Stirrups per ACI 318-19 with ideCAD
How does ideCAD define stirrup details according to ACI 318-19?
According to 25.7.1.6.1, stirrups used for torsion or integrity reinforcement can be made up of two pieces of reinforcement. This option can be choosen by users.
To anchore shear and torsional reinforcement properly, it is automatically done a hook or bend at the end of the reinforcement.
According to 25.7.1.6, stirrups are anchored ends get through with 135- degree standard hooks around a longitudinal bar automatically.
Symbols
ld = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
d = distance from extreme fiber to centroid of longitudinal tension reinforcement, in.
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normalweight concrete of the same compressive strength
db = nominal diameter of bar, wire, or prestressing strand, in
f'c = specified comprehensive strength of concrete, psi
fyt = specified yield strength of transverse reinforcement, psi
Stirrup legs should be extended to the compression and tension surfaces of the member as cover requirements and be anchored at both ends. To anchor shear and torsional reinforcement properly, it requires a hook or bend at the end of the reinforcement.
According to 25.7.1.2, each bend in the continuous portion of a single or multiple U-stirrup and each bend in a closed stirrup enclose a longitudinal bar or strand between anchored ends.
Straight deformed bar and wire anchorage are forbidden. A standard hook provides the anchorage for a No. 5 or D31 or smaller stirrup. According to 25.7.1.3, the anchorage of the deformed bar should be:
For No.5 bars and smaller and for No.6 through No.8 bars with fyt ≤ 40 000 psi, a standard hook should use.
For No.6 through No.8 bars with fyt > 40 000 psi, a standard hook around a longitudinal bar plus an embedment between midheight of the member and the outside end of the hook equal to or greater than 0.014dbfyt / (λ(√f’c ). λ is given in Table 25.4.3.2.
Modification factor | Condition | Value of factor |
|---|---|---|
Lightweight λ | Lightweight concrete | 0.75 |
Normalweight concrete | 1.0 | |
| Epoxy-coated or zinc and epoxy dual-coated reinforcement | 1.2 |
Uncoated or zinc-coated (galvanized) reinforcement | 1.0 | |
Confining reinforcement ψr | For No. 11 and smaller bars with | 1.0 |
Other | 1.6 | |
Location ψo | For No. 11 and smaller diameter hooked bars:
| 1.0 |
Other | 1.25 | |
Concrete strength ψe | fc' < 6000 psi | fc' / 15000 + 0.6 |
fc' ≥ 6000 psi | 1.0 |
For a No. 6, No. 7, or No. 8 stirrup with fyt of only 40,000 psi, a standard stirrup hook around a longitudinal bar provides sufficient anchorage. The embedment should be checked for a No. 6, No. 7, or No. 8 stirrup with higher strength. A 135-degree or 180-degree hook is preferred, but a 90-degree hook may be used provided the free end of the 90-degree hook is extended to the full 12 bar diameters as required in 25.3.2.
The Anchorage of each leg of welded wire reinforcement forming a single U-stirrup should be
(a) Two longitudinal wires spaced at a 2 in. spacing along the member at the top of the U
(b) One longitudinal wire located not more than d/4 from the compression face and a second wire closer to the compression face and spaced not less than 2 in. from the first wire. The second wire is permitted to be located on the stirrup leg beyond a bend or on a bend with an inside diameter of bend of at least 8db.
Because it is not possible to bend a No. 6, No. 7, or No. 8 stirrup tightly around a longitudinal bar, and due to the force in a bar with design stress greater than 40,000 psi, stirrup anchorage depends on both the type of hook and whatever development length is provided. A longitudinal bar within a stirrup hook limits the width of any flexural cracks, even in a tension zone. Because such a stirrup hook cannot fail by splitting parallel to the plane o the hooked bar, the hook strength as used in 25.4.3.1(a) has been adjusted to reflect cover and confinement around the stirrup hook.
In joists, a small bar or wire can be anchored by a standard hook, not engaging longitudinal reinforcement, allowing a continuously bent bar to form a series of single-leg stirrups along the length of the joist.
For single leg stirrup of welded wire reinforcement, anchorage of the reinforcement is with two longitudinal wires at a minimum spacing of 2 in., according to 25.7.1.5.
At least the greater of d/4 or 2 in. from d/2 should be arranged for the inner longitudinal wire
Stirrups are closed for torsion or integrity reinforcement. Transverse wires is perpendicular to the axis of the member. According to 25.7.1.6, stirrups are anchored
Ends get through with 135-degree standard hooks around a longitudinal bar
According to 25.7.1.6.1, stirrups used for torsion or integrity reinforcement can be made up of two pieces of reinforcement: a single U-stirrup anchored according to 25.7.1.6(a) closed by a crosstie where the 90-degree hook of the crosstie.
Except for torsion or integrity reinforcement, closed stirrups can be made using pairs of U-stirrups spliced to form a closed unit with lap lengths of at least 1.3ld.
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