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CONTENTS
Volume 25, Number 1, January 2020
 

Abstract
The modal strain energy method is one of the efficient methods for detecting damage in the structures. Due to existing some limitations in real-world structures, sensors can only be located on a limited number of degrees of freedom (DOFs) of a structure. Therefore, the mode shape values in all DOFs of structures cannot be measured. In this paper, a modified modal strain energy based index (MMSEBI) is introduced to locate damaged elements of structures when a limited number of sensors are used. The proposed MMSEBI is based on the reconstruction of mode shapes using Improved Reduction System (IRS) method. Therefore, in the first step by employing IRS method, mode shapes in slave degrees of freedom are estimated by those of master degrees of freedom. In the second step, the proposed MMSEBI is used to located damage elements. In order to evaluate the efficiency of the proposed method, two numerical examples are considered under different damage patterns considering the measurement noise. Moreover, the universal threshold based on statistical hypothesis testing principles is applied to damage index values. The results show the effectiveness of the proposed MMSEBI for the structural damage localization when comparing with the available damage index named MESBI. The results demonstrate that the presented method can be used as a practical strategy for structural damage identification, especially when a limited number of sensors are installed on the structure. Finally, the combination of MMSEBI and IRS method can provide a reliable tool to identify the location of damage accurately.

Key Words
damage detection; modal strain energy; degrees of freedom; IRS method

Address
(1) Shahin Lale Arefi, Amin Gholizad:
Department of Civil Engineering, University of Mohaghegh Ardabili, P.O. Box 56199-11397, Ardabil, Iran;
(2) Seyed Mohammad Seyedpoor:
Department of Civil Engineering, Shomal University, Amol, Iran.

Abstract
It is important to take into account the thermal behavior in assessing the structural condition of bridges. An effective method of studying the temperature effect of long-span bridges is numerical simulation based on the solar radiation models. This study aims to develop a time-varying solar radiation model which can consider the real-time weather changes, such as a cloud cover. A statistical analysis of the long-term monitoring data is first performed, especially on the temperature data between the south and north anchors of the bridge, to confirm that temperature difference can be used to describe real-time weather changes. Second, a defect in the traditional solar radiation model is detected in the temperature field simulation, whereby the value of the turbidity coefficient tu is subjective and cannot be used to describe the weather changes in real-time. Therefore, a new solar radiation model with modified turbidity coefficient γ is first established on the temperature difference between the south and north anchors. Third, the temperature data of several days are selected for model validation, with the results showing that the simulated temperature distribution is in good agreement with the measured temperature, while the calculated results by the traditional model had minor errors because the turbidity coefficient tu is uncertainty. In addition, the vertical and transverse temperature gradient of a typical cross-section and the temperature distribution of the tower are also studied.

Key Words
solar radiation; turbidity coefficient; heat-transfer analysis; temperature distribution; structural health monitoring

Address
(1) Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, 210096, Nanjing, China;
(2) School of Civil Engineering, Southeast University, 210096, Nanjing, China.

Abstract
This paper aims at enlightening the properties, computational and implementation issues related to Kalman filter based state estimation algorithms and sliding mode observers, by applying them for estimating the states of a smart structure system. The Kalman based estimators considered in this work are Kalman filter and information filter and, the sliding mode observers considered are Utkin observer and higher order sliding mode observer. A fourth order linear time invariant model of a piezo actuated beam is used in this work. This structure is embedded with four number of piezo patches, of which two act as sensors, one as disturbance actuator and the other as control actuator. The performance of the state estimation algorithms is evaluated through simulation, for the first two vibrating modes of the piezo actuated structure, when the structure is maintained at first mode and second mode resonance.

Key Words
smart structure; piezo actuated structure; state estimation; Kalman filter; information filter; Utkin observer; higher order sliding mode observer

Address
Department of Instrumentation and Control Systems Engineering, PSG College of Technology, Coimbatore - 641004, India.


Abstract
This paper proposes a model-based approach for structural damage identification and quantification. Using pseudo modal strain energy and mode shape vectors, a damage-sensitive objective function is introduced which is suitable for damage estimation and quantification in shear frames. Whale optimization algorithm (WOA) is used to solve the problem and report the optimal solution as damage detection results. To illustrate the capability of the proposed method, a numerical example of a shear frame under different damage patterns is studied in both ideal and noisy cases. Furthermore, the performance of the WOA is compared with particle swarm optimization algorithm, as one the widely-used optimization techniques. The applicability of the method is also experimentally investigated by studying a six-story shear frame tested on a shake table. Based on the obtained results, the proposed method is able to assess the health of the shear building structures with high level of accuracy.

Key Words
damage detection; shear frame; pseudo modal strain energy; mode shape; whale optimization algorithm

Address
(1) M. Mohamadi Dehcheshmeh:
School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran;
(2) A. Zare Hosseinzadeh:
School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, OK, USA;
(3) G. Ghodrati Amiri:
Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.

Abstract
The nonlinear dynamics of a directly forced clamped-clamped-free-free magneto-rheological elastomer (MRE) sandwich shell has been experimentally investigated. Experiments have been conducted on an aluminium shallow shell (shell A) and an MRE-aluminium sandwich shallow shell with single curvature (shell B). An electrodynamic shaker has been used to directly force shells A and B in the vicinity of their fundamental resonance frequency; a laser displacement sensor has been used to measure the vibration amplitude to construct the frequency-response curves. It was observed that for an aluminium shell (shell A), that at small forcing amplitudes, a weak softening-type nonlinear behaviour was observed, however, at higher forcing amplitudes the nonlinear dynamical behaviour shifted and a strong hardening-type response occurred. For the MRE shell (shell B), the effect of forcing amplitude showed softening at low magnetic fields and hardening for medium magnetic fields; it was also observed the mono-curved MRE sandwich shell changed dynamics to quasiperiodic displacement at some frequencies, from a periodic displacement. The presence of a magnetic field, initial curvature, and forcing amplitude has significant qualitative and quantitative effects on the nonlinear dynamical response of a mono curved MRE sandwich shell.

Key Words
shallow shell; experimentation; mechanics; nonlinear experiments; magneto-rheological elastomer

Address
(1) Jiawei Zhang, Yuechuan Tao:
School of Electrical and Information Engineering, The University of Sydney, Sydney, NSW2006, Australia;
(2) Tanju Yildirim, Guru Prakash Neupane:
Research School of Electrical, Energy and Materials Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, ACT 2601, Australia;
(3) Jiang Bingnong:
School of Mechanical and Mechatronic Engineering, University of Technology Sydney, Sydney NSW2007;
(4) Weihua Li:
School of Mechanical, Materials, Mechatronic and Biomedical Engineering, University of Wollongong, Wollongong 2522, Australia.

Abstract
In order to protect a structure over its full life cycle, a novel tuned mass damper (TMD), the so-called semi-active eddy current pendulum tuned mass damper (SAEC-PTMD), which can retune its frequency and damping ratio in real-time, is proposed in this study. The structural instantaneous frequency is identified through a Hilbert-Huang transformation (HHT), and the SAECPTMD pendulum is adjusted through an HHT-based control algorithm. The eddy current damping parameters are discussed, and the relationship between effective damping coefficients and air gaps is fitted through a polynomial function. The semi-active eddy current damping can be adjusted in real-time by adjusting the air gap based on the linear-quadratic-Gaussian (LQG)-based control algorithm. To verify the vibration control effect of the SAEC-PTMD, an idealized linear primary structure equipped with an SAECPTMD excited by harmonic excitations and near-fault pulse-like earthquake excitations is proposed as one of the two case studies. Under strong earthquakes, structures may go into the nonlinear state, while the Bouc-Wen model has a wild application in simulating the hysteretic characteristic. Therefore, in the other case study, a nonlinear primary structure based on the Bouc-Wen model is proposed. An optimal passive TMD is used for comparison and the detuning effect, which results from the cumulative damage to primary structures, is considered. The maximum and root-mean-square (RMS) values of structural acceleration and displacement time history response, structural acceleration, and displacement response spectra are used as evaluation indices. Power analyses for one earthquake excitation are presented as an example to further study the energy dissipation effect of an SAECPTMD. The results indicate that an SAEC-PTMD performs better than an optimized passive TMD, both before and after damage occurs to the primary structure.

Key Words
uned mass damper; semi-active control; variable pendulum; eddy current damping; variable damping; nonlinear control

Address
(1) Department of Disaster Mitigation for Structures, Tongji University, Shanghai, 200092, P.R. China;
(2) State Key Laboratory for Disaster Reduction of Civil Engineering, Tongji University, Shanghai, 200092, P.R. China.

Abstract
Wind measurements were made on the Canton Tower at a height of 461 m above ground during the Typhoon Vincente, the wind-induced accelerations and displacements of the tower were recorded as well. Comparisons of measured wind parameters at upper level of atmospheric boundary layer with those adopted in wind tunnel testing were presented. The measured turbulence intensity can be smaller than the design value, indicating that the wind tunnel testing may underestimate the crosswind structural responses for certain lock-in velocity range of vortex shedding. Analyses of peak factors and power spectral density for acceleration response shows that the crosswind responses are a combination of gust-induced buffeting and vortex-induced vibrations in the certain range of wind directions. The identified modal frequencies and mode shapes from acceleration data are found to be in good agreement with existing experimental results and the prediction from the finite element model. The damping ratios increase with amplitude of vibration or equivalently wind velocity which may be attributed to aerodynamic damping. In addition, the natural frequencies determined from the measured displacement are very close to those determined from the acceleration data for the first two modes. Finally, the relation between displacement responses and wind speed/direction was investigated.

Key Words
field measurements; wind characteristics; crosswind responses; modal identification; Canton Tower

Address
(1) X.G. Hua, K. Xu, Z.Q. Chen:
Key Laboratory forWind and Bridge Engineering of Hunan Province, College of Civil Engineering, Hunan University, 410082 Changsha, Hunan, China;
(2) Y.W. Wang:
Department of Civil and Structural Engineering, Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China;
(3) Q. Wen:
Hunan Provincial Key Laboratory of Structural Engineering forWind Resistant and Vibration Control, Hunan University of Science and Technology, 411201, Xiangtan, China.

Abstract
Due to the superior properties of nanoparticles, using them has been increased in concrete production technology. In this study, the effect of zinc oxide (ZnO) nanoparticles on the mechanical and smart properties of concrete was studied. At the first, the ZnO nanoparticles are dispersed in water using shaker, magnetic stirrer and ultrasonic devices. The nanoparticles with 3.5, 0.25, 0.75, and 1.0 volume percent are added to the concrete mixture and replaced by the appropriate amount of cement to compare with the control sample without any additives. In order to study the mechanical and smart properties of the concrete, the cubic samples for determining the compressive strength and cylindrical samples for determining tensile strength with different amounts of ZnO nanoparticles are produced and tested. The most important finding of this paper is about the smartness of the concrete due to the piezoelectric properties of the ZnO nanoparticles. In other words, the concrete in this study can produce the voltage when subjected to mechanical load and vice versa it can induce the mechanical displacement when subjected to external voltage. The experimental results show that the best volume percent for ZnO nanoparticles in 28-day samples is 0.5%. In other words, adding 0.5% ZnO nanoparticles to the concrete instead of cement leads to increases of 18.70% and 3.77% in the compressive and tensile strengths, respectively. In addition, it shows the best direct and reverse piezoelectric properties. It is also worth to mention that adding 3.5% zinc oxide nanoparticles, the setting of cement is stopped in the concrete mixture.

Key Words
experimental study; zinc oxide nanoparticles; compressive strength; tensile strength; piezoelectric

Address
(1) Amir Arbabi, Mahmood Rabani Bidgoli:
Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran;
(2) Reza Kolahchi:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam.

Abstract
The authors address the problem of ameliorating or updating existing educational buildings. This building typology is quite sensitive to social and media pressure, mainly when accidents have occurred nearby. When a building is classified as unsatisfactory, the current code requirements oblige one to re-design the building with significant penalty factors in the resistance values. Often the only solution is to destroy the existing facility and to build a new one. When attempting to preserve the existing building, higher levels of safety are demanded by the society and this can only be achieved by innovative system architectures. The authors propose and discuss a prototype that can be easily adopted to retrofit small educational buildings as the ones common in small municipalities. The higher performance is pursued by a special design of the control scheme, with new control devices and special control laws.

Key Words
active control; building amelioration; braking control; educational buildings; structural control paradigm

Address
SIART s.r.l., Via dei Mille, 73, 27100 Pavia PV, Italy.


Abstract
Researchers up to date have introduced several Structural Health Monitoring (SHM) techniques with varying advantages and drawbacks for each. Satellite positioning systems (GPS, GLONASS and GALILEO) based techniques proved to be promising, especially for high natural period structures. Particularly, the GPS has proved sufficient performance and reasonable accuracy in tracking real time dynamic displacements of flexible structures independent of atmospheric conditions, temperature variations and visibility of the monitored object. Tall structures are particularly sensitive to oscillations produced by different sources of dynamic actions; such as typhoons. Wind forces induce in the structure both longitudinal and perpendicular displacements with respect to the wind direction, resulting in torsional effects, which are usually more complex to be detected. To efficiently track the horizontal rotations of the in-plane sections of such flexible structures, two main issues have to be considered: a suitable sensor topology (i.e., location, installation, and combination of sensors), and the methodology used to process the data recorded by sensors. This paper reports the contributions of the measurements recorded from dual frequency GPS receivers and uni-axial accelerometers in a full-scale experimental campaign. The Canton tower in Guangzhou-China is the case study of this research, which is instrumented with a long-term structural health monitoring system deploying both accelerometers and GPS receivers. The elaboration of combining the obtained rather long records provided by these two types of sensors in detecting the torsional behavior of the tower under ambient vibration condition and during strong wind events is discussed in this paper. Results confirmed the reliability of GPS receivers in obtaining the dynamic characteristics of the system, and its ability to capture the torsional response of the tower when used alone or when they are combined with accelerometers integrated data.

Key Words
structural health monitoring; torsional response; typhoons; GPS; accelerometers; long period structure

Address
(1) Raed J. AlSaleh:
Department of Civil and Environmental Engineering – German Jordanian University, Jordan;
(2) Clemente Fuggini:
Research and Innovation – RINA, Italy.

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