Lightweight main beam structure of large-tonnage crane

Relates to the technical field of cranes, in particular to a light-weight girder structure of a large-tonnage crane. The light-weight girder structure comprises a box groove body consisting of a top plate, two end plates and two inverted trapezoidal side plates, a long notch hole is formed in the center of the plate face of the side plate so that the side plate can be in a frame plate shape, the upper hole edge of the long notch hole is arranged to be an upper arc edge protruding downwards in an arc mode, the lower hole edge of the long notch hole is arranged to be a lower arc edge protruding upwards in an arc mode, and a plurality of inclined supporting plates arranged in the length direction of the side plate at intervals are connected between the upper arc edge and the lower arc edge. The inclination directions of every two adjacent inclined supporting plates are opposite, and rib plates in the axial direction of the inclined supporting plates are fixed to the inner plate faces of the inclined supporting p