考虑局部屈曲加劲钢箱形构件极限承载力的纤维梁柱模型

Fiber beam-column element model for ultimate bearing capacity of stiffened steel box section members considering local buckling

大型桥梁加劲钢箱形构件的极限承载力会受到板件局部稳定性能的影响,而目前尚缺乏成熟的可直接计入局部屈曲的高效计算模型。归纳总结国内外钢构件计算方法对局部屈曲的处理方式,明确以有效应力法即采用板件(或加劲板)平均受压应力-应变曲线简化局部屈曲效应的研究思路。通过有限元程序ANSYS二次开发钢板拉压非对称本构模型,提出一种可直接计入局部屈曲的纤维梁柱模型。材料本构模型中受压应力-应变曲线通过小型的加劲板板壳模型得到,且全面考虑了焊接残余应力与几何缺陷。搜集已开展的钢箱梁、钢桥塔及钢拱肋的稳定性试验,采用提出的纤维梁柱模型、板壳模型与传统弹塑性梁柱模型进行分析,展示截面纤维划分策略,验证文中纤维梁柱模型的可靠性与高效性;通过设置不同的缺陷参数,探讨缺陷水平与局部屈曲对各个构件极限承载力的影响。研究表明,随着缺陷水平的严重,局部屈曲会显著降低极限承载力,提出的纤维梁柱单元模型能够有效地预测加劲钢箱形构件的极限承载力,具有较广泛的应用前景。

Ultimate bearing capacity of large stiffened steel box section members for bridges is affected by plate local buckling,but a highly efficient calculation model which can directly include local buckling is still lacked.Through summarizing the approaches to consider local buckling in current computational methods for steel members,it is proposed to use the average compressive stress-strain curves to simplify the local buckling effects.A novel fiber beam-column element model considering the local buckling for stiffened steel box section members is then presented.It is implemented through the development of the unsymmetrical uniaxial constitutive model in the ANSYS program interface.Noted that,the compressive part of the unsymmetrical uniaxial constitutive model,namely the average compressive stress-strain curve of stiffened plates,is obtained from the shell finite element model,in which geometrical imperfections and residual stresses are simulated.Experimental specimens of steel box girder,steel tower,and steel arch rib in literature are respectively analyzed using the proposed beam-column element model,shell finite element model,and the conventional elastic-plastic beam model.The modelling strategy of the stffened steel box section using the fiber section method is illustrated.And the proposed beam-column model is validated.The influence laws of defect level and local buckling on the ultimate bearing capacity of the specimens are discussed.The results show that with the deterioration of defects,the ultimate bearing capacity of the stiffened box section members decreases significantly due to local buckling.The proposed fiber beam-column element model can effectively predict the ultimate bearing capacity of stiffened steel box section member with a wide prospect of application.