box unit 200 the portion of the reinforcing steel bar 240 protruding out of the end plate peripheral opening 212 not only can pass through adjacent column steel box unit but also can butt another corresponding reinforcing steel bar e g directly butting by a steel bar connector 400 as shown in fig1 b to extend the length required for the column otherwise the portion of the reinforcing steel bar 240 protruding out of the end plate peripheral opening 212 can be anchored on an outer surface of the end plate 210 by for example a t headed anchor head 500 as shown in fig5 b the steel ring 250 not shown can be hung on the side plate 230 and provided to hook the reinforcing steel bar 240 in order to fixedly position the reinforcing steel bar 240 in the column and to maintain the spacing between the reinforcing steel bar 240 and the side plate 230 and as the column is under load the steel ring 250 may also transfer the column stress between the reinforcing steel bar 240 and the side plate 230 the above mentioned angle steel bar 220 may further connect to end plate 210 by an angle steel bar connecting piece 260 moreover the end plate 210 includes at least a flange 213 protruding perpendicularly out from the circumference of the surface of the end plate 210 thus a joint sleeve 270 can be used to sheathe among flanges 213 of the end plate 210 for column steel box unit 200 and by means of a full penetration.