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CONTENTS
Volume 81, Number 6, March25 2022
 


Abstract
The safety problems of giant hydraulic structures such as dams caused by terrorist attacks, earthquakes, and wars often have an important impact on a country's economy and people's livelihood. For the national defense department, timely and effective assessment of damage to or impending damage to dams and other structures is an important issue related to the safety of people's lives and property. In the field of damage assessment and vulnerability analysis, it is usually necessary to give the damage assessment results within a few minutes to determine the physical damage (crack length, crater size, etc.) and functional damage (decreased power generation capacity, dam stability descent, etc.), so that other defense and security departments can take corresponding measures to control potential other hazards. Although traditional numerical calculation methods can accurately calculate the crack length and crater size under certain combat conditions, it usually takes a long time and is not suitable for rapid damage assessment. In order to solve similar problems, this article combines simulation calculation methods with machine learning technology interdisciplinary. First, the common concrete gravity dam shape was selected as the simulation calculation object, and XFEM (Extended Finite Element Method) was used to simulate and calculate 19 cracks with different initial positions. Then, an LSTM (Long-Short Term Memory) machine learning model was established. 15 crack paths were selected as the training set and others were set for test. At last, the LSTM model was trained by the training set, and the prediction results on the crack path were compared with the test set. The results show that this method can be used to predict the crack propagation path rapidly and accurately. In general, this article explores the application of machine learning related technologies in the field of mechanics. It has broad application prospects in the fields of damage assessment and vulnerability analysis.

Key Words
crack growth of gravity dam; curve similarity; damage assessment; LSTM; machine learning; XFEM

Address
Kefan Zhang, Fangyun Lu, Yong Peng and Xiangyu Li: College of Liberal Art and Science, National University of Defense Technology, 410073 Changsha, P.R. China

Abstract
Generally, the goal of seismic retrofit design of an existing structure using energy dissipation devices is to determine the optimum design parameters of a retrofit device to satisfy a specified limit state with minimum cost. However, the presence of multiple parameters to be optimized and the computational complexity of performing non-linear analysis make it difficult to find the optimal design parameters in the realistic 3D structure. In this study, genetic algorithm-based optimal seismic retrofit methods for determining the required number, yield strength, and location of steel slit dampers are proposed to retrofit an asymmetric soft first-story structure. These methods use a multi-objective and single-objective evolutionary algorithms, each of which varies in computational complexity and incorporates nonlinear time-history analysis to determine seismic performance. Pareto-optimal solutions of the multi-objective optimization are found using a non-dominated sorting genetic algorithm (NSGAII). It is demonstrated that the developed multi-objective optimization methods can determine the optimum number, yield strength, and location of dampers that satisfy the given limit state of a three-dimensional asymmetric soft first-story structure. It is also shown that the single-objective distribution method based on minimizing plan-wise stiffness eccentricity turns out to produce similar number of dampers in optimum locations without time consuming nonlinear dynamic analysis.

Key Words
genetic algorithm optimization; multi objective optimization; seismic retrofit; slit dampers; soft first-story

Address
Assefa Jonathan Dereje and Jinkoo Kim: Department of Global Smart City, Sungkyunkwan University, Suwon, Republic of Korea

Abstract
To obtain the seismic response of lead-cored rubber, shape memory alloy (SMA)-rubber isolation Plate-shell Integrated Concrete Liquid-Storage Structure (PSICLSS), based on a PSICLSS in a water treatment plant, built a scale experimental model, and a shaking table test was conducted. Discussed the seismic responses of rubber isolation, SMA-rubber isolation PSICLSS. Combined with numerical model analysis, the vibration characteristics of rubber isolation PSICLSS are studied. The results showed that the acceleration, liquid sloshing height, hydrodynamic pressure of rubber and SMA-rubber isolation PSICLSS are amplified when the frequency of seismic excitation is close to the main frequency of the isolation PSICLSS. The earthquake causes a significant leakage of liquid, at the same time, the external liquid sloshing height is significantly higher than internal liquid sloshing height. Numerical analysis showed that the low-frequency acceleration excitation causes a more significant dynamic response of PSICLSS. The sinusoidal excitation with first-order sloshing frequency of internal liquid causes a more significant sloshing height of the internal liquid, but has little effect on the structural principal stresses. The sinusoidal excitation with first-order sloshing frequency of external liquid causes the most enormous structural principal stress, and a more significant external liquid sloshing height. In particular, the principal stress of PSICLSSS with long isolation period will be significantly enlarged. Therefore, the stiffness of the isolation layer should be properly adjusted in the design of rubber and SMA-rubber isolation PSICLSS.

Key Words
concrete; liquid storage structure; rubber isolation; shaking table test; shape memory alloy; vibration characteristic

Address
Xuansheng Cheng, Lei Qi, Shanglong Zhang: Western Engineering Research Center of Disaster Mitigation in Civil Engineering of the Ministry of Education, Lanzhou University of Technology, Lanzhou 730050, China
Yiting Mu, Lingyu Xia: Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province, Lanzhou University of Technology, Lanzhou 730050, China

Abstract
The aim of this paper is to investigate nonlinear dynamic responses of functionally graded composite beam resting on the nonlinear viscoelastic foundation subjected to moving mass with temperature rising. The non-linear strain-displacement relationship is considered in the finite strain theory and the governing nonlinear dynamic equation is obtained by using the Hamilton's principle. The Galerkin's decomposition technique is utilized to discretize the governing nonlinear partial differential equation to nonlinear ordinary differential equation and then the governing equation is solved by using of multiple time scale method. The influences of temperature rising, material distribution parameter, nonlinear viscoelastic foundation parameters, magnitude and velocity of the moving mass on the nonlinear dynamic responses are investigated. Also, the buckling temperatures of the functionally graded beams based on the finite strain theory are obtained.

Key Words
functionally graded material; moving mass; nonlinear foundation; nonlinear vibration; temperature effect

Address
M. Alimoradzadeh and S.D. Akbas: Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran

Abstract
A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

Key Words
buckling-restrained brace; component test; design recommendation; longitudinally profiled steel core; lowcycle fatigue

Address
Junkai Lu: School of Civil Engineering, Northeast Forestry University, Harbin 150040, China
Yong Ding: Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin, 150090, China; Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology,
Harbin Institute of Technology, Harbin, 150090, China; School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China
Bin Wu: School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China
Yingying Li: Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin, 150090, China; Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology,
Harbin Institute of Technology, Harbin, 150090, China; School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China
Jiaxin Zhang: Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin, 150090, China; Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology,
Harbin Institute of Technology, Harbin, 150090, China; School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

Abstract
Earth is facing a serious problem of pollution and scarcity of energy sources. The synthetic fibers used in automobile and Aerospace manufacturing sectors are non-renewable and harmful to environment. International Agency such as FAA and SAE is forcing for green fuel, green materials and structures. Further exploration is much needed to understand its potential in structural applications. In the current study, hemp and Jute fibre based composites were developed and tested for assessing their suitability for possible applications in automobile and aerospace sectors. Composites were undergone tensile test, water absorption test, and fatigue analysis to understand its behavior under various loading conditions. The finite element analysis has been carried out to understand the fatigue behaviour of composites. The results revealed that the usage of hemp and jute fibre reinforced composites can improve mechanical properties and have shown a viable alternative to replace synthetic fibres such as glass fibres for specific applications. Hemp reinforced bio-composites have shown better performance as compared to Jute reinforced bio-composites while water resistance characteristics for hemp is poorer to jute fibres.

Key Words
composites; fatigue analysis; hemp; Jute; moisture absorption; natural fibres

Address
B. Ravi Kumar and S.S. Hariharan: School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, Tamilnadu 613402, India

Abstract
Timber-Concrete Composite construction system consists of combining timber beam or deck and concrete with different connectors. Different fastener types are used in Timber-Concrete Composite systems. In this paper, the effects of two types of fasteners on structural behavior are compared. First, the notches were opened on timber beam, and combined with reinforced concrete slab by fasteners. This system is called as Notched Connection System. Then, timber beam and reinforced concrete slab were combined by new type designed fasteners in another model. This system is called as Notched-Slab Approach. Two laboratory models were constructed and bending tests were performed to examine the fasteners' effectiveness. Bending test results have shown that heavy damage to concrete slab occurs in Notched Connection System applications and the system becomes unusable. However, in Notched-Slab Approach applications, the damage concentrated on the fastener in the metal notch created in the slab, and no damage occurred in the concrete slab. In addition, non-destructive experimental measurements were conducted to determine the dynamic characteristics. To validate the experimental results, initial finite element models of both systems were constituted in ANSYS software using orthotropic material properties, and numerical dynamic characteristics were calculated. Finite element models of Timber-Concrete Composite systems are updated to minimize the differences by manual model updating procedure using some uncertain parameters such as material properties and boundary conditions.

Key Words
dynamic characteristics; finite element model; non-destructive experimental measurements; notched-slab approach; notched connection; timber-concrete composite

Address
Semih Yilmaz: Department of Architecture, Karadeniz Technical University, 61080, Trabzon, Turkey
Olguhan Sevket Karahasan: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Ahmet Can Altunisik: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Nilhan Vural: Department of Architecture, Karadeniz Technical University, 61080, Trabzon, Turkey
Serhat Demir: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey

Abstract
Abstract. In the hogging bending moment area, continuous composite beams are subjected to the ultimate limit state of lateral-torsional buckling (LTB), which depends on web stiffness as well as concrete slab and shear connection stiffnesses. The design of the LTB and the determination of the elastic critical moment are produced approximately, using the European Standard EN 1994-1-1:2004, for continuous composite steel beams, but is applicable only for those with a plane web steel profile. Also, and from the previous researches, the elastic critical moment of the continuous composite beams with corrugated sinusoidal web steel profiles was determined. In this paper, a finite element analysis (FEA) model was developed using the ANSYS 16 software, to determine the elastic critical moments of continuous composite steel beams with various corrugated web profiles, such as trapezoidal, zigzag, and rectangular profiles, which were evaluated against numerical data of the sinusoidal one from the literature. Ultimately, the failure load of a composite steel beam with various web profiles was predicted by studying 46 models, based on FEA modeling, and a procedure for predicting the elastic critical moment of composite beams with various web steel profiles was proposed. When compared to sinusoidal web profiles, the trapezoidal, zigzag, and rectangular web profiles required an average increase in load capacity and stiffness of 7%, 17.5%, and 28%, respectively, according to the finite element analysis. Also, the rectangular web steel profile has a greater stiffness and load capacity. In contrast, the sinusoidal web has lower values for these characteristics.

Key Words
Ansys 16; continuous composite beams; corrugated steel webs profiles; elastic critical moment; lateraltorsional buckling

Address
Yousry B.I. Shaheen: Civil Engineering Department, Faculty of Engineering, Menoufia University, Menoufia, Egypt
Ashraf M. Mahmoud: Civil Engineering Department, Faculty of Engineering, Modern University for Technology and Information (MTI), Al-Mokattam, Cairo, Egypt

Abstract
This paper studies the dynamic behavior of laminated composite circular cylindrical shells interacting with a fluid. The mathematical formulation of the dynamic problem for an elastic body is developed based on the variational principle of virtual displacements and the relations of linear elasticity theory. The behavior of an ideal compressible fluid is described by the potential theory, the equations of which together with boundary conditions are transformed to a weak form. The hydrodynamic pressure exerted by the fluid on the internal surface of the shell is calculated according to the linearized Bernoulli equation. The numerical implementation of the mathematical formulation has been done using the semi-analytical finite element method. The influence of the ply angle and lay-up configurations of laminated composites on the natural vibration frequencies and the hydroelastic stability boundary have been analyzed for shells with different geometrical dimensions and under different kinematic boundary conditions set at their edges. It has been found that the optimal value of the ply angle depends on the level of filling of the shell with a fluid. The obtained results support the view that by choosing the optimal configuration of the layered composite material it is possible to change upwards or downwards the frequency and mode shape, as well as the critical velocity for stability loss over a wide range.

Key Words
cylindrical shell; elasticity theory; FEM; layered composite material; natural vibrations; potential fluid; stability

Address
Sergey A. Bochkarev and Sergey V. Lekomtsev: Institute of Continuous Media Mechanics, Ural Branch Russian Academy of Sciences, 1, Acad. Korolev Street, Perm, 614068, Russian Federation

Abstract
The present paper describes a general procedure of the structural safety assessment for the independent type C tank of LNG bunkering ship. This strength assessment procedure consists of two main scheme, global Finite Element Analysis (FEA) model primarily for hull structure assessment and detailed LNG Tank structures FEA model including the cylindrical tank itself and saddle-support structures. Two kinds of mechanism are used, fixed and slides constraints in fore and rear of the saddlesupport structures that result in a variation of the reaction forces. Finite Element (FE) analyses have been performed and verified by the strength acceptance criteria to evaluate the safety adequacy of yielding and buckling of the hull and supporting structures. The detail of FE model for an LNG type C tank and its saddle supports was made, which includes the structural members such as cylindrical tank shell, ring stiffeners, swash bulkhead, and saddle supports. Subsequently, the FE buckling analysis of the Type C tank has been performed under external pressure following International Gas Containment (IGC) code requirements. Meanwhile, the assessment is also performed for yielding and buckling strength evaluation of the cylindrical LNG tank according to the PD 5500 unfired fusion welded pressure vessels code. Finally, a complete procedure for assessing the structural strength of 500 CBM LNG cargo tank, saddle support and hull structures have been provided.

Key Words
FE analysis; LNG bunkering ship; LNG type C tank; structural assessment review

Address
Teguh Muttaqie: Research Center for Hydrodynamics Technology, National Research and Innovation Agency, BRIN, Jakarta, Indonesia
DongHo Jung: Department of Offshore Platform Research Division, Korea Research Institute of Ships and Ocean Engineering (KRISO), Daejeon, Republic of Korea
Sang-Rai Cho: Ulsan Lab., Inc., Ulsan, Republic of Korea
Jung Min Sohn: Department of Naval Architecture and Marine Systems Engineering, Pukyong National University, Busan, Republic of Korea; Department of Marine Design Convergence Engineering, Pukyong National University, Busan, Republic of Korea


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