Design & Detailing req. for BEAMS of Special Moment Resisting Frame

#beams of Special moment resisting frame(SMRF) require the following consideration for design and detailing as per ACI 318-19.

The following are the critical points for their design & detailing:

Longitudinal Reinforcement:

1) Rein. ratio shall not exceed 0.025(i.e. 2.5%)

2) Positive moment strength at the joint face shall be at least one-half the negative moment strength provided at that face of the joint

3) Both -ve & +ve moment strength at any section along member length shall be at least 1/4 the maximum moment strength provided at the face of either joint.

Transverse Reinforcement:

1) Spacing of the hoops shall not exceed the least of:

= d/4

= 6 in

= 6db 

2) Where hoops are not required, stirrups shall be spaced at d/2 throughout the length of the beam.

3) Hoops shall be provided in the following regions of a beam:

= Over a length equal to twice the beam depth measured from the face of the supporting column toward the midspan, at both ends of the beam.

= Over lengths equal to twice the beam depth on both sides of a section where flexural yielding is likely to occur as a result of lateral displacements beyond the elastic range of behavior.

4) Due to inelastic rotation, transverse reinforcement is also required where yielding is expected.

Dimensional Limits:

Beams shall satisfy:

1) Clear span "ln" shall be at least 4d

2) Width "bw" shall be at least the lesser of 0.3h and 10 in. (Ref: 18.6.2.1 of ACI 318-19)

3) Projection of the beam width beyond the width of the supporting column on each side shall not exceed the lesser of c2 and 0.75c1.

Hook Angle:

1) 135-degree angle 

2) Hook Length 3" or 6db

Lap Splice:

Spacing of the transverse rein. enclosing the lap spliced bars shall not exceed the lesser of d/4 and 4". Lap splices shall not be used in the following locations:

1) Within the joints

2) Within a distance of twice the beam depth from the face of the joint

3) 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

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Reference: ACI 318-19

Written By: Muhammad Abrar (m.abrarahmad477@gmail.com)