Bridge erecting machine and span crossing method thereof

According to the bridge girder erection machine and the span crossing method thereof, the middle supporting guide rail in the bridge direction can be arranged on the erected beam plate, the first hoisting crown block and the second hoisting crown block are moved to the rear portion of the main beam, and the second hoisting crown block and the erected beam plate are anchored. The front branch guide rail is temporarily fixed on the front branch device, and the front branch device and the front branch guide rail are separated from the front cover beam. And after the rear supporting device is lifted and collected, the middle supporting walking wheel box moves forwards along the middle supporting guide rail, and the first hoisting crown block and the second hoisting crown block move backwards until the second hoisting crown block moves to the tail end position of the main beam. And the anchoring of the second hoisting crown block and the erected beam plate is relieved, and the second hoisting crown block and the e