Study On Vortex-induced Vibration Of The Parallel Steel Boxgirders With Bowl-shaped Section

With the growth of population and economy,the demand for traffic volume has also increased sharply,and bridges with wider decks can meet the traffic demand.In actual bridge engineering,the structure of parallel double main girder bridges is usually adopted to meet the requirements.A large number of studies have shown that when the distance between the bridge decks is small,there will be a certain degree of aerodynamic interference between the two main beams,which will increase the vortex-induced resonance response of the bridge.In this study,with a 328 m main span cable-stayed bridge as a background,combined with wind tunnel test methods,the vortex-induced resonance performance of the double bridge main girder is studied.The main content of the study is as follows:(1)The development history of long-span bridges and bridge wind resistance research are reviewed,especially vortex-induced vibration research,and introduce the current wind resistance research of double-width bridges.(2)A wind tunnel test of a segmental model with a scale ratio of 1:60 was carried out to test the vortex vibration characteristics of a single main girder.By changing the net spacing between two girders and increasing the damping ratio of the model,the effects of the spacing and damping ratio of the girders on the vortex vibration starting wind speed,wind speed locking interval and the maximum amplitude of vortex vibration of a double bowl shaped steel box girder were studied in detail.At the same time,compared with the similar wind tunnel test results of Tianjin Tanggu Haihe Bridge,the difference of interference effect of different double girder section forms is explored.(3)Based on the calculation theory of vortex-induced vibration,combined with classical vortex-induced force model and vortex-induced force span correlation function,the vertical vortex vibration amplitude obtained from the wind tunnel test of the segment model is converted to three-dimensional full bridge span-wise vortex vibration amplitude,and based on the wind tunnel test results of the bridge,the vortex vibration limits in wind resistant codes of various countries are compared and studied.For the bowl-shaped steel box girder section studied in this study,the main research conclusions are as follows:(1)The vortex vibration characteristics of the double-width main beam are significantly different from that of the single-width main beam.In the double-width parallel state,for vertical vortex-induced vibration,the windward side main beam has a suppressive effect on the leeward side main beam vertical vortex-induced vibration,+5 °The vertical vortex-induced vibration amplitude of the main beam on the windward side at the angle of attack is greater than that of a single main beam,while the main beam on the leeward side has almost no obvious vibration;for the torsional vortex-induced vibration,the angle of attack is +3°,+5° The torsion amplitude of the next two main beams increases significantly at the same time,which is much larger than the torsion amplitude of a single main beam;(2)The starting wind speed and the wind speed lock zone of the vortex-induced vibration are not changed when the net spacing between the two main beams is changing.After the damping ratio is increased,the vortex response of the two main beams is significantly reduced;(3)Compared with the section of another double-width non-bowl-shaped main girder,the interference between the cross-sections of the double-width bowl-shaped main girder significantly increases the torsional vortex response of the main girder on both sides at the same time,but the response to the vertical vortex-induced vibration is on the windward side.The main beam restrains the vortex-induced vibration of the main beam on the leeward side.It shows that different types of main beam sections have different interference effects;(4)Whether to consider whether the cross-directional correlation of the vortex-induced force and the correlation of the mode shape have a significant impact on the calculation results of the real bridge amplitude.