Abstract: Partially fabricated building systems include pre-fabricated wall panel subassemblies formed of steel tubing. A subassembly includes a rigid frame defining a shallow rectanguloid volume with an outer face and an inner face. The frame includes at least one horizontal dividing member, a plurality of vertical support members, some located above and others below the horizontal dividing member(s), with a surface of the vertical support members oriented flush with an outside face of the frame, a plurality of strut members oriented at an angle to the vertical and horizontal extend between at least one portion of said frame across at least some of the vertical support members and are rigidly connected thereto with an outer surface of said strut members being oriented flush with the inner face of the frame. A number of steel post oriented in a vertical, spaced apart relationship, are rigidly connected to the inner face of the frame.