Closure method for mid-span steel box girders of large-span floating system cable-stayed bridge

The invention discloses a closure method for mid-span steel box girders of a large-span floating system cable-stayed bridge. The closure method comprises the following steps: temporary longitudinal bridge direction limiting is conducted on steel box girder sections at a main tower; the mid-span steel box girders are assembled by a cantilever; the mid-span steel box girders on the two sides of a closure opening are monitored, and a closure section steel box girder is manufactured according to the monitoring result; the temporary longitudinal bridge direction limit is released, the mid-span steel box girders in the direction away are moved from the closure gap, and first temporary locking is carried out; the closure section steel box girder is hoisted; the first temporary locking is released, the mid-span steel box girders are moved towards the closure gap to be reset, and second temporary locking is carried out; the relative postures of the closure section steel box girder and the mid-span steel box girders ar