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CONTENTS
Volume 31, Number 6, December 2020
 

Abstract
Large cylindrical floating-roof tanks, constructed as oil containers, are usually distributed regularly in open area and easily exposed to severe wind loads. However, wind pressures around these grouped squat tanks appear to have not been clearly given in design codes or thoroughly studied in existing researches. This paper conducts a detailed investigation on wind loads on the external wall of a four-tank group in square arrangement. To achieve that, wind tunnel tests are carried out on both empty and full tank groups, considering various wind angles and spacing. Results show that 3 regions in elevation can be identified on the tank shell according to the circumferential wind pressure distribution. The upper 2 regions cover a relatively small portion of the shell where excessive negative pressures are spotted, setting an alarm to the design of the top angle and stiffening rings. By comparing results on grouped tanks to those on an isolated tank, grouping effects concerning wind angle, tank position in group and spacing are discussed. Deviations on pressure distributions that will compromise structural safety are outlined, including the increase of negative pressures, the shift of maximum pressure locations as well as the change of positive pressure range. And, several potentially unfavourable wind pressure distributions are selected for further analyses.

Key Words
cylindrical tanks with floating roof; wind loads; grouping effect; square arrangement; wind tunnel test; stiffening rings

Address
Qing Liu, Yang Zhao, Shuqi Cai and Shilin Dong:Space Structures Research Center, Zhejiang University, Hangzhou 310058, China

Abstract
To investigate the structural behaviour of grouped tanks under wind loads, 2 problems need to be figured out, wind pressures on tank shells and critical loads of the shell under these pressure distribution patterns. Following the wind tunnel tests described in the companion paper, this paper firstly seeks to obtain wind loads on the external wall in a squarely-arranged cylindrical tank group by numerical simulation, considering various layouts. The outcomes demonstrate that the numerical method can provide similar results on wind pressures and better insights on grouping effects through extracted streamlines. Then, geometrically nonlinear analyses are performed using several selected potentially unfavourable wind pressure distributions. It is found that the critical load is controlled by limit point buckling when the tank is empty while excessive deformations when the tank is full. In particular, significant reductions of wind resistance are found on grouped full tanks compared to the isolated tank, considering both serviceability and ultimate limit state, which should receive special attention if the tank is expected to resist severe wind loads with the increase of liquid level.

Key Words
cylindrical tanks with floating roof; wind loads; grouping effect; square arrangement; computational fluid dynamics; stability behaviour; nonlinear finite element analysis

Address
Qing Liu, Yang Zhao, Shuqi Cai and Shilin Dong: Space Structures Research Center, Zhejiang University, Hangzhou 310058, China

Abstract
Wind load is the principal cause for a large number of the collapse of transmission lines around the world. The transmission line is traditionally designed for wind load according to a linear equivalent method, in which dynamic effects of wind are not appropriately included. Therefore, in the present study, incremental dynamic analysis is utilized to investigate the stability behavior of a 400 kV transmission line under wind load. In that case, the effects of vibration of cables and aerodynamic damping of cables were considered on the stability behavior of the transmission line. Superposition of the harmonic waves method was used to calculate the wind load. The corresponding wind speed to the beginning of the transmission line collapse was determined by incremental dynamic analysis. Also, the effect of the yawed wind was studied to determine the critical attack angle by the incremental dynamic method. The results show the collapse mechanisms of the transmission line and the maximum supportable wind speed, which is predicted 6m/s less than the design wind speed of the studied transmission line. Based on the numerical modeling results, a retrofitting method has been proposed to prevent failure of the tower members under design wind speed.

Key Words
collapse of transmission tower; wind load; stability analysis; performance of transmission line; dynamic response; incremental dynamic analysis

Address
Hadi Sarmasti, Karim Abedi and Mohammad Reza Chenaghlou: Department of Civil Engineering, Sahand University of Technology, Tabriz, Iran

Abstract
As the height and flexibility of high-rise buildings increase, the wind loads become more dominant and the combination coefficient of Equivalent Static Wind Loads (ESWLs) should be considered when they are used in the structural design. In the first phase of the study, a brief introduction to the theory on the combination coefficient for high-rise buildings was given and then the time history of wind-induced responses of a 208-meter high-rise building with an elliptical cross-section was presented based on the wind tunnel test results for pressure measurement. The correlation between wind-induced responses was analyzed and the combination coefficients of ESWLs of the high-rise buildings using Turkstra's rule, and Asami's method, were calculated and compared with related design codes, e.g., AIJ-RLB, ASCE 7-10, and China Load Code for structural design. The results of the study showed that the combination coefficients from Asami's method are conservative compared with the other three methods. The results of this paper would be helpful to the wind-resistant design of high-rise buildings with elliptical cross-section.

Key Words
high-rise buildings with elliptical cross-section; combination coefficient; correlation of wind-induced responses; equivalent static wind loads

Address
Qinhua Wang:Department of Civil and Environmental Engineering, Shantou University, Shantou 515063, China/ Key Laboratory of Structure and Wind Tunnel of Guangdong Higher Education Institutes, Shantou 515063, China
Shuzhi Yu and Chiujen Ku:Department of Civil and Environmental Engineering, Shantou University, Shantou 515063, China
Ankit Garg:Department of Civil and Environmental Engineering, Shantou University, Shantou 515063, China/ Guangdong Engineering Center for Structure Safety and Health Monitoring, Shantou University, Shantou 515063, China

Abstract
Despite the current technologic developments, failures in existent tensile fabric structures (TFS) subjected to wind do happen. However, design pressure coefficients are only obtained for large projects. Moreover, studies on TFSs with realistic supporting frames, comparing static and dynamic analyses and discussing the design implications, are lacking. In this study, fluid-Structure analyses of a TFS supported by masts and inclined cables, by subjecting it to different wind speeds, are carried out, to gain more understanding in the above-referred aspects. Wind-induced stresses in the fabric and axial forces in masts and cables are assessed for a hypar by using computational fluid dynamics. Comparisons are carried out versus an equivalent static analysis and also versus loadings deemed representative for design. The procedure includes the so-called form-finding, a finite element formulation for the TFS and the fluid formulation. The selected structure is deemed realistic, since the supporting frame is included and the shape and geometry of the TFS are not uncommon. It is found that by carrying out an equivalent static analysis with the determined pressure coefficients, differences of up to 24% for stresses in the fabric, 5.4% for the compressive force in the masts and 21% for the tensile force in the cables are found with respect to results of the dynamic analysis. If wind loads commonly considered for design are used, significant differences are also found, specially for the reactions at the supporting frame. The results in this study can be used as an aid by designers and researchers.

Key Words
tensile fabric structure; fluid-structure interaction; finite element simulation; form-finding; wind-induced forces

Address
Jesús G. Valdés-Vázquez, Adrián D. García-Soto, Alejandro Hernández-Martínez : Department of Civil Engineering, Universidad de Guanajuato, Av. Juárez 77, Colonia Centro, C.P. 36000, Guanajuato, GTO., México
José L. Nava: 2Department of Geomatic and Hydraulic Engineering, Universidad de Guanajuato,
Av. Juárez 77, Colonia Centro, C.P. 36000, Guanajuato, GTO., México


Abstract
Methods for stochastic simulation of non-Gaussian wind pressure have increasingly addressed the efficiency and accuracy contents to offer an accurate description of the extreme value estimation of the long-span and high-rise structures. This paper presents a linear prediction and z-transform (LPZ) based Cumulative distribution function (CDF) mapping algorithm for the simulation of multivariate non-Gaussian fluctuating wind pressure. The new algorithm generates realizations of non-Gaussian with prescribed marginal probability distribution function (PDF) and prescribed spectral density function (PSD). The inverse linear prediction and z-transform function (ILPZ) is deduced. LPZ is improved and applied to non-Gaussian wind pressure simulation for the first time. The new algorithm is demonstrated to be efficient, flexible, and more accurate in comparison with the FFT-based method and Hermite polynomial model method in two examples for transverse softening and longitudinal hardening non-Gaussian wind pressures.

Key Words
Non-Gaussian wind pressure; LPZ spectral analysis; CDF-mapping; Multivariate simulation

Address
Lei Jiang:School of civil engineering and architecture, Jiangsu University of science and technology, Zhenjiang 212005, China/ Department of Civil Engineering, School of Mechanism and Engineering Science,
Shanghai University, 333 Nanchen Road, Shanghai 200444, China
Chunxiang Li: Department of Civil Engineering, School of Mechanism and Engineering Science,
Shanghai University, 333 Nanchen Road, Shanghai 200444, China
Jinhua Li: 3Department of Civil Engineering, East China Jiaotong University, Nanchang 330013, China

Abstract
Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.

Key Words
aerodynamic stability/instability; bridge aerodynamics; flutter, time-domain methods; wind loads

Address
Mitja Papinutti:Faculty of Civil and Geodetic Engineering, University of Ljubljana, Ljubljana, Slovenia/ Department of Structural Engineering, Faculty of Engineering, Norwegian University of Science and Technology, Trondheim, Norway
Matjaž Četina, Boštjan Brank:Faculty of Civil and Geodetic Engineering, University of Ljubljana, Ljubljana, Slovenia
Øyvind W. Petersen and Ole Øiseth: Department of Structural Engineering, Faculty of Engineering, Norwegian University of Science and Technology, Trondheim, Norway


Abstract
Wind load is typically considered as one of the governing design loads acting on a structure. Understanding its nature is essential in evaluation of its action on the structure. Many codes and standards are founded on state of the art knowledge and include step by step procedures to calculate wind loads for various types of structures. One of the most accepted means for calculating wind load is using Gust Load Factor or base bending Moment Gust Load Factor (MGLF), where codes are adjusted based on local data available. Although local data may differ, the general procedure is the same. In this paper, ASCE 7-16 (2017), which is used as the main reference in the U.S., and Korean Building Code (KBC 2016) are compared in evaluation of wind loads. The primary purpose of this paper is to provide insight on each code from a structural engineering perspective. Herein, discussion focuses on where the two codes are compatible and differ. In evaluating the action of wind loads on a building, knowledge of the dynamic properties of the structure is critical. For this study, the design of four figurative high-rise buildings with dual systems was analyzed.

Key Words
wind load; code; gust effect factor; ASCE; KBC; high-rise building

Address
Hamidreza Alinejad, Seung Yong Jeong and Thomas H.-K. Kang:Department of Architecture and Architectural Engineering & Engineering Research Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea


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