Parametric Optimization And Design Of Bridge TMD System

Bridge structures are prone to vibration problems under external dynamicexcitations like winds, earthquake and passing crowds. Excessive vibrations can resultin comfortlessness when vehicles and crowds passing by, meanwhile, structuralelements may also suffer from high risk of fatigue failure. Many investigations havebeen carried out for mitigating vibrations and Tuned Mass Damper (TMD) is one ofthe most widely used methods. In this study, investigations are made of the parametricoptimization, robustness and reliability analysis of vibration control by using bothSingle Tuned Mass Damper (STMD) and Multiple Tuned Mass Damper (MTMD) inthe presence of structural damping and modeling uncertainty. A pedestrian bridge inMian yang city, Sichuan is used to illustrate the mitigating effect of the TMD systems.The main research contents and achievements are introduced as follows:(1)An introduction of bridge vibrations and methods of vibration control aresummarized, and the TMD control theory is reviewed and the main work of the thesisis outlined.(2) The optimal parameter of STMD considering structural damping in mainstructure is obtained by using a numerical optimization method, and the relativedisplacement between TMD and the attendant structure is also formulated in thispaper. It is shown that the estimation formula of TMD relative displacement, asderived by Den Hartog based on the concept that the energy dissi pated by the TMD isequal to the work done by the applied loads, is merely suitable to calculate TMDrelative displacement in the resonance region (0.9</p<1.1) on the undampedstructure, and the TMD relative displacement is overestimated by using Den Hartogformula in the presence of structural damping.(3)A combined method of Monte Carlo simulation and pattern search scheme isutilized to obtain the optimal parameter of MTMD. The numerical results show thatMTMD outperforms than STMD in terms of control efficiency and wider frequencycontrol range. In the same mass ratio of MTMD, the control performance is enhancedfor increased number of TMD unit, and the optimal damping of each TMD unit isdecreased, resulting in the larger TMD relative displacement.(4) An analysis of robustness both on STMD and MTMD, by altering dynamicparameters of the controlled structure, is preformed. Analysis shows that the control efficiency is more sensitive to the variation of structural frequency than the variationof structural damping ratio. Increasing the mass ratio of TMD helps to promote therobustness of control efficiency.(5) Due to the uncertainty in TMD parameters, a probabilistic model is formattedto describe the uncertainty. The reliability of vibration suppress ion is alsoinvestigated. It is shown that the number of TMD in STMD system and MTMDsystem will affect the reliability of vibration suppression.(6) A numerical example based on a footbridge which located next to theMianYang city is studied, and then according to the bridge parameters which areacquired by ANSYS and field test, an optimal design of vibration reduction by usingTMD and numerical analysis is preformed, which verify the advantageous effect ofTMD for damping bridge vibrations.