An interlocking system of tubular members is provided for support of conveyors and mezzanines, each tubular member having cutouts and slots for assembly with other of the tubular members to form elbow joints, tee joints and cross joints, and stiffener brackets to reinforce the interlocking joints to form a strong support structure without the need for welding. A mezzanine conveyor assembly is also provided that includes a support structure constructed of non-welded interlocking tubular members reinforced with stiffener brackets, with a mezzanine/platform and at least one conveyor supported on the support structure.