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Volume 29, Number 3, September 2019

When a railway vehicle runs in crosswinds, the unsteady aerodynamic forces acting on the train induced by the vehicle speed, crosswind velocity and local landforms are a common problem. To investigate the dynamic performance of a railway vehicle due to the influence of unsteady aerodynamic forces caused by local landforms, a vehicle aerodynamic model and vehicle dynamic model were established. Then, a wind-loaded vehicle system model was presented and validated. Based on the wind-loaded vehicle system model, the dynamic response performance of the vehicle, including safety indexes and vibration characteristics, was examined in detail. Finally, the effects of the crosswind velocity and vehicle speed on the dynamic response performance of the vehicle system were analyzed and compared.

Key Words
railway vehicle; unsteady aerodynamic forces; dynamic performance; landforms

Zhengwei Chen, Tanghong Liu , Zhaijun Lu and Dongrun Liu: Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,
Central South University, Changsha 410075, P.R. China
Joint International Research Laboratory of Key Technology for Rail Traffic Safety, Changsha 410075, P.R. China
National & Local Joint Engineering Research Center of Safety Technology for Rail Vehicle, Changsha 410075, P.R. China
Ming Li and Miao Yu: P&T Research Center, CRRC Tangshan Co., Ltd., Tangshan 063035, P.R. China

Multispan suspension bridges make a good alternative to single-span ones if the crossed strait or river width exceeds 2-3 km. However, multispan three-tower suspension bridges are found to be very sensitive to the wind load due to the lack of effective longitudinal constraint at their central tower. Moreover, at certain critical wind speed values, the aerostatic instability with sharply deteriorating dynamic characteristics may occur with catastrophic consequences. An attempt of an in-depth study on the aerostatic stability mode and damage mechanism of three-tower suspension bridges is made in this paper based on the assessment of strain energy and dynamic characteristics of three particular three-tower suspension bridges in China under different wind speeds and their further integration into the aerostatic stability analysis. The results obtained on the three bridges under study strongly suggest that their aerostatic instability mode is controlled by the coupled action of the anti-symmetric torsion and vertical bending of the two main-spans\' deck, together with the longitudinal bending of the towers, which can be regarded as the first-order torsion vibration mode coupled with the first-order vertical bending vibration mode. The growth rates of the torsional and vertical bending strain energy of the deck after the aerostatic instability are higher than those of the lateral bending. The bending and torsion frequencies decrease rapidly when the wind speed approaches the critical value, while the frequencies of the anti-symmetric vibration modes drop more sharply than those of the symmetric ones. The obtained dependences between the critical wind speed, strain energy, and dynamic characteristics of the bridge components under the aerostatic instability modes are considered instrumental in strength and integrity calculation of three-tower suspension bridges.

Key Words
three-tower suspension bridge; aerostatic instability; instability mode; strain energy; dynamic characteristics

Wen-ming Zhang and Kai-rui Qian: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing 211189, China
Li Wang: Shandong Provincial Transport Planning and Design Insititue, Ji\'nan 250031, China
Yao-jun Ge: State Key Lab for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

While establishing adequate load paths in the light-frame wood structures is critical to maintain the overall structural integrity and avoid significant damage under extreme wind events, the understanding of the load paths is limited by the high redundant nature of this building type. The objective of the current study is to evaluate the system effects and investigate the load paths in the wood structures especially the older buildings for a better performance assessment of the existing building stock under high winds, which will provide guidance for building constructions in the future. This is done by developing building models with configurations that are suspicious to induce failure per post damage reconnaissance. The effect of each configuration to the structural integrity is evaluated by the first failure wind speed, a major indicator beyond the linear to the nonlinear range. A 3D finite-element (FE) building model is adopted as a control case that is modeled using a validated methodology in a highly-detailed fashion where the nonlinearity of connections is explicitly simulated. This model is then altered systematically to analyze the effects of configuration variations in the model such as the gable end sheathing continuity and the gable end truss stiffness, etc. The resolution of the wind loads from scaled wind tunnel tests is also discussed by comparing the effects to wind loads derived from large-scale wind tests.

Key Words
residential buildings; load paths; load sharing; wind loads; finite element

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

This paper presents an overview of wind turbine research techniques including the recent application of hybrid testing. Wind turbines are complex structures as they are large, slender, and dynamic with many different operational states, which limits applicable research techniques. Traditionally, numerical simulation is widely used to study turbines while experimental tests are rarer and often face cost and equipment restrictions. Hybrid testing is a relatively new simulation method that combines numerical and experimental techniques to accurately capture unknown or complex behaviour by modelling portions of the structure experimentally while numerically simulating the remainder. This can allow for increased detail, scope, and feasibility in wind turbine tests. Hybrid testing appears to be an effective tool for future wind turbine research, and the few studies that have applied it have shown promising results. This paper presents a literature review of experimental and numerical wind turbine testing, hybrid testing in structural engineering, and hybrid testing of wind turbines. Finally, several applications of hybrid testing for future wind turbine studies are proposed including multi-hazard loading, damped turbines, and turbine failure.

Key Words
wind turbine; hybrid testing; wind tunnel; shaking table; multi-hazard

Eric R. Lalonde: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China;
Department of Civil and Environmental Engineering, University of Western Ontario, London, Canada
Kaoshan Dai: Department of Civil Engineering, Sichuan University, Chengdu, China
Wensheng Lu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Girma Bitsuamlak: Department of Civil and Environmental Engineering, University of Western Ontario, London, Canada

The assessment of wind-induced vibration for tall reinforced concrete (RC) buildings requires the accurate estimation of their dynamic properties, e.g., the fundamental vibration periods and damping ratios. In this study, RC frame-shear wall systems designed under gravity and wind loadings have been evaluated by utilising 3D FE modelling incorporating eigen-analysis to obtain the elastic periods of vibration. The conducted parameters consist of the number of storeys, the plan aspect ratio (AR) of buildings, the core dimensions, the space efficiency (SE), and the leasing depth (LD) between the internal central core and outer frames. This analysis provides a reliable basis for further investigating the effects of these parameters and establishing new formulas for predicting the fundamental vibration periods by using regression analyses on the obtained results. The proposed constrained numerically based formula for vibration periods of tall RC frame-shear wall office buildings in terms of the height of buildings reasonably agrees with some cited formulas for vibration period from design codes and standards. However, the same proposed formula has a high discrepancy with other cited formulas from the rest of design codes and standards. Also, the proposed formula agrees well with some cited experimentally based formulas.

Key Words
reinforced concrete; shear walls; office buildings; vibration period; wind load; space efficiency; leasing depth

Ali Al-Balhawi: School of Computing, Engineering and Built Environment, Glasgow Caledonian University,
Cowcaddens Road, Glasgow G4 0BA, Scotland, UK;
Civil Engineering Department, Engineering College, Mustansiriyah University, Baghdad, Iraq
Binsheng Zhang: School of Computing, Engineering and Built Environment, Glasgow Caledonian University,
Cowcaddens Road, Glasgow G4 0BA, Scotland, UK

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