Flexural Reinforcement (BRD) per ACI 318-19 with ideCAD
How does ideCAD control beam flexural reinforcement detailing according to ACI 318-19?
Longitudinal reinforcement detailing is applied automatically in accordance with ACI 9.7.
Longitudinal reinforcement detailing is applied according to ACI Chapter 18 in earthquake resistant structure beams.
Notation
bw = web width or diameter of circular section, in.
d = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, in.
db = nominal diameter of bar, wire, or prestressing strand, in
fy = specified yield strength of nonprestressed reinforcement, psi
fyt = specified yield strength of transverse reinforcement, psi
h = overall thickness, height, or depth of member, in.
la = additional embedment length beyond centerline of support or point of inflection, in.
ld = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
lu = unsupported length of column or wall, in.
Mn = nominal flexural strength at section, in.-lb
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
Vn = nominal shear strength, lb
Vu = factored shear force at section, lb
βb = 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 12db (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, ld 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;
Vu ≤ (2/3)ϕVn at the cutoff point
For No. 11 bars and smaller, continuing reinforcement provides double the area required for flexure at the cutoff point, and Vu ≤ (3/4)ϕVn
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 60bws/fyt. Maximum spacing s shall be d/(8βb).
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 fy at the face of the support.
According to ACI 9.7.3.8.3, the diameter of the positive moment tension reinforcement db, should be limited such that ld 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.
ld ≤ (1.3Mn /Vu+la) if the end of reinforcement is confined by a compressive reaction
ld ≤ (Mn /Vu+la) if the end of reinforcement is not confined by a compressive reaction
Mn is the nominal flexural strength of the cross-section. At support, la is the embedment length beyond the center of the support. At a point of inflection, la is the embedment length beyond the point of inflection limited to the maximum of values d and 12db.
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 ,12db, and ln/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
