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Volume 23, Number 5, November 2016

The across-wind dynamic loads on L-shaped tall buildings with various geometric dimensions were investigated through a series of wind tunnel testing. The lift coefficients, power spectral densities and vertical correlation coefficients of the across-wind loads were analyzed and discussed in details. Taking the side ratio and terrain category as key variables, empirical formulas for estimating the across-wind dynamic loads on L-shaped tall buildings were proposed on the basis of the wind tunnel testing results. Comparisons between the predictions by the empirical formulas and the wind tunnel test results were made to verify the accuracy and applicability of the proposed formulas. Moreover, a simplified procedure to evaluate the across-wind dynamic loads on L-shaped tall buildings was derived from the proposed formulas. This study aims to provide a simple and reliable way for the estimation of across-wind dynamic loads on L-shaped tall buildings.

Key Words
tall buildings; wind tunnel testing; across-wind load; lift coefficient; power spectral density

Yi Li: School of Civil Engineering, Hunan University of Science and Technology, Xiangtan, 411201, Hunan, China;
College of Civil Engineering, Hunan University, Changsha, 410082, Hunan, China;
Hubei Key Laboratory of Roadway Bridge and Structure Engineering, Wuhan University of Technology, Wuhan, 430070, Hubei, China
Qiu-Sheng Li: Department of Architecture and Civil Engineering, City University of Hong Kong, Kowloon, Hong Kong

Section model wind tunnel test is currently the main technique to investigate the flutter performance of long-span bridges. Further study about applying the wind tunnel test results to the aerodynamic optimization is still needed. Systematical parameters and test principle of the bridge section model are determined by using three long-span steel truss suspension bridges. The flutter critical wind at different attack angles is obtained through section model flutter test. Under the most unfavorable working condition, tests to investigate the effects that upper central stabilized plate, lower central stabilized plate and horizontal stabilized plate have on the flutter performance of the main beam were conducted. According to the test results, the optimal aerodynamic measure was chosen to meet the requirements of the bridge wind resistance in consideration of safety, economy and aesthetics. At last the credibility of the results is confirmed by full bridge aerodynamic elastic model test. That the flutter reduced wind speed of long-span steel truss suspension bridges stays approximately between 4 to 5 is concluded as a reference for the investigation of the flutter performance of future similar steel truss girder suspension bridges.

Key Words
steel truss; suspension bridge; section model; aerodynamic measure; wind tunnel testing

Kai Wang: Research Centre for Wind Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China;
Sichuan Railway Investment Group Company Limited, Chengdu, Sichuan 610041, China
Haili Liao and Mingshui Li: Research Centre for Wind Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China

Wind-induced and earthquake-induced excitations on tall structures can be effectively controlled by Tuned Liquid Damper (TLD). This work presents a numerical simulation procedure to study the performance of tuned liquid tank- structure system through o-transformation based fluid-structure coupled solver. For this, a \'C\' based computational code is developed. Structural equations are coupled with fluid equations in order to achieve the transfer\'of sloshing forces to structure for damping. Structural equations are solved by fourth order Runge-Kutta method while fluid equations are solved using finite difference based sigma transformed algorithm. Code is validated with previously published results. The minimum displacement of structure is observed when the resonance condition of the coupled system is satisfied through proper tuning of TLD. Since real-time excitations are random in nature, the performance study of TLD under random excitation is also carried out in which the Bretschneider spectrum is used to generate the random input wave.

Key Words
tuned liquid damper; liquid sloshing; transformation; random excitation; computational fluid mechanics

M. Eswaran and G.R. Reddy: Structural and Seismic Engineering Section, Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai, 400085, India

Catastrophe models appraise the natural risk of the built-infrastructure simulating the interaction of its exposure and vulnerability with a hazard. Because of unique configurations and reduced number, mid/high-rise buildings present singular challenges to the assessment of their damage vulnerability. This paper presents a novel approach to estimate the vulnerability of mid/high-rise buildings (MHB) which is used in the Florida Public Hurricane Loss Model, a catastrophe model developed for the state of Florida. The MHB vulnerability approach considers the wind pressure hazard exerted over the building\'s height as well as accompanying rain. The approach assesses separately the damages caused by wind, debris impact, and water intrusion on building models discretized into typical apartment units. Hurricane-induced water intrusion is predicted combining the estimates of impinging rain with breach and pre-existing building defect size estimates. Damage is aggregated apartment-by-apartment and story-by-story, and accounts for vertical water propagation. The approach enables the vulnerability modeling of regular and complex building geometries in the Florida exposure and elsewhere.

Key Words
mid/high rise buildings vulnerability; interior damage; impinging rain; cyclone risk

Gonzalo L. Pita: Johns Hopkins University, Baltimore, MD, USA
ean-Paul Pinelli: Florida Institute of Technology, Melbourne, FL, USA
Kurt Gurley: University of Florida, Gainesville, FL, USA
Johann Weekes: Stanley D. Lindsey & Associates, Ltd, Atlanta, GA, USA
Steve Cocke: Florida State University, Tallahassee, FL, USA
Shahid Hamid: Florida International University, Miami, FL, USA

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier–Stokes equations with the typical two-equation model (i.e., the standard k-e model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the k-e model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the k-e model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

Key Words
rectangular bodies; wind direction; aspect ratio; surface pressure distribution; wind-tunnel measurement; k-e model; Computational Fluid Dynamics

Young Tae Lee, Soo Ii Boo and Hee Chang Lim:School of Mechanical Engineering, Pusan National University, San 30, Jangjeon-Dong, Geumjeong-Gu, Busan, 609-735, South Korea
Kunio Misutani: Department of Architecture, Tokyo Polytechnic University, Atsugi, Kanagawa, 243-0297, Japan

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