Abstract
Wind tunnel test is often adopted to assess the site-specific wind characteristics for the design of bridges as
suggested by current design standards. To investigate the wind characteristics of flat and mountainous terrain, two topographic
models are tested in a boundary layer wind tunnel. The wind characteristics, including the vertical and horizontal mean wind
speed distributions, the turbulence intensity, and the wind power spectra, are presented. They are investigated intensively in
present study with the discussions on the effect of wind direction and the effect of topography. It is indicated that for flat terrain,
the wind direction has negligible effect on the wind characteristics, however, the assumption of a homogenous wind field for the
mountainous terrain is not applicable. Further, the non-homogeneous wind field can be defined based on a proposed approach if
the wind tunnel test or on-site measurement is performed. The calculated turbulence intensities and wind power spectra by using
the measured wind speeds are also given. It is shown that for the mountainous terrain, engineers should take into account the
variability of the wind characteristics for design considerations.
Key Words
flat terrain; mountainous terrain; nonhomogeneous wind field; turbulence intensity; wind power spectra; wind
tunnel test
Address
Jiawu Li, Jun Wang, Feng Wang and Guohui Zhao:1) School of Highway, Chang'an University, Xi'an 710064, Shannxi, China
2)Key Laboratory for Bridge and Tunnel of Shannxi Province, Chang' an University, Xi'an, China
Shucheng Yang:1) School of Highway, Chang'an University, Xi'an 710064, Shannxi, China
2)Key Laboratory for Bridge and Tunnel of Shannxi Province, Chang' an University, Xi'an, China
3)Civil and Environmental Department, Western University, London, Ontario, Canada
Abstract
The conformal mapping method (CMM) has been broadly exploited in the study of fluid flows over airfoils and
other research areas, yet it's hard to find relevant research in bridge engineering. This paper explores the feasibility of CMM in
streamlined box girder bridges. Firstly, the mapping function transforming a unit circle to the streamlined box girder was solved
by CMM. Subsequently, the potential flow solution of aerostatic pressure on the streamlined box girder was obtained and was
compared with numerical simulation results. Finally, the aerostatic pressure attained by CMM was utilized to estimate the
aerostatic coefficient and flutter performance of the streamlined box girder. The results indicate that the solution of the aerostatic
pressure by CMM on the windward side is satisfactory within a small angle of attack. Considering the windward aerostatic
pressure and coefficient of correction, CMM can be employed to estimate the rate of change of the lift and moment coefficients
with angle of attack and the influence of the geometric shape of the streamlined box girder on flutter performance.
Abstract
Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced
wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely
studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of
attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the
presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests,
comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient
shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an
interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Karman vortex resonance wind
speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the
wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced
wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models.
One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%,
showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding
force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.
Key Words
sharp-edged bluff body; unsteady galloping; vortex induced vibration; wind angle of attack; wind tunnel tests
Address
Cong Chen, Niccolo Wieczorek, Julian Unglaub and Klaus Thiele: Institute of Steel Structures, Technische Universität Braunschweig, Beethovenstr. 51, Brunswick, 38106, Lower Saxony, Germany
Bingyu Dai:Zhejiang Province Institute of Architectural Design and Research (ZIAD), Anji Road 18, Hangzhou, 310006, Zhejiang Province, China
Abstract
The pressure-mitigating effects of a high-speed train passing through a tunnel with a partially reduced cross-section
are investigated via the numerical approach. A compressible, three-dimensional RNG k-Εturbulence model and a hybrid mesh
strategy are adopted to reproduce that event, which is validated by the moving model test. Three step-like tunnel forms and two
additional transitions at the tunnel junction are proposed and their aerodynamic performance is compared and scrutinized with a
constant cross-sectional tunnel as the benchmark. The results show that the tunnel step is unrelated to the pressure mitigation
effects since the case of a double-step tunnel has no advantage in comparison to a single-step tunnel, but the excavated volume is
an essential matter. The pressure peaks are reduced at different levels along with the increase of the excavated earth volume and
the peaks are either fitted with power or logarithmic function relationships. In addition, the Arc and Oblique-transitions have
very limited gaps, and their pressure curves are identical to each other, whereas the Rec-transition leads to relatively lower
pressure peaks in CP max, CP min, and ΔCP, with 5.2%, 4.0%, and 4.1% relieved compared with Oblique-transition. This study
could provide guidance for the design of the novel railway tunnel.
Address
Wenhui Li, Tanghong Liu, Xiaoshuai Huo, Zijian Guo and Yutao Xia:1)Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,
Central South University, Changsha 410075, PR China
2)Joint International Research Laboratory of Key Technology for Rail Traffic Safety, Changsha 410075, PR China
3)National & Local Joint Engineering Research Center of Safety Technology for Rail Vehicle, Changsha 410075, PR China
Abstract
Analyzing the typhoon wind hazards is crucial to determine the extreme wind load on engineering structures in the
typhoon prone region. In essence, the typhoon hazard analysis is a high-dimensional problem with randomness arising from the
typhoon genesis, environmental variables and the boundary layer wind field. This study suggests a dimension reduction
approach by decoupling the original typhoon hazard analysis into two stages. At the first stage, the randomness of the typhoon
genesis and environmental variables are propagated through the typhoon track model and intensity model into the randomness of
the key typhoon parameters. At the second stage, the probability distribution information of the key typhoon parameters,
combined with the randomness of the boundary layer wind field, could be used to estimate the extreme wind hazard. The
Chinese southeast coastline is taken as an example to demonstrate the adequacy and efficiency of the suggested decoupling
approach.
Key Words
decoupling approach; probability density evolution method; typhoon hazards; typhoon intensity; typhoon track
Address
Xu Hong:1)College of Civil Engineering, Hefei University of Technology, Tunxi Road 193, Anhui Province, 230009, China
2)Anhui Key Laboratory of Civil Engineering Structures and Materials, Tunxi Road 193, Anhui Province, 230009, China
Jie Li:1)College of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
2)State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
