Shear Wall Shear Design per ACI 31819 with ideCAD
How does ideCAD calculate shear wall shear strength according to ACI 31819?
Wall design shear strengths are calculated automatically.
Wall required shear strengths are calculated automatically.
Notation
A_{cv } = 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}
A_{cw} = area of concrete section of an individual pier, horizontal wall segment, or coupling beam resisting shear, in^{2}.
b_{w }= width of compression face of member, in.
D = dead load
E _{ } = earthquake load
f_{c}^{'}_{ }= specified compressive strength of concrete, psi
√f_{c}‘ = square root of 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 = overall thickness, height, or depth of member, in.
h_{w} = height of entire wall from base to top, or clear height of wall segment or wall pier considered, in.
h_{wcs} = height of entire structural wall above the critical section for flexural and axial loads, in.
l_{n} _{ } = length of clear span measured facetoface of supports, in.
l_{u} _{ } = unsupported length of wall, in.
l_{w } = length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in.
L _{ } = live load
L_{r} _{ } = roof live load
M_{u}_{ }= factored moment at section, in.lb
M_{pr } = probable flexural strength of members, with or without axial load, determined using the properties of the member at joint faces assuming a tensile stress in the longitudinal bars of at leasts 1.25f_{y} and a strength reduction factor ϕ of 1.0, in.lb
n_{s} = number of stories above the critical section
P_{n}_{ } = nominal axial compressive strength of member, lb
P_{u}_{ } = factored axial force; to be taken as positive for compression and negative for tension, lb
R _{ } = rain load
S _{ } = snow load
N_{u}_{ } = factored axial force normal to cross section occurring simultaneously with V_{u} or T_{u}; to be taken as positive for compression and negative for tension, lb
positive for compression and negative lb
V_{e }= design shear force for load combinations including earthquake effects, lb
V_{c }= nominal shear strength provided by concrete, lb
V_{n }= nominal shear strength, lb
V_{s }= nominal shear strength provided by shear reinforcement, lb
V_{u }= factored shear force at section, lb
w_{u }= factored load per unit length of beam or oneway slab, lb/in.
W_{ } = wind load
α_{c }= coefficient defining the relative contribution of concrete strength to nominal wall shear strength
ϕ = strength reduction factor
Ω_{v} = overstrength factor equal to the ratio of M_{pr}/M_{u} at the wall critical section
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength
ω_{v} = factor to account for dynamic shear amplification
ρ_{l }= ratio of area of distributed longitudinal reinforcement to gross concrete area perpendicular to that reinforcement
ρ_{t }= ratio of area of distributed transverse reinforcement to gross concrete area perpendicular to that reinforcement
Wall required strength is calculated in accordance with the factored load combinations in Load Factors and Combinations per ACI 31819 with ideCAD title. The required shear strength of a wall V_{u} , is obtained from Load Combinations given in ACI Table 5.3.1.
The shear wall is designed leg by leg for each of the design load combinations given above.
Strength reduction factors ϕ is determined according to using ACI Table 21.2.1.
Shear design strength at all sections should satisfy the condition ϕV_{n} ≥ V_{u.}
According to ACI 11.5.4.3, nominal shear strength V_{n} is calculated by ACI Eq. (11.5.4.3) given below;
α_{c} = 3 for h_{w}/l_{w} ≤ 1.5
α_{c} = 2 for h_{w}/l_{w} ≥ 2.0
α_{c} is calculated by linear interpolation between 3 and 2 for 1.5 < h_{w}/l_{w} < 2.0.
For walls subjected to a net axial tension, α_{c} is calculated according to ACI Eq. (11.5.4.3);
According to ACI 11.5.4.2, the maximum inplane shear strength of the shear wall or shear wall leg is given below;
Earthquake Resistant Structures
Special structural walls
Concrete Shear Wall Design per ACI 31819 §11, §18.10 title also contains requirements for the dimensions and details of special structural walls and all components. Design provisions for special structural walls depend on the ratio of the wall dimensions, such as (h_{w}/l_{w}) and (l_{w}/b_{w}).
Design shear forces for structural shear walls are obtained from lateral load analysis with suitable load factors increased to account for two approaches given below.
flexural overstrength at critical sections where yielding of critical sections is expected,
dynamic amplification due to higher mode effects,
According to ACI 18.10.3.1, the design shear force V_{e} should be calculated by ACI Eq. (18.10.3.1);
The required shear strength of a wall V_{u} is obtained from lateral load analysis with factored load combinations given in ACI Table 5.3.1.
The overstrength factor, Ω_{v,} is calculated in accordance with ACI Table 18.10.3.1.2 given below.
Condition 




 1.0 
M_{pr} given in ACI Table 18.10.3.1.2 is calculated by using a strength reduction factor, ϕ of 1.0 and longitudinal reinforcement with an effective yield stress equal to 1.25f_{y}.
According to ACI 18.10.3.1.3, if h_{wcs}/l_{w} < 2.0, ωv should be taken as 1.0 for shear walls. Otherwise, ω_{v} should be calculated by ACI Eq. (18.10.3.1.3);
n_{s} is the number of stories above the critical section, and the minimum value of n_{s} is 0.007*h_{wcs}.
According to ACI 18.10.4.1, shear strength, V_{n}, should be calculated by ACI Eq. (18.10.4.1) given below.
α_{c} = 3 for h_{w}/l_{w} ≤ 1.5
α_{c} = 2 for h_{w}/l_{w} ≥ 2.0
α_{c} is calculated by linear interpolation between 3 and 2 for 1.5 < h_{w}/l_{w} < 2.0.
λ=1 for normalweight concrete.
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 h_{w}/l_{w} ≤ 2.0, the reinforcement ratio ρ_{l} should be at least the reinforcement ratio ρ_{t}.
According to ACI 18.10.4.4, for all vertical wall segments that resist lateral loads, the maximum value of V_{n} should be 8√f_{c}‘A_{cv}. For any one of the individual vertical wall segments, the maximum value of V_{n} should be 10√f_{c}‘A_{cw}.
According to ACI 18.10.4.5, For horizontal wall segments and coupling beams, the maximum value of V_{n} should be 10√f_{c}‘A_{cw}.