Lower side bed frame of double-layer iron frame bed

A lower side bed frame of a double-layer iron frame bed, comprising:

• two transverse rods symmetrically parallel to each other in a front-and-rear direction,
• two longitudinal rods symmetrically parallel to each other in a left-and-right direction,
• four columns arranged vertically,
• two supporting feet, and
• a connecting rod for connecting the two supporting feet, wherein:
• the two longitudinal rods and the two transverse rods form a rectangular frame,
• the four columns are respectively connected to four corners of the rectangular frame,
• each of the four columns comprises an upper column and a lower column that are configured be inserted together in an up-and-down direction,
• an upper end of the lower column comprises a joint section formed by reducing a diameter of the upper end of the lower column,
• the upper column is sleeved on the joint section,
• an end portion of each of the two longitudinal rods is fixedly connected to the lower column,
• an end surface of each of the two transverse rods is connected with a locking piece,
• the locking piece is configured to abut an outer side of the upper column and an outer side of the lower column,
• a first portion of the locking piece extending upwardly beyond an upper surface of each of the two transverse rods is locked with an upper bolt,
• the upper bolt enables the locking piece, the upper column, and the joint section to be locked together,
• a second portion of the locking piece extending downward beyond a lower surface of each of the two transverse rods is locked with a lower bolt,
• the lower bolt enables the locking piece and the lower column to be locked together,
• the two supporting feet are matched with the two transverse rods in a one-to-one correspondence,
• the two supporting feet are located below a middle position of the two transverse rods,
• the connecting rod is connected between the two supporting feet and is configured to pull the two supporting feet in a longitudinal direction of the lower side bed frame,
• end portions of the connecting rod are detachably insertion-connected with the two supporting feet,
• an end surface of the connecting rod comprises a U-shaped steel groove corresponding to a corresponding one of the two supporting feet,
• the U-shaped steel groove is clamped to the corresponding one of the two supporting feet,
• a tongue piece protrudes from a bottom surface of the U-shaped steel groove,
• the corresponding one of the two supporting feet comprises a buckle opening, and
• the tongue piece is configured to be inserted into the buckle opening.