Questions and answers from Dr. Alirezaei
Regarding the percentage of reinforcement in retaining wall and shear wall. Are the values mentioned in paragraph 9-19-4 of the ninth topic (attached file) only related to the retaining wall or should they be observed in the shear wall as well? Another question is that the vertical and horizontal reinforcement values in paragraph 9-15-16-14 are related to the shear wall with both medium and special ductility?
The values mentioned in this paragraph are related to all walls. The percentage of reinforcement in normal and special walls is different according to ACI318-14. According to this regulation, for normal walls, the minimum percentage of wall reinforcement is determined as follows:
a) If the shear Vu created in the wall is less than 0.5ϕVc, the minimum shear and longitudinal and transverse reinforcement for the wall is considered as follows.
For bars 16 and less in the case where fy is 4200 kg/cm2, minimum longitudinal reinforcement ρℓ=0.0012 and minimum transverse reinforcement ρt=0.002.
For bars 16 and less in the case that fy<4200 kg/cm2, minimum longitudinal reinforcement ρℓ=0.0015 and minimum transverse reinforcement ρt=0.0025.
For bars larger than 16 with any yield stress, minimum longitudinal reinforcement ρℓ=0.0015 and minimum transverse reinforcement ρt=0.0025.
b) If the shear Vu created in the wall is greater than 0.5ϕVc, the minimum longitudinal shear reinforcement ρℓ must be greater than the value obtained from the following relationship and in any case not less than 0.0025.
≥0.0025+0.5(2.5−ℎ/ )(−0.0025)
The value of ρℓ obtained from the above equation does not need to be considered more than the value of ρt given before.
Also, the minimum value of ρt is considered equal to 0.0025.
11.6.1 If in-plane Vu ≤ 0.5ϕVc, minimum ρℓ and minimum ρt shall be in accordance with Table 11.6.1. These limits need not be satisfied if adequate strength and stability can be demonstrated by structural analysis.
11.6.2 If in-plane Vu ≥ 0.5ϕVc, (a) and (b) shall be satisfied: (a) ρℓ shall be at least the greater of the value calculated by Eq. (11.6.2) and 0.0025, but need not exceed ρt in accordance with Table 11.6.1.
ρℓ ≥ 0.0025 + 0.5(2.5 – hw/ℓw)(ρt – 0.0025)
(b) ρt shall be at least 0.0025
c) If the shear Vu created in the wall is greater than ϕVc, shear reinforcements should be considered for the wall based on the following relationship.
=(**)/
where Av is the area of the shear reinforcements at a distance S from each other. Vertical reinforcements should be determined based on paragraph (b) above.
Maximum spacing of transverse reinforcements:
The maximum distance of transverse reinforcements is limited to the lowest three values of lw/5, 3h and 45 cm.
Maximum distance of longitudinal reinforcements:
The maximum distance of longitudinal reinforcements is limited to the lowest three values of lw/3, 3h and 45 cm.
For special walls according to ACI318-14, the percentage of reinforcement is as follows:
The ratio of longitudinal and transverse reinforcements in shear walls must be at least 0.0025, unless the shear Vu in the wall does not exceed 0.27 Acvλ×sqrt(fc′). In this case, the ratio of longitudinal and transverse reinforcement can be reduced according to clause 11.6.
18.10.2.1 The distributed web reinforcement ratios, ρℓ and ρt, for structural walls shall be at least 0.0025, except that if Vu does not exceed 0.27Acvλ×sqrt(fc′), ρℓ and ρt shall be permitted to be reduced to the values in 11.6.
Amin Gholizadeh:
How to reinforce the U-shaped section of the shear wall with the opening
Structure Design Question Group link
(Assembly of Designers of Tabriz)
@Tabrizporsemancivil
This post is written by AminNajafgholizadeh