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Chapter 15 Beam-Column and Slab-Column Joints

15.1 Scope

15.1.1

This chapter shall apply to the design and detailing of cast-in-place beam-column and slab-column joints.

15.2 General

15.2.1

Beam-column and slab-column joints shall satisfy 15.3 for transfer of column axial force through the floor system.

15.2.2

If gravity load, wind, earthquake, or other lateral forces cause transfer of moment at beam-column or slab-column joints, the shear resulting from moment transfer shall be considered in the design of the joint.

15.2.3

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.

15.2.4

A beam-column joint shall be considered to be restrained if the joint is laterally supported on four sides by beams of approximately equal depth.

15.2.5

A slab-column joint shall be considered to be restrained if the joint is laterally supported on four sides by the slab.

15.3 Transfer of Column Axial Force Through the Floor System

15.3.1

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.

15.4 Detailing of Joints

15.4.1

Beam-column and slab-column joints that are restrained in accordance with 15.2.4 or 15.2.5, respectively, and are not part of a seismic-force-resisting system need not satisfy the provisions for transverse reinforcement of 15.4.2.

15.4.2

The area of all legs of transverse reinforcement in each principal direction of beam-column and slab-column joints shall be at least the greater of (a) and (b):
(a)
(b)
where b is the dimension of the column section perpendicular to the direction under consideration.

15.4.2.1

At beam-column and slab-column joints, an area of transverse reinforcement calculated in accordance with 15.4.2 shall be distributed within the column height not less than the deepest beam or slab element framing into the column.

15.4.2.2

For beam-column joints, the spacing of the transverse reinforcement s shall not exceed one-half the depth of the shallowest beam.

15.4.3

If longitudinal beam or column reinforcement is spliced or terminated in a joint, closed transverse reinforcement in accordance with 10.7.6 shall be provided in the joint, unless the joint region is restrained in accordance with 15.2.4 or 15.2.5.

15.4.4

Development of longitudinal reinforcement terminating in the joint shall be in accordance with 25.4.