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CONTENTS
Volume 25, Number 4, October 2017
 

Abstract
This work presents a static and free vibration analysis of functionally graded metal–ceramic (FG) beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. A new displacement field containing integrals is proposed which involves only three variables. Based on the suggested theory, the equations of motion are derived from Hamilton\'s principle. This theory involves only three unknown functions and accounts for parabolic distribution of transverse shear stress. In addition, the transverse shear stresses are vanished at the top and bottom surfaces of the beam. The Navier solution technique is adopted to derive analytical solutions for simply supported beams. The accuracy and effectiveness of proposed model are verified by comparison with previous research. A detailed numerical study is carried out to examine the influence of the deflections, stresses and natural frequencies on the bending and free vibration responses of functionally graded beams.

Key Words
bending, Free vibration; Functionally graded materials; integral; Hamilton

Address
Nafissa Zouatnia and Amar Kassou: Department of Civil Engineering, Laboratory of Structures, Geotechnics and Risks (LSGR), Hassiba Benbouali University of Chlef, Algeria, BP 151, Hay Essalam, UHB Chlef, Chlef (02000), Algeria
Lazreg Hadji : Département of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret (14000), Algeria;
Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria


Abstract
The post-flutter state of streamlined steel box girder is studied in this paper. Firstly, the nonlinear aerodynamic self-excited forces of the bridge deck cross section were investigated by CFD dynamic mesh technique and then the nonlinear flutter derivatives were identified on this basis. Secondly, based on the 2-degree-of-freedom (DOF) coupling flutter theory, the torsional amplitude and the nonlinear flutter derivatives were introduced into the traditional direct flutter calculation method, and the original program was improved to the \"post-flutter state analysis program\" so that it can predict not only the critical flutter velocity but also the movement of the girder in the post-flutter state. Finally, wind tunnel tests were set to verify the method proposed in this paper. The results show that the effect of vertical amplitude on the nonlinear flutter derivatives is negligible, but the torsional amplitude is not; with the increase of wind speed, the post-flutter state of streamlined steel box girder includes four stages, namely, \"ittle amplitude zone\", \"step amplitude zone\", \"linearly growing amplitude zone\" and \"divergence zone\"; damping ratio has limited effect on the critical flutter velocity and the steady state response in the post-flutter state; after flutter occurs, the vibration form is a single frequency vibration coupled with torsional and vertical DOF.

Key Words
streamlined steel box girder; post-flutter state; soft flutter; CFD; wind tunnel tests

Address
Junfeng Guo, Shixiong Zheng, Jinbo Zhu and Chengjing Hong:
School of Civil Engineering, Southwest Jiaotong University, Chengdu, China, 610031
Yu Tang: chool of Civil Engineering and Architecture, Southwest Petroleum University, Chengdu, China, 610500


Abstract
In view of the importance of the wind-structure interaction for tall and slender structures, an aeroelastic model test of the 610m-high TV tower with a complex and unique structural configuration and appearance carried out successfully. The assembled aeroelastic model of the TV tower with complex shape and structure was designed and made to ensure the similarities of the major natural frequencies and the corresponding mode shapes. The simulation of the atmospheric boundary layer with higher turbulent intensity is presented. Since the displacement and acceleration responses at several measurement sections were directly measured in the wind tunnel test, a multi-mode approach was presented to indirectly estimate the displacement and acceleration responses at arbitrary structural floors based on the measured ones. It can be seen that it is remarkable for the displacement and acceleration responses of the TV tower in the two horizontal directions under wind loads and is small for the dynamic response of the torsional displacement and acceleration.

Key Words
TV tower; wind tunnel test; aeroelastic model; simulation of atmospheric boundary layer; displacement response; acceleration response

Address
Quanshun Ding and Ledong Zhu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
Department of Bridge Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China


Abstract
Nonlinear vibration and instability of cylindrical shell conveying fluid-nanoparticles mixture flow are studied in this article. The surrounding elastic medium is modeled by Pasternak foundation. Mixture rule is used for obtaining the effective viscosity and density of the fluid-nanoparticles mixture flow. The material properties of the elastic medium and cylindrical shell are assumed temperature-dependent. Employing first order shear deformation theory (FSDT), the motion equations are derived using energy method and Hamilton\'s principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The effects of different parameters such as volume percent of nanoparticles, boundary conditions, geometrical parameters of cylindrical shell, temperature change, elastic foundation and fluid velocity are shown on the frequency and critical fluid velocity of the structure. Results show that with increasing volume percent of nanoparticles in the fluid, the frequency and critical fluid velocity will be increases.

Key Words
cylindrical shell; instability; fluid-nanoparticles mixture flow; temperature-dependent; DQM

Address
Maryam Shokravi: Buein Zahra Technical University, Buein Zahra, Qazvin, Iran
Nader Jalili: Piezoactive Systems Laboratory, Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA

Abstract
When bridges are constructed with lower heights from the ground, the formed channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to \"ground effects.\" So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been performed. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number (St), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability.

Key Words
ground effects; wind tunnel test; closed box girder; aerodynamic force coefficients; St number; VIV; critical flutter wind speeds

Address
Wenhao Mao: State Key Laboratory for Disaster Reduction in Civil Engineering, 1239 Siping Road, Shanghai, China;
Key Laboratory of Ministry of Communications for Bridge Structure Wind resistance, 1239 Siping Road, Shanghai, China
Zhiyong Zhou: State Key Laboratory for Disaster Reduction in Civil Engineering, 1239 Siping Road, Shanghai, China



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