跨海大桥U-RC组合桥墩设计

Design of U-RC composite pier of sea-crossing bridge

为解决跨海桥梁桥墩施工与防腐问题,提出了超高性能混凝土(UHPC)-钢筋混凝土(RC)组合桥墩新结构,简称U-RC组合桥墩,以UHPC外筒作为永久模柱,现浇内核钢筋混凝土;以平潭海峡大桥为工程背景,开展了U-RC组合桥墩的结构设计与计算,并与原设计方案的工程量和造价进行了比较;进行了3根内核RC柱、3根UHPC模柱、3根U-RC组合桥墩的极限承载力试验,测量了试件的混凝土纵向应变与横向应变,研究了试件的破坏形态与裂缝发展过程,得到了试件的极限承载力试验值,分析了U-RC组合桥墩的受力性能。研究结果表明:U-RC组合桥墩的承载力大于设计内力,满足现行规范要求;采用UHPC模柱取代钢模板的桥墩设计方案,可节约钢材约2 410t,工程造价节省约30%;3根UHPC圆筒的极限荷载均值为1 342kN,3根RC柱的极限荷载均值为1 370kN,二者之和小于3根U-RC组合桥墩极限荷载均值3 033kN,说明UHPC模柱对核心混凝土有一定的套箍作用,采用简单迭加方法计算U-RC组合桥墩的轴压极限承载力是可行且偏保守的;在轴压试验中,U-RC组合桥墩的破坏模式为核心混凝土的横向变形导致UHPC模柱出现竖向裂缝,并与核心混凝土在界面处分离;达到极限荷载破坏时,外包UHPC层出现纵向裂缝,荷载增大,裂缝增长,并有混凝土剥落现象,但U-RC组合桥墩破坏时其外包UHPC层纵向应变未达到极限压应变。

In order to solve the construction and anti-corrosion problems of pier of sea-crossing bridge,a new structure of composite pier of ultra-high performance concrete（UHPC）and reinforced concrete（RC）（short for U-RC composite pier）was designed,and UHPC cylinder was taken as permanent cylinder to cast core reinforced concrete.The Pingtan Strait Bridge was taken as project background,the structure design and calculation of U-RC composite pier were carried out,and the workload and cost of U-RC composite pier were compared with the ones of original design scheme.The ultimate bearing capacity tests of three core reinforced concrete columns,three UHPC cylinders and three U-RC composite piers were carried out,the longitudinal andtransverse strains of concrete for the specimens were measured,the failure modes and the developments of cracks were observed,the test values of ultimate bearing capacities were obtained,and the mechanical properties of U-RC composite pier were analyzed.Research result indicates that the bearing capacity of U-RC composite pier is greater than the design value of internal force,which meets the current specification requirement.The design scheme that adopts UHPC cylinder to replace steel template,can save about 2 410 tof steel,and the total cost saves nearly 30%.The average bearing capacities of three UHPC cylinders and three RC columns are1 342 kN and 1 370 kN,respectively,and their sum is less than the average bearing capacity of three U-RC composite piers（3 033 kN）,which indicates that the UHPC cylinder has certain confinement effect for core concrete,and it is feasible and conservative to calculate the ultimate bearing capacity of U-RC pier under axial compression with simple superposition method.In the axial compression experiment,the failure mode of U-RC composite pier is that the lateral deformation of core concrete leads to the vertical fracture of UHPC cylinder and the separation of UHPC and core concrete at the interface.At the ultimate load,the coating UHPC layers have vertical cracks that grow with the increase of the load,and the flaking and spalling phenomena of concrete appear.But when the U-RC composite pier is damaged,the longitudinal strain of coating UHPC does not reach the ultimate compressive strain.