Mo. Rev. Stat. § 292.490
If in any house, building or structure in process of erection or construction in this state (except a private house, used exclusively as a private residence), the distance between the enclosing walls is more than twenty-four feet, in the clear, there shall be built, kept and maintained, proper intermediate supports for the joists, which supports shall be either brick walls, or iron or steel columns, beams, trusses, or girders, and the floors in all such houses, buildings, or structures, in process of erection and construction, shall be designed and constructed in such manner as to be capable of bearing in all their parts, in addition to the weight of the floor construction, partitions and permanent fixtures, and mechanisms that may be set upon the same, a live load of fifty pounds for every square foot of surface in such floors, and it is hereby made the duty of the owner, lessee, builder or contractor or subcontractor of such house, building or structure, or the superintendent or agent of either, to see that all the provisions of this section are complied with.
§ 292.490, RSMo