ACI-318 2019

The ACI 318-19 design code implementation in RAM Concrete Wall utilizes the majority of the design logic contained in the ACI 318-14 code

This section documents notable changes made to the implementation of ACI 318-19.

Limit for Nominal Shear Strength, Vn

V_n at any horizontal section shall not exceed

8 \sqrt{{f'}_{c}} A_{cv}

according to Section 11.5.4.2

In-plane Shear Capacity and ac

In the determination of the shear capacity, V_n, the coefficient α_c is calculated according to Section 11.5.4.3 when the wall is under compression and according to Section 11.5.4.4. when the wall is under tension. It is a function of the wall’s height (h_w); in the program this height is given by the maximum height of the walls that belong to the same Wall Design Group.

Amplification of Shear Demand for Special Structural Walls

Section 18.10.3 introduces an amplified ultimate shear, V_e, for special structural walls.

According to this section, V_e is calculated as following:

V_{e} = Ω_{v} ω_{v} V_{u} \leq 3 V_{u}

ACI 318-19 (18.10.3.1)

where

V_u	=	the shear force obtained from lateral load analysis with factored load combinations
Ω_v	=	the overstrength factor and is defined by Table 18.10.3.1.2.
ω_v	=	the dynamic shear amplification factor and is defined per Section 18.10.3.1.3. For walls with h_wcs/l_w < 2.0, ω_v is taken as 1.0, otherwise it is calculated as:

\begin{matrix} ω_{v} = 0.9 + \frac{n_{s}}{10} & when n_{s} \leq 6 \\ ω_{v} = 1.3 + \frac{n_{s}}{30} \leq 1.8 & when n_{s} > 6 \end{matrix}

ACI 318-19 (18.10.3.1.3)

The minimum value of n_s is 0.007h_wcs.

Minimum Shear Reinforcement

Per Section 11.6, minimum ρ_l and ρ_t are provided for in-plane shear when

V_{u} \leq 0.5 ϕ α_{c} λ \sqrt{{f'}_{c}} A_{cv}

Also, if in-plane $V_{u} \leq 0.5 ϕ α_{c} λ \sqrt{{f'}_{c}} A_{cv}$ , (a) and (b) checks are applied:

ρ_l should be at least the greater of 0.0025 or the value calculated by

ρ_{t} = 0.0025 + 0.5 (2.5 - \frac{h_{w}}{l_{w}}) (ρ_{t} - 0.0025)

ACI 318-19 (11.6.2)

ρ_t should be at least 0.0025.

Out-of-Plane Shear Capacity

Given that cross section of walls match the following criteria: Av < Av, min, out of plane shear capacity is calculated according to Table 22.5.5.1 Eq(c):

V_{c} = [8 λ_{s} λ {(p_{w})}^{\frac{1}{3}} \sqrt{{f'}_{c}} + \frac{N_{u}}{6 A_{g}}] b_{w} d

ACI 318-19 (22.5.5.1.c)

Axial load, N_u, is positive for compression and negative for tension.

It is important to note that currently the λ modification factor considered by the program is always 1.00, corresponding to normal weight concrete.

The value of V_c is limited to a maximum of $5 λ \sqrt{{f'}_{c}} b_{w} d$ , according to Section 22.5.5.1.1, and is not taken less than zero.

The value of N_u/6A_g is limited to a maximum of 0.05f’c, according to Section 22.5.5.1.2.

The size effect modification factor, λ_s, is calculated according to the following expression:

λ_{s} = \sqrt{\frac{2}{1 + \frac{d}{10}}} \leq 1

ACI 318-19 (22.5.5.1.3)

Strength Reduction Factor

The strength reduction factor, ϕ, is determined from Table 21.2.2 based on the net tensile strain, ε_ty.

Lightweight Concrete Factor

Lightweight concrete factors are not implemented in the determination of concrete wall shear capacity. The design considers normal weight concrete and uses λ = 1 in all cases.