Beam-column and slab-column joints that transfer moment to columns shall satisfy the detailing provisions in 15.4. Beam-column joints within special moment frames, slab-column joints within intermediate moment frames, and beam-column and slab-column joints in frames not designated as part of the seismic-force-resisting systems in structures assigned to Seismic Design Categories D, E, or F, shall satisfy Chapter 18.
If f'c of a column is greater than 1.4 times that of the floor system, transmission of axial force through the floor system shall be in accordance with (a), (b), or (c):
(a) Concrete of compressive strength specified for the column shall be placed in the floor at the column location. Column concrete shall extend outward at least 2 ft into the floor slab from face of column for the full depth of the slab and be integrated with floor concrete.
(b) Design strength of a column through a floor system shall be calculated using the lower value of concrete strength with vertical dowels and spirals as required to achieve adequate strength.
(c) For beam-column and slab-column joints that are restrained in accordance with 15.2.4 or 15.2.5, respectively, it shall be permitted to calculate the design strength of the column on an assumed concrete strength in the column joint equal to 75 percent of column concrete strength plus 35 percent of floor concrete strength, where the value of column concrete strength shall not exceed 2.5 times the floor concrete strength.
When the specified compressive strength of concrete in a column is greater than 1.4 times that specified for a floor system, the following additional requirements shall be adhered to:
- All of the design provisions of Section 15.3 (unmodified) are adhered to.
- The concrete construction is supervised and inspected continuously by a full-time professional engineer responsible for the concrete placement special inspection. Such professional engineer shall not delegate this responsibility to any subordinates.