ACI-318 2019

The ACI 318-19 design code implementation in RAM Concrete Beam 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.

Maximum Spacing of Legs of Shear Reinforcement Across Section

Sec. 9.7.6.2.2 defines a new spacing limit of legs across the width of beams. This limit is detailed in the following table:

Required V_s	Maximum s (in.) for nonprestressed beams across width
$\leq 4 \sqrt{{f'}_{c}} b_{w} d$	the lesser of d or 24 in.
$> 4 \sqrt{{f'}_{c}} b_{w} d$	the lesser of d/2 or 12 in.

When Maximum s is exceeded, the program will give the warning message: "Maximum spacing of legs across the Beam width exceeded".

Maximum fy for Obtaining Minimum Flexural Reinforcement

The value of fy used in the determination of minimum reinforcement is limited to a maximum of 80,000 psi according to Sec. 9.6.1.2.

Concrete Shear Capacity

Equation a of Table 22.5.5.1 has been implemented to calculate the concrete shear capacity:

V_{c} = [2 λ \sqrt{{f'}_{c}} + \frac{N_{u}}{6 A_{g}}] b_{w} d

ACI 318-19 (22.5.5.1.a)

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.

Minimum Shear Reinforcement

As required by Section 9.6.3.1, the minimum area for shear reinforcement in Beams is provided in all regions where $V_{u} > ϕ λ \sqrt{{f'}_{c}} b_{w} d$ except for the cases in Table 9.6.3.1. For these cases, at least A_vmin is provided where $V_{u} > ϕ V_{c}$ .

For most of cases, ACI 318-14 had a threshold of $V_{u} > 0.5 ϕ V_{c}$ . Given that V_c has changed for ACI 318-19, this limit is now applied in terms of f’_c, b_w and d.

Table 9.6.3.1 remains unchanged since ACI 318-14.

Ductility Strain Limit

Beams are designed as tension controlled according to Section 9.3.3.1.

Strength Reduction Factor

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

Reinforcement Details, Modification Factor for Development of Reinforcement

Table 25.4.2.5 provides new modification factors for the development of deformed bars in tension based on reinforcement grade. These factors for Grade 80 and Grade 100 have not been implemented, a factor of 1.0 is always used as for Grade 40 and Grade 60.

Table 25.4.3.2 provides new modification factor values for the development of hooked bars in tension. These have not been implemented, the values given in Table 25.4.3.2 of ACI 318-14 are used.

Serviceability Requirements, Effective Moment of Inertia

Section 24.2.3.5 provides new equations to calculate the effective moment of inertia. These new equations have been implemented.

Lightweight Concrete Factor

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