Cross-shaped downward-inserting conversion connecting structure of variable-cross-section steel pipe column

An upper partition plate and a lower partition plate are both located in the upper end of a lower circular pipe column and both connected with the lower circular pipe column, an upper circular pipe column is arranged on the upper partition plate, and a downward-inserting circular pipe column, the middle of a full-length stiffening plate, the right portion of a left stiffening plate and the left portion of a right stiffening plate are all located between the upper partition plate and the lower partition plate and all connected with the upper partition plate and the lower partition plate. The middle part of the full-length stiffening plate penetrates through and is connected with the front and rear parts of the upper end of the lower tubular column and the front and rear parts of the lower insertion tubular column along the front and rear directions; the right part of the left stiffening plate penetrates through and is connected with the left part of the upper end of the lower circular pipe column and the left