Column Reinforcement Limits per ACI 31819 with ideCAD
How does ideCAD control column reinforcement limits according to ACI 31819?
Longitudinal and Transverse reinforcement limits are controlled automatically.
A_{ch}_{ } = crosssectional area of a member measured to the outside edges of transverse reinforcement, in.^{2}
A_{g }_{ } = gross area of concrete section, in^{2}
A_{sh}_{ } = total crosssectional 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 }= crosssectional 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 centertocenter 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 _{ } = centertocenter spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
s_{o} _{ } = centertocenter 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 outtoout of spirals
The transverse reinforcement area is applied to provide the equation ϕVn ≥ Vu, described in Column Shear Design per ACI 31819 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 EarthquakeResistant 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;
Onefourth 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.
Transverse Reinforcement Area  Conditions  Applicable expressions  

A_{sh} for rectengular hoop  and  Maximum value of (a) and (b) 

or  Maximum value of (a), (b), and (c)  
ρ_{s} for spiral or cicular hoop  and  Maximum value of (d and (e) 

or  Maximum value of (d), (e), and (f) 
The concrete strength factor k_{f} and confinement effectiveness factor k_{n} are calculated as given below;