波形钢腹板矮塔斜拉桥施工阶段稳定性分析

Analysis on Stability of Extradosed Cable-stayed Bridge with Corrugated Steel Webs under Construction

波形钢腹板矮塔斜拉桥以其新颖的结构形式、优良的受力特性、较好的材料利用效率,修建数量日益增多,因其多采用薄壁钢腹板和刚构薄壁高墩的结构形式,使得对该类桥型施工过程中稳定性问题的研究就显得尤为重要。研究方法:利用ANSYS有限元软件建立朝阳沟波形钢腹板矮塔斜拉桥空间块体+板壳组合单元精细计算模型,计算纯剪切荷载作用下钢腹板的失稳模态;选取施工关键阶段,计算悬臂施工状态的弹性稳定性;考虑材料非线性、几何非线性和混凝土材料的开裂和压碎特性,计算悬臂施工状态非线性稳定性。结果表明:波形钢腹板构造按弹性屈曲强度公式计算最小值为348.3 MPa(合成剪切屈曲),有限元方法计算的剪切屈曲最小值为517.9 MPa,均大于材料剪切屈服强度199 MPa,结构承载力按剪切屈服强度控制;矮塔斜拉桥拉索的弹性支撑作用,增强了波形钢腹板稳定性,施工中主要是主墩的平面内侧倾失稳,不会出现波形钢腹板的失稳情况;考虑材料非线性和几何非线性求得悬臂施工阶段的非线性稳定系数仅为弹性稳定系数的41%～34%,悬臂越长,非线性效应对稳定性的影响越突出;施工荷载对悬臂施工状态的稳定性影响很大,最不利工况下结构的非线性稳定系数为5.13,结构稳定性仍满足规范要求。

With the new structural style, excellent mechanical performance and higher material utilization of extradosed bridge with corrugated steel webs, the number of this kind of bridge are increasing more and more. With application of thin-walled corrugated steel webs and rigid frame thin-walled high piers, the research on the stability of such kind of bridge during construction stage is becoming more and more important.Research methods: The instability modes of steel webs under pure shear force are obtained by utilizing the fine calculation model of Chaoyanggou extradosed cable-stayed bridge with corrugated steel webs which is modeled as space block and shell elements with ANSYS FE software. The elastic stability of the selected crucial cantilever construction stage is calculated. The nonlinear stability during cantilever construction stage is also calculated considering the material nonlinearity, geometric nonlinearity as well as concrete crush and crack. The result shows that(1) The minimum elastic buckling strength of the bridge corrugated steel webs calculated by the formula is 348.3 MPa(interactive shear buckling), and that calculated by the finite element method is 517.9 MPa, which are all larger than the material shear yield strength(199 MPa). The bearing capacity of structure is controlled by the shear yield strength.(2) The stability happened happened of corrugated steel webs is enhanced because of the elastic supports of bridge cables, so the main instability mode is not the corrugated steel webs instability, it is the in-plane lateral buckling of main pier during the construction stage.(3) The nonlinear stability coefficient of cantilever construction stage considering material and geometric nonlinearity is 41%-34% of elastic stability coefficient. When the cantilever length increases, the influence of nonlinear effect on the stability will become more obvious.(4) The construction loads have significant impact on the stability of cantilever construction stage, the nonlinear stability coefficient under the most unfavorable load case is only 5.13, but the structure stability still satisfies the specification requirements.