Shear Wall Reinforcement Limits per ACI 318-19 with ideCAD

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

• Longitudinal and Transverse reinforcement limits are controlled automatically.

Notation

Acv = gross area of concrete section bounded by web thickness and length of section in the direction of shear force considered in the case of walls, and gross area of concrete section in the case of diaphrams. Gross area is total area of defined section minus area of any openings, in.2
fc' = specified compressive strength of concrete, psi
√fc = square root of specified compressive strength of concrete, psi
fy = specified yield strength for nonprestressed reinforcement, psi
fyt = specified yield strength of transverse reinforcement, psi
hw = height of entire wall from base to top, or clear height of wall segment or wall pier considered, in.
lw = length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in.
Mu = factored moment at section, in.-lb
Vn = nominal shear strength, lb
Vu = factored shear force at section, lb
αc = coefficient defining the relative contribution of concrete strength to nominal wall shear strength
ϕ = strength reduction factor
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength
ρl = ratio of area of distributed longitudinal reinforcement to gross concrete area perpendicular to that reinforcement
ρt = ratio of area of distributed transverse reinforcement to gross concrete area perpendicular to that reinforcement

According to ACI 11.6.1, minimum values of reinforcement ratios are given below.

The minimum value of distributed longitudinal reinforcement ratio ρl is 0.0025

The minimum value of distributed transverse reinforcement ratio ρt is 0.0025

Earthquake Resistant Structures

Special structural walls

According to ACI 18.10.2.1, the minimum value of distributed longitudinal reinforcement ratio, ρl, and distributed transverse reinforcement ratio, ρt, should be 0.0025, except that if Vu < λ√fc‘Acv , ρt can be reduced to the values in ACI 11.6 explained above. Maximum reinforcement spacing in each direction in structural walls is 18 inches.

According to ACI 18.10.2.2, if Vu > 2λ√fc‘Acv or hw/lw ≥ 2.0, at least two curtains of reinforcement should be used in a shear wall.

According to ACI 18.10.2.4, walls or wall piers with hw/lw ≥ 2.0 that are effectively continuous from the base of the structure to the top of the wall and are designed to have a single critical section for flexure and axial loads should have longitudinal reinforcement at the ends of a vertical wall segment that satisfies conditions given below;

• minimum longitudinal reinforcement ratio in area 0.15lw from the end of a vertical wall segment and over a width equal to the wall thickness should be 6√fc‘/fy.

• Longitudinal reinforcement should extend vertically above and below the critical section at least the greater of lw and Mu/3Vu.

• No more than 50 percent of the longitudinal reinforcement should be terminated at any one section.

According to ACI 18.10.4.3, shear walls should have distributed shear reinforcement in two orthogonal directions in the plane of the wall. If hw/lw ≤ 2.0, the reinforcement ratio ρl should be at least the reinforcement ratio ρt.

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