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Mechanical analysis of bi-functionally graded sandwich nanobeams
Luat, Doan Trac,Van Thom, Do,Thanh, Tran Trung,Van Minh, Phung,Van Ke, Tran,Van Vinh, Pham Techno-Press 2021 Advances in nano research Vol.11 No.1
In this study, the bending, free vibration and buckling analysis of a novel bi-functionally graded sandwich nanobeam are investigated for the first time via a nonlocal refined simple shear deformation theory. The novel sandwich beam consists of one ceramic core and two different functionally graded face sheets, which has a significant potential application in various fields of practical engineering and industry. The Eringen's nonlocal elastic theory has been used in cooperation with a refined simple shear deformation theory as well as Hamilton's principle to derive the equations of motion. Closed-form solution based on Navier's technique is used to solve the equations of motion of simply supported nanobeams. The present numerical results are compared with the available solutions to demonstrate the accuracy of the present theory. The influence of some parameters such as the slender ratio, the power-law index, the skin-core-skin thicknesses and the small-scale parameter on the bending, free vibration and buckling behavior of bi-functionally graded sandwich nanobeams are carried out carefully.
Nguyen-Vu Luat,Hongseok Lee,Jiuk Shin,Ji-Hun Park,Tae-Sang Ahn,Kihak Lee 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.4
This paper presents experimental and numerical investigations of a new seismic enhancement method for existing reinforced concrete (RC) frames by using an external sub-structure, the hybrid seismic retrofit method (HSRM) system. This retrofit system is an H-shaped frame bolt-connected to an existing RC frame with an infilled-concrete layer between their gaps. Two RC frames were built, one with and one without HSRM, and tested under cyclic loading. The experimental findings showed that the retrofitted RC frame was superior to the non-retrofitted specimen in terms of initial stiffness, peak load, and energy dissipation capacity. A numerical simulation using a commercial program was employed for verification with the experiments. The results obtained from the simulations were consistent with those from the experiments, indicating the finite element (FE) models can simulate the seismic behaviors of bare RC frame and retrofitted RC frame using HSRM.
Nguyen-Vu Luat,Jiuk Shin,Sang Whan Han,Ngoc-Vinh Nguyen,Kihak Lee 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.3
This study aims to propose a new intelligence technique of predicting the ultimate capacity of axially loaded circular concrete-filled steel tube (CCFST) columns. A hybrid system based on one of the evolution algorithm – Genetic Algorithm (GA), fused with a well-known data-driven model of multivariate adaptive regression splines (MARS), namely G-MARS, was proposed and applied. To construct the MARS model, a database of 504 experimental cases was collected from the available literature. The GA was utilized to determine an optimal set of MARS’ hyperparameters, to improve the prediction accuracy. The compiled database covered five input variables, including the diameter of the circular cross section-section (D), the wall thickness of the steel tube (t), the length of the column (L), the compressive strength of the concrete (fc'), and the yield strength of the steel tube (fy). A new explicit formulation was derived from MARS in further analysis, and its estimation accuracy was validated against a benchmark model, G-ANN, an artificial neural network (ANN) optimized using the same metaheuristic algorithm. The simulation results in terms of error range and statistical indices indicated that the derived formula had a superior capability in predicting the ultimate capacity of CCFST columns, relative to the G-ANN model and the other existing empirical methods.
Numerical Modelling of Bond-slip Behavior between Steel Rebars and Concrete
Nguyen Vu Luat(니옌부루왓),Lee, Kihak(이기학) 한국콘크리트학회 2021 한국콘크리트학회 학술대회 논문집 Vol.33 No.2
This study investigates the bond behavior of rebars in concrete by simulating pull out test in commercial finite element software, LS-DYNA. An 1-D slide line contact model was used for modeling sliding of rebars along the concrete which is capable for investigating bond slip between steel and concrete. The accuracy of this approach was illustrated through the comparison of numerical results and pull out test data.