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Volume 26, Number 3, September 2020

This research is dedicated to slope stability analysis using novel intelligent models. By coupling a neural network with spotted hyena optimizer (SHO), salp swarm algorithm (SSA), shuffled frog leaping algorithm (SFLA), and league champion optimization algorithm (LCA) metaheuristic algorithms, four predictive ensembles are built for predicting the factor of safety (FOS) of a single-layer cohesive soil slope. The data used to develop the ensembles are provided from a vast finite element analysis. After creating the proposed models, it was observed that the best population size for the SHO, SSA, SFLA, and LCA is 300, 400, 400, and 200, respectively. Evaluation of the results showed that the combination of metaheuristic and neural approaches offers capable tools for estimating the FOS. However, the SSA (error = 0.3532 and correlation = 0.9937), emerged as the most reliable optimizer, followed by LCA (error = 0.5430 and correlation = 0.9843), SFLA (error = 0.8176 and correlation = 0.9645), and SHO (error = 2.0887 and correlation = 0.8614). Due to the high accuracy of the SSA in properly adjusting the computational parameters of the neural network, the corresponding FOS predictive formula is presented to be used as a fast yet accurate substitution for traditional methods.

Key Words
geotechnical engineering; slope stability analysis; neural computing; metaheuristic optimizer

(1) Xinyu Ye:
School of civil engineering, Central South University, Changsha 410075, China;
(2) Hossein Moayedi:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(3) Hossein Moayedi:
Faculty of Civil Engineering, Duy Tan University, Da Nang 550000, Vietnam;
(4) Mahdy Khari:
Department of Civil Engineering, East Tehran Branch, Islamic Azad University, Tehran, Iran;
(5) Loke Kok Foong:
Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(6) Loke Kok Foong:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam.

Disasters, including earthquakes and landslides, have enormous economic and social losses besides their impact on environmental disruption. Iran, and particularly its Western part, is known as an earthquake susceptible area due to numerous strong ground motions. Studying ecological changes due to climate change can improve the public and expert sector's awareness and response to future disastrous events. Synthetic Aperture Radar (SAR) data and Interferometric Synthetic Aperture Radar (InSAR) technologies are appropriate tools for modeling and surface deformation modeling. This paper proposes an efficient approach to detect ground deformation changes using Sentinel-1A. The focal point of this research is to map the ground surface deformation modeling is presented using InSAR technology over Sarpol-e Zahab on 25th November 2018 as a study case. For surface deformation modeling and detection of the ground movement due to earthquake SARPROZ in MATLAB programming language is used and discussed. Results show that there is a general ground movement due to the Sarpol-e Zahab earthquake between -7 millimeter to +18 millimeter in the study area. This research verified previous researches on the advanced image analysis techniques employed for mapping ground movement, where InSAR provides a reliable tool for assisting engineers and the decision-maker in choosing proper policies in a time of disasters. Based on the result, 574 out of 682 damaged buildings and infrastructures due to the 2017 Sarpol-e Zahab earthquake have moved from -2 to +17 mm due to the 2018 earthquake with a magnitude of 6.3 Richter. Results show that mountainous areas have suffered land subsidence, where urban areas had land uplift.

Key Words
sentinel; SAR; InSAR; forest; disaster monitoring; earthquake

(1) Loke Kok Foong:
Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(2) Loke Kok Foong:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(3) Ali Jamali:
Faculty of Surveying Engineering, Apadana Institute of Higher Education, Shiraz, Iran;
(4) Zongjie Lyu:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(5) Zongjie Lyu:
Faculty of Civil Engineering, Duy Tan University, Da Nang 550000, Vietnam.

To study oceanic and meteorological problems related to climate change, Korea has been operating several ocean research stations (ORSs). In 2011, the Gageocho ORS was attacked by Typhoon Muifa, and its structural members and several observation devices were severely damaged. After this event, the Gageocho ORS was rehabilitated with 5 m height to account for 100-yr extreme wave height, and the vibration measurement system was equipped to monitor the structural vibrational characteristics including natural frequencies and modal damping ratios. In this study, a mass reallocation method is presented for structural model updating of the Gageocho ORS based on the experimentally identified natural frequencies. A preliminary finite element (FE) model was constructed based on design drawings, and several of the candidate baseline FE models were manually built, taking into account the different structural conditions such as corroded thickness. Among these candidate baseline FE models, the most reasonable baseline FE model was selected by comparing the differences between the identified and calculated natural frequencies; the most suitable baseline FE model was updated based on the identified modal properties, and by using the pattern search method, which is one of direct search optimization methods. The mass reallocation method is newly proposed as a means to determine the equivalent mass quantities along the height and in a floor. It was found that the natural frequencies calculated based on the updated FE model was very close to the identified natural frequencies. In conclusion, it is expected that these results, which were obtained by updating a baseline FE model, can be useful for establishing the reference database for jacket-type offshore structures, and assessing the structural integrity of the Gageocho ORS.

Key Words
Gageocho Ocean Research Station; jacket-type offshore structure; model updating; mass reallocation method; pattern search

(1) Byungmo Kim, Jin-Hak Yi:
Department of Convergence Study on the Ocean Science and Technology, Ocean Science and Technology School, Korea Maritime and Ocean University, Busan, South Korea;
(2) Jin-Hak Yi:
Coastal Development and Ocean Energy Research Center, Korea Institute of Ocean Science and Technology, Busan, South Korea.

The goal of this study is to analytically and non-stochastically generate structural uncertainty behaviors of isotropic beams and laminated composite plates under plane stress conditions by using an interval finite element method. Uncertainty parameters of structural properties considering resistance and load effect are formulated by interval arithmetic and then linked to the finite element method. Under plane stress state, the isotropic cantilever beam is modeled and the laminated composite plate is crossply lay-up [0/90]. Triangular shape with a clamped-free boundary condition is given as geometry. Through uncertainties of both Young's modulus for resistance and applied forces for load effect, the change of structural maximum deflection and maximum von-Mises stress are analyzed. Numerical applications verify the effective generation of structural behavior uncertainties through the non-stochastic approach using interval arithmetic and immediately the feasibility of the present method.

Key Words
structural uncertainties; laminated composite plate; finite element method; interval arithmetic

(1) Quoc Hoan Doan, Anh Tuan Luu, Dongkyu Lee, Jaehong Lee:
Department of Architectural Engineering, Sejong University, Seoul 05006, Republic of Korea;
(2) Joowon Kang:
Department of Architecture, Yeungnam University, Gyeongsan 38541, Republic of Korea.

Structural damage to an arch dam is often of major concern and must be evaluated for probable rehabilitation to ensure safe, regular, normal operation. This evaluation is crucial to prevent any catastrophic or failure consequences for the life time of the dam. If specific major damage such as a large crack occurs to the dam body, the assessments will be necessary to determine the current level of safety and predict the resistance of the structure to various future loading such as earthquakes, etc. This study investigates the behavior of an arch dam cracked due to water pressure. Safety factors (SFs), of shear and compressive tractions were calculated at the surfaces of the contraction joints and the cracks. The results indicated that for cracking with an extension depth of half the thickness of the dam body, for both cases of penetration and non-penetration of water load into the cracks, SFs only slightly reduces. However, in case of increasing the depth of crack extension into the entire thickness of the dam body, the friction angle of the cracked surface is crucial; however, if it reduces, the normal loading SFs of stresses and joints tractions reduce significantly.

Key Words
arch concrete dams; cracking; safety and performance evaluation; stage construction; Morrow Point dam

(1) Xiangyang Zhang, Weixun Yong, Jian Zhou:
School of Resources and Safety Engineering, Central South University, Changsha, 410083, China;
(2) Xiangyang Zhang, Weixun Yong:
Kunming Prospecting Design Institute Of China Nonferrous Metals Industry Co., Ltd., Kunming, 650051, China;
(3) Vahid Bayat:
Faculty of Civil Engineering, Tarbiat Modares University, Tehran, Iran;
(4) Mohammadreza Koopialipoor:
Faculty of Civil and Environmental Engineering, Amirkabir University of Technology, 15914, Tehran, Iran;
(5) Danial Jahed Armaghani:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam.

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe2O4 and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

Key Words
flexoelectricity; vibration analysis; sandwich plates; modified couple stress theory; electro-magnetic fields

(1) Mohammad Khorasani, Luca Lampani:
Department of Mechanical and Aerospace Engineering, Sapienza University, Via Eudossiana 18, 00184, Rome, Italy;
(2) Arameh Eyvazian, Mohammed Karbon:
Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar;
(3) Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia;
(4) Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(5) Tamer A. Sebaey:
Department of Mechanical Design and Production, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Sharkia, Egypt;
(6) Tamer A. Sebaey:
Department of Engineering Management, College of Engineering, Prince Sultan University, Riyadh, Saudi Arabia.

Modern swarm intelligence heuristic search methods are widely applied in the field of structural health monitoring due to their advantages of excellent global search capacity, loose requirement of initial guess and ease of computational implementation etc. To this end, a hybrid strategy is proposed based on butterfly optimization algorithm (BOA) and differential evolution (DE) with purpose of effective combination of their merits. In the proposed identification strategy, two improvements including mutation and crossover operations of DE, and dynamic adaptive operators are introduced into original BOA to reduce the risk to be trapped in local optimum and increase global search capability. The performance of the proposed algorithm, hybrid butterfly optimization and differential evolution algorithm (HBODEA) is evaluated by two numerical examples of a simply supported beam and a 37-bar truss structure, as well as an experimental test of 8-story shear-type steel frame structure in the laboratory. Compared with BOA and DE, the numerical and experimental results show that the proposed HBODEA is more robust to detect the reduction of stiffness with limited sensors and contaminated measurements. In addition, the effect of search space, two dynamic operators, population size on identification accuracy and efficiency of the proposed identification strategy are further investigated.

Key Words
butterfly optimization algorithm; differential evolution; hybrid algorithm; structural damage detection; parameter identification; dynamic adaptive operator

(1) Hongyuan Zhou, Guangcai Zhang, Xiaojuan Wang, Pinghe Ni:
Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China;
(2) Jian Zhang:
Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China.

Exact solution for nonlinear behavior of clamped-clamped functionally graded (FG) buckled beams is presented. The effective material properties are considered to vary along the thickness direction according to exponential-law form. The in-plane inertia and damping are neglected, and hence the governing equations are reduced to a single nonlinear fourth-order partial-integraldifferential equation. The von Karman geometric nonlinearity has been considered in the formulation. Galerkin procedure is used to obtain a second order nonlinear ordinary equation with quadratic and cubic nonlinear terms. Based on the mode of the corresponding linear problem, which readily satisfy the boundary conditions, the frequencies for the nonlinear problem are obtained using the Jacobi elliptic functions. The effects of various parameters such as the Young's modulus ratio, the beam slenderness ratio, the vibration amplitude and the magnitude of axial load on the nonlinear behavior are examined.

Key Words
buckled beam; exact solution; functionally graded material; nonlinear vibration

(1) Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj 11942, Saudi Arabia;
(2) Ecole Nationale d'Ingenieurs de Tunis (ENIT), Civil Engineering Laboratory. B.P. 37, Le belvedere 1002, Tunis, Tunisia.

Hybrid simulation (HS) is a versatile tool for structural performance evaluation under dynamic loads. Although real structural responses are often multiple-directional owing to an eccentric mass/stiffness of the structure and/or excitations not along structural major axes, few HS in this field takes into account structural responses in multiple directions. Multi-directional loading is more challenging than uni-directional loading as there is a nonlinear transformation between actuator and specimen coordinate systems, increasing the difficulty of suppressing loading error. Moreover, redundant actuators may exist in multi-directional hybrid simulations of large-scale structures, which requires the loading strategy to contain ineffective loading of multiple actuators. To address these issues, lately a new strategy was conceived for accurate reproduction of desired displacements in bi-directional hybrid simulations (BHS), which is characterized in two features, i.e., iterative displacement command updating based on the Jacobian matrix considering nonlinear geometric relationships, and force-based control for compensating ineffective forces of redundant actuators. This paper performs performance validation and application of this new mixed loading strategy. In particular, virtual BHS considering linear and nonlinear specimen models, and the diversity of actuator properties were carried out. A validation test was implemented with a steel frame specimen. A real application of this strategy to BHS on a full-scale 2-story frame specimen was performed. Studies showed that this strategy exhibited excellent tracking performance for the measured displacements of the control point and remarkable compensation for ineffective forces of the redundant actuator. This strategy was demonstrated to be capable of accurately and effectively reproducing the desired displacements in large-scale BHS.

Key Words
bi-directional hybrid simulation; bi-directional pseudo-dynamic test; mixed force-displacement loading; redundant actuator; force distribution optimization

(1) Zhen Wang, Ge Yang, Bin Wu:
School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China;
(2) Zhen Wang, Qiyang Tan, Siyu Zhu, Guoshan Xu, Bin Wu:
School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China;
(3) Pengfei Shi:
China Construction Science & Technology Corporation Limited, Beijing 100195, China;
(4) Pengfei Shi, Jianyun Sun:
China State Construction Engineering Corporation Limited, Technical Center, Beijing 101300, China.

The present article reports the feasibility of the electrical energy generation from ambient low-frequency vibration using a piezoelectric material mounted on a bimorph cantilever beam actuator. A corresponding higher-order analytical model is developed using MATLAB in conjunction with finite element method under low-frequency with both damped and undamped conditions. An alternate model is also developed to check the material and dimensional viability of both piezoelectric materials (mainly focussed to PVDF and PZT) and the base material. Also, Genetic Algorithm is implemented to find the optimum dimensions which can produce the higher values of voltage at low-frequency frequencies (≤ 100 Hz). The delamination constraints are employed to avoid inter-laminar stresses and to increase the fracture toughness. The delamination has been done using a Teflon sheet sandwiched in between base plates and the piezo material is stuck to the base plate using adhesives. The analytical model is tested for both homogenous and isotropic material characteristics of the base material and extended to investigate the effect of the different geometrical parameters (base plate dimensions, piezo layer dimensions and placement, delamination thickness and placement, excitation frequency) on the model responses of the bimorph cantilever beam. It has been observed that when the base material characteristics are homogenous, the efficiency of the model remains higher when compared to the condition when it is of isotropic material. The necessary convergence behaviour of the current numerical model has been established and checked for the accuracy by comparing with available published results. Finally, using the results obtained from the model, a prototype is fabricated for the experimental validation via a suitable circuit considering Glass fibre and Aluminium as the bimorph material.

Key Words
piezoelectric materials; PZT; PVDF; bimorph actuator; glass fibre

(1) Kaushik Mishra:
School of Mechanical Engineering, VIT Vellore, Vellore-632014, Tamil Nadu, India;
(2) Subrata K. Panda, Vikash Kumar, Hukum Chand Dewangan:
Department of Mechanical Engineering, NIT Rourkela, Rourkela-769008, Odisha, Sundergarh, India.

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