铁路简支梁桥上部结构洪水荷载计算方法及应用

Water Load Computational Method of Superstructure of Simply Supported Girder Railway Bridge and Application

在发生极端洪水时,铁路桥梁上部结构可能会被淹没,在洪水荷载作用下出现滑移、倾覆等。针对常见铁路简支梁桥上部结构形式,采用计算水动力学方法对上部结构洪水荷载的影响因素及计算方法开展研究,并应用于桥梁上部结构抗洪能力分析。结果表明:洪水作用在桥梁上部结构的水平推力、竖向升力和倾覆力矩主要受淹没度、接近比、弗劳德数、截面形式、宽高比等因素影响;淹没度的影响最显著,各分力系数在上部结构从部分淹没变为完全淹没的过程中变化较大,但淹没度大于3之后保持不变;接近比在小于4时有增大洪水荷载的作用;弗劳德数越大,洪水荷载系数越小;在完全淹没条件下,宽高比越小的结构所受洪水荷载越大;相同条件下箱梁比T梁所受推力和升力更小,但力矩更大。位于水流湍急河段的桥梁一般在部分淹没状态下以滑移失稳形式水毁,其中铁路箱梁的抗洪性能最优,单线T梁的抗洪性能最差。

During extreme floods,the superstructures of railway bridges may be submerged and may experience damage such as slipping and overturning under the action of water load.Focusing on the common form of superstructure of simply supported girder railways bridge,this study employs computational fluid dynamics methods to investigate the influencing factors of water loads on superstructure,computational methods,and their application in the assessment of bridge flood resistance capabilities.The results indicate that the horizontal drag,vertical lift,and overturning moment acting on the bridge superstructure are mainly influenced by factors such as inundation ratio,proximity ratio,Froude number,cross-sectional form,and aspect ratio.Among them,the inundation ratio has the most significant impact,with each component force coefficient changing significantly as the superstructure transfers from partially submerged to fully submerged,while these coefficients remain unchanged once the inundation ratio exceeds 3.The proximity ratio increases the water loads when it is less than 4.The larger the Froude number,the smaller the water loads coefficient.Under fully submerged conditions,structures with a smaller aspect ratio experience greater water loads.Under the same conditions,box girders experience less drag and lift but greater moment than T-beams.Bridges located in rapidly flowing river sections generally fail by slipping in a partially submerged state,among which railway box girders have the best flood resistance performance while single-line T-beams have the worst.