平潭海峡公铁大桥钢桁梁预压主桁减小桥面系与主桁共同作用技术

Technique to Mitigate Deck-Main Truss Interaction of Steel Truss Girder by Preloading Main Truss for Pingtan Straits Rail-cum-Road Bridge

平潭海峡公铁大桥深水高墩区非通航孔桥采用跨径为80(88)m的双层钢-混结合简支钢桁梁结构。为减小简支钢桁梁桥面系与主桁的共同作用,改善公路横梁面外受力,针对传统方案的不足,提出了预压主桁上弦、缩短并滞后安装公路纵梁和副桁弦杆的方案。通过对3种预压方案比选,采用平行钢丝索预压主桁上弦方案。在主桁上弦两端设置张拉锚箱(锚箱间设置平行钢丝索,共8根),采用梁端对称张拉钢丝索的方式,分2个阶段(端部节间预压和中间节间预压)进行主桁上弦预压;在完成主桁上弦预压以及公路纵、横梁与副桁弦杆的组焊后,释放预压力,在公路横梁形成面外预反变形,从而抵消桥面系与主桁共同作用在公路横梁形成的面外弯曲。

The non-navigational channel bridge that is located in the deep water area and has high piers adopts the simply-supported steel truss structure of a steel-concrete composite system.The bridge accommodates separated upper and lower decks,with spans of 80(88)m in length.To mitigate the main truss-deck interaction of the simply-supported steel truss girder and improve the out-of-plane load bearing condition of the cross beams in vehicle deck,a scheme of preloading the upper chords of main truss,shortening the installation time and delaying the installation of the stringers and members of the subsidiary truss was selected,to overcome the disadvantages of the traditional methods.A number of three schemes were compared,and the one suggesting preloading the upper chord of the main truss by using parallel steel wire cables was employed.The anchor boxes for cable tensioning were installed on the two ends of the upper chord of the main truss,between which the parallel steel wire cables were installed and a total of 8 cables were used.The steel wire cables were symmetrically tensioned at the girder ends to preload the upper chord of the main truss in two phases,including preloading the end truss panels and preloading the central truss panel.After the completion of upper chord preloading for the main truss and the assembly and welding of stringers,cross beams and subsidiary truss members of the vehicle deck,the preloading pressure was released to force the cross beam to generate out-of-plane counter camber,so as to counterbalance the out-of-plane bending of the cross beams in vehicle deck induced by the main truss-deck interaction.