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CONTENTS
Volume 32, Number 5, May 2021
 

Abstract
To gain insight into the wind-induced safety concerns associated with attached tower cranes during the construction of super-tall buildings, a 606 m level frame-core tube super-tall building is selected to investigate the wind-induced vibration response and fragility of an outer-attached tower crane at all stages of construction. The wind velocity time history samples are artificially generated and used to perform dynamic response analyses of the crane to observe the effects of wind velocity and wind direction under its working and non-working resting state. The adverse effects of the relative displacement response at different connection supports are also identified. The wind-resistant fragility curves of the crane are obtained by introducing the concept of incremental dynamic analysis. The results from the investigation indicate that a large relative displacement between the supports can substantially amplify the response of the crane at high levels. Such an effect becomes more serious when the lifting arm is perpendicular to the plane of the connection supports. The flexibility of super-tall buildings should be considered in the design of outer-attached tower cranes, especially for anchorage systems. Fragility analysis can be used to specify the maximum appropriate height of the tower crane for each performance level.

Key Words
super-tall building; attached tower crane; construction; wind-induced vibration response; fragility analysis; incremental dynamic analysis; pushover analysis

Address
Yi Lu:Department of Civil Engineering, Dalian University of Technology, Dalian, China

Luo Zhang:Department of Civil Engineering, Dalian University of Technology, Dalian, China

Zheng He:Department of Civil Engineering, Dalian University of Technology, Dalian, China/State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China

Fan Feng:Department of Civil Engineering, Dalian University of Technology, Dalian, China

Feng Pan:Engineering Research Institute, Shanghai Construction No.5 (Group) Co., Ltd, Shanghai, China

Abstract
Aerodynamic measures have been widely used for improving the flutter stability of long-span bridges, and this paper focuses their windproof ability to improve the wind environment for vehicles. The whole wind environment around a long-span bridge located in high altitude mountainous areas is first studied. The local wind environment above the deck is then focused by two perspectives. One is the windproof effects of aerodynamic measures, and the other is whether the bridge with aerodynamic measures meets the requirement of flutter stability after installing extra wind barriers in the future. Furthermore, the effects of different wind barriers are analyzed. Results show that aerodynamic measures exert potential effects on the local wind environment, as the vertical stabilizer obviously reduces wind velocities behind it while the closed central slot has limited effects. The suggested aerodynamic measures have the ability to offset the adverse effect of the wind barrier on the flutter stability of the bridge. Behind the wind barrier, wind velocities decrease in general, but in some places incoming flow has to pass through the deck with higher velocities due to the increase in blockage ratio. Further comparison shows that the wind barrier with four bars is optimal.

Key Words
mountainous terrain; wind environment; truss girder; aerodynamic measures; wind barriers; windproof ability; flutter stability

Address
Zewen Wang:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Haojun Tang:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Yongle Li:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Junjie Guo:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Zhanhui Liu:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Abstract
The concept of Performance objective assessment is extended to wind engineering. This approach applies using the Database-Assisted Design technique, relying on the aerodynamic database provided by the National Institute of Standards and Technology (NIST). A structural model of a low-rise building is analyzed to obtain influence coefficients for internal forces and displacements. Combining these coefficients with time histories of pressure coefficients on the envelope produces time histories of load effects on the structure, for example knee and ridge bending moments, and eave lateral drift. The peak values of such effects are represented by an extreme-value Type I Distribution, which allows the estimation of the gust wind speed leading to the mean hourly extreme loading that cause specific performance objective compromises. Firstly a fully correlated wind field over large tributary areas is assumed and then relaxed to utilize the denser pressure tap data available but with considerably more computational effort. The performance objectives are determined in accordance with the limit state load combinations given in the ASCE 7-16 provisions, particularly the Load and Resistance Factor Design (LRFD) method. The procedure is then repeated for several wind directions and different dominant opening scenarios to determine the cases that produce performance objective criteria. Comparisons with two approaches in ASCE 7 are made.

Key Words
Database-Assisted Design; internal pressures; Computational Wind Engineering; design codes and standards

Address
Ali Merhi:Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy NY, U.S.A

Chris W. Letchford:Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy NY, U.S.A

Abstract
Snow accumulation on the road frequently induces a big traffic problem in the cold snowy region. Accurate prediction on snow distribution is fundamental for solving drifting snow disasters on roads. The present study adopts the transient method to simulate the wind-induced snow distribution on embankment based on the mixture multiphase model and dynamic mesh technique. The simulation and field measurement are compared to confirm the applicability of the simulation. Furthermore, the process of snow accumulation is revealed. The effects of friction velocity and snow concentration on snow accumulation are analyzed to clarify its mechanism. The results show that the simulation agrees well with the field measurement in trends. Moreover, the snow accumulation on the embankment can be approximately divided into three stages with time, the snow firstly deposited on the windward side, then, accumulation occurs on the leeward side which induced by the wake vortex, finally, the snow distribution reaches an equilibrium state with the slope of approximately 7°. The friction velocity and duration have a significant influence on the snow accumulation, and the vortex scale directly affected the snow deposition range on the embankment leeward side.

Key Words
snowdrift; embankment; snow accumulation; field measurement; numerical simulation

Address
Wenyong Ma:State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures, Shijiazhuang Tiedao University, Shijiazhuang 050043, China/ School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China/ Innovation Center for Wind Engineering and Wind Energy Technology of Hebei Province, Shijiazhuang, 050043, China/ China Railway Design Corporation, Tianjin, 300251, China

Feiqiang Li:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China

Yuanchun Sun:China Railway Design Corporation, Tianjin, 300251, China

Jianglong Li:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China

Xuanyi Zhou:State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China

Abstract
Onshore wind turbines may experience substantially different wind loads depending on their working conditions, i.e., rotation velocity of rotor blades, incoming freestream wind velocity, pitch angle of rotor blades, and yaw angle of the wind-turbine tower. In the present study, aerodynamic loads acting on a horizontal axis wind turbine were accordingly quantified for the high tip speed ratio (TSR) at high yaw angles because these conditions have previously not been adequately addressed. This was analyzed experimentally on a small-scale wind-turbine model in a boundary layer wind tunnel. The wind-tunnel simulation of the neutrally stratified atmospheric boundary layer (ABL) developing above a flat terrain was generated using the Counihan approach. The ABL was simulated to achieve the conditions of a wind-turbine model operating in similar inflow conditions to those of a prototype wind turbine situated in the lower atmosphere, which is another important aspect of the present work. The ABL and wind-turbine simulation length scale factors were the same (S=300) in order to satisfy the Jensen similarity criterion. Aerodynamic loads experienced by the wind-turbine model subjected to the ABL simulation were studied based on the high frequency force balance (HFFB) measurements. Emphasis was put on the thrust force and the bending moment because these two load components have previously proven to be dominant compared to other load components. The results indicate several important findings. The loads were substantially higher for TSR=10 compared to TSR=5.6. In these conditions, a considerable load reduction was achieved by pitching the rotor blades. For the blade pitch angle at 90°, the loads were ten times lower than the loads of the rotating wind-turbine model. For the blade pitch angle at 12°, the loads were at 50% of the rotating wind-turbine model. The loads were reduced by up to 40% through the yawing of the wind-turbine model, which was observed both for the rotating and the parked wind-turbine model.

Key Words
wind turbine, flat terrain, atmospheric boundary layer, aerodynamic loads, wind-tunnel experiments

Address
Danijel Bosnar:Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia/ Institute of Theoretical and Applied Mechanics, Prosecká 76, 19000 Prague, Czech Republic

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

Stanislav Pospíšil:Institute of Theoretical and Applied Mechanics, Prosecká 76, 19000 Prague, Czech Republic

Michael Macháček:Institute of Theoretical and Applied Mechanics, Prosecká 76, 19000 Prague, Czech Republic

Abstract
The wind-blown sand effect on the high-speed train is investigated. Unsteady RANS equation and the SST k–ω turbulent model coupled with the discrete phase model (DPM) are utilized to simulate the two-phase of air-sand. Sand impact force is calculated based on the Hertzian impact theory. The different cases, including various wind velocity, train speed, sand particle diameter, were simulated. The train's flow field characteristics and the sand impact force were analyzed. The results show that the sand environment makes the pressure increase under different wind velocity and train speed situations. Sand impact force increases with the increasing train speed and sand particle diameter under the same particle mass flow rate. The train aerodynamic force connected with sand impact force when the train running in the wind-sand environment were compared with the aerodynamic force when the train running in the pure wind environment. The results show that the head car longitudinal force increase with wind speed increasing. When the crosswind speed is larger than 35m/s, the effect of the wind- sand environment on the train increases obviously. The longitudinal force of head car increases 23% and lateral force of tail increases 12% comparing to the pure wind environment. The sand concentration in air is the most important factor which influences the sand impact force on the train.

Key Words
wind-blown sand; Hertzian impact; high-speed train; Granular flows

Address
Yani Zhang:National Innovation Centre of High-speed Train, Qingdao 266000, China

Chen Jiang:Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,Central South University, Changsha 410075, China

Xuhe Zhan:National Innovation Centre of High-speed Train, Qingdao 266000, China/ Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,
Central South University, Changsha 410075, China

Abstract
The turbine industry demands a reliable design with affordable cost. As technological advances begin to support turbines of huge sizes, and the increasing importance of wind turbines from day to day make design safety conditions more important. Wind turbines are exposed to environmental conditions that can affect their installation, durability, and operation. International Electrotechnical Commission (IEC) 61400-1 design load cases consist of analyses involving wind turbine operating conditions. This design load cases (DLC) is important for determining fatigue loads (i.e., forces and moments) that occur as a result of expected conditions throughout the life of the machine. With the help of FAST (Fatigue, Aerodynamics, Structures, and Turbulence), an open source software, the NREL 5MW land base wind turbine model was used. IEC 61400-1 wind turbine design standard procedures assessed turbine behavior and fatigue damage to the tower base of dynamic loads in different design conditions. Real characteristic wind speed distribution and multi-directional effect specific to the site were taken into consideration. The effect of these conditions on the economic service life of the turbine has been studied.

Key Words
wind turbine; Fatigue analysis; cumulative fatigue damage; design load cases; IEC 61400-1

Address
Onur Gunes:Department of Civil Engineering, Istanbul Technical University, Istanbul, Turkey

Elif Altunsu:Department of Civil Engineering, Istanbul Technical University, Istanbul, Turkey/ Department of Civil Engineering, İstanbul University-Cerrahpasa, İstanbul, Turkey

Ali Sari:Department of Civil Engineering, Istanbul Technical University, Istanbul, Turkey

Abstract
The streamlined box is a common type of girders for long-span suspension bridges. Spanning deep canyons, long-span bridges are frequently attacked by strong winds with large angles of attack. In this situation, the flow field around the streamlined box changes significantly, leading to reduction of the flutter performance. The wind fairings have different effects on the flutter performance. Therefore, this study examines the flutter performance of box girders with different wind fairings at large angles of attack. Computational fluid dynamics (CFD) simulations were carried out to extract the flutter derivatives, and the critical flutter state of a long-span bridge was determined. Further comparisons of the wind fairings were investigated by a rapid method which is related to the input energy by the aerodynamic force. The results show that a reasonable type of wind fairings could improve the flutter performance of long-span bridges at large angles of attack. For the torsional flutter instability, the wind fairings weaken the adverse effect of the vortex attaching to the girder, and a sharper one could achieve a better result. According to the input energies on the girder with different wind fairings, the symmetrical wind fairings are more beneficial to the flutter performance.

Key Words
angles of attack; box girders; flow field characteristics; flutter performance; numerical simulations; wind fairings

Address
Haojun Tang:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China/ Wind Engineering Key Laboratory of Sichuan Province, Chengdu 610031, China

Hang Zhang:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Wei Mo:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Yongle Li:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China/ Wind Engineering Key Laboratory of Sichuan Province, Chengdu 610031, China

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