Butt-joining and positioning structure of vertical bar with hook hole

A storage shelf structure comprising:

• two vertical bars that abut each other, wherein a first vertical bar from said two vertical bars is on top of a second vertical bar from said two vertical bars;
• wherein the first vertical bar and the second vertical bar are parallel to each other;
• wherein each vertical bar is a rectangular hollow tube having four side walls, wherein at least two side walls from said four side walls each have a plurality of hook holes formed therein arranged at intervals;
• wherein opposite ends of each vertical bar have a butt-joining opening respectively, wherein each of the at least two side walls from said four side walls of each vertical bar have a first locking through hole and a second locking through hole that are spaced apart from the hook holes of each vertical bar respectively;
• wherein the hook holes of the second vertical bar are arranged between one of the butt-joining openings of the second vertical bar and the second locking through hole or the first locking through hole of the second vertical bar;
• and
• a bidirectional plug-in butt-joining member comprising at least three side walls, wherein two side walls from said at least three side walls each have:
• a first positioning hole, a second positioning hole, and two elongated holes located between the first positioning hole and the second positioning hole, wherein the two elongated holes each have a first height and the hooks holes of the first and second vertical bars each have a second height;
• wherein the first height is approximately twice the size of the second height;
• wherein the bidirectional plug-in butt-joining member is inserted within a corresponding butt-joining opening from said butt-joining openings of each of the vertical bars respectively so that a top portion of the bidirectional plug-in butt-joining member is located within the first vertical bar and a bottom portion of the bidirectional plug-in butt-joining member is located within the second vertical bar;
• wherein the elongated holes of the bidirectional plug-in butt-joining member align with the hook holes of the second vertical bar;
• the first positioning holes of the bidirectional plug-in butt-joining member align with the first locking through holes of the first vertical bar to receive a first pair of fasteners respectively to secure the first vertical bar to the bidirectional plug-in butt-joining member;
• and the second positioning holes of the bidirectional plug-in butt-joining member align with the second locking through holes of the second vertical bar to receive a second pair of fasteners respectively to secure the second vertical bar to the bidirectional plug-in butt-joining member;
• at least one horizontal cross bar, wherein each horizontal cross bar has an end portion comprising a plurality of hooks;
• wherein the hooks of a first horizontal cross bar from said at least one horizontal cross bar are inserted through the hook holes of a corresponding side wall from said at least two side walls of the second vertical bar and the elongated holes from a corresponding side wall from said two side walls of the bidirectional plug-in butt-joining member to secure the first horizontal cross bar to the second vertical bar in a perpendicular orientation.