Flexural Reinforcement (BRD) per ACI 318-19 with ideCAD

How does ideCAD control beam flexural reinforcement detailing according to ACI 318-19?

Notation

b_w = web width or diameter of circular section, in.
d = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, in.
d_b = nominal diameter of bar, wire, or prestressing strand, in
f_y = specified yield strength of nonprestressed reinforcement, psi
f_yt = specified yield strength of transverse reinforcement, psi
h = overall thickness, height, or depth of member, in.
l_a = additional embedment length beyond centerline of support or point of inflection, in.
l_d = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
l_u = unsupported length of column or wall, in.
M_n = nominal flexural strength at section, in.-lb
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
V_n = nominal shear strength, lb
V_u = factored shear force at section, lb
β_b = ratio of area of reinforcement cut off to total area of tension reinforcement at section.
ϕ = strength reduction factor

According to ACI 9.7.3.3, Longitudinal reinforcement extends beyond the point at which it is no longer required to resist flexure for a distance equal to the maximum value of d and 12d_b (ACI Fig. R9.7.3.2). This requirement does not apply to the support of simply-supported spans and the free ends of the cantilevers.

In accordance with ACI 9.7.3.4, Longitudinal reinforcement is extended at least embedment length, l_d from the point where terminated tension reinforcement is no longer required to resist flexure. In ACI Fig. R9.7.3.2. “x” indicates the point where terminated tension reinforcement is no longer required to resist flexure.

According to ACI 9.7.3.3, Flexural tension reinforcement is not to be terminated in a tension zone unless any of the following conditions is satisfied;

• V_u ≤ (2/3)ϕV_n at the cutoff point

• For No. 11 bars and smaller, continuing reinforcement provides double the area required for flexure at the cutoff point, and V_u ≤ (3/4)ϕV_n

• A stirrup or hoop area in excess of that required for shear and torsion is provided along each terminated bar over a distance 3/4d from the cutoff point. Excess stirrup or hoop area shall be at least 60b_ws/f_yt. Maximum spacing s shall be d/(8β_b).

Termination of reinforcement

According to ACI 9.7.3.8.1, at simple supports, at least one-third of the maximum positive moment reinforcement should extend to the support at least 6 in. along the beam bottom.

According to ACI 9.7.3.8.2, at other supports, at least one-fourth of the maximum positive moment reinforcement should extend to the support at least 6 in. along the beam bottom. If the beam is earthquake resistant structure beam, at least one-fourth of the maximum positive moment reinforcement should be anchored to develop f_y at the face of the support.

According to ACI 9.7.3.8.3, the diameter of the positive moment tension reinforcement d_b, should be limited such that l_d for that reinforcement satisfies one of the following two situations below. If reinforcement terminates beyond the centerline of supports by a standard hook at least equivalent to a standard hook, the two situations below need not be satisfied.

• l_d ≤ (1.3M_n /V_u+l_a) if the end of reinforcement is confined by a compressive reaction

• l_d ≤ (M_n /V_u+l_a) if the end of reinforcement is not confined by a compressive reaction

M_n is the nominal flexural strength of the cross-section. At support, l_a is the embedment length beyond the center of the support. At a point of inflection, l_a is the embedment length beyond the point of inflection limited to the maximum of values d and 12d_b.

The application of this provision is illustrated in ACI Fig. R9.7.3.8.3.

According to ACI 9.7.3.8.4, At support, at least one-third of the negative moment reinforcement should have an embedment length beyond the point of inflection at least the maximum of values d ,12d_b, and l_n/16.

Beams of Earthquake Resistant Structures

Ordinary moment frames

All the flexural reinforcement detailing described above is valid for beams of ordinary moment frames.

Beams should have a minimum of two continuous bars at the top and bottom faces.

Intermediate moment frames

All the flexural reinforcement detailing described above is valid for beams of intermediate moment frames.

Beams should have a minimum of two continuous bars at the top and bottom faces.

Special moment frames

All the flexural reinforcement detailing described above is valid for beams of special moment frames.

Beams should have a minimum of two continuous bars at the top and bottom faces.

According to ACI 18.6.3.3, if hoop or spiral reinforcement is provided over the lap length, lap splices of longitudinal reinforcement should be permitted. The maximum value of the transverse reinforcements spacing surrounding the lap-spliced bars should be lesser than d/4 and 4 in. Lap splices shall not be used in locations given below:

• Within the joints

• Within a distance of twice the beam depth from the face of the joint

• Within a distance of twice the beam depth from critical sections where flexural yielding is likely to occur as a result of lateral displacements beyond the elastic range of behavior