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CONTENTS
Volume 19, Number 5, May 2017
 

Abstract
In a previous study, the potential of damping suspension bridges with active stay cables has been evaluated on a numerical model of a suspension bridge, and demonstrated experimentally on a laboratory mockup. In this paper, we extend our study to explore two different configurations of the active stay-cables: one classical configuration, corresponding to attaching the active stay-cables between the top of the pylons and the deck (configuration I) and, another configuration, consisting of attaching the stay-cables between the base of the pylons and the catenary (configuration II). The analysis confirmed that both configurations are effective with a slight superiority of the second configuration. The study is conducted numerically and experimentally on a suspension bridge mock-up, by considering two types of active stay-cables. The experimental results confirmed the numerical predictions, and demonstrated the effectiveness of the second configuration.

Key Words
suspension bridge; active control; collocated control; integral force feedback

Address
Zhui Tian: Active Structures Laboratory, Université Libre de Bruxelles (ULB) 50, Av. F. D. Roosevelt (CP 165/42), Brussels, Belgium
State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi\'an Jiaotong University, Xi\'an 710049, China
Bilal Mokrani, David Alaluf, Jun Jiang and André Preumont: Active Structures Laboratory, Université Libre de Bruxelles (ULB) 50, Av. F. D. Roosevelt (CP 165/42), Brussels, Belgium

Abstract
Ratcheting behavior of 90 elbow piping subject to internal pressure 20 MPa and reversed bending 20 kN was investigated using experimental method. The maximum ratcheting strain was found in the circumferential direction of intrados. Ratcheting strain at flanks was also very large. Moreover, the effect of temperature on ratcheting strain of 90 elbow piping was studied through finite element analysis, and the results were compared with room condition (25). The results revealed that ratcheting strain of 90 elbow piping increased with increasing temperature. Ratcheting boundary of 90 elbow piping was determined by Chaboche model combined with C-TDF method. The results revealed that there was no relationship between the dimensionless form of ratcheting boundary and temperature.

Key Words
elbow pipe; ratcheting strain; temperature; reversed bending; Chaboche model; ANSYS

Address
Xiaohui Chen: School of Control Engineering, Northeastern University, Qinhuangdao 066004, China;
College of Mechanical Engineering, Yanshan University, Qinhuangdao, 066004, China
Xingang Wang: School of Control Engineering, Northeastern University, Qinhuangdao 066004, China
Xu Chen: School of Chemical Engineering and Technology, Tianjin University, 300072, China


Abstract
Semi-active devices use the building\'s own motion to produce resistive forces and are thus strictly dissipative and require little power. Devices that independently control the binary open/closed valve state can enable novel device hysteresis loops that were not previously possible. However, some device hysteresis loops cannot be obtained without active analog valve control allowing slower, controlled release of stored energy, and is presents an ongoing limitation in obtaining the full range of possibilities offered by these devices. This in silico study develops a proportional-derivative feedback control law using a validated nonlinear device model to track an ideal diamond-shaped force-displacement response profile using active analog valve control. It is validated by comparison to the ideal shape for both sinusoidal and random seismic input motions. Structural application specific spectral analysis compares the performance for the non-linear, actively controlled case to those obtained with an ideal, linear model to validate that the potential performance will be retained when considering realistic nonlinear behaviour and the designed valve control approach. Results show tracking of the device force-displacement loop to within 3-5% of the desired ideal curve. Valve delay, rather than control law design, is the primary limiting factor, and analysis indicates a ratio of valve delay to structural period must be 1/10 or smaller to ensure adequate tracking, relating valve performance to structural period and overall device performance under control. Overall, the results show that active analog feedback control of energy release in these devices can significantly increase the range of resetable, valve-controlled semi-active device performance and hysteresis loops, in turn increasing their performance envelop and application space.

Key Words
nonlinear; control; design; semi-active; earthquake; energy dissipation; valve control

Address
Geoffrey W. Rodgers, J. Geoffrey Chase and Sylvain Corman: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand

Abstract
Traditional structural dynamic analysis and Structural Health Monitoring (SHM) of large scale concrete civil structures rely on manufactured embedding transducers to obtain structural dynamic properties. However, the embedding of manufactured transducers is very expensive and low efficiency for signal acquisition. In dynamic structural analysis and SHM areas, piezoelectric transducers are more and more popular due to the advantages like quick response, low cost and adaptability to different sizes. In this paper, the applicable feasibility assessment of the designed \"artificial\" piezoelectric transducers called Concrete Piezoelectric Smart Module (CPSM) in dynamic structural analysis is performed via three major experiments. Experimental Modal Analysis (EMA) based on Ibrahim Time Domain (ITD) Method is applied to experimentally extract modal parameters. Numerical modal analysis by finite element method (FEM) modeling is also performed for comparison. First ten order modal parameters are identified by EMA using CPSMs, PCBs and FEM modeling. Comparisons are made between CPSMs and PCBs, between FEM and CPSMs extracted modal parameters. Results show that Power Spectral Density by CPSMs and PCBs are similar, CPSMs acquired signal amplitudes can be used to predict concrete compressive strength. Modal parameter (natural frequencies) identified from CPSMs acquired signal and PCBs acquired signal are different in a very small range (~3%), and extracted natural frequencies from CPSMs acquired signal and FEM results are in an allowable small range (~5%) as well. Therefore, CPSMs are applicable for signal acquisition of dynamic responses and can be used in dynamic modal analysis, structural health monitoring and related areas.

Key Words
modal analysis; power spectral density; structural health monitoring; numerical analysis; ITD

Address
Nan Zhang: School of Civil and Construction Engineering, Oregon State University, 101 Kearney Hall, Corvallis,
OR, USA 97331
Huaizhi Su: State Key Laboratory of Hydrology-Water Resources and Hydropower Engineering, Hohai University, Nanjing 210098, China



Abstract
The purpose of this paper is to study the capabilities of the impulse response method in length and flaw detecting for concrete piles and provide a suggested method to find small-size flaws in piles. In this work, wavelet transform is used to decompose the recorded time domain signal into a series of levels. These levels are narrowband, so the mix of different dominant bandwidths can be avoided. In this study, the impulse response method is used to analyze the signal obtained from the wavelet transform to improve the judgment of the flaw signal so as to detect the flaw location. This study provides a new way of thinking in non-destructive testing detection. The results show that the length of a pile is easy to be detected in the traditional reflection time or frequency domain method. However, the small flaws within pile are difficult to be found using these methods. The proposed approach in this paper is able to greatly improve the results of small-size flaw detection within piles by reducing the effects of any noise and clarifying the signal in the frequency domains.

Key Words
piles; impulse response method; signal processing; wavelet transform; non-destructive testing

Address
Sheng-Huoo Ni, Yu-Zhang Yanga and Chia-Rong Lyu: Department of Civil Engineering, National Cheng Kung University, Tainan,Taiwan 70101, ROC

Abstract
A series of field vibration tests are conducted on the Runyang Suspension Bridge during both the construction and operational stages. The purpose of this study is devoted to the analysis of the dynamic characteristics of the suspension tower. After the tower was erected, an array of accelerometers was deployed to study the evolution of its modal parameters during the construction process. Dynamic tests were first performed under the freestanding tower condition and then under the tower-cable condition after the superstructure was installed. Based on the identified modal parameters, the effect of the pile-soil-structure interaction on dynamic characteristics of the suspension tower is investigated. Moreover, the stiffness of the pile foundation is successfully identified using a probabilistic finite model updating method. Furthermore, challenges of identifying the dynamic properties of the tower from the coupled responses of the tower-cable system are discussed in detail. It\'s found that compared with the identified results from the freestanding tower, the longitudinal and torsional natural frequencies of the tower in the tower-cable system have changed significantly, while the lateral mode frequencies change slightly. The identified modal results from measurements by the structural health monitoring system further confirmed that the vibrations of the bridge subsystems (i.e., the tower, the suspended deck and the main cable) are strongly coupled with one another.

Key Words
system identification; suspension bridge tower; ambient vibration test; pile-soil-structure interaction; tower-cable system; structural health monitoring system

Address
Zhijun Li and Xiuli Xu: College of Civil Engineering, Nanjing Tech University, Nanjing, 211800, China
Dongming Feng: Weidlinger Transportation Practice, Thornton Tomasetti, New York, NY 10005, USA
Maria Q. Feng: Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027, USA

Abstract
A mathematical model of electro-thermoelasticity has been constructed in the context of a new consideration of heat conduction with memory-dependent derivative. The governing coupled equations with time-delay and kernel function, which can be chosen freely according to the necessity of applications, are applied to several concrete problems. The exact solutions for all fields are obtained in the Laplace transform domain for each problem. According to the numerical results and its graphs, conclusion about the proposed model has been constructed. The predictions of the theory are discussed and compared with dynamic classical coupled theory. The result provides a motivation to investigate conducting thermoelectric viscoelastic materials as a new class of applicable materials.

Key Words
magneto-thermo-viscoelasticity; thermoelectric materials; memory-dependent derivative; time-delay; kernel function; numerical results

Address
Magdy A. Ezzat:Department of Mathematics, Faculty of Education, Alexandria University, Egypt
Ahmed S. El Karamany: Department of Mathematical and Physical Sciences, Nizwa University, Nizwa -611, P.O. Box 1357, Oman
A.A. El-Bary: Arab Academy for Science and Technology, P.O. Box 1029, Alexandria, Egypt

Abstract
Structural modeling of unencapsulated ionic polymer metal composite (u-IPMC) actuators that are used for flapping the insect scale-flapping wing of micro air vehicles (FMAV) in dry environmental conditions is carried out. Structural modeling for optimization of design parameters for retention of water, maximize actuation performance and to study the influence of water activity on the actuation characteristics of u-IPMC is explored for use in FMAV. The influence of equivalent weight of Nafion polymer, cations, concentration of cations, pre-treatment procedures on retention of water of u-IPMCs and on actuation parameters, flapping angle, flexural stiffness and actuation displacement are investigated. IPMC designed with Nafion having equivalent weight 900-1100, pre-heated at 300C and with sodium as the cations is promising for optimum retention of water and actuation performance. The actuation parameters while in operation in dry and humid environment with varying water activity can be tuned to desirable frequency, deflection, flap angle and flexural stiffness by changing the water activity and operational temperature of the environment.

Key Words
ionic polymer metal composite (IPMC) actuators; structural modeling; retention of water; water activity and actuation performance

Address
J. Sakthi Swarrup and Ganguli Ranjan:Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India
Madras Giridhar: Department of Chemical Engineering, Indian Institute of Science, Bangalore-560012, India

Abstract
Design of piezoelectric energy harvester for a wide operating frequency range is a challenging problem and is currently being investigated by many researchers. Widening the operating frequency is required, as the energy is harvested from ambient source of vibration which consists of spectrum of frequency. This paper presents a new technique to increase the operating frequency range which is achieved by designing a harvester featured by a propped cantilever beam with variable over hang length. The proposed piezoelectric energy harvester is modeled analytically using Euler Bernoulli beam theory and the effectiveness of the harvester is demonstrated through experimentation. The results from analytical model and from experimentation reveal that the proposed energy harvester generates an open circuit output voltage ranging from 36.43 V to 11.94 V for the frequency range of 27.24 Hz to 48.47 Hz. The proposed harvester produces continuously varying output voltage and power in the broadened operating frequency range.

Key Words
broadband; energy harvester; piezoelectric; propped beam; resonance; vibration

Address
R. Usharani: Department of Instrumentation and Control Engineering, Seshasayee Institute of Technology,
Tiruchirappalli,Tamilnadu ,India. 620010
G. Uma and M. Umapathy: Department of Instrumentation and Control Engineering, National Institute of Technology,
Tiruchirappalli, Tamilnadu ,India. 620015
S.B. Choi: Department of Mechanical Engineering, Inha University, Incheon, Korea



Abstract
In this paper, an adaptive fuzzy sliding mode controller (AFSMC) is designed to reduce dynamic responses of seismically excited structures. In the conventional sliding mode control (SMC), direct implementation of switching-type control law leads to chattering phenomenon which may excite unmodeled high frequency dynamics and may cause vibration in control force. Attenuation of chattering and its harmful effects are done by using fuzzy controller to approximate discontinuous part of the sliding mode control law. In order to prevent time-consuming obtaining of membership functions and reduce complexity of the fuzzy rule bases, adaptive law based on Lyapunov function is designed. To demonstrate the performance of AFSMC method and to compare with that of SMC and fuzzy control, a linear three-story scaled building is investigated for numerical simulation based on the proposed method. The results indicate satisfactory performance of the proposed method superior to those of SMC and fuzzy control.

Key Words
sliding mode control; adaptive fuzzy control; chattering-free

Address
Hosein Ghaffarzadeh and Keyvan Aghabalaei: Department of Civil Engineering, University of Tabriz, Tabriz, Iran


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