The Structure Strength Research Of Steel Anchor Box Based On The Sub-modeling Method

In order to make theoretical research in strength of steel anchor box structure on a cable stayed bridge,detailed finite element calculation and related analysis are made in this paper using the sub-modelingmethod of ANSYS software, which take the steel anchor box over the maximal cable force in SZ28beamfrom one Yangtze River Bridge for example.The results find that there are stress concentrations on steel anchor box, which lead to the no uniformstress transform and over-admission-stress valve, especially when the structure of the steel anchor box isnot reasonable, such as the unreasonable way of plate layout and the inappropriate plate structure. Throughthe stress concentration is reduced sharply and all the stresses are within the admission after the structureimprovement, the situation can and will not disappear according to the theory of cable force transformation.Therefore monitoring is needed when the steel anchor box is working. The calculation shows the cableforce is transformed in the way of pressure stress in the steel anchor box and that the pressure stress valveis a bit higher in each plate of the steel anchor box. Meanwhile the cable force is transformed in the mainwelding line as shear force primarily and tensile force (pressure force) secondary, the latter results from thelocal bending moment of the eccentric cable force. But because of the large vertical seize of the steelanchor box and the local structure break, the small tensile force result in high tensile stress at the bottom ofcombination between the anchor box and the web plate of the beam, and the small pressure force result inhigh pressure stress at the top of combination between the anchor box and the web plate of the beam. Thecalculation of the stress amplitude because of the vehicle dynamic load using the nominal stress and hotstress recommended by International Institute of Welding (IIW) and classification societies shows that thefatigue stress amplitude of the steel anchor box is within the admission valve recommended by standards,which means that the vehicle dynamic load can affect less on the steel anchor box.Aiming at the improvement steel anchor box structure, the advantage of sub-modeling method isobtained by comparing the results of sub-modeling method, traditional equivalent plate thickness methodand the nonlinear contact method, which can be concluded as follows: the lower difficulty of modeling andmore accurate of the result, especially the shell-to-solid skill used in this paper, which can reflect thethickness effect of each plate. Therefore sub-modeling method is an effective way in analysis andcalculating the local small size structure of big complex structure.