The steel box is mainly composed of a base plate, a side door, a front door and a back door. There is a waist-shaped hole on the pillar which realize sliding and folding of the side door as well as connecting the side door and the base. The back door is an integrated structure which hangs between the two side doors. The foldable front door, with a semi-embedded latch, may implement loading and unloading under stacking condition.
The bearing capacity of the base is 1.5 tons, and the maximum stress is186Mpa, which is the stress concentration point. It is located at the weld joint between the support leg and the frame of the base. Most of the rest of the stress is no bigger than 52Mpa, and the allowable stress is less than 235Mpa.
The above figure shows that under the condition of three layers of foldable box, the stress of the bottom layer foldable box column is158Mpa.The yield stress value of the material is less than 235Mpa.