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CONTENTS
Volume 14, Number 5, September 2011
 

Abstract
Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

Key Words
wind uplift; rigid roof; flexible roof; dynamic procedure; wind tunnel; design pressure; certification.

Address
Baskaran, A.: National Research Council of Canada, 1200 Montreal Rd., Ottawa, Canada, K1A 0R6
Murty,B. and Tanaka, H.: Department of Civil Engineering, University of Ottawa, Ottawa, Canada, K1N 6N5

Abstract
Without output covariance estimation, one reference-based Stochastic Subspace Technique (SST) for extracting modal parameters and flutter derivatives of bridge deck is developed and programmed. Compared with the covariance-driven SST and the oscillation signals incurred by oncoming or signature turbulence that adopted by previous investigators, the newly-presented identification scheme is less time-consuming in computation and a more desired accuracy should be contributed to high-quality free oscillated signals excited by specific initial displacement. The reliability and identification precision of this technique are confirmed by a numerical example. For the 3-DOF sectional models of Sutong Bridge deck (streamlined) and Suramadu Bridge deck (bluff) in wind tunnel tests, with different wind velocities, the lateral bending, vertical bending, torsional frequencies and damping ratios as well as 18 flutter derivatives are extracted by using SST. The flutter derivatives of two kinds of typical decks are compared with the pseudo-steady theoretical values, and the performance of H1*, H3*, A1*, A3*is very stable and well-matched with each other, respectively. The lateral direct flutter derivatives P5*, P6* are comparatively more accurate than other relevant lateral components. Experimental procedure seems to be more critical than identification technique for refining the estimation precision.

Key Words
bridge; parameter identification; flutter derivative; stochastic subspace technique; wind tunnel test.

Address
F.Y. Xu : School of Civil Engineering, Dalian University of Technology, Dalian 116024, China
A.R. Chen, D.L. Wang and R.J. Ma : Department of Bridge Engineering, Tongji University, Shanghai 200092, China

Abstract
A Computational Fluid Dynamics model is presented in this study for the simulation of the complex fluid flows with free surfaces inside the Tuned Liquid Column Dampers in horizontal motion. The characteristics of the fluid model of the TLCD in horizontal motion include the free surface of the multiphase flow and the horizontal moving frame. In this study, the time depend unsteady Standard k-

Key Words
CFD; TLCD; VOF; sliding mesh.

Address
Cheng-Hsin Chang : Department of Civil Engineering and Wind Engineering Research Center Tamkang University, Tamsui, Taipei County, Taiwan

Abstract
Drag forces on a rectangular louvered panel, both as a free-standing structure and as a component in a generic low-rise building model, were obtained in a wind tunnel study. When tested in a building model, the porosity ratio of the wall opposite the louvered panel was varied to investigate its effect on the loading of the louvered panel. Both mean and pseudo-steady drag coefficients were obtained. Comparisons with the provisions for porous walls in contemporary loading standards indicate that for some opposite wall porosity ratios, the standards specify significantly different wind loads (larger and smaller) than obtained from this wind tunnel study.

Key Words
louver; porosity; wind loading; drag coefficients.

Address
D. Zuo and S. Wayne: Department of Civil and Environmental Engineering Texas Tech University, Lubbock, TX, USA
C.W. Letchford : School of Engineering, University of Tasmania, Hobart, Tasmania, Australia

Abstract
In this paper, a stabilized large eddy simulation technique is developed to predict turbulent flow with high Reynolds number. Streamline Upwind Petrov-Galerkin (SUPG) stabilized method and three-step technique are both implemented for the finite element formulation of Smagorinsky sub-grid scale (SGS) model. Temporal discretization is performed using three-step technique with viscous term treated implicitly. And the pressure is computed from Poisson equation derived from the incompressible condition. Then two numerical examples of turbulent flow with high Reynolds number are discussed. One is lid driven flow at Re = 105 in a triangular cavity, the other is turbulent flow past a square cylinder at Re = 22000. Results show that the present technique can effectively suppress the instabilities of turbulent flow caused by traditional FEM and well predict the unsteady flow even with coarse mesh.

Key Words
large eddy simulation; finite element method; high Reynolds number; Streamline Upwind Petrov-Galerkin; subgrid-scale model.

Address
Cheng Huang, Bao Yan, Dai Zhou and Jinquan Xu: School of Naval Architecture, Ocean and Civil engineering, Shanghai Jiao Tong University, Shanghai 200240, China

Abstract
During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on assessing the behaviour of self supported transmission line towers under downburst loading. A parametric study is performed to determine the critical downburst configurations causing maximum axial forces for various members of a tower. The sensitivity of the internal forces developing in the tower

Key Words
downburst; transmission lines; finite element; self supported transmission towers.

Address
Mohamed M. Darwish : March Consulting Associates Incorporation Saskatoon, Saskatchewan, Canada, S7K 0B8
Ashraf A. El Damatty : Department of Civil and Environmental Engineering, The University of Western Ontario London, Ontario, Canada, N6A 5B9


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