Doctor of Philosophy (PhD)
Department of Civil and Environmental Engineering
With the continuous increase of span lengths, the aerodynamic characteristics of long-span bridges under external wind excitation have become much more complex and wind-induced vibration has always been a problem of great concern. The present research targets on the aerodynamic performance of long-span bridges under wind load with an emphasis on bridge flutter and buffeting.
For the aerodynamic flutter analysis of long-span bridges, the present research investigated the effects of the wind turbulence on flutter stability. The characterizations of the self-excited forces are presented in both the frequency-domain and in the time-domain, and the flutter analysis is conducted under both uniform and turbulent flows. The effect of wind turbulence is directly modeled in time-domain to avoid the complicated random parametric excitation analysis of the equation of motion used in previous studies. It is found that turbulence has a stabilizing effect on bridge aerodynamic flutter. A probabilistic flutter analysis of long-span bridges involving random and uncertain variables is also conducted, which can provide more accurate and adequate information than the critical flutter velocity for wind resistance design of long-span bridges.
For the buffeting analysis of long-span bridges, the stress-level buffeting analysis of the bridge under spatial distributed forces is conducted to investigate the effects of wind turbulence on the fatigue damage of long-span bridges. It is found that the increase of the turbulence intensity has a strengthening effect on the buffeting-induced fatigue damage of long-span bridges. For buffeting control, a lever-type TMD system is proposed for suppressing excessive buffeting responses of long-span bridges. The lever-type TMD with an adjustable frequency can overcome the drawback of excessive static stretch of the spring of traditional hanging-type TMD and be adaptive to the change of the environment and the structure itself. To effectively apply the lever-type TMD to future feedback control design, the control performance of the lever-type TMD for excessive buffeting responses of long-span bridges has been studied. The effects of wind velocity and attack angle and the stiffness reduction of bridge girder on the control efficiency have also been investigated to determine the adjustment strategy of the lever-type TMD. It is found that the control efficiency of the lever-type TMD varies greatly with the change of the location of the mass block. The lever-type TMD should be adjusted accordingly based on comprehensive consideration of the environment change and specific control objectives.
Liu, Shuqian, "Aerodynamic Flutter and Buffeting of Long-span Bridges under Wind Load" (2019). LSU Doctoral Dissertations. 4837.
Cai, Steve C.S.