Questions and answers from Dr. Alirezaei:
According to clause 9.7.5.1 of ACI318-14 regulations, if you need torsional longitudinal reinforcements, you should distribute them in the perimeter of the section and their distance should not exceed 12 inches or 30 cm. In other words, the torsional longitudinal reinforcements should be placed at maximum intervals of 30 cm on the inner environment of closed silencers. Also, at least one longitudinal armature should be placed in each corner of the closed silence. The diameter of the torsional longitudinal reinforcements should not be less than 1/24 of the distance of the silencers or 10 mm.
9.7.5.1 If torsional reinforcement is required, longitudinal torsional reinforcement shall be distributed around the perimeter of closed stirrups that satisfy 25.7.1.6 or hoops with a spacing not greater than 12 in. The longitudinal reinforcement shall be inside the stirrup or hoop, and at least one longitudinal bar or tendon shall be placed in each corner.
9.7.5.2 Longitudinal torsional reinforcement shall have a diameter at least 0.042 times the transverse reinforcement spacing, but not less than 3/8 in.
So we have:
For a beam with a depth of 45 cm, assuming the use of longitudinal reinforcements with a diameter of 20 and transverse reinforcements with a diameter of 10 and a cover value of 4.5 cm, we have:
S=45-2(4.5+1.0+1.0)=32 cm
Therefore, the distance between the center of the upper and lower longitudinal reinforcements is more than 30 cm, and if this beam needs torsional longitudinal reinforcements, a torsional reinforcement is also needed in the middle of the beam. However, in the case of using a beam ceiling, due to the interference of this middle armature with the transverse armatures of the beam, according to my personal opinion and that of many designers, for beams with a depth of 45 cm, it is possible to skip the placement of the longitudinal torsion armature.
For a beam with a depth of 50 cm, assuming the use of longitudinal reinforcements with a diameter of 20 and transverse reinforcements with a diameter of 10 and a cover value of 4.5 cm, we have:
S=50-2(4.5+1.0+1.0)=37 cm
The amount of the distance is large and to meet the code of regulations, a torsional longitudinal reinforcement is needed in the middle of the beam.
Therefore, for beams with a depth of more than 50 cm, if torsional reinforcement is needed in the middle of the height, longitudinal torsional reinforcement needs to be placed.
Amin Gholizadeh:
How to reinforce the U-shaped section of the shear wall with the opening
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This post is written by AminNajafgholizadeh