A flexible footbridge with main span of 460 m was taken as an object in order to analyze the problem of vibration serviceability of long-span suspension footbridge (LSSF) induced by crosswind. Fluctuating wind time histories with different turbulence intensities were generated with spectral representation method. Rational-function-expressed self-excited force was calculated based on 18 flutter derivatives identified by numerical simulation method. The influence of self-excited force on buffeting response was compared with those of structural damping through nonlinear buffeting response analysis in time domain under crosswind. The influences of turbulence intensity on buffeting response and comfort were analyzed. The mitigation effects of central buckle and wind-resistant cable with different design parameters on the buffeting response of bridge were discussed. Results show that self-excited force has a non-negligible influence on buffeting response of LSSF. Turbulence intensity increases by 50% under the crosswind with a mean wind speed of 15 m/s, and the buffeting response of the bridge increases by 30%-68%. Central buckle can obviously reduce vertical vibration at 1/4 span and 3/4 span. Increasing the stiffness of wind-resistant cable can effectively reduce lateral vibration at mid-span and vertical vibration.
Jian-ming TANG,Xu XIE. Investigation on vibration serviceability of long-span suspension footbridge under crosswind. Journal of ZheJiang University (Engineering Science), 2021, 55(10): 1903-1911.
Tab.1Comparison of dynamic characteristics between fine model and equivalent model
Fig.3Aerostatic forces of main girder
Fig.4Flow chart of nonlinear buffeting analysis in time domain
Fig.5Layout of simulated points for fluctuating wind
脉动风编号
位置
模拟风速
模拟点数
ttot /s
1
主梁
u
49
50 176
2
主梁
w
49
50 176
3
南塔
u
10
10 240
4
北塔
u
10
10 240
5
主缆
u
49
50 176
Tab.2Parameters of fluctuating wind simulation
Fig.6Samples of simulated fluctuating wind and validation
Fig.7Hybrid mesh used in CFD simulation
Fig.8Aerostatic force coefficients and their derivatives of stiffening girder
Fig.9Flutter derivatives of stiffening girder at 0° wind attack angle
Fig.10Influence of self-excited force and structural damping on buffeting displacement responses of main girder
Fig.11Comparison of buffeting responses at mid-span of main girder under different turbulence intensities
舒适性分级
舒适度
ay,peak /（m·s?2）
az,peak /（m·s?2）
CL1
非常舒适
<0.1
<0.5
CL2
中等舒适
0.1~0.3
0.5~1.0
CL3
不太舒适
0.3~0.8
1.0~2.5
CL4
不能忍受
>0.8
>2.5
Tab.3Comfort levels and corresponding acceleration ranges[20]
Fig.12Acceleration time history and comfort evaluation results
Fig.13Central buckle layout of different models
Fig.14Influence of central buckle on buffeting displacement responses of main girder
振型
fnat /Hz
C-1
C-2
1阶对称侧弯
0.197 6
0.222 8
1阶反对称侧弯与扭转
0.250 5
0.271 0
1阶反对称竖弯
0.256 8
0.271 0
1阶对称竖弯
0.280 1
0.282 6
1阶对称扭转
0.398 8
0.400 8
1阶反对称扭转
0.416 5
0.433 8
Tab.4Bridge dynamic characteristics after increasing area of wind-resistant cable
Fig.15Influence of wind-resistant cable on buffeting displacement responses of main girder
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