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CONTENTS
Volume 26, Number 6, June 2018
 

Abstract
A realistic FEM structural model is developed to predict the behavior, load transfer, force distribution and performance of a riverine platform under earthquake and environmental loads. The interaction between the transfer plate and the piles supporting the platform is investigated. Transfer plate structures have the ability to redistribute the loads from the superstructure above to piles group below, to provide safe transits of loads to piles group and thus to the soil, without failure of soil or structural elements. The distribution of piles affects the distribution of stress on both soil and platform. A materially nonlinear earthquake response spectrum analysis was performed on this riverine platform subjected to earthquake and environmental loads. A fixed connection between the piles and the platform is better in the design of the piles and the prospect of piles collapse is low while a hinged connection makes the prospect of damage high because of the larger displacements. A fixed connection between the piles and the platform is the most demanding case in the design of the platform slab (transfer plate) because of the high stress values developed.

Key Words
riverine platform; pile group foundation; soil-pile interaction; earthquake loads; environmental loads; materially nonlinear analysis; response spectrum analysis; FEM

Address
Ahmed Abdelraheem Farghaly : Department of Civil and Architectural Constructions, Faculty of Industrial Education, Sohag University, Sohag 82524, Egypt
Denise-Penelope N. Kontoni: Department of Civil Engineering, Technological Educational Institute of Western Greece, 1 M. Alexandrou Str., Koukouli, GR-26334 Patras, Greece


Abstract
This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D\'Alembert\'s principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it\'s basically consistent about the divergence instability regularities in the flow separation model.

Key Words
membrane structure; orthotropy; geometrical nonlinearity; flow separation; aerodynamic instability; critical velocity of divergence instability

Address
Yun-ping Xu: China Resources Land Limited (Chongqing), Chongqing 400050, P.R. China
Zhou-lian Zheng: College of Civil Engineering, Chongqing Univ., Chongqing 400045, P. R. China; and Chongqing Juanzhu College, Chongqing 400072, P.R. China
Chang-jiang Liu: State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology,Chengdu, 610059, China
Kui Wu and Wei-ju Song: College of Civil Engineering, Chongqing Univ., Chongqing 400045, P.R. China



Abstract
Tornadoes are vertical swirling air formed because of the existence of layers of air with contrasting features of temperature, wind flow, moisture, and density. Tornadoes induce completely different wind forces than a straight-line (SL) wind. A suitably designed building for an SL wind may fail when exposed to a tornado-wind of the same wind speed. It is necessary to design buildings that are more resistant to tornadoes. In tornado-damaged areas, dome buildings seem to have less damage. As a dome structure is naturally wind resistant, domes have been used in back yards, as single family homes, as in-law quarters, man caves, game rooms, storm shelters, etc. However, little attention has been paid to the tornadic wind interactions with dome buildings. In this work, the tornado forces on a dome are computed using Computational Fluid Dynamics (CFD) for tornadic and SL wind. Then, the interaction of a tornado with a dome and a prism building are compared and analyzed. This work describes the results of the tornado wind effect on dome and prism buildings. The conclusions drawn from this study are illustrated in visualizations. The tornado force coefficients on a dome building are larger than SL wind forces, about 120% more in x- and y-directions and 280% more in z-direction. The tornado maximum pressure coefficients are also higher than SL wind by 150%. The tornado force coefficients on the prism are larger than the forces on the dome, about 100% more in x- and y-directions, and about 180% more in z-direction. The tornado maximum pressure coefficients on prism also are greater those on dome by 150% more. Hence, a dome building has less tornadic load than a prism because of its aerodynamic shape.

Key Words
tornado wind; CFD simulation; force and pressure coefficients; dome and prism building

Address
Majdi A.A. Yousef and Panneer R. Selvam: Department of Civil Engineering, University of Arkansas, 4190 Bell Engineering, Fayetteville, AR, 72701, USA
Jai Prakash: Department of Mathematics, University of Botswana, Private Bag UB 0022 Gaborone, Botswana, Southern Africa



Abstract
An accurate determination of wind speed distribution is the basis for an evaluation of the wind energy potential required to design a wind turbine, so it is important to estimate unknown parameters of wind speed distribution. In this paper, Gumbel distribution is used in modelling wind speed data, and alternative robust estimation methods to estimate its parameters are considered. The methodologies used to obtain the estimators of the parameters are least absolute deviation, weighted least absolute deviation, median/MAD and least median of squares. The performances of the estimators are compared with traditional estimation methods (i.e., maximum likelihood and least squares) according to bias, mean square deviation and total mean square deviation criteria using a Monte-Carlo simulation study for the data with and without outliers. The simulation results show that least median of squares and median/MAD estimators are more efficient than others for data with outliers in many cases. However, median/MAD estimator is not consistent for location parameter of Gumbel distribution in all cases. In real data application, it is firstly demonstrated that Gumbel distribution fits the daily mean wind speed data well and is also better one to model the data than Weibull distribution with respect to the root mean square error and coefficient of determination criteria. Next, the wind data modified by outliers is analysed to show the performance of the proposed estimators by using numerical and graphical methods.

Key Words
Gumbel distribution; least absolute deviation; median/MAD estimator; Monte-Carlo simulation; wind speed data

Address
Demet Aydin: Department of Statistics, Faculty of Science and Letters, Sinop University, 57000, Turkey

Abstract
Excitation mechanism of interference effect between two tall buildings is investigated with wind tunnel experiments. Synchronized building surface pressure and flow field measurements by particle image velocimetry (PIV) are conducted to explore the relationship between the disturbed wind flow field and the consequent wind load modification for twin buildings in tandem. This reveals evident excitation mechanisms for the fluctuating across-wind loads on the buildings. For small distance (X/D < 3) between two buildings, the disturbed flow pattern of impaired vortex shedding is observed and the fluctuating across-wind load on the downstream building decreases. For larger distance (X/D> 3), strong correlation between the across-wind load of the downstream building and the oscillation of the wake of the upstream building is found. By further analysis with conditional sampling and phase-averaged techniques, the coherent flow structures in the building gap are clearly observed and the wake oscillation of the upstream building is confirmed to be the reason of the magnified across-wind force on the downstream building. For efficient PIV measurement, the experiments use a square-section high-rise building model with geometry scale smaller than the usual value. Interference factors for all three components of wind loads on the building models being surrounded by another identical building with various configurations are measured and compared with those from previous studies made at large geometry scale. The results support that for interference effect between buildings with sharp corners, the length scale effect plays a minor role provided that the minimum Reynolds number requirement is met.

Key Words
high-rise buildings; wind loads; interference effect; Reynolds number; PIV

Address
G.B. Zu: Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong
K.M. Lam: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology,Clear Water Bay, Hong Kong



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