Large-span flexible arch skew back joining construction method

The invention discloses a large-span flexible arch skew back joining construction method. The method includes steps that (1) a beam erecting crane is mounted on an upper chord member of a steel truss beam when skew backs of the steel truss beam are pushed to a position above a temporary pier support; (2) the beam erecting crane automatically runs to positions of the skew backs after being mounted and debagged, and begins to erect flexible arch members, a one-way backslide method for erecting is adopted for the beam erecting crane, suspenders are mounted at first, then a flexible arch temporary support is mounted, and finally arch ribs are mounted; (3) the step (2) is repeated until only a last arch section space of a flexible arch is not erected, and a skew back joining opening is reserved; and (4) a finite-element analysis software is utilized to realize analog computation for the state of the joining opening, and a software analysis result basically matches with an actual joining opening measurement result, but still has vertical deviation, transverse deviation and longitudinal and horizontal deviation. By the aid of the method, the flexible arches can be erected outside an operation limit of a highway, stress-free joining of the skew backs of the flexible arches is realized, and the difficulty in erection of the flexible arches above the highway is resolved.