Research on Flutter Stability of Three-Tower Four-Span Suspension Bridge at Construction Stage
This paper studies the flutter stability of the suspension bridge with two main spans during the erection of the stiffening girder.An existing suspension bridge with two main spans of 800 m and two side spans of 230 and 348 m is used as a case.The different erection stages of the suspension bridge were numerically simulated to analyze the characteristics of the vertical and torsional vibration modes of the bridge.The equation to calculate the ideal flutter critical wind velocities on flat deck was used to calculate the flutter critical wind velocities at different erection stages of the stiffening girder and under different combinations of vibration modes,to determine the most unfavorable erection stage and mode combination.Based on the calculations,wind tunnel tests were conducted to investigate the flutter critical wind velocities of the original stiffening girder and those of the stiffening girder equipped with vertical stabilizers along the longitudinal centerline of the bridge.It was shown that the modal characteristics of the three-tower four-span suspension bridge at the construction stage were complex,during the flutter analysis,the intervention of one main span to the other should be considered.When the erection of the stiffening girder was completed at rates of 8.5%and 19.8%,the flutter critical state should be determined in accordance with the flexural-torsional mode combination with vibrations of the north main span as the dominance.When the erection of the stiffening girder was completed at a rate of 29.3%or above,the flutter critical state should be determined in accordance with the flexural-torsional mode combination with vibrations of the south main span as the dominance,and the completion of 40.8%was the most unfavorable condition.The flutter critical wind velocities of the original stiffening girder of the bridge were low,after added with vertical stabilizers along the longitudinal centerline of the bridge,the flutter critical wind velocities have been effectively improved.