The structures made of square hollow steel sections by using the directly welded joints without any reinforcement are fabricated easily and economically , which can be found in many applications all over the world 由方管直接焊接组成的结构,节点构造简单,不需加固件,不仅方便了加工,还降低了造价,故在国内外已被广泛应用到各种工程领域。