斜拉桥曲线钢桥塔稳定性能研究

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

斜拉桥曲线钢桥塔具有线型较为复杂、整体长细比较大、整体结构均由薄壁构件组成等特点,其稳定性已成为结构设计的关键控制因素。为了研究曲线钢桥塔在自重、缆索系统传来的桥梁上部结构恒载以及汽车荷载等主要竖向荷载作用下的稳定性,进一步明确钢桥塔建模的单元类型选择、失稳模态和受力特征,以一座跨径布置为(200+200)m的曲线形钢塔斜拉桥为研究对象,采用ANSYS通用有限元软件对钢桥塔分别建立空间杆系单元模型和空间板壳单元模型,对其稳定性进行数值仿真计算与分析,得到弹性状态下的失稳模态和失稳临界荷载,以及计入非线性因素影响后的极限承载力、极限承载力状态下的应力分布和结构变形。空间杆系单元模型采用Beam4单元将斜拉桥主梁模拟为鱼骨刺模型,采用Link 10单元模拟拉索并施加初始张拉力,采用Beam 188单元模拟桥塔。空间板壳单元模型中,主梁和拉索的模拟方式与杆系单元模型相同,桥塔则采用Shell143单元按实际构造进行模拟。桥塔所用Q345钢材的材料非线性模拟采用多线性随动强化模型,并取第一类稳定分析中得到的一阶屈曲模态作为结构初始几何缺陷的形状。计算可得:1)采用空间杆系单元模型算得的桥塔第一类稳定安全系数为94.51,计入双重非线性和结构初始缺陷影响的第二类稳定安全系数为19.89。采用空间板壳单元模型算得的桥塔第一类稳定失稳模态首先表现为壁板局部的面外屈曲,对应的稳定安全系数为25.15,发生整体失稳时对应的稳定安全系数为61.42;2)第二类稳定最小安全系数为12.90,失稳模态表现为局部失稳,桥塔外壁和加劲肋的应力及弹性应变集中区域主要位于拉索中部区域,桥塔内部的加劲肋、中腹板和横隔板构件的应力与弹性应变集中区域主要位于拉索处的横隔板,桥塔内部塑性应变主要集中于横隔板的拉索锚固区域。板壳单元模型算得的钢桥塔两类失稳模态均表现为局部屈曲,对应的屈曲荷载特征值远小于整体失稳对应的屈曲荷载特征值,进行稳定安全性判断时需重点关注壁板、塔内拉锚索区等关键部位的受力和变形情况。

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 cablestayed bridge as a fishbone model,Link10 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 Shell143 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.