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CONTENTS
Volume 24, Number 5, May 2017
 

Abstract
The aerodynamic characteristics of vehicles are critical to assess vehicle safety and passenger comfort for vehicles running on long span bridges in a windy environment. However, in previous wind–vehicle–bridge (WVB) system analysis, the aerodynamic interference between the vehicle and the bridge was seldom considered, which will result in changing aerodynamic coefficients. In this study, the aerodynamic coefficients of a high-sided truck on the ground (ground case) and a typical bridge deck (bridge deck case) are determined in a wind tunnel. The effects of existent structures including the bridge deck and bridge accessories on the high-sided vehicle\'s aerodynamic characteristics are investigated. A three-dimensional analytical framework of a fully coupled WVB system is then established based on the finite element method. By inputting the aerodynamic coefficients of both cases into the WVB system separately, the vehicle safety and passenger comfort are assessed, and the critical accidental wind speed for the truck on the bridge in a windy environment is derived. The differences in the bridge response between the windward case and the leeward case are also compared. The results show that the bridge deck and the accessories play a positive role in ensuring vehicle safety and improving passenger comfort, and the influence of aerodynamic interference on the response of the bridge is weak.

Key Words
wind–vehicle–bridge system; aerodynamic interference; vehicle stability; critical wind speed; bridge response

Address
Wanshui Han, Huanju Liu, Jun Wu and Yangguang Yuan: Department of Bridge Engineering, Chang

Abstract
As concrete is most usable material in construction industry it\'s been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. In this study, buckling of horizontal concrete columns reinforced with Zinc Oxide (ZnO) nanoparticles is analyzed. Due to the presence of ZnO nanoparticles which have piezoelectric properties, the structure is subjected to electric field for intelligent control. The Column is located in foundation with vertical springs and shear modulus constants. Sinusoidal shear deformation beam theory (SSDBT) is applied to model the structure mathematically. Micro-electro-mechanic model is utilized for obtaining the equivalent properties of system. Using the nonlinear stress-strain relation, energy method and Hamilton\'s principal, the motion equations are derived. The buckling load of the column is calculated by Difference quadrature method (DQM). The aim of this study is presenting a mathematical model to obtain the buckling load of structure as well as investigating the effect of nanotechnology and electric filed on the buckling behavior of structure. The results indicate that the negative external voltage applied to the structure, increases the stiffness and the buckling load of column. In addition, reinforcing the structure by ZnO nanoparticles, the buckling load of column is increased.

Key Words
buckling of concrete column; ZnO nanoparticles; External voltage; difference quadrature method; foundation

Address
Amir Arbabi, Reza Kolahchi and Mahmood Rabani Bidgoli: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran

Abstract
The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

Key Words
central-slotted plate; aerodynamic interference; flutter derivatives; flutter performance; large angles of attack

Address
Haojun Tang: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China;
CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Hong Kong, China
Yongle Li and Haili Liao: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China
Xinzhong Chen: National Wind Institute, Department of Civil, Environmental and Construction Engineering, Texas Tech University, Lubbock, Texas 79409-1023, USA
K.M. Shum: CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Hong Kong, China




Abstract
Modelling an equilibrium atmospheric boundary layer (ABL) in computational wind engineering (CWE) and relevant areas requires the boundary conditions, the turbulence model and associated constants to be consistent with each other. Among them, the inflow boundary conditions play an important role and determine whether the equations of the turbulence model are satisfied in the whole domain. In this paper, the idea of modeling an equilibrium ABL through specifying proper inflow boundary conditions is extended to the SST k-w model, which is regarded as a better RANS model for simulating the blunt body flow than the standard k-w model. Two new sets of inflow boundary conditions corresponding to different descriptions of the inflow velocity profiles, the logarithmic law and the power law respectively, are then theoretically proposed and numerically verified. A method of determining the undetermined constants and a set of parameter system are then given, which are suitable for the standard wind terrains defined in the wind load code. Finally, the full inflow boundary condition equations considering the scale effect are presented for the purpose of general use.

Key Words
computational fluid dynamics; computational wind engineering; self-sustainable equilibrium atmospheric boundary layer; boundary conditions; SST k-w Model

Address
Yi Yang and Zhuangning Xie: State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, China
Ming Gu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji Univeristiy, Shanghai, 200092, China


Abstract
A novel three-degree-of-freedom (DOF) forced vibration system has been developed for identification of aeroelastic (self-excited) load parameters used in time-domain response analysis of wind-excited flexible structures. This system is capable of forcing sinusoidal motions on a section model of a structure that is used in wind tunnel aeroelastic studies along all three degrees of freedom - along-wind, cross-wind, and torsional - simultaneously or in any combination thereof. It utilizes three linear actuators to force vibrations at a consistent frequency but varying amplitudes between the three. This system was designed to identify all the parameters, namely, aeroelastic- damping and stiffness that appear in self-excited (motion-dependent) load formulation either in time-domain (rational functions) or frequency-domain (flutter derivatives). Relatively large displacements (at low frequencies) can be generated by the system, if required. Results from three experiments, airfoil, streamlined bridge deck and a bluff-shaped bridge deck, are presented to demonstrate the functionality and robustness of the system and its applicability to multiple cross-section types. The system will allow routine identification of aeroelastic parameters through wind tunnel tests that can be used to predict response of flexible structures in extreme and transient wind conditions.

Key Words
flutter; parameter identification; time-domain, wind tunnel tests, forced vibration system

Address
Heather Scot Sauder: CPP Wind Engineering, Fort Collins, CO 80525, USA;
Department of Aerospace Engineering, Iowa State University, Ames, IA 50011, USA
Partha P. Sarkar: Department of Aerospace Engineering, Iowa State University, Ames, IA 50011, USA


Abstract
In this work, wind tunnel tests of pressure measurements are carried out to assess the global aerodynamic interference factors, the local wind pressure interference factors, and the local lift spectra of an square high-rise building interfered by an identical cross-sections but lower height building arranged in various relative positions. The results show that, when the interfering building is located in an area of oblique upstream, the RMS of the along-wind, across-wind, and torsional aerodynamic forces on the test building increase significantly, and when it is located to a side, the mean across-wind and torsional aerodynamic forces increase; In addition, when the interfering building is located upstream or staggered upstream, the mean wind pressures on the sheltered windward side turn form positive to negative and with a maximum absolute value of up to 1.75 times, and the fluctuating wind pressures on the sheltered windward side and leading edge of the side increase significantly with decreasing spacing ratio (up to a maximum of 3.5 times). When it is located to a side, the mean and fluctuating wind pressures on the leading edge of inner side are significantly increased. The three-dimensional flow around a slightly-shorter disturbing building has a great effect on the average and fluctuating wind pressures on the windward or cross-wind faces. When the disturbing building is near to the test building, the vortex shedding peak in the lift spectra decreases and there are no obvious signs of periodicity, however, the energies of the high frequency components undergo an obvious increase.

Key Words
tall buildings; wind tunnel pressure measurements; global aerodynamics interference factor; local wind pressure interference factor; local lift spectra

Address
Huang Dongmei and He Xuhui: School of Civil Engineering, Central South University, Changsha 410075, China;
High-speed Railway Construction Technology National Engineering Laboratory, Changsha 410075, China
Zhu Xue, He Shiqing and He Hua: School of Civil Engineering, Central South University, Changsha 410075, China



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