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Volume 39, Number 3, May10 2021
 


Abstract
This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.

Key Words
aluminum foam sandwich; fatigue; three-point bending; S-N curve

Address
Chang Yan: Xi'an University of Technology, Xi'an Shaanxi 710048, China
Chuanhe Jing: Fuzhou Boe Optoelectronics Technology Co., Ltd. Fujian, Fuzhou 350000, China
Xuding Song: Key Laboratory of Road Construction Technology & Equipment of Chang

Abstract
In the present paper, a Monte Carlo-based framework is developed to investigate the accuracy and reliability of analytical fragility curves of steel moment-resisting frames and simple SDOF systems. It is also studied how the effectiveness of incremental dynamic analysis (IDA) and multiple stripes analysis (MSA) approaches, as two common nonlinear dynamic analysis methods, are influenced by the number of records and analysis stripes in fragility curves producing. Results showed that the simple SDOF systems do not provide accurate and reliable fragility curves compared with realistic steel moment-resisting structures. It is demonstrated that, the effectiveness of nonlinear dynamic analysis approaches is dependent on the fundamental period of structures, where in short-period structures, IDA is found to be more effective approach compared with MSA. This difference between the effectiveness of two analysis approaches decreases as the fundamental period of structures become longer. Using of 2 or 3 analysis stripes in MSA approach leads to significant inaccuracy and unreliability in the estimated fragility curves. Additionally, 15 number of ground motion records is recommended as a threshold of significant unreliability in estimated fragility curves, constructed by MSA.

Key Words
Monte Carlo simulations; fragility curves; steel moment-resisting frames; SDOF systems; incremental dynamic analysis; multiple stripes analysis; effectiveness; accuracy; reliability

Address
Saman Yaghmaei-Sabegh and Ali Jafari: Department of Civil Engineering, University of Tabriz, Tabriz, Iran
Mahdi Eghbali: Department of Civil Engineering, Faculty of Engineering, University of Zanjan, Zanjan, Iran

Abstract
In a railway bridge, the CRTS II slab ballastless track is subjected to interlayer connection failures, such as void under slab, mortar debonding, and fastener fracture. This study investigates the influences of interlayer connection failure on the safe operation of high-speed trains. First, a train-track-bridge coupled vibration model and a bridge-track deformation model are established to study the running safety of a train passing a deformed bridge with interlayer connection failure. For each type of the interlayer connection failure, the effects of the failure locations and ranges on the track irregularity are studied using the deformation model. Under additional bridge deformation, the effects of interlayer connection failure on the dynamic responses of the train are investigated by using the track irregularity as the excitation to the vibration model. Finally, parametric studies are conducted to determine the thresholds of additional bridge deformations considering interlayer connection failure. Results show that the interlayer connection failure significantly affects the running safety of high-speed train and must be considered in determining the safety thresholds of additional bridge deformation in the asset management of high-speed railway bridges.

Key Words
additional bridge deformation; dynamic response; high-speed railway; interlayer connection failure; mapping relationship; safety threshold

Address
Hongye Gou: Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China;
Key Laboratory of High-Speed Railway Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China
Chang Liu, Rui Xie, Lixiang Zhao and Qianhui Pu: Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Yi Bao: Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA

Abstract
The main purpose of this research work is to investigate the critical buckling load of functionally graded (FG) porous plates with graphene platelets (GPLs) reinforcement using generalized differential quadrature (GDQ) method at thermal condition. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the plate thickness direction. Generally, the thermal distribution is considered to be nonlinear and the temperature changing continuously through the thickness of the nanocomposite plates according to the power-law distribution. To model closed cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme are used, through which mechanical properties of the structures can be extracted. Based on the third order shear deformation theory (TSDT) and the Hamilton's principle, the equations of motion are established and solved for various boundary conditions (B.Cs). The fast rate of convergence and accuracy of the method are investigated through the different solved examples and validity of the present study is evaluated by comparing its numerical results with those available in the literature. A special attention is drawn to the role of GPLs weight fraction, GPLs patterns through the thickness, porosity coefficient and distribution of porosity on critical buckling load. Results reveal that the importance of thermal condition on of the critical load of FGP-GPL reinforced nanocomposite plates.

Key Words
FG porous material; GPL reinforced material; Third order shear deformation theory (TSDT); buckling load; nonlinear thermal distribution; GDQ method; Halpin-Tsai micromechanical modeling

Address
Guohui Wei: R & D department, Beijing Scistar Technology Co., Ltd., Beijing, 100070, China
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
Based on Reissner's mixed variational theorem (RMVT), the authors develop a semi-analytical finite element (FE) method for a three-dimensional (3D) bending analysis of nonhomogeneous orthotropic, complete and incomplete toroidal shells subjected to uniformly-distributed loads. In this formulation, the toroidal shell is divided into several finite annular prisms (FAPs) with quadrilateral cross-sections, where trigonometric functions and serendipity polynomials are used to interpolate the circumferential direction and meridian-radial surface variations in the primary field variables of each individual prism, respectively. The material properties of the toroidal shell are considered to be nonhomogeneous orthotropic over the meridian-radial surface, such that homogeneous isotropic toroidal shells, laminated cross-ply toroidal shells, and single- and bi-directional functionally graded toroidal shells can be included as special cases in this work. Implementation of the current FAP methods shows that their solutions converge rapidly, and the convergent FAP solutions closely agree with the 3D elasticity solutions available in the literature.

Key Words
bending; finite annular prism methods; functionally graded materials; Reissner

Address
Chih-Ping Wu and En Li: Department of Civil Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan, R.O.C.

Abstract
Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

Key Words
fiber reinforced concrete; magnetic water; polypropylene (PP) fibers; workability; compressive strength; flexural strength

Address
Mokhtar Ansari: Department of Civil Engineering, Bozorgmehr University of Qaenat, Qaen, Iran
Amir Safiey: Departmnet of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, CO, USA

Abstract
This study proposes a new and highly-accurate artificial intelligence model, namely ANN-IP, which combines an interior-point (IP) algorithm and artificial neural network (ANN), to improve the axial compression capacity prediction of elliptical concrete-filled steel tubular (CFST) columns. For this purpose, 145 tests of elliptical CFST columns extracted from the literature are used to develop the ANN-IP model. In this regard, axial compression capacity is considered as a function of the column length, the major axis diameter, the minor axis diameter, the thickness of the steel tube, the yield strength of the steel tube, and the compressive strength of concrete. The performance of the ANN-IP model is compared with the ANN-LM model, which uses the robust Levenberg–Marquardt (LM) algorithm to train the ANN model. The comparative results show that the ANN-IP model obtains more magnificent precision (R^2 = 0.983, RMSE = 59.963 kN, a20-index = 0.979) than the ANN-LM model (R^2 = 0.938, RMSE = 116.634 kN, a20-index = 0.890). Finally, a new Graphical User Interface (GUI) tool is developed to use the ANN-IP model for the practical design. In conclusion, this study reveals that the proposed ANN-IP model can properly predict the axial compression capacity of elliptical CFST columns and eliminate the need for conducting costly experiments to some extent.

Key Words
artificial neural network, axial compression capacity, elliptical concrete-filled steel tubular column, interior-point algorithm, graphical user interface

Address
Viet-Linh Tran: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul 05006, South Korea;
Department of Civil Engineering, Vinh University, Vinh 461010, Vietnam
Yun Jang: Department of Computer Engineering, Sejong University 98 Gunja-dong, Gwangjin-gu, Seoul 05006, South Korea
Seung-Eock Kim: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul 05006, South Korea

Abstract
The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

Key Words
steel reinforced concrete; L-shaped column; planar joint; space joint; pseudo-static test; seismic behavior; loading angle; hysteretic performance

Address
Zongping Chen: College of Civil Engineering and Architecture, Guangxi University, 100# east daxue road, Nanning,530004, China;
Key Laboratory of Disaster Prevention and Structure Safety of Chinese Ministry of Education, Guangxi University,
100# east daxue road, Nanning,530004, China
Jinjun Xu: College of Civil Engineering, Nanjing Tech University, No. 30, Puzhu South Road, Nanjing,211800, China
Ni Wang: College of Civil and Environment Engineering, Chang' an University, Middle section of South Second Ring Road, Xi


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