Static And Dynamic Wind Performance Analysis And Research On Influencing Factors Of A Cable-stayed Bridge Over The Han River

With the continuous improvement of bridge theoretical knowledge and the demand for bridge spans when crossing rivers,canyons and oceans,bridge design is more and more inclined to adopt light and long-span structural forms on the basis of satisfying safety.The structural stiffness of such long-span bridges decreases continuously due to the increase of the span,while the softness of the structure makes it very sensitive to the external wind environment.At present,the problem of wind-induced bridge vibration has become a control factor that must be considered in the wind-resistant design of large-span bridges during construction and operation.Therefore,this paper takes a proposed twin-tower and double-cable plane cable-stayed bridge over the Han River with a main span of 370m as the engineering background to study the static and dynamic wind performance and influencing factors of this long-span cable-stayed bridge.The purpose of this study is to provide a reference for the preliminary wind resistance design of the Han Jiang Bridge.This paper mainly focuses on the following aspects:(1)A three-dimensional finite element dynamic model of the Han Jiang Bridge was established by ANSYS APDL and its dynamic characteristics were calculated.The study found that compared with the closed box-section cable-stayed bridge of the same span,its torsional bending ratio is smaller,the torsional stiffness is insufficient,and the structure is more likely to have bending-torsional coupling flutter,which reflects the importance of wind resistance analysis of openπ-section.In addition,the equivalent mass per unit length of the main beam is calculated to provide data preparation for the later numerical simulation.(2)The two-dimensional grid calculation model of theπ-shaped beam section of the Han Jiang Bridge was established by Pointwise software,and the static wind three-component force coefficient of the bridge section was identified by the software Fluent.Then,the influence of different parameters on the three-component force coefficient is further considered on this basis.The study found that the change of the slope ratio of the bridge deck has a great influence on the resistance coefficient and the wind resistance design,the three-component force coefficient obtained from the bridge section without the transverse slope can be used for the subsequent wind resistance analysis;the difference of the three-component force coefficient between the condition with guardrail in the completed bridge state and the condition without guardrail in the construction stage is obvious and the wind resistance design should be calculated and analyzed separately for these two conditions;the beam height change within±12.0%has little effect on the blunt characteristics of the bridge section,and the beam height can be appropriately adjusted based on this range and other factors in the design.(3)A two-dimensional grid calculation model of"rigid motion area+dynamic grid area+static grid area"was established.With the help of the software Fluent,based on the loose coupling method,the self-compiled Newmark-βalgorithm program is docked with Fluent to solve the wind-induced vortex vibration problem of the bridge section.The amplitudes of the vertical degrees of freedom of the bridge section and the vortex shedding frequency changes under different incoming wind speeds are obtained by calculating the vortex-induced response of 9 wind speed conditions under the 0°wind angle of attack,and the"locked"interval is determined.Then,the instantaneous vortex shedding change and vertical vortex vibration mechanism of the beam section in a complete cycle are further analyzed.Finally,the influence of three groups of different vertical damping ratios within 1%of the maximum allowable value on the vortex-induced vibration performance is considered.It is found that the vertical vortex vibration of the bridge is not very sensitive to the change of damping ratio.(4)The same two-dimensional grid calculation model was used as in the vortex-induced vibration simulation,and the flutter derivatives were identified by the time-domain method of forced vibration flutter derivatives using the software Fluent.Then,the critical wind speed of the Han Jiang cable-stayed bridge was identified by using MATLAB to compile the Scanlan two-dimensional flutter critical wind speed calculation program.By comparing with the flutter test wind speed at the bridge site,it is found that the bridge is not prone to flutter damage.Finally,the effects of wind angle of attack and the slope rate of the bridge deck on the flutter stability of the Han Jiang Bridge are analyzed.The study found that the change of the wind angle of attack in the range of-5°-5°has a great influence on the flutter derivatives H~*1,H~*2,H~*3,H~*4,and the maximum change of H~*2 is close to 50%.Within the reduced wind speed of 13,the changes of the three bridge deck cross-slope slope ratios of 0%,1.5%and 2%have little effect on the aerodynamic derivatives of theπ-shaped beam section.The presence of 1.5%and 2%cross-slope ratios increases the critical flutter wind speed of the bridge compared with the case of no bridge deck cross-slope.