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CONTENTS
Volume 33, Number 3, September 2021
 


Abstract
The use of tensioned structures, such as membranes, as solutions for roofing and other kinds of covers has become more and more frequent. Current regulations do not provide detailed information about the coefficients needed to develop efficient designs, regarding wind loads. A lot of simulations and tests have been performed on different geometries which are typically used in these kinds of designs. However, no precise and clear standard has been established, yet, in order to regulate efficiently this application. Current regulations consider only simple geometries, while the effects of the interference between multiple covers or between a cover and the near urban environment is completely absent. In this paper are presented the results obtained from testing a 1:75 scale complex geometry model in a boundary layer wind tunnel. More precisely a model of a parking lot for vans, roofed with a complex geometry tensioned membrane was tested in order to measure its pressure distribution. Due to the high complexity of the geometry and in order to obtain a better description of the effects of the wind it was decided to lead wind tunnel tests to validate and to verify the load conditions over the roof. Information about wind load distributions for simple geometries such as cones, hyperboloids, etc. alone can be easily found in current technical bibliography. However, when designs are based on more complex shapes, including arrays of simpler shapes, a profound lack of information is observed. Therefore, it is not possible to calculate the wind loads over the membrane which are needed to dimension the supporting structure.

Key Words
structures; tensile; wind load; wind tunn

Address
Juan S. Delnero: Laboratorio de Capa Límite y Fluidodinámica Ambiental (UIDET LaCLyFA), Facultad de Ingeniería,
UNLP. Calle 116 e/47 y 48 – (1900) La Plata – Pcia. de Bs. As. – Argentina/ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Avda. Rivadavia 1917, CP C1033AAJ,Cdad. de Buenos Aires, Argentina

Julio Marañón Di Leo: Laboratorio de Capa Límite y Fluidodinámica Ambiental (UIDET LaCLyFA), Facultad de Ingeniería,UNLP. Calle 116 e/47 y 48 – (1900) La Plata – Pcia. de Bs. As. – Argentina/ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Avda. Rivadavia 1917, CP C1033AAJ,Cdad. de Buenos Aires, Argentina

Mariano A. Martinez: Grupo de Fluidodinámica Computacional, Universidad Nacional de La Plata,
Calle 116 e/47 y 48 – (1900) La Plata – Pcia. de Bs. As. – Argentina

Abstract
The aerodynamic performance of a scaled high-speed train model mounted on a double-track viaduct was studied through a wind tunnel test. The pressure distribution of different loops and the centerline on the streamlined nose region, as well as the aerodynamic load coefficients of the leading car were explored under yaw effects ranging from Β=-30° to Β=30°. Results showed that Reynolds effects became independent when the wind speed surpassed 40 m/s, the corresponding Re of which equals 6.51 x 105. The pressures recorded along the centerline of train nose for the upstream scenario, was more sensitive to the yaw effects as the largest pressure difference gradually broadened against yaw angles. In addition, the pressure coefficients along the centerline and symmetrical taps of the loops, approximately fit a quadratic relationship with respect to yaw angles. The presence of the tracks and viaduct decks somehow mitigated the intensity of the airflow at downstream side. The experimental test also revealed that, the upstream configuration provided higher mean side force, yawing, and rolling moments up to Β=20° whereas over that angle the force and moments exhibited the opposite performance. 40 m/s, the corresponding Re of which equals 6.51

Key Words
aerodynamic coefficient; pressure distribution; viaduct; wind tunnel test; yaw angle

Address
Wenhui Li, Tanghong Liu, Zhengwei Chen, Xiaoshuai Huo, Zijian Guo and Yutao Xia: Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,Central South University, Changsha 410075, PR China

Pedro Martinez-Vazquez: School of Engineering, University of Birmingham, B15 2TT, U.K.

Abstract
Considering the wind loads and track irregularity as external excitation, the wind-train-bridge dynamic analysis model considering the longitudinal freedom of train is established in the present study. In the model, the wind load of train-bridge system under the train-induced wind field and the combined wind field is obtained by employing Computational Fluid Dynamics (CFD) method. With the CRH2 high-speed train and a 10-span simply-supported box girder bridge as an example, the whole history of the train running on the bridge under the combined effect of train-induced wind and crosswind is simulated to analyze the dynamic response of the train-bridge system. In addition, the operational safety indicators of the train are evaluated. According to the obtained results, the dynamic response of vehicles and bridges increases with the train speed without the consideration of the crosswind. In the combined wind field, the train-induced wind exerts a greater impact on the dynamic response of the vehicle, but has a less influence on that of the bridge simultaneously. Moreover, the influence of wind velocity is greater than that of train speed. When the wind-train-bridge dynamic response analysis is carried out based on traditional methods, the calculated wind load of the train-bridge system is too high, making the calculated responses too large to be consistent with actual values.

Key Words
dynamic response; railway bridge; running safety; train-induced wind effect; wind-train-bridge system

Address
Yujing Wang:School of traffic engineering, Shandong Jianzhu University, JiNan, 250101, China/ Shandong Co-Innovation Center for Disaster Prevention and Mitigation of Civil Structures, Jinan 250101, China

Weiwei Guo:School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

He Xia:School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

Shanshan Wang:Shandong Hi-speed Group Co., Ltd., Jinan 250098, China

Man Xu:Central Research Institute of Building and Construction CO., LTD. MCC, Beijing 100088, China

Abstract
Double-skin façades (DSFs) have been increasingly implemented on tall buildings with the goal of improving building energy efficiency, natural ventilation and visual appearance. It is commonly known that wind and earthquakes represent major environmental load types impacting tall buildings. However, at this point, the aerodynamic characteristics of tall buildings equipped with porous façades are still relatively unknown, although it may be expected that the addition of porous outer skins will substantially affect the overall building aerodynamics. The scope of the present study is therefore to carefully review all the relevant parameters playing an important role in the aerodynamic characteristics of tall buildings with porous façades. Fluid flow and turbulence through porous surfaces were reviewed first with an emphasis on the wake and pressure drop behind perforated plates to analyze the phenomena of fundamental fluid mechanics relevant for porous surfaces. As the inflow characteristics predominantly dictate the aerodynamic characteristics of tall buildings, it is therefore useful to review major wind types, including the atmospheric boundary layer (ABL) and strong local winds, which have previously proved to cause major structural damage and failure. In order to be able to properly assess the aerodynamic loading of tall buildings with porous façades, it is necessary to understand the aerodynamic features of tall buildings with smooth surfaces. For this reason, the aerodynamic performance of smooth tall buildings was reviewed, as were the design features commonly adopted to mitigate adverse wind effects. The existing and rather sparse current knowledge of the aerodynamic characteristics of porous DSFs of high- and low-rise buildings is outlined. Based on the provided information, it is clear that a substantial amount of knowledge still needs to be acquired in the future in regard to various aerodynamic features of tall buildings with porous DSFs, particularly concerning wind loads, building energy efficiency, pedestrian wind comfort, renewable energy aspects, air pollution dispersion and dilution. It is expected that the optimal approach to advancing this topic is in combining field measurements, laboratory experiments and computational modeling.

Key Words
aerodynamic characteristics; porous façades; review; tall buildings

Address
Petar Škvorca: Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia

Hrvoje Kozmar: Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia

Abstract
Transmission line (TL) structures are exposed mostly to particular environmental conditions, which are likely to damage the line. Long experience in power systems shows that the reliability of TLs in nature is closely related to climate conditions. The purpose of this study is to develop a probabilistic framework for estimating the annual failure probability of 400 kV TL components considering the coincidence of multiple hazards with the Scenario Sampling method. Regression equations are presented to account for two sources of uncertainty including the eccentricity of connection in tower modeling, and the temperature effect on the conductor's ultimate tension in loading. The correlation matrix for maximum wind speed, maximum radial ice thickness, and temperature in the studied line is presented by analyzing local meteorological data. These correlation coefficients impose a constraint on the magnitudes of the occurrence models. The tower system used in the reliability analysis is addressed by eliminating critical members and studying changes in demand-to-capacity ratios in other members. Bi-modal bounds are used to estimate the annual failure probability of the TL system. Finally, the TL towers' fragility curves for various wind speeds as well as for different values of radial ice thickness at a constant wind speed are presented within the proposed framework.

Key Words
fragility; ice thickness; load coincidence; scenario sampling; system reliability; temperature effect; transmission line; wind speed

Address
Amir Mahmoudi:Amir Mahmoudi:Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran/ Power Industry Structures Research Department, Niroo Research Institute (NRI), Tehran, Iran

Kourosh Nasrollahzadeh:Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Mohammad Ali Jafari: Power Industry Structures Research Department, Niroo Research Institute (NRI), Tehran, Iran



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