Research on Stability of Curved Steel Pylon of Cable-Stayed Bridge

Curved steel pylon of cable-stayed bridge has the characteristics of complex cable shape, large overall slenderness ratio, and the overall structure is composed of thin-walled members. Its stability has become the key control factor of structural design. In order to research the stability of the curved steel pylon under the main vertical loads such as dead weight, dead load of the bridge superstructure from the cable system and vehicle load, further clarify the element type selection, instability mode and stress characteristics, a curved steel pylon cable-stayed bridge with a span of ( 200+ 200) m is taken as the research object, and the ANSYS general finite element software is used to establish a spatial beam element model and a spatial shell element model for the steel pylon. The model is numerically calculated and analyzed for its stability to obtain the instability mode and instability critical load in the elastic state, as well as the ultimate bearing capacity, the stress distribution, structural deformation in the ultimate bearing capacity state after considering the influence of nonlinear factors. In the spatial beam element model, Beam 4 element is used to simulate the main girder of the cable-stayed bridge as a fishbone model, Link 10 element is used to simulate the cable and the initial tension is applied, and Beam 188 element is used to simulate the pylon. In the spatial shell element model, the main beam and cable are simulated in the same way as the beam element model, and Shell 143 element is used to simulate the pylon according to the actual structure. The material nonlinear simulation of Q345 steel used in the pylon adopts the MKIN model, and the first-order buckling mode obtained in the first type of stability analysis is taken as the shape of the initial geometric defect of the structure.
Through calculating:1) The first type stability safety factor of the pylon calculated using the beam element model is 94. 51, and the second type stability safety factor, which considering the effects of double nonlinearity and structural initial defects, is 19. 89. The first type of stable instability mode of the pylon calculated by the spatial shell element model is firstly shown as local out-of-plane buckling of the wall plate, the corresponding stability safety factor is 25. 15, and the stability safety factor is 61. 42 in case of overall instability; 2) The second type of stability has a minimum safety factor of 12. 90, and the instability mode is local instability. The stress and elastic strain concentration areas of the outer wall and stiffeners of the pylon are mainly located in the middle of the cable. The stress and elastic strain concentration area of the stiffeners, middle webs and diaphragm inside the pylon is mainly located at the diaphragm at the cable, and the plastic strain inside the pylon is mainly concentrated in the cable anchorage area of the diaphragm. The two types of instability modes of the steel pylon calculated by the shell element model are local buckling, and the corresponding buckling load characteristic value is much smaller than that of the overall instability. It is necessary to pay attention to the stress and deformation of key parts such as the wall plate and the inner anchorage zone of the pylon when making stability and safety judgment.