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Wind and Structures
  Volume 29, Number 3, September 2019 , pages 163-175

Aerostatic instability mode analysis of three-tower suspension bridges via strain energy and dynamic characteristics
Wen-ming Zhang, Kai-rui Qian, Li Wang and Yao-jun Ge

    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

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