超大跨混合梁斜拉桥极限承载能力研究

Study of Ultimate Load Bearing Capacity of Very Long Span Hybrid Girder Cable-Stayed Bridges

为研究超大跨混合梁斜拉桥在汽车荷载作用下的塑性区发展过程和极限状态下的破坏机理,以贵州鸭池河特大桥(主跨800m双塔双索面混合梁斜拉桥,边跨主梁采用预应力混凝土箱梁,主跨主梁采用钢桁梁)为背景,采用ANSYS软件建立全桥有限元模型,逐级施加汽车荷载,分析不考虑断索和考虑断索2种情况下该桥的破坏过程和承载能力。结果表明:随着荷载的增加,钢桁梁先产生受压塑性区和受拉塑性区,随后斜拉索到达屈服应力;不考虑断索情况下,斜拉索逐步屈服后钢桁梁受压塑性区和受拉塑性区不断扩大,结构最终失效,破坏表现出略好的延性;考虑断索情况下,第1根斜拉索屈服后断裂引起周围斜拉索的连续瞬时断裂导致结构破坏,破坏呈现明显的脆性;不考虑断索和考虑断索情况下,极限状态时的荷载系数λ分别为11.69和11.12。

To study the development processes of the plastic zones of the very long span hybrid girder cable-stayed bridges under the truck loads and the failure mechanism of the bridges under the ultimate loads,the Yachi River Bridge（a hybrid girder cable-stayed bridge with double pylons,double cable planes and with a main span of 800 m.The main girders for the side spans being the prestressed concrete box girders while the main girder for the main span being the steel truss girder）in Guizhou was cited as an example.The software ANSYS was used to create the finite element model for the whole bridge of the bridge and by way of applying the truck loads in grades,the failure processes and load bearing capacity of the bridge under the 2 cases that the breaking of the stay cables was considered or not considered were analyzed.The results demonstrate that with the increase of the truck loads,the compressive and tensile plastic zones appear in the steel truss girder first and after that,the stay cables will reach the yielding stress.Under the case that the breaking of the stay cables is not considered,following the gradual yielding of the cables,the compressive and tensile plastic zones of the truss girder increasingly develop,the structure will eventually fail and the failure of the structure in such case exhibits the slightly good ductility.Under the case that the breaking of the stay cables is considered,the breaking of the first stay cable after the yielding of the cable causes the adjacent cables to successively and instantaneously break,will eventually cause the structure to fail and the failure of the structure in such case exhibits the obvious brittleness.Under the case that the breaking of the cables is considered or not considered,the load coefficientsλat the time of the ultimate state are respectively 11.69 and 11.12.