Preloading device and preloading method for hanging basket anchorage pull rod-type jack of bridge box girder

The invention discloses a preloading device and a preloading method for a hanging basket anchorage pull rod-type jack of a bridge box girder. The preloading device comprises a hanging basket, a front lower cross beam, a rear lower cross beam, a bottom mold support platform, a pair of steering frames and a plurality groups of hanging basket and bottom mold support platform preloading mechanisms. The preloading method comprises the following steps: 1) fixing the pair of the steering frames and pre-burying a nut sleeve; 2) mounting and positioning a feedthrough jack support seat; 3) mounting a preloading force transfer piece; 4) preloading the hanging basket and the bottom mold support platform by the preloading force transfer piece. The preloading device disclosed by the invention is compact in structure and convenient to use; according to the preloading method disclosed by the invention, the preloading load can be reduced automatically to ensure safe use when the hanging basket and the bottom mold support platform are deformed greatly by over-high stress. By the preloading method disclosed by the invention, load can be applied to two points symmetrically and the load can also be applied to a plurality of points symmetrically, so that the preloading method is flexible; the preloading device and the preloading method are low in cost and can be used repeatedly, the test cycle is greatly shortened, and the test cost is reduced.