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CONTENTS
Volume 27, Number 3, September 2018
 

Abstract
A reliability analysis method is proposed in this paper based on the maximum entropy (MaxEnt) principle in which constraints are specified in terms of the fractional moments instead of integer moments. Then a multiplicative dimensional reduction method (M-DRM) is introduced to compute the fractional moments. The method is applicable for both explicit and implicit limit state functions of complex structures. After two examples illustrate the accuracy and efficiency of this method in comparison to the Monte Carlo simulation (MCS), the method is used to analyze the flutter reliability of suspension bridge. The results show that the empirical formula method in which the limit state function is explicitly represented as a function of variables is only a too conservative estimate for flutter reliability analysis but is not accurate adequately. So it is not suitable for reliability analysis of bridge flutter. The actual flutter reliability analysis should be conducted based on a finite element method in which limit state function is implicitly represented as a function of variables. The proposed M-DRM provide an alternate and efficient way to analyze a much more complicated flutter reliability of long span suspension bridge.

Key Words
reliability analysis; failure probability; flutter; multiplicative dimensional reduction method (M-DRM); principle of maximum entropy

Address
Junfeng Guo, Shixiong Zheng, Jin Zhang and Jinbo Zhu: School of Civil Engineering, Southwest Jiaotong University, Chengdu, China, 610031
Longqi Zhang: Department of road and bridge engineering, Sichuan Vocational and Technical College of Communications,
Chengdu, China, 611130


Abstract
The design wind pressure for low-rise buildings in the ASCE 7-10 is defined by procedures that are categorized into the Main Wind Force-Resisting System (MWFRS) and the Components and Cladding (C&C). Some of these procedures were originally developed based on steel portal frames of industrial buildings, while the residential structures are a completely different structural system, most of which are designed as low-rise light-frame wood constructions. The purpose of this study is to discuss the rationality (or irrationality) of the extension of the wind loads calculated by the ASCE 7-10 to the light-frame wood residential buildings that represent the most vulnerable structures under extreme wind conditions. To serve this purpose, the same approach as used in the development of Chapter 28 of the ASCE 7-10 that envelops peak responses is adopted in the present study. Database-assisted design (DAD) methodology is used by applying the dynamic wind loads from Louisiana State University (LSU) database on a typical residential building model to assess the applicability of the standard by comparing the induced responses. Rather than the postulated critical member demands on the industrial building such as the bending moments at the knee, the maximum values at the critical points for wood frame buildings under wind loads are used as indicators for the comparison. Then, the critical members are identified through these indicators in terms of the displacement or the uplift force at connections and roof envelope. As a result, some situations for each of the ASCE 7 procedures yielding unconservative wind loads on the typical low-rise residential building are identified.

Key Words
aerodynamics; buildings; low-rise; databases; structural designs; wind forces; wind tunnels; ASCE; standards and codes

Address
Jing He and C.S. Cai:Department of Civil and Env. Eng., Louisiana State University, Baton Rouge, LA 70803, USA
Fang Pan: Southwest Research Institute, San Antonio, TX 78228, USA

Abstract
With the continuous increase of span lengths, modern bridges are becoming much more flexible and more prone to flutter under wind excitations. A reasonable probabilistic flutter analysis of long-span bridges involving random and uncertain variables may have to be taken into consideration. This paper presents a method for estimating the reliability index and failure probability due to flutter, which considers the very important variables including the extreme wind velocity at bridge site, damping ratio, mathematical modeling, and flutter derivatives. The Aizhai Bridge in China is selected as an example to demonstrate the numerical procedure for the flutter reliability analysis. In the presented method, the joint probability density function of wind speed and wind direction at the deck level of the bridge is first established. Then, based on the fundamental theories of structural reliability, the reliability index and failure probability due to flutter of the Aizhai Bridge is investigated by applying the Monte Carlo method and the first order reliability method (FORM). The probabilistic flutter analysis can provide a guideline in the design of long-span bridges and the results show that the structural damping and flutter derivatives have significant effects on the flutter reliability, more accurate and reliable data of which is needed.

Key Words
flutter reliability; critical flutter velocity; long-span suspension bridges; flutter derivatives; Monte Carlo method; first order reliability method

Address
Shuqian Liu and C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, USA, LA 70803
Yan Han and Chunguang Li: School of Civil Engineering, Changsha University of Science & Technology, Changsha, China, 410004

Abstract
In this study, aerodynamic characteristics of a horizontal axis wind turbine (HAWT) were evaluated and discussed in terms of measured data in existing onshore wind farm. Five wind turbines (T1, T2, T3, T4 and T5) were selected, and hub-height wind speed, UD, wind turbine power output, P and turbine rotational speed,

Key Words
aerodynamic problem; structural dynamic analysis; wind energy; wind loads; wind velocity; wind-structure interaction

Address
Akin Ilhan and Besir Sahin: Department of Mechanical Engineering, Faculty of Engineering, Cukurova University, 01330 Adana, Turkey
Mehmet Bilgili: Department of Mechanical Engineering, Faculty of Ceyhan Engineering, Cukurova University, 01950 Adana, Turkey

Abstract
This paper deals with wind fragility and risk analysis of high rise buildings subjected to stochastic wind load. Conventionally, such problems are dealt in full Monte Carlo Simulation framework, which requires extensive computational time. Thus, to make the procedure computationally efficient, application of metamodelling technique in fragility analysis is explored in the present study. Since, accuracy by the conventional Least Squares Method (LSM) based metamodelling is often challenged, an efficient Moving Least Squares Method based adaptive metamodelling technique is proposed for wind fragility analysis. In doing so, artificial time history of wind load is generated by three wind field models: i.e., a simple one based on alongwind component of wind speed; a more detailed one considering coherence and wind directionality effect, and a third one considering nonstationary effect of mean wind. The results show that the proposed approach is more accurate than the conventional LSM based metamodelling approach when compared to full simulation approach as reference. At the same time, the proposed approach drastically reduces computational time in comparison to the full simulation approach. The results by the three wind field models are compared. The importance of non-linear structural analysis in fragility evaluation has been also demonstrated.

Key Words
wind fragility; metamodelling; Moving Least Squares Method; risk; Monte Carlo Simulation; RC building

Address
Apurva Bhandari, Gaurav Datta and Soumya Bhattacharjya: Department of Civil Engineering, Indian Institute of Engineering Science and Technology (IIEST) Shibpur,
Howrah.-711103, West Bengal, India



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