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CONTENTS
Volume 27, Number 3, March 2021
 


Abstract
This article presents the damage evaluation and pattern recognition for the newly proposed fiber reinforced polymer (FRP)/steel-confined reinforced concrete columns. The interaction of FRP material, steel tube, and reinforced concrete lead to complex damage mechanisms and invisible damage modes. The prevailing acoustic emission (AE) technique was applied to monitor the damage process and detect the sheltered damages under cyclic loading. Characteristic AE parameters, such as energy and duration, were extracted to disclose the damage evolution and evaluate the damage state. Three typical damage stages were identified. The fuzzy C.means (FCM) algorithm and particle swarm optimization (PSO) algorithm were applied as efficient clustering tools to discriminate different damage signals of FRP/steel-confined RC columns. Five types of damage mechanisms were identified and illustrated based on the statistical analysis of typical AE features. Furthermore, typical damage waveforms were extracted, the frequency content of each damage signal was discussed on the basis of wavelet transform.

Key Words
FRP/steel-confined RC column; acoustic emission; pattern recognition; cluster analysis; wavelet analysis

Address
(1) Fangzhu Du, Dapeng Qiu:
School of Civil Engineering, Shandong Jianzhu University, Jinan, Shandong 250101, China;
(2) Dongsheng Li:
School of Civil Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China.

Abstract
This paper evaluates the limit load, shakedown limit and ratchet limit of the oblique nozzle based on the linear matching method (LMM). In order to study the influencing factors of the limit load, shakedown limit and ratchet limit of the oblique nozzle, oblique nozzle models with different dip angles, diameter-to-thickness ratios of the oblique nozzle and diameterto- thickness ratios of the main pipe are established, respectively. Firstly, the limit load, shakedown limit and ratchet limit of the oblique nozzle are studied. At the same time, the influence of the loading mode on the shakedown limit and ratchet limit is also studied. Secondly, oblique nozzles with different defect lengths, widths and depths are established, respectively. The influence of loading paths on shakedown limit and ratchet limit of oblique nozzles with defects are also studied. Finally, shakedown limit and ratchet limit diagrams are obtained based on linear matching method. The correctness of shakedown limit and ratchet limit diagrams is validated by ABAQUS incremental elastic-plastic analysis.

Key Words
oblique nozzle; LMM; limit load; shakedown limit; ratchet limit

Address
(1) Xiaohui Chen, Kunmin Zhuang:
School of Control Engineering, Northeastern University, Qinhuangdao, 066004, China;
(2) Xiaohui Chen:
School of Mechanical Engineering & Automation, Yanshan University, Qinhuangdao, 066004, China;
(3) Kunmin Zhuang:
School of Aerospace Engineering, Xiamen University, Xiamen, 361005, China;
(4) Xuanchen Zhu, Haofeng Chen:
Department of Mechanical & Aerospace Engineering, University of Strathclyde, G1 1XJ, UK.

Abstract
The purpose of the paper is to investigate the expectations of smart mentality and citizen participation in technology-driven cities. 150 mainstream trend reports, white papers, and research summaries are analyzed in one corpus as business, governmental, and university research cooperations. The changing trends of the related academic literature frame the study. Keyword statistics, word pairs, content networks, and correlation matrix reveal the expected citizen participation. The most referenced top ten cities and their strategies support the understanding of the smart mentality behind the participation. According to the findings, open data, communities, collective participation, socio-technical engagement, and empowerment are the most expected human factors. Anonymity, neighborhood-based implementations, and temporary human roles are underrepresented in the corpus, as well as the privacy concerns and ethical issues. However, the emerging AI technology and the interpretative metaphors with rainforest, team player, and public agora urge a focus also on these indicators with a contribution of citizen engagement. The paper provides governmental policymaking and the academic research of technology-driven cities with a citizen-centric and complex summary.

Key Words
smart citizen; smart city; technology-driven cities; intelligent environments; civic participation; community; smartmentality; open data; empowerment; privacy; ethics; interpretative metaphors

Address
Budapest Business School University of Applied Sciences, Budapest, Hungary.


Abstract
Earthquakes cause severe damages to bridge structures, and rocking isolation of piers has become a superior option for the seismic protection of bridges during earthquakes. A seismic isolation method with free rocking mode is proposed for railway bridge piers with medium height. Experimental and numerical analysis are conducted to evaluate the seismic performance of the rocking-isolated bridge pier. Shaking table test is carried out with a scaled model by using three strong input earthquake records. The measured data includes displacement, acceleration and time history response of the pier-top and the bending moment of the pier-bottom. Test results show that the expected uplift and rocking of the isolated pier occur under strong earthquakes and the rocking-isolated pier has self-centering capacity. Slight damage appears at the collision surface between pier and base due to pier uplift, while there is no damage in the pier body. The bending moment of pier-bottom is less affected by the spectrum of input ground motions. The two-spring model is provided to simulate the isolated pier with free rocking mode under earthquakes. A seismic response analysis model for the rocking-ioslated pier is established with the assistance of OpenSees platform. The simulated results agree well with the measured results by shaking table test. Therefore, the seismic isolation method with a self-centering pier is worthy of promotion for railway bridges in high seismic risk regions.

Key Words
seismic isolation; railway bridges; free rocking mode; self-centering pier; shaking table test and numerical simulation

Address
School of Civil Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China.


Abstract
Third-party interference caused by construction activities have seriously jeopardized the security of underground pipelines. Following the process of "signal collection—feature extraction and selection—multi-time scale identifying— combining results by voting", this paper proposes a multi-time scale surveillance system for interference prevention of thirdparty threats on the nearby pipeline by using ground vibration monitors. The system focuses on the two major urban construction activities induced by excavator breaking hammers and road cutters, and presents excellent performance under the noise of traffic and pedestrian. Three features including the short-time zero-crossing rate, subset differential parameter and the Mel frequency cepstrum coefficients are selected by the analysis of the maximal information coefficient and feature importance for identifying the patterns of different third-party activities. The crucial part of the surveillance system consists of the two random forest-based classifiers trained by 0.5 s samples and 8 s samples respectively, and the alarm depends on the voting of the two classifiers, which brings the perspectives on different time scales for decision making. In the test, 96.14% of the threat vibration signals can be detected, while only 0.45% of the environmental noise signals cause false alarms.

Key Words
underground pipeline; third-party interference; multi-time scale; ground vibration monitoring; vibration signal feature; feature selection; random forest

Address
(1) Zelong Liu, Renzhu Peng, Yan Zhang, Suzhen Li:
College of Civil Engineering, Tongji Univeristy, Siping 1239, Shanghai, China;
(2) Suzhen Li:
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji Univeristy, Siping 1239, Shanghai, China.

Abstract
To improve seismic behavior of structures, a two-level control system is proposed in this paper where by combining two vertical shear panels in series in a chevron bracing configuration, Double-Vertical Shear Panel, D-VSP is introduced. Utilizing two-levels of energy absorption for two different earthquake intensity levels, D-VSP is expected to beneficially change dynamic behavior parameters like strength, stiffness and damping ratio through increasing ductility. To validate research, a VSP is modeled in ABAQUS and related numerical results are compared to those of a previous experimental work. Pushover, quasistatic cyclic and seismic analyses are conducted on two models. The hysteresis curves show symmetric two-level behavior with stable strength and stiffness leading to increase ductility ratio up to 29.4%. Maximum displacement and maximum base shear under seismic loading decrease 5.91 and 11.18% respectively under moderate earthquakes when D-VSP system uses only first fuse, saving second fuse for severe earthquakes. However, in a strong earthquake, both of the shear panels absorb seismic energy and can control vibration better than conventional systems with one level control mechanism. The proposed system using a weaker panel can better control an extensive range of earthquakes as well as the earthquake with foreshocks.

Key Words
Chevron bracing; cyclic behavior; energy dissipation; vertical shear link; two-level control system; seismic response

Address
(1) Mohsen Zare Golmoghany, Seyed Mehdi Zahrai:
School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran;
(2) Seyed Mehdi Zahrai:
Department of Civil Engineering, University of Ottawa, Canada.

Abstract
Experimental and discrete element methods were used to investigate the effects of distance between two preexisting cracks, bridge area (The length of the bridge area) and its angularities on the shear behaviour of bridge area. A punchthrough shear test was used to model the gypsum (concrete like) cracks under shear loading. Gypsum samples (concrete like) with dimension of 120 mm × 120 mm × 50 mm were prepared in the laboratory. Within the specimen model and near its four corners, four vertical notches were provided. Three different configuration systems were prepared for notches; i.e., paralell and in plane, inside echelon and outside echelon configuration systems, respectively. In these configurations, the length of cracks were taken as 2 cm, 4 cm and 6 cm based on the cracks configuration systems. Then, 9 specimens with different lengths of the bridge area and bridge area angles were prepared. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm × 100 mm. similar to those for cracks configuration systems in the experimental tests i.e., 9 models with different lengths of the bridge area and bridge area angularities were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the lengths of the bridge area and bridge area angularities. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the lengths of the bridge area. The strength of samples decreases by increasing the crack length. Also, the outside echelon crack configuration system has the maximum value of strength while the inside echelon crack configuration system has the minimum value of specimen's tensile strength. The failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

Key Words
punch-through shear test; lengths of the bridge area; bridge area inclinations; PFC2D

Address
(1) Alireza Bagher Shemirani:
Faculty of Civil, Water & Environmental Engineering, Shahid Beheshti University, Tehran, Iran;
(2) M.S. Amini, K. Shahriar, P. Moarefvand:
Department of Mining and metallurgical engineering, Amirkabir university, Tehran, Iran;
(3) V. Sarfarazi:
Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran;
(4) Hadi Haeri:
State Key Laboratory for Deep GeoMechanics and Underground Engineering, Beijing, 100083, China.

Abstract
Since the complex continuous wavelet transform (CCWT) based pile damage detection method is empirical and subjective, an improved algorithm for pile damage localization based on CCWT is proposed by introducing K-means clustering and fast Fourier transform (FFT). In this method, the K-means clustering algorithm is used to accurately calculate the time coordinates of two energy concentrating points caused by the incident and reflected waves, respectively. Meanwhile, FFT is employed to estimate the concerned frequency band of the response signal. Therefore, a specific region in the time frequency plane is defined objectively and it can be used to search the phase angle turning points and localize pile damage. The proposed method is verified by numerical examples of piles with single and multiple damage positions. A parameter analysis is also conducted to investigate how damage depth and damage degree in piles affect the accuracy and effectiveness of the proposed method. The results demonstrate that the proposed method is able to localize a pile with a damage at least 2.5 m away from the pile head when the damage degree is as less as 5%. After that, dynamic tests of an actual square reinforced concrete pile and an actual circular reinforced concrete pile are investigated to verify the application of the proposed method on practical engineering. Although the proposed method is capable of localizing actual piles more accurately than the CCWT method, the problem of interference points needs to be addressed by mutual verification with other pile damage localization methods.

Key Words
complex continuous wavelet transform; K-means clustering algorithm; fast Fourier transform; phase angle; damage localization

Address
(1) Jing-Liang Liu, Cheng-Xu Lin, Yong-Peng Luo:
College of Transportation and Civil Engineering, Fujian Agriculture and Forestry University, Fuzhou 350002, China;
(2) Xi-Jun Ye:
School of Civil Engineering, Guangzhou University, Guangzhou 510006, China;
(3) Wen-Ting Zheng:
College of Civil Engineering, Fujian University of Technology, Fuzhou 350118, China.

Abstract
In this paper, a crack identification using Artificial Neural Network (ANN) is investigated to predict the crack depth in pipeline structure based on modal analysis technique using Finite Element Method (FEM). In various fields, ANN has become one of the most effective instruments using computational intelligence techniques to solve complex problems. This paper uses Particle Swarm Optimization (PSO) to enhance ANN training parameters (bias and weight) by minimizing the difference between actual and desired outputs and then using these parameters to generate the network. The convergence study during the process proves the advantage of using PSO based on two selected parameters. The data are collected from FEM based on different crack depths and locations. The provided technique is validated after collecting the data from experimental modal analysis. To study the effectiveness of ANN-PSO, different hidden layers values are considered to study the sensitivity of the predicted crack depth. The results demonstrate that ANN combined with PSO (ANN-PSO) is accurate and requires a lower computational time in terms of crack identification based on inverse problem.

Key Words
FEM dynamic analysis; experimental modal analysis; crack prediction; ANN; PSO

Address
(1) Meriem Seguini, Djamel Nedjar:
Laboratory of Mechanic of Structures and Stability of Constructions LM2SC, Faculty of Architecture and Civil Engineering, Laboratory of Applied Mechanics, University of Sciences and Technology of Oran Mohamed Boudiaf, Bp 1505 Elmenouar Oran, Algeria;
(2) Samir Khatir:
Faculty of Civil Engineering, Ho Chi Minh City Open University, Ho Chi Minh City, Viet Nam;
(3) Djilali Boutchicha:
LMA, Mechanical Engineering Department, USTO-MB, BP 1055 El Menaour, Oran 31000, Algeria;
(4) Magd Abdel Wahab:
Institute of Research and Development, Duy Tan University, 03 Quang Trung, Da Nang 550000, Viet Nam;
(5) Magd Abdel Wahab:
Soete Laboratory, Faculty of Engineering and Architecture, Ghent University, Technologiepark Zwijnaarde 903, B-9052, Zwijnaarde, Belgium.

Abstract
To isolate vibration at a low-frequency range and at the same time to provide sufficient loading support to the isolated structure impose a challenge in vibration isolation. Quasi-zero stiffness (QZS) vibration isolator, as a potential solution to the challenge, has been widely investigated due to its unique property of high-static & low-dynamic stiffness. This paper provides an in-depth analysis and potential optimization of a typical QZS vibration isolator to illustrate the complexity and importance of design optimization. By carefully examining the governing fundamentals of the QZS vibration isolator, a simplified approximation of force and stiffness relationship is derived to enable the characteristic analysis of the QZS vibration isolator. The explicit formulae of the amplitude-frequency response (AFR) and transmissibility of the QZS vibration isolator are obtained by employing the Harmonic Balance Method. The transmissibility curves under force excitation with different values of nonlinear coefficient, damping ratio, and amplitude of excitation are further investigated. As the result, an optimization of the structural parameter has been demonstrated using a comprehensive objective function with considering multiple dynamic characteristic parameters simultaneously. Finally, the genetic algorithm (GA) is adopted to minimise the objective function to obtain the optimal stiffness ratios under different conditions. General recommendations are provided and discussed in the end.

Key Words
quasi-zero stiffness; vibration isolation; dynamic characteristics optimization; genetic algorithm

Address
(1) Huan Li, Yang Yu, Jianchun Li, Yancheng Li:
School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo 2007, Australia;
(2) Jianchun Li:
Tianjin Key Laboratory of Civil Structure Protection and Reinforcement, Tianjin Chengjian University, Tianjin, 300384, China;
(3) Yancheng Li:
College of Civil Engineering, Nanjing Tech University, Nanjing 211800, China.

Abstract
The development of image sensors enables the application of vision-based techniques to the non-contact displacement measurement of large-scale structures. The features of the physical targets are critical to the accuracy, stability and anti-interference of the displacement measurement results. In this study, a novel m-sequence target and the associated circular correlation processing technique are developed for real-time displacement measurement. The properties of the m-sequence as a pseudo-random sequence are introduced. The vision-based displacement calculation method is then derived from the correlation property of the m-sequence. The algorithms and measurement systems are integrated in the LabVIEW environment. To verify the anti-interference performance of the developed system, static and dynamic experimental tests are carried out with various forms of interference, such as partial occlusion, uneven illumination, out of focus and smoke effect. Experimental results indicate that the developed system cannot only accurately measure structural displacement, but also has outstanding antiinterference performance, even if 30% of the target is masked.

Key Words
computer vision; m-sequence; displacement measurement; target tracking; structural health monitoring

Address
(1) Yi-ding Hu, Jian-yi Yan:
Faculty of Intelligent Manufacturing, Wuyi University, Jiangmen 529020, China;
(2) Qi Xia:
School of Civil Engineering, Southeast University, Nanjing, China;
(3) Rong-rong Hou, Yong Xia:
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China.

Abstract
The low-cycle fatigue performance of shear panel damper (SPD) highly depends on the geometry of its shape and the criterion considered for its design. The main contribution of the current study is to find the optimum shape of the SPD subjected to cyclic loading by considering two different objective functions. The maximum equivalent plastic strain and the ratio of energy dissipation through plastic deformation to the maximum equivalent plastic strain are selected as the first and second objective functions, respectively. Since the optimization procedure requires high computational efforts, a hybrid computational approach is used to perform two paramount phases of estimating the inelastic responses of the SPD and solving the optimization problem. In the first phase, as an alternative for the time-consuming finite element analysis of the SPD, a weighted-support vector machine model is developed to predict the inelastic responses of the SPDs during the optimization process. In the second phase, the optimum shape of the SPD is found by using the whale optimization algorithm (WOA). The results indicate that both design criteria lead to the optimum-shaped SPDs with a significant improvement in their low cycle fatigue performance in comparing with the initial rectangular shape while a slight reduction in their energy dissipation capacity. Moreover, the second design criterion is slightly better in the performance improvement of the optimum-shaped SPDs compared with the first one. In addition, the weighted-based SVM approach can accurately predict the inelastic responses of the SPDs under cyclic loading, and its combination with WOA results in finding the optimum solutions quickly.

Key Words
shear panel damper; energy dissipation; shape optimization; support vector machine; whale optimization algorithm

Address
(1) Mohsen Khatibinia, Aghdas Ahrari, Seyyed Reza Sarafrazi:
Department of Civil Engineering, University of Birjand, Birjand, Iran;
(2) Sadjad Gharehbaghi:
Department of Civil Engineering, Sharif University of Technology, Tehran, Iran.


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