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CONTENTS
Volume 21, Number 3, September 2015
 

Abstract
In this paper, a free vibration analysis of functionally graded beam made of porous material is presented. The material properties are supposed to vary along the thickness direction of the beam according to the rule of mixture, which is modified to approximate the material properties with the porosity phases. For this purpose, a new displacement field based on refined shear deformation theory is implemented. The theory accounts for parabolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Based on the present refined shear deformation beam theory, the equations of motion are derived from Hamilton\'s principle. The rule of mixture is modified to describe and approximate material properties of the FG beams with porosity phases. The accuracy of the present solutions is verified by comparing the obtained results with the existing solutions. Illustrative examples are given also to show the effects of varying gradients, porosity volume fraction, aspect ratios, and thickness to length ratios on the free vibration of the FG beams.

Key Words
functionally graded beam; shear deformation theory; porosity; vibration

Address
L. Hadji:Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algérie;
Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie
E.A. Adda Bedia: Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie


Abstract
Vertical profiles of mean and fluctuating wind velocities over water waves were studied, by performing Large-Eddy Simulations (LES) on a fully developed turbulent boundary layer over simplified water waves. The water waves were simplified to two-dimensional, periodic and non-evolving. Different wave steepness defined by a/y (a: wave amplitude; y : wavelength) and wave age defined by c/U (c: phase velocity of the wave; U: bulk velocity of the air) were considered, in order to elaborate the characteristics of mean and fluctuating wind profiles. Results shows that, compared to a static wave, a moving wave plays a lesser aerodynamic role as roughness as it moves downstream slower or a little faster than air, and plays more aerodynamic roles when it moves downstream much faster than air or moves in the opposite direction to air. The changes of gradient height, power law index, roughness length and friction velocity with wave age and wave amplitude are presented, which shed light on the wind characteristics over real sea surfaces for wind engineering applications.

Key Words
large-eddy simulation; wave age; wave amplitude; wind profiles

Address
Shuyang Cao and Jinxin Cao:State Key Lab for Disaster Reduction in Civil Engineering, Tongji University, Siping Road 1239, Shanghai, China
Enzhen Zhang: School of Civil Engineering, Tongji University, Siping Road 1239, Shanghai, China
Liming Sun: Tongji Architectural Design (Group) Co. Ltd, Siping Road 1230, Shanghai, China



Abstract
A method for analyzing the coupled wind-vehicle-bridge system is proposed that also considers the shielding effect of the bridge tower with triangular wind barriers. The static wind load and the buffeting wind load for both the bridge and the vehicle are included. The shielding effects of the bridge tower and the triangular wind barriers are incorporated by taking the surface integral of the wind load. The inter-history iteration is adopted to solve the vehicle-bridge dynamic equations with time-varying external loads. The results show that after installing the triangular wind barriers in the area of the bridge tower, the bridge response and the vehicle safety factors change slightly. The peak value of the train car body acceleration is significantly reduced when the wind barrier size is increased.

Key Words
suspension bridge; vehicle-bridge interaction; wind load; wind barrier

Address
Nan Zhang:School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
Beijing Key Laboratory of Structure Wind Engineering and Urban Wind Environment, Beijing 100044, China
Guanghui Ge and He Xia:School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China
Xiaozhen Li:School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China


Abstract
A series of wind tunnel tests were conducted on tapered super high-rise buildings with a square cross section by applying synchronous pressure measurement technology. The effects of global strategy of chamfered modification on aerodynamic loads and wind-induced responses were investigated. Moreover, local aerodynamic strategies of opening a ventilation slot in the corner of equipment and refuge floors were carried out. Results show that the global strategy of tapered elevation increased the vortex shedding frequency, but reduced vortex shedding energy, leading to reduction of across-wind aerodynamic loads and responses. Chamfered modification suppressed the across-wind vortex shedding effect on tapered buildings. Opening the ventilation slot further suppressed the strength of vortex shedding and reduced the residual energy related to vortex shedding in aerodynamic loads of chamfered buildings. Finally, the optimized locations of local aerodynamic strategies were suggested.

Key Words
A series of wind tunnel tests were conducted on tapered super high-rise buildings with a square cross section by applying synchronous pressure measurement technology. The effects of global strategy of chamfered modification on aerodynamic loads and wind-induced responses were investigated. Moreover, local aerodynamic strategies of opening a ventilation slot in the corner of equipment and refuge floors were carried out. Results show that the global strategy of tapered elevation increased the vortex shedding frequency, but reduced vortex shedding energy, leading to reduction of across-wind aerodynamic loads and responses. Chamfered modification suppressed the across-wind vortex shedding effect on tapered buildings. Opening the ventilation slot further suppressed the strength of vortex shedding and reduced the residual energy related to vortex shedding in aerodynamic loads of chamfered buildings. Finally, the optimized locations of local aerodynamic strategies were suggested.

Address
Ting Deng, Xianfeng Yu and Zhuangning Xie: School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, China

Abstract
As concrete wind-turbine towers are increasingly being used in wind-farm construction, there is a growing need to understand the behavior of concrete wind-turbine towers. In particular, experimental evaluations of concrete wind-turbine towers are necessary to demonstrate the dynamic characteristics and load-carrying capacity of such towers. This paper describes a model test of a prestressed concrete wind-turbine tower that examines the dynamic characteristics and load-carrying performance of the tower. Additionally, a numerical model is presented and used to verify the design approach. The test results indicate that the first natural frequency of the prestressed concrete wind turbine tower is 0.395 Hz which lies between frequencies 1P and 3P (0.25–0.51 Hz). The damper ratio is 3.3%. The maximum concrete compression stresses are less than the concrete design compression strength, the maximum tensile stresses are less than zero and the prestressed strand stresses are less than the design strength under both the serviceability and ultimate limit state loads. The maximum displacement of the tower top are 331 mm and 648 mm for the serviceability limit state and ultimate limit state, respectively, which is less than L/100 = 1000 mm. Compared with traditional tall wind-turbine steel towers, the prestressed concrete tower has better material damping properties, potential lower maintenance cost, and lower construction costs. Thus, the prestressed concrete wind-turbine tower could be an innovative engineering solution for multi-megawatt wind turbine towers, in particular those that are taller than 100 m.

Key Words
prestressed concrete wind turbine tower; model test; numerical simulation; dynamic characteristics; steel wind turbine tower

Address
Hongwang Ma, Dongdong Zhang, Ze Ma and Qi Ma: Department of Civil Engineering, Shanghai Jiaotong University, Shanghai, 200240, China


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