Study On Aerodynamic Measures And Vortex-Induced Vibration Performance Of Cable-Stayed Bridge With ? Section

As a typical blunt section,? section composite beam is very sensitive to wind.The windinduced vibration of ? type section,especially vortex-induced vibration(VIV),is a prominent problem.It is significant to study its vibration performances and aerodynamic measures.Aiming at ? section composite beam of cable-stayed bridges,the characteristics of VIV are discussed by means of wind tunnel tests and numerical simulations.The change laws of vibration responses with section parameters are studied and the effects of different aerodynamic measures are compared.The occurring reasons of VIV and action mechanisms of aerodynamic measures are also discussed.The main research contents of this paper are as follows:(1).The aspect ratio range of ? type section of cable-stayed bridges in engineering application is summarized and segmental model vibration tests of three aspect ratio models are carried out.The change laws of vibration responses with aspect ratio are studied.The characteristic of multiple VIV lock-in ranges and overlapping phenomenon of vertical bending and torsional VIV responses at high wind speed are discussed.According to the results,there are two vertical bending and torsional VIV lock-in ranges for different aspect ratio ? sections,in which the amplitude of low wind speed vertical bending VIV increases slightly with the increase of aspect ratio while the amplitude of low wind torsional VIV decreases with increase of aspect ratio.Also,there is an overlapping phenomenon between vertical bending and torsional responses at high wind speed ranges,during which the development of one vibration mode is affected by the energy transference of another mode.(2).The effects of wind fairings,lower central stabilizer,L-shaped deflectors and lower horizontal deflectors are compared.The change laws of effect of aerodynamic measures with aspect ratio of section and dimension parameters of measures.The effects of wind fairings,lower central stabilizers and lower horizontal deflectors are not universal while the effect of Lshaped deflector is the best.The larger its horizontal width and vertical height are,the better the effect will be.The VIV phenomenon disappears when the width and height are respectively equal to 2/3 and 1/2.(3).Numerical simulations of static flow around ? section were carried out and evolution lows of vortex shedding were analyzed by FLUENT.The occurring reasons of VIV and action mechanisms of aerodynamic measures were discussed by comparing the differences of flow pattern,vortex shedding and surface pressure distribution between original and aerodynamic sections.The results show that the re-attachment of the surface separated flow and karmanvortex-street on the original section are the main reasons of vertical bending VIV.Torsional vortex-induced force caused by huge pressures differences between the upper and lower surface at the leading edge is the main cause of torsional VIV.The disappearance of the re-attachment phenomenon is the main reason for eliminating the vertical bending VIV.The respectively distributions of positive and negative pressure on the lower surface of the leading and back-end of L-shaped deflectors counteract the torsional vortex-induced force of the original section,which suppresses the torsional VIV.