矮塔斜拉桥钢箱梁超高腹板局部稳定性分析

Local Stability Analysis of Ultra-High Web of Steel Box Girder of Short Tower Cable-Stayed Bridge

随着钢结构桥梁跨径的增大,腹板高度也随之增高,给结构的局部稳定性带来了较多隐患。鉴于宁波中兴大桥钢箱梁超高腹板局部稳定性问题,采用有限元软件ANSYS建立局部节段模型,给出相应边界条件和荷载工况,模拟压、弯、剪复合荷载作用对腹板局部稳定的影响。研究表明:腹板竖向加劲的布置对维持腹板的稳定十分重要,若不设置腹板竖向加劲肋,第一阶弹性屈曲失稳稳定系数为2.9<4.0,不符合设计最低要求;当腹板厚度从12 mm增加到22 mm时,线弹性稳定系数可以从4.1提高到6.0,但钢箱梁失稳模态仍为外腹板失稳;当腹板线弹性稳定系数大于设计限值4.0且弹塑性强度稳定安全系数大于设计限值1.75时,进一步增大竖向加劲肋刚度的必要性有限。

Structural instability refers to the loss of equilibrium when the external forces on the structure reach a certain level,and the deformation increases rapidly with a slight disturbance,eventually causing the structure to be damaged.As the span of steel bridge increases,the web height also increases,which brings more potential problems to the local stability of the structure.In view of the local stability of the super high web of the Ningbo Zhongxing Bridge,this paper uses the finite element software ANSYS to establish the local segmental model,gives the corresponding boundary conditions and load conditions,and simulates the effect of the composite load of compression,bending and shear on the local stability of the web.The study shows that:the arrangement of vertical stiffening of web is very important to maintain the stability of web;if no vertical stiffening ribs of web are set,the first-order elastic buckling instability stability coefficient is 2.9<4.0,which does not meet the design minimum requirement;when the thickness of web increases from 12 mm to 22 mm,the linear elastic stability coefficient can be increased from 4.1 to 6.0,but the instability mode of steel box beam is still external web instability;when the thickness of web increases from 12mm to 22 mm,the linear elastic stability coefficient can be increased from 4.1 to 6.0,but the instability mode of steel box beam is still external web instability;when the linear elastic stability coefficient is greater than the design limit of 4.0 and the elastic-plastic strength stability safety factor is greater than the design limit of 1.75,the need to further increase the stiffness of the vertical stiffening ribs is limited.