Column Reinforcement Limits per ACI 318-19 with ideCAD

How does ideCAD control column reinforcement limits according to ACI 318-19?

• Longitudinal and Transverse reinforcement limits are controlled automatically.

A_ch = cross-sectional area of a member measured to the outside edges of transverse reinforcement, in.²
A_g = gross area of concrete section, in²
A_sh = total cross-sectional area of transverse reinforcement, including crossties, within spacing s and perpendicular to dimension b_c, in.²
A_v = area of shear reinforcement within spacing s, in.²
A_v,_min = minimum area of shear reinforcement within spacing s, in.²
b_c = cross-sectional dimension of member core measured to the outside edges of the transverse reinforcement composing area A_sh, in.
b_w = width of compression face of member, in.
d_b = nominal diameter of bar, wire, or prestressing strand, in.
f_c^' = specified compressive strength of concrete, psi
f_y = specified yield strength for nonprestressed reinforcement, psi
f_yt = specified yield strength of transverse reinforcement, psi
h_x = maximum center-to-center spacing of longitudinal bars laterally supported by corners of crossties or hoop legs around the perimeter of a column or wall boundary element, in.
k_f = concrete strength factor
k_n = confinement effectiveness factor
l_o = length, measured from joint face along axis of member, over which special transverse reinforcement must be provided, in.
l_u = unsupported length of column or wall, in.
l_w = length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in.
n_l = number of longitudinal bars around the perimeter of a column core with rectilinear hoops that are laterally supported by the corner of hoops or by seismic hooks.
P_u = factored axial force; to be taken as positive for compression and negative for tension, lb
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
s_o = center-to-center spacing of transverse reinforcement within the length l_o, in.
V_c = nominal shear strength provided by concrete, lb
V_n = nominal shear strength, lb
V_u = factored shear force at section, lb
ϕ = strength reduction factor
ρ_s = ratio of volume of spiral reinforcement to the total volume of core confined by the spiral, measured out-to-out of spirals

The transverse reinforcement area is applied to provide the equation ϕVn ≥ Vu, described in Column Shear Design per ACI 318-19 with ideCAD title for all columns.

Minimum and maximum longitudinal reinforcement

For nonprestressed columns,

• minimum longitudinal reinforcement area is 0.01A_g

• maximum longitudinal reinforcement area is 0.08A_g.

Minimum shear reinforcement

A minimum area of shear reinforcement, (A_v)_min should be provided in all sections where V_u > 0.5ϕV_c.

According to ACI 10.6.2.2; If shear reinforcement is required, A_v,min is equal to the greater of the following relations;

Columns of Earthquake-Resistant Structures

Ordinary moment frames

All of the reinforcement limits described above are valid for columns of ordinary moment frames.

Intermediate moment frames

All of the reinforcement limits described above are valid for columns of ordinary moment frames.

Special moment frames

For columns of special moment frames,

• minimum longitudinal reinforcement area is 0.01A_g

• maximum longitudinal reinforcement area is 0.06A_g.

Over column clear height, longitudinal reinforcement shall be selected such that 1.25l_d≤l_u/2.

Spacing of transverse reinforcement shall not exceed the least of conditions give below;

• One-fourth of the minimum column dimension

• For Grade 60 or S420, 6d_b of the smallest longitudinal bar

• For Grade 80, 5d_b of the smallest longitudinal bar

• s_o, as calculated by: (The value of s_o shall not exceed 6 in. and need not be taken less than 4 in.)

The amount of transverse reinforcement is in accordance with ACI Table 18.7.5.4.

The concrete strength factor k_f and confinement effectiveness factor k_n are calculated as given below;

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