A Preliminary Study On The Wind-induced Vibration And Evolution Mechanism Of The Old Tacoma Narrows Bridge

With the advancement of science and technology and the requirements of mankind,the bridge project will inevitably develop in the trend of a very large span and an ultra-long span.Wind resistance design of bridges will inevitably become one of the most critical factors in the bridge construction process.The wind damage of the old Tacoma Narrows Bridge is the most important event in the field of wind resistance in bridges,thorough research on it is necessary.So,the purpose of this paper is to study more precisely the wind-induced vibration and evolution of the old Tacoma Bridge.The main work of this thesis includes:(1)In this paper,based on a large number of predecessors' research work on H-sections similar to those of the old Tacoma Bridge,the refined model sections and the H-sections with relatively wide aspect ratio B/H=5:1 are compared.The Strouhal number and the critical wind speed of the flutter are closer to the real bridge than the H-section.At the same time,the influence of different torsional-bending frequency ratios on the vibration process was studied.It was found that when ?(27)20.1 was used,the model would suffer the same wind-destroying process as the old Tacoma Bridge.The experiment reproduces the vibration process of the old Tacoma Bridge.The phenomenon of vertical vibration suppression of torsional vibration was found and proved by designing a single degree of freedom torsion test.(2)The flutter derivative at the low wind speed of the old Tacoma Bridge section was identified by the forced vibration test,and the critical velocity of the flutter is the same as the free vibration test using the critical flutter velocity calculation method which verify correctness of flutter derivatives.The reason why the flutter instability of the bridge is clear is that the flutter derivative is caused by the negative change.(3)Based on the nonlinear Motion-Induced Aerodynamic Force(MIAF)Model,the first and third order components of the lift torque are analyzed.The work of aerodynamics during a vibration cycle was studied by using aerodynamic hysteresis theory.The aerodynamic mechanism of the "soft" flutter phenomenon of the old Tacoma Bridge is explained.By taking a work-equivalent approach,the torsional impetus aerodynamic damping including the aerodynamic damping of the three torque terms was considered.The aerodynamic mechanism of vertical vibration suppression torsional vibration is explained.