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CONTENTS
Volume 30, Number 2, February 2020
 

Abstract
A butterfly web girder is a box-shaped girder with discretely distributed side openings along the spanwise direction. Until now, there have been few studies related to the aerodynamic performance of the butterfly web bridge. The objective of the current study was to clarify the effects of the side openings on the aerodynamic performance of the girder. Two butterfly web girders with side ratios B/D = 3.24 and 5, where B is the girder width and D is the depth, were examined through a series of wind tunnel tests. A comparison of the results for butterfly web girders and conventional box girders of the same shape confirmed that the side openings stabilized the vortex-induced vibration and galloping when B/D = 3.24, whereas the vortex-induced vibration and torsional flutter were stabilized when B/D = 5. The change in the flow field due to the side openings contributed to the stabilization against the vibration. These findings not only confirmed the good aerodynamic performance of the butterfly web bridge but also provided a new method to stabilize the box girder against aerodynamic instabilities via discretely distributed side openings.

Key Words
butterfly web bridge; galloping; torsional flutter; vortex-induced vibration; Kármán vortex

Address
Jiaqi Wang: Dept. of Civil and Earth Resources Engineering, Kyoto Univ., Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Tomomi Yagi:Dept. of Civil and Earth Resources Engineering, Kyoto Univ., Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Jun Ushioda:Dept. of Civil and Earth Resources Engineering, Kyoto Univ., Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Kyohei Noguchi:Dept. of Civil and Earth Resources Engineering, Kyoto Univ., Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Naoki Nagamoto:Structural Engineering Service Dept., Sumitomo Mitsui Construction co., ltd., Tsukuda, Chuou-ku, Tokyo 104-0051, Japan
Hiroyuki Uchibori:Structural Engineering Service Dept., Sumitomo Mitsui Construction co., ltd., Tsukuda, Chuou-ku, Tokyo 104-0051, Japan

Abstract
In this paper, critical fluid velocity and frequency of laminated pipe conveying fluid are presented. Each layer of the pipe is reinforced by functionally graded carbon nanotubes (FG-CNTs). The internal fluid is assumed turbulent and the induced forces are calculated by momentum equations. The pipe is resting on viscoelastic foundation with spring, shear and damping constants. The motion equations are derived based on classical shell theory and energy method. Differential quadrature method (DQM) is used for solution and obtaining the critical fluid velocity. The effects of volume percent and distribution of CNT, boundary condition, lamina layer number, length to radius ration of pipe, viscoelastic medium and fluid velocity are shown on the critical fluid velocity. Results show that with increasing the lamina layer number, the critical fluid velocity increases.

Key Words
critical fluid velocity; laminated pipeline; nanocomposite; turbulent internal fluid; viscoelastic foundation

Address
M.M. Ghaitani, A. Majidian:Department of Mechanical Engineering, Sari Branch, Islamic Azad University, Sari, Iran, P.O.B. 4816119318, Sari, Iran
V. Shokri: Department of Mechanical Engineering, Sari Branch, Islamic Azad University, Sari, Iran, P.O.B. 4816119318, Sari, Iran

Abstract
Probabilistic information regarding directional extreme wind speeds is important for the precise estimation of the design wind loads on structures. A joint probability distribution model of directional extreme typhoon wind speeds is established using Monte Carlo simulation and empirical copula function to fully consider the correlations of extreme typhoon wind speeds among the different directions. With this model, a procedure for estimating directional extreme wind speeds for given return periods, which ensures that the overall risk is distributed uniformly by direction, is established. Taking 5 typhoon-prone cities in China as examples, the directional extreme typhoon wind speeds for given return periods estimated by the present method are compared with those estimated by the method proposed by Cook and Miller (1999). Two types of directional factors are obtained based on Cook and Miller (1999) and the UK standard

Key Words
directional extreme wind speeds of typhoons; empirical copula function; directional assessment; Monte Carlo simulation

Address
Jingcheng Wang: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Yong Quan:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Ming Gu:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Previous research has shown that wind acceleration components produce a signal that can vibrate single-degree of-freedom oscillators, whose dynamic responses enable to configure design spectra for structures subject to wind. These wind design spectra present an alternative method for evaluating the dynamic response of structures and are a suitable tool for running modal analyses. Here, a generalised method for producing wind design spectra is proposed. The method consists of scaling existing spectra to adjust to a wider range of building properties and terrain conditions. The modelling technique is tested on a benchmark building to prove that its results are consistent with experimental evidence reported in the past.

Key Words
wind design spectra; wind loading; wind aerodynamics; performance-based design

Address
School of Engineering, University of Birmingham, B15 2TT, United Kingdom

Abstract
To determine tornadic wind loads, the wind pressure, forces and moments induced by tornadoes on civil structures have been studied. However, in most previous studies, only the individual building of interest was included in the wind field, which may be suitable to simulate the case where a tornado strikes rural areas. The statistical data has indicated that tornadoes induce more significant fatalities and property loss when they attack densely populated areas. To simulate this case, all buildings in the community of interest should be included in the wind field. However, this has been rarely studied. To bridge this research gap, this study will systematically investigate the influence of a community of buildings on tornadic wind fields by modeling all buildings in the community into the wind field (designated as \"the Community case under straight-line winds\") are also simulated. The results demonstrate that the presence of a number of buildings completely destroys the pattern of regular circular strips in the distribution of tangential velocity and pressure on horizontal planes. Above the roof height, the maximum tangential velocity is lower in the Community case under tornadic winds than that in the Single-building case under tornadic winds because of the higher surface friction in the Community case; below the roof height, greater tangential velocity and pressure are observed in the Community case under tornadic wind fields, and more unfavorable conditions are observed in the Community case under tornadic winds than under the equivalent straight-line winds.

Key Words
translating tornadic wind fields; computational fluid dynamics; gable-roofed buildings; straight-line wind

Address
Zhi Li:Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, 1401 Pine St, Rolla, MO 65409
Ryan Honerkamp:Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, 1401 Pine St, Rolla, MO 65409
Guirong Yan:Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, 1401 Pine St, Rolla, MO 65409
Ruoqiang Feng: Structural Engineering Service Dept., Sumitomo Mitsui Construction co., ltd., Tsukuda, Chuou-ku, Tokyo 104-0051, Japan

Abstract
In the traditional buffeting response analysis method, the spanwise incomplete correlation of buffeting forces is always assumed to be same as that of the incident wind turbulence and the action of the signature turbulence is ignored. In this paper, three typical bridge decks usually adopted in the real bridge engineering, a single flat box deck, a central slotted box deck and a two-separated paralleled box deck, were employed as the investigated objects. The wind induced pressure on these bridge decks were measured via a series of wind tunnel pressure tests of the sectional models. The influences of the wind speed in the tests, the angle of attack, the turbulence intensity and the characteristic distance were taken into account and discussed. The spanwise root coherence of buffeting forces was also compared with that of the incidence turbulence. The signature turbulence effect on the spanwise root coherence function was decomposed and explained by a new empirical method with a double-variable model. Finally, the formula of a sum of rational fractions that accounted for the signature turbulence effect was proposed in order to fit the results of the spanwise root coherence function. The results show that, the spanwise root coherence of the drag force agrees with that of incidence turbulence in some range of the reduced frequency but disagree in the mostly reduced frequency. The spanwise root coherence of the lift force and the torsional moment is much larger than that of the incidence turbulence. The influences of the wind speed and the angle of attack are slight, and they can be ignored in the wind tunnel test. The spanwise coherence function often involves several narrow peaks due to the signature turbulence effect in the high reduced frequency zone. The spanwise coherence function is related to the spanwise separation distance and the spanwise integral length scales, and the signature turbulence effect is related to the deck-width-related reduced frequency.

Key Words
buffeting force; root coherence function; empirical model; signature turbulence; incident wind turbulence

Address
Qi Zhou:Guangdong Engineering Center for Structure Safety and Health Monitoring, Shantou University No.243 Daxue Road, Shantou, Guangdong Province, China
Ledong Zhu:State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, No.1239 Siping Road, Shanghai, China
Chuangliang Zhao:State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, No.1239 Siping Road, Shanghai, China
Pengjie Ren:State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, No.1239 Siping Road, Shanghai, China


Abstract
Building wind pressure coefficient transiting test is a new method to test the building wind pressure coefficient by using the wind generated by a moving vehicle, which is susceptible to natural wind and other factors. In this paper, the Commonwealth Advisory Aeronautical Research Council standard model with a scale ratio of 1:300 is used as the test object, and the wind pressure coefficient transiting test is repeated under different natural wind conditions to study the influence of natural wind. Natural wind is measured by an ultrasonic anemometer at a fixed location. All building wind pressure coefficient transiting tests meet the test conditions, and the vehicle\'s driving speed is 72 km/h. The mean wind pressure coefficient, the fluctuating wind pressure coefficient, and the correlation coefficient of wind pressure are used to describe the influence of natural wind on the building wind pressure coefficient transiting test qualitatively and quantitatively. Some rules, which can also help subsequent transiting tests, are also summarized.

Key Words
transiting test method; moving vehicle; natural wind; CAARC; wind pressure coefficient; ultrasonic anemometer; Reynolds number effect

Address
Lulu Liu:School of Civil Engineering, Zhengzhou University, Zhengzhou, China/ Zhengzhou Key Laboratory of Disaster Prevention and Control for Cable Structure, China
Shengli Li: School of Civil Engineering, Zhengzhou University, Zhengzhou, China/ Zhengzhou Key Laboratory of Disaster Prevention and Control for Cable Structure, China
Pan Guo:School of Civil Engineering, Zhengzhou University, Zhengzhou, China/ Zhengzhou Key Laboratory of Disaster Prevention and Control for Cable Structure, China
Xidong Wang:School of Civil Engineering, Zhengzhou University, Zhengzhou, China/ Zhengzhou Key Laboratory of Disaster Prevention and Control for Cable Structure, China


Abstract
Vibrations of a wind turbine blade have a negative impact on its performance and result in failure of the blade, therefore an approach to effectively control vibration in turbine blades are sought by wind industry. The small domestic horizontal axis wind turbine blades induce flap wise (out-of-plane) vibration, due to varying wind speeds. These flap wise vibrations are transferred to the structure, which even causes catastrophic failure of the system. Shape memory alloys which possess physical property of variable stiffness across different phases are embedded into the composite blades for active vibration control. Previously Shape memory alloys have been used as actuators to change their angles and orientations in fighter jet blades but not used for active vibration control for wind turbine blades. In this work a GFRP blade embedded with Shape Memory Alloy (SMA) and tested for its vibrational and material damping characteristics, under martensitic and austenite conditions. The embedment portrays 47% reduction in displacement of blade, with respect to the conventional blade. An analytical model for the actuated smart blade is also proposed, which validates the harmonic response of the smart blade.

Key Words
wind turbine blade; smart blade; Ni-Ti alloy; actuation; Shape Memory Alloy (SMA)

Address
Yuvaraja Mani, Jagadeesh Veeraragu, Sangameshwar S. and Rudramoorthy Rangaswamy: Department of Mechanical Engineering, PSG college of Technology, Peelamedu, Coimbatore, Tamilnadu-641004, India


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