A load-carrying floor for a truck or trailer includes a plurality of extruded aluminum hollow floor panels wherein each panel includes spaced apart inside and outside walls connected to each other by spaced apart first and second end walls. A primary cross-member is located between and extends parallel to the first and second end walls and interconnects the inside and outside walls. The panels are abutted with each other to define a floor section including: (i) an inner load-carrying surface; (ii) an outer surface; (iii) a plurality of seams; and, (iv) opposite left and right edge regions. One-piece extruded aluminum left and right rails are connected by welding to the left and right edge regions of the floor section, respectively.