitive loads. Moreover, with the increase in number of applications of wireless SHM systems, energy efficiency and cost reduction for this type of amplifiers is becoming a requirement. General lab grade amplifiers are big and costly, and not built for outdoor environments. Although some piezoceramic power amplifiers are available in the market, none of them are specifically targeting the wireless constraints and low power requirements. In this paper, a piezoceramic transducer amplifier for wireless active SHM systems has been designed. Power requirements are met by two digital On/Off switches that set the amplifier in a standby state when not in use. It provides a stable

Key Words
structural health monitoring; wireless sensor network; amplifier; active sensing; miniature PZT amplifier.

Address
Claudio Olmi, Gangbing Song and Leang-San Shieh: Department of Electrical Engineering, University of Houston, 77204, USA
Gangbing Song : Department of Mechanical Engineering, University of Houston, 77204, USA
Yi-Lung Mo : Department of Civil Engineering, University of Houston, 77204, USA

Abstract
This paper presents a multi-functional system, consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device, and its applications in stay cables. The proposed system is capable of offering multiple functions: (1) mitigating excessive vibrations of cables, (2) estimating cable tension, and (3) harvesting energy for wireless sensors used health monitoring of cable-stayed bridges. In the proposed system, the EMI device, consisting of permanent magnets and a solenoid coil, can converts vibration energy into electrical energy (i.e., induced emf); hence, it acts as an energy harvesting system. Moreover, the cable tension can be estimated by using the emf signals obtained from the EMI device. In addition, the MR damper, whose damping property is controlled by the harvested energy from the EMI device, can effectively reduce excessive cable vibrations. In this study, the multi-functionality of the proposed system is experimentally evaluated by conducting a shaking table test as well as a full-scale stay cable in a laboratory setting. In the shaking table experiment, the energy harvesting capability of the EMI device for wireless sensor nodes is investigated. The performance on the cable tension estimation and the vibration mitigation are evaluated using the full-scale cable test setup. The test results show that the proposed system can sufficiently generate and store the electricity for operating a wireless sensor node twice per day, significantly alleviate vibration of a stay cable (by providing about 20% larger damping compared to the passive optimal case), and estimate the cable tension accurately within a 2.5% error.

Key Words
multi-functionality; stay cable; electromagnetic induction; vibration mitigation; tension estimation; energy harvesting.

Address
Hyung-Jo Jung and In-Ho Kim : Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea
Jeong-Hoi Koo : Department of Mechanical and Manufacturing Engineering, Miami University of Ohio, USA

Abstract
Hybrid acceleration-impedance sensor nodes on Imote2-platform are designed for damage monitoring in steel girder connections. Thus, the feasibility of the sensor nodes is examined about its performance for vibration-based global monitoring and impedance-based local monitoring in the structural systems. To achieve the objective, the following approaches are implemented. First, a damage monitoring scheme is described in parallel with global vibration-based methods and local impedance-based methods. Second, multi-scale sensor nodes that enable combined acceleration-impedance monitoring are described on the design of hardware components and embedded software to operate. Third, the performances of the multi-scale sensor nodes are experimentally evaluated from damage monitoring in a lab-scaled steel girder with bolted connection joints.

Key Words
acceleration; impedance; hybrid; structural health monitoring; Imote2 sensor platform; multiscale sensor node.

Address
Jeong-Tae Kim, Jae-Hyung Park, Dong-Soo Hong and
Duc-Duy Ho: Department of Ocean Eng., Pukyong National University, Busan, Korea

Abstract
The present paper is devoted to vibration canceling and shape control of piezoelastic slender beams. Taking into account the presence of electric networks, an extended electromechanically coupled Bernoulli-Euler beam theory for passive piezoelectric composite structures is shortly introduced in the first part of our contribution. The second part of the paper deals with the concept of passive shape control of beams using shaped piezoelectric layers and tuned inductive networks. It is shown that an impedance matching and a shaping condition must be fulfilled in order to perfectly cancel vibrations due to an arbitrary harmonic load for a specific frequency. As a main result of the present paper, the correctness of the theory of passive shape control is demonstrated for a harmonically excited piezoelelastic cantilever by a finite element calculation based on one-dimensional Bernoulli-Euler beam elements, as well as by the commercial finite element code of ANSYS using three-dimensional solid elements. Finally, an outlook for the practical importance of the passive shape control concept is given: It is shown that harmonic vibrations of a beam with properly shaped layers according to the presented passive shape control theory, which are attached to an resistor-inductive circuit (RL-circuit), can be significantly reduced over a large frequency range compared to a beam with uniformly distributed piezoelectric layers.

Key Words
piezoelastic modeling of beams; shape control; passive vibration control; design optimization of slender piezoelastic beams; electric network; vibration damping with RL-circuit.

Address
J. Schoeftner and H. Irschik : Institute of Technical Mechanics, Johannes Kepler University of Linz, A-4040 Linz,Altenbergerstr.69, Austria


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