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CONTENTS
Volume 31, Number 3, May10 2019
 

Abstract
Modular steel buildings consist of prefabricated room-sized structural units that are manufactured offsite and installed onsite. The inter-module connections must fulfill the assembly construction requirements and soundly transfer the external loads. This work proposes an innovative assembled connection suitable for modular buildings with concrete-filled steel tube columns. The connection uses pretensioned strands and plugin bars to vertically connect the adjacent modular columns. The moment-transferring performance of this inter-module connection was studied through monotonic and cyclic loading tests. The results showed that because of the assembly construction, the connected sections were separated under lateral bending, and the prestressed inter-module connection performed as a weak semirigid connection. The moment strength at the early loading stage originated primarily from the contact bonding mechanism with the infilled concrete, and the postyield strength depended mainly on the tensioned strands. The connection displayed a self-centering-like behavior that the induced deformation was reversed during unloading. The energy dissipation originated primarily from frictional slipping of the plugin bars and steel strands. The moment transferring ability was closely related to the section dimension and the arrangements of the plugin bars and steel strands. A simplified strength calculation and evaluation method was also proposed, and the effectiveness was validated with the test data.

Key Words
modular steel building; inter-module connection; pretensioned strand; moment resistance; hysteresis performance

Address
(1) Yujie Yu:
School of Civil Engineering, Central South University, No. 22 Shaoshan South Road, Changsha, Hunan 410075, China;
(2) Zhihua Chen:
Department of Civil Engineering, Tianjin University, No. 92 Weijin Road, Nankai District, Tianjin 300072, China;
(3) Aoyi Chen:
Tianjin Architecture Design Institute, No. 95 Qixiangtai Road, Hexi District, Tianjin 300074, China.

Abstract
Early detection of damage bonding state such as insufficient bonding strength and interface partial contact defect for the explosive clad pipe is crucial in order to avoid sudden failure and even catastrophic accidents. A generalized and efficient model of the explosive clad pipe can reveal the relationship between bonding state and vibration characteristics, and provide foundations and priory knowledge for bonding state detection by signal processing technique. In this paper, the slender explosive clad pipe is regarded as two parallel elastic beams continuously joined by an elastic layer, and the elastic layer is capable to describe the non-uniform bonding state. By taking the characteristic beam modal functions as the admissible functions, the Rayleigh-Ritz method is employed to derive the dynamic model which enables one to consider inhomogeneous system and any boundary conditions. Then, the proposed model is validated by both numerical results and experiment. Parametric studies are carried out to investigate the effects of bonding strength and the length of partial contact defect on the natural frequency and forced response of the explosive clad pipe. A potential method for identifying the bonding quality of the explosive clad pipe is also discussed in this paper.

Key Words
explosive clad pipe; bonding strength; partial contact defect; Rayleigh-Ritz method

Address
(1) School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, P.R. China;
(2) State Key Laboratory for Manufacturing and Systems Engineering, Xi'an Jiaotong University, Xi'an 710049, P.R. China.

Abstract
This study deals with the nonlinear static analysis of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) truncated conical shells subjected to axial load based on the classical shell theory. Detailed studies for both nonlinear buckling and post-buckling behavior of truncated conical shells. The truncated conical shells are reinforced by single-walled carbon nanotubes which alter according to linear functions of the shell thickness. The nonlinear equations are solved by both the Airy stress function and Galerkin method based on the classical shell theory. In numerical results, the influences of various types of distribution and volume fractions of carbon nanotubes, geometrical parameters, elastic foundations on the nonlinear buckling and post-buckling behavior of FG-CNTRC truncated conical shells are presented. The proposed results are validated by comparing with other authors.

Key Words
nonlinear buckling and post-buckling; FG-CNTRC; truncated conical shells; galerkin method

Address
(1) Do Quang Chan:
University of Transport Technology, Hanoi - 54 Trieu Khuc, Thanh Xuan, Hanoi, Vietnam;
(2) Pham Dinh Nguyen, Vu Dinh Quang, Vu Thi Thuy Anh, Nguyen Dinh Duc:
Avanced Materials and Structures Laboratory, University of Engineering and Technology, 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam;
(3) Nguyen Dinh Duc:
Vietnam-Japan University, Luu Huu Phuoc, My Dinh 1, Nam Tu Liem, Ha Noi, Vietnam;
(4) Nguyen Dinh Duc:
National Research Laboratory, Department of Civil and Environmental Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Korea.

Abstract
The study investigates the free vibration of a nano-scale sandwich beam by an extended high order approach, which has not been reported in the existing literature. First-order shear deformation theory for steel skins and so-called high-order sandwich panel theory for the core are applied. Next, the modified couple stress theory is used for both skins and cores. The Hamilton principle is utilized for deriving equations and corresponding boundary conditions. First, in the study the three-mode shapes natural frequencies for various material parameters are investigated. Also, obtained results are evaluated for two types of stiff and soft cores and isotropic, homogenous steel skins. In the research since the governing equations and also the boundary conditions are nonhomogeneous, therefore some closed-form solutions are not applicable. So, to obtain natural frequencies, the boundary conditions are converted to initial conditions called the shooting method as the numerical one. This method is one of the most robust approaches to solve complex equations and boundary conditions. Moreover, three types of simply supported on both sides of the beam (S-S), simply on one side and clamp supported on the other one (S-C) and clamped supported on both sides (C-C) are scrutinized. The parametric study is followed to evaluate the effect of nano-size scale, geometrical configurations for skins, core and material property change for cores as well. Results show that natural frequencies increase by an increase in skins thickness and core Young modulus and a decrease in beam length, core thickness as well. Furthermore, differences between obtained frequencies for soft and stiff cores increase in higher mode shapes; while, the more differences are evaluated for the stiff one.

Key Words
shooting method; modified couple stress theory; free vibration; nano-scale sandwich beam

Address
Faculty of Engineering, Shahrekord University, Shahrekord, Iran.


Abstract
This paper investigates the parametric instability (PI) of multilayered composite conical shells (MLCCSs) under axial load periodically varying the time, using the first order shear deformation theory (FOSDT). The basic equations for the MLCCSs are derived and then the Galerkin method is used to obtain the ordinary differential equation of the motion. The equation of motion converted to the Mathieu-Hill type differential equation, in which the DI is examined employing the Bolotin\'s method. The expressions for left and right limits of dimensionless parametric instability regions (PIRs) of MLCCSs based on the FOSDT are obtained. Finally, the influence of various parameters; lay-up, shear deformations (SDs), aspect ratio, as well as loading factors on the borders of the PIRs are examined.

Key Words
composite structures; dynamic analysis; instability; vibration; axial load

Address
(1) John Lair, David Hui:
Department of Mechanical Engineering, University of New Orleans, New Orleans, Louisiana, USA;
(2) Abdullah H. Sofiyev:
Department of Civil Engineering, Faculty of Engineering, Suleyman Demirel University, Isparta, Turkey;
(3) Viktor Gribniak:
Laboratory of Innovative Building Structures, Vilnius Gediminas Technical University, Vilnius, Lithuania;
(4) Ferruh Turan:
Department of Civil Engineering, Faculty of Engineering, Ondokuz Mayis University, Samsun, Turkey.

Abstract
Pure torsion loading conditions were not frequently occurred in practical engineering, but the torsional researches were important since it's the basis of mechanical property researches under complex loading. Then a 3D finite element model with precise material constitutive models was established, and the effectiveness was verified with test data. Parametric studies with varying factors as steel yield strength, concrete strength and sectional height-width ratio, were performed. Internal stress state and the interaction effect between encased steel tube and the core concrete were analyzed. Results indicated that due to the confinement effect between steel tube and core concrete, the torsional strength of CFT columns was greatly improved comparing to plain concrete columns. The steel ratio would greatly influence the torque share between the steel tube and the core concrete. Then the torsional strength calculation formulas for core concrete and the whole CFT column were proposed. The proposed formula could be simpler and easier to use with guaranteed accuracy. Related design codes were more conservative than the proposed formula, but the proposed formula presented more satisfactory agreement with experimental results.

Key Words
concrete-filled steel tube (CFT); pure torsion; finite element analysis; torsional bearing capacity; section shearing stiffness

Address
(1) Fa-xing Ding, Shi-jing Sheng, Yu-jie Yu, Zhi-wu Yu:
School of Civil Engineering, Central South University, Changsha 410075, P.R. China;
(2) Fa-xing Ding:
Engineering Technology Research Center for Prefabricated Construction
Industrialization of Hunan Province, Changsha 410075, P.R. China.

Abstract
This paper presents a finite element model for predicting the behaviour of high-strength steel bolted beam-tocolumn joints under monotonic loading. The developed numerical model considers the effects of material nonlinearities and geometric nonlinearities. The accuracy of the developed model is examined by comparing the predicted results with independent experimental results. It is demonstrated that the proposed model accurately predicts the ultimate flexural resistances and moment-rotation curves for high-strength steel bolted beam-to-column joints. Mechanical performance of three joint configurations with various design details is examined. A parametric study is carried out to investigate the effects of key design parameters on the behaviour of bolted beam-to-column joints with double-extended endplates. The plastic flexural capacities of the beam-to-column joints from the experimental programme and numerical analysis are compared with the current codes of practice. It is found that the initial stiffness and plastic flexural resistance of the high-strength steel beam-to-column joints are overestimated. Proper modifications need to be conducted to ensure the current analytical method can be safely used for the bolted beam-to-column joints with high-performance materials.

Key Words
high-strength steel; beam-to-column joint; numerical analysis; design codes

Address
School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia.


Abstract
This paper describes an experimental study of steel beam-column connections with or without expanded beam flanges with different geometries. The objectives of this study are to elucidate the cyclic behavior of these connections, identify the location of the plastic hinge zone, and provide useful test data for future numerical simulations. Five connection specimens are designed and tested under cyclic load. The test setup consists of a beam and a column connected together by a connection with or without expanded beam flanges. A constant axial force is applied to the column and a time varying point load is applied to the free end of the beam, inducing shear and moment in the connection. Because the only effect to be studied in the present work is the expanded beam flange, the sizes of the beam and column as well as the magnitude of the axial force in the column are kept constant. However, the length, width and shape of the expanded beam flanges are varied. The responses of these connections in terms of their hysteretic behavior, failure modes, stiffness degradation and strain variations are experimentally obtained and discussed. The test results show that while the influence of the expanded beam flanges on hysteretic behavior, stiffness degradation and energy dissipation capacity of the connection is relatively minor, the size of the expanded beam flanges does affect the location of the plastic hinge zone and strain variations in these beam-column joints. Furthermore, in terms of ductility, moment and rotational capacities, all five connections behave well. No weld fracture or premature failure occurs before the formation of a plastic hinge in the beam.

Key Words
beam-column connections; expanded beam flanges; cyclic tests; hysteretic behavior; plastic hinge

Address
(1) Hongwei Ma, Zeqing Wan, Kun Wang:
College of Civil Science and Engineering, Yangzhou University, Yangzhou, Jiangsu 225127, P.R. China;
(2) Jiwei Wang:
College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu 210098, P.R. China;
(3) Eric M. Lui:
Department of Civil & Environmental Engineering, Syracuse University, Syracuse, NY 13244, USA.


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