Analysis Of Mechanical Characteristics Of S-curved Cable-stayed Bridge With Steel Box Girder

The S-curved steel box girder cable-stayed bridge is a kind of multi-curved cablestayed bridge,whose structure is more complicated than that of straight or singlecurved cable-stayed bridge.Due to the fact that the numbers of this kind of bridges are far less than that of straight cable-stayed bridges,there are not many relevant studies.The abnormal phenomena such as beam transverse displacement,deflection,downwarping and bearing void are easy to occur during construction or use.The main reason for these phenomena is that the stress characteristics are not fully recognized by people,and the results of design calculation are quite different from the actual situation.Based on the research results of domestic and foreign,this paper takes an actual Scurved steel box girder cable-stayed bridge as an example to discuss the mechanical behavior under the loads of temperature,vehicle and earthquake to enhance the understanding of stress characteristics for this kind of bridges.The results can provide reference for the design and construction of such bridges.The main research contents and conclusions are as follows:(1)The appropriate calculation model was discussed and validated.Combined with the actual bridge construction monitoring,the finite element software was used to establish a calculation model with the shell element and beam element.The applicability of the calculation model was verified by comparision with the beam element model and field measured data.(2)The temperature effect of asphalt concrete pavement was analyzed.The model established by shell element and beam element was applied to analyze the changes of temperature stress and displacement of the bridge in the process of asphalt concrete pavement.The results show that due to the effect of paving temperature,large deformation and stress appeared in the structure,and the bridge had a certain degree of torsion.The maximum longitudinal displacement of the girder was 22.8 cm,the maximum vertical displacement was 25.9 cm,the maximum torsion angle was 2.96 degree,and the maximum tensile stress of steel box girder was 143.0 MPa,which may endanger the safety of the structure.It is suggested that asphalt concrete paving should be considered as an important working condition in design and calculation,and the continuous paving should be replaced by intermittent paving.(3)The effect of ambient temperature was analyzed.The changes of structural displacement and stress under the action of annual temperature difference and sunshine were calculated respectively.The results show that under the action of sunshine,the longitudinal deformation of the bridge was large,the vertical deformation and lateral displacement were small.The torsion effect of ambient temperature on bridge was small,which was far less than that of asphalt concrete pavement.The maximum compressive stress of the structure was 69.2 MPa,the maximum tensile stress was 60.4MPa under sunlight,which were smaller than the temperature effect of asphalt concrete pavement.(4)The torsion effect of vehicle was analyzed.The effects of lane loading,centrifugal force and impact force under eccentric load were calculated.The results show that the torsion of box girder was obvious when the lateral loads were unbalanced.The warping effect was obvious in the most bending section with lateral partial load under the action of centrifugal force of vehicle.The torsion effect of the bridge under the most unfavorable load was calculated.In order to improve the torsional effect of the bridge,the torsional effect of the bridge after pasting GFRP was calculated,and it was concluded that pasting GFRP can significantly improve the torsional effect of the bridge.(5)The seismic effect of the bridge was analyzed.The dynamic characteristics of the bridge were analyzed,and the appropriate seismic wave was selected,the dynamic time-history of one-dimension and multi-dimension were analyzed.The dynamic characteristics and seismic response of the bridge were discussed.It was concluded that the vertical displacement and transverse torsional deformation were obvious,and the torsional displacement and torque of the main girder were large under the action of transverse seismic wave.The results show that the torsional displacement of the main girder was the smallest due to the longitudinal seismic wave excitation,which can be ignored.The torsional displacement produced by the vertical seismic wave excitation was the second,which was 4.51 degrees.The transverse seismic wave excitation had a greater impact on the torsional displacement of the main girder,which was 6.12 degrees,and it was close to the torsion displacement produced by the seismic combination condition 5 and 6.It was the decisive factor for the transverse torsion of the main girder.