Longitudinal bars shall have a diameter at least 0.042 times the stirrup spacing, but not less than 9 mm (3/8 in). The maximum diameters of reinforcement to be used in the various locations is set by the user. Standard hooks for stirrups and ties are limited to No. 8 bars, d b =25mm (1.0in.)
Minimum and maximum diameter of reinforcement
IF torsional reinforcement is required, there shall be at least one longitudinal bar in every corner of the stirrups. Longitudinal bars shall have a diameter at least 0.042 times the stirrup spacing, but not less than 9 mm (3/8 in). Longitudinal Bars
The maximum diameters of reinforcement to be used in the various locations is set by the user.
Standard hooks for stirrups and ties are limited to No.8 bars, db=25mm (1.0in.) and smaller.
And the 90-degree hook with 6db extension is further limited to No. 5, db=16mm (0.625in.) bars and smaller. Longitudinal Bars
For primary reinforcement there is no limit on bar size.
Minimum distance between bars
The minimum clear horizontal distance between individual parallel bars, s cl,min, is given by;
scl,min ≥ MAX [db, 25 mm] metric units
scl,min ≥ MAX [db, 1in] US units
IF the above check fails then a Warning is displayed.
Where parallel reinforcement is placed in two or more layers, bars in the upper layers shall be placed directly above the bars in the bottom layer with clear distance between layers not less than 25mm (1in.).
Maximum spacing of tension bars
The spacing of reinforcement closest to the tension face, s is given by;1
s ≤ MIN[380mm280MPa/fs-2.5cc, 300mm(280MPa/fs)] metric units s ≤ MIN[15in40000psi/fs-2.5cc, 12in(40000psi/fs)] US units
where Longitudinal Bars
fs = calculated stress in reinforcement at service load; it shall be permitted to take
= (2/3)fy(As,reqd/As,prov)
cc = the least distance from surface of reinforcement to the tension face
IF the above check fails then a Warning is displayed
IF torsional reinforcement is required:
the longitudinal reinforcement required for torsion shall be distributed around the perimeter of the closed stirrups with maximum spacing of 300mm (12 in.)2
Minimum area of beam reinforcement
The minimum area of longitudinal tension reinforcement, A s,min, is given by;3
- As,min ≥ MAX[ (f’c0.5/(4fy))bwd, 1.4MPabwd/ fy ] metric units
- As,min ≥ MAX[ (3 f’c0.5/(fy)bwd, 200Psibwd/ fy ] US units
where Longitudinal Bars
f’c = specified compressive strength of concrete
fy = specified yield strength of reinforcement
b w =web width; for statically determinate members with a flange in tension
=MIN(2*bw, beff) 4
d = distance from extreme compression fiber to centroid of longitudinal compression reinforcement
The above equation is used wherever reinforcement is needed, except where such reinforcement is at least one-third greater than that required by analysis, in which case As,min not required.
Minimum area of slab reinforcement
For ACI 318-08 and ACI 318-115
For structural slabs of uniform thickness the minimum area of tensile reinforcement in the direction of the span is:
- For US-units:
- IF Grade 40 to 50 deformed bars are used
- As,min,reqd ≥ bh0.0020
- IF Grade 50 to 60 deformed bars or welted wire reinforcement are used
- As,min,reqd ≥ bh0.0018
- For metric units:
- IF Grade 280 to 350 deformed bars are used
- As,min,reqd ≥ bh0.0020
- IF Grade 350 to 420 deformed bars or welted wire reinforcement are used
- As,min,reqd ≥ bh0.0018
- IF yield stress exceeding 420 MPa
- As,min,reqd ≥ bh [MAX(0.0014 , 0.0018*420/fy)]
Maximum area of reinforcement
Footnotes
- ACI 318-08, ACI 318-11, ACI 318M-08 and ACI 318M-11 Section 10.6.4
- ACI 318-08, ACI 318-11, ACI 318M-08 and ACI 318M-11 Section 10.5.6.2
- ACI 318-08, ACI 318-11, ACI 318M-08 and ACI 318M-11 Section 10.5.1
- Assumption; the member is statically determinate in design
- ACI 318-08 and ACI 318-11 and ACI 318M-11 Section 7.12.2.1 and 10.5.4
- Notes on ACI 318-08 Chap. 6 Section 10.3.5 Longitudinal Bars
- ACI 318-08, ACI 318-11, ACI 318M-08 and ACI 318M-11 Section 10.2.7.3
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