Reinforcement Detailing of Joints per ACI 318-19 with ideCAD

How does ideCAD define beam-column joint reinforcement details according to ACI 318-19?

Notation

d_b = nominal diameter of bar, wire, or prestressing strand, in
f_c^' = specified compressive strength of concrete, psi
√fc‘ = square root of specified compressive strength of concrete, psi
f_y = specified yield strength of nonprestressed reinforcement, psi
l_d = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
l_dc = development length in compression of deformed bars and deformed wire, in.
l_dh = development length in tension of deformed bar or deformed wire with a standard hook, measured from outside end of hook, point of tangency, toward critical section, in.
l_dm = the required development length if bar is not entirely embedded in confined concrete, in.
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength

Beam-Column Joint Transverse Reinforcement

According to ACI 15.3.1.1, beam-column joints should satisfy ACI 15.3.1.2 , 15.3.1.3 and 15.3.1.4 unless all three conditions are satisfied:

• Beam-column joint is considered confined by transverse beams in accordance with ACI 15.2.8 for all shear directions considered

• Beam-column joint is not part of a designated seismic-force-resisting system

• Beam-column joint is not part of a structure assigned to Seismic Design Category D, E, or F

According to ACI 15.3.1.2, Beam-column joints consist of ties, spirals, or hoops. Requirements of ACI 25.7.2 should be satisfied for ties. The requirements of ACI 25.7.3 should be satisfied for spirals. The requirements of ACI 25.7.4 should be satisfied for hoops.

According to ACI 15.3.1.3, at least two layers of horizontal transverse reinforcement should be provided within the depth of the shallowest beam framing into the joint.

According to ACI 15.3.1.4, maximum joint transverse reinforcement spacing, s, should be 8 in. within the depth of the deepest beam framing into the joint.

Longitudinal Reinforcement

According to ACI 15.3.3.1, the development of longitudinal reinforcement should be in accordance with Development of Reinforcement per ACI 318-19 with ideCAD title.

According to ACI 15.3.3.2, Longitudinal reinforcement terminated in the beam-column joint with a standard hook should have the hook turned toward the mid-depth of the beam or column.

Beam-Column Joint for Earthquake-Resistant Structures

Ordinary moment frames

All the conditions described above are valid for joints of ordinary moment frames.

Intermediate moment frames

All the conditions described above are valid for joints of intermediate moment frames.

According to ACI 18.4.4.3, if longitudinal reinforcement is terminated in a beam-column joint, it should extend to the far face of the joint core. The longitudinal reinforcement should be developed in tension in accordance with ACI 18.8.5 and in compression in accordance with ACI 25.4.9.

According to ACI 18.4.4.4, the maximum spacing of transverse reinforcement, s, is the lesser of three values given below within the height of the deepest framing into the joint:

• For Grade 60 or S420, the smaller 8d_b of the smallest longitudinal bar is enclosed and 8 in.

• For Grade 80, the smaller 6d_b of the smallest longitudinal bar is enclosed and 6 in.

• One-half of the smallest cross-sectional dimension of the column.

Special moment frames

All the conditions described above are valid for joints of intermediate moment frames.

According to ACI 18.8.3.1, Beam-column joint transverse reinforcement should satisfy ACI 18.7.5.2, ACI 18.7.5.3, ACI 18.7.5.4, and ACI 18.7.5.7, except as permitted in ACI 18.8.3.2.

According to ACI 18.8.3.2, the amount of transverse reinforcement required by ACI 18.7.5.4 can be reduced by one-half, and the spacing required by ACI 18.7.5.3 can be increased to 6 in. within the overall depth h of the shallowest framing beam where the following conditions are satisfied:

• where beams frame into all four sides of the joint

• where each beam width is at least three-fourths the column width

According to ACI 18.8.3.3, if beam-column joint confinement is not provided by a beam framing into the joint, longitudinal beam reinforcement outside the column core should be confined by transverse reinforcement passing through the column. This transverse reinforcement spacing should satisfy the requirements of ACI 18.6.4.4. Also, this transverse reinforcement should satisfy the requirements of ACI 18.6.4.2 and ACI 18.6.4.3.

Development Length of Bars in Tension

According to ACI 18.8.5.1, for bar size No.3 through No.11 terminating in a standard hook, l_dh is calculated by ACI Eq. (18.8.5.1) given below for nor;

The value of λ is 1.00 for normal-weight concrete. The hook should be located within the confined core of a column or of a boundary element, with the hook bent into the joint.

According to ACI 18.8.5.3, for bar size No.3 through No.11, the minimum development length in tension for a straight bar, l_d, should be the greater of the given two conditions below:

• 2.5 times the length in accordance with ACI 18.8.5.1 if the depth of the concrete cast in one lift beneath the bar does not exceed 12 in.

• 3.25 times the length in accordance with ACI 18.8.5.1 if the depth of the concrete cast in one lift beneath the bar does not exceed 12 in.

According to ACI 18.8.5.4, Straight bars terminated at a joint should pass through the confined core of a column or boundary element. If the reinforcement bar is not entirely embedded in a confined volume of concrete, the required development length, l_dm, is increased on the premise that the limiting bond stress outside the confined region is less than that inside.