# Coupling Beam Design per ACI 318-19 with ideCAD (v12)

**How does ideCAD design coupling beams according to ACI 318-19?**

Boundary Elements of Special Structural Wall requirements are met automatically.

**Notation**

* A_{ch } = *cross-sectional area of a member measured to the outside edges of transverse reinforcement, in.

^{2}

*gross area of concrete section bounded by web thickness and length of section in the direction of shear force considered in the case of walls, and gross area of concrete section in the case of diaphrams. Gross area is total area of defined section minus area of any openings, in.*

**A**_{cv }=^{2}

*area of concrete section of an individual pier, horizontal wall segment, or coupling beam resisting shear, in*

**A**_{cw}=^{2}.

*gross area of concrete section, in*

**A**_{g }=^{2}

*total cross-sectional area of transverse reinforcement, including crossties, within spacing s and perpendicular to dimension*

**A**_{sh }=*, in.*

**b**_{c}^{2}

*cross-sectional dimension of member core measured to the outside edges of the transverse reinforcement composing area*

**b**_{c }=*, in.*

**A**_{sh}*width of compression face of member, in.*

**b**_{w }=*dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direction of the span for which moments are being determined, in.*

**c**_{1 }=*dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direction perpendicular to*

**c**_{2 }=*in.*

**c**_{1},*specified compressive strength of concrete, psi*

**f**_{c}^{'}_{ }=

**√f**_{c}‘*square root of specified compressive strength of concrete, psi*

**=***specified yield strength for nonprestressed reinforcement, psi*

**f**_{y }=*specified yield strength of transverse reinforcement, psi*

**f**_{yt }=

**h****=**overall thickness, height, or depth of member, in.

**h**_{w}**=**height of entire wall from base to top, or clear height of wall segment or wall pier considered, in.

**h**_{wcs}**=**height of entire structural wall above the critical section for flexural and axial loads, in.

*length of clear span measured face-to-face of supports, in.*

**l**_{n}_{ }=

**l**_{w }**=**length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in.

**s****=**center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.

**s**_{o}**=**center-to-center spacing of transverse reinforcement within the length

*, in.*

**l**_{o}*nominal shear strength, lb*

**V**_{n }=*angle definin the orientation of reinforcement*

**α =**According to **ACI 18.10.7.1, **coupling beams with * (l_{n}/h) ≥ 4* should satisfy the requirements of

*Beams of Special Moment Frames*(

**ACI 18.6**). In addition, the wall boundary is designed as a column. If it can be shown by analysis that the beam has sufficient lateral stability, the following two provisions specified in

**ACI 18.6.2.1**

**need not be satisfied;**

Minimum width

should be lesser of**b**_{w}and 10 in.**0.3h**The beam width projection beyond the supporting column's width on each side should be less than the smallest value of

and**c**_{2}.**0.75c**_{1}

According to **ACI 18.10.7.2, **coupling beams with * (l_{n}/h) < 4 *and with

*should be reinforced with two intersecting groups of diagonally placed bars symmetrical about the midspan.*

**V**_{u}≥ 4λ√f_{c}^{‘}A_{cw}According to **ACI 18.10.7.3, **coupling beams not governed by **ACI 18.10.7.1** or **18.10.7.2** can be reinforced either with two intersecting groups of diagonally placed bars symmetrical about the midspan or with the wall boundary is designed as a column.

According to **ACI 18.10.7.3,** Coupling beams reinforced with two intersecting groups of diagonally placed bars symmetrical about the midspan should satisfy the conditions given below;

is calculated by**V**_{n}**ACI Eq. (18.10.7.4);**

is the angle between the diagonal bars and the longitudinal axis of the coupling beam.**α**Each group of diagonal bars shall consist of a minimum of four bars provided in two or more layers.

According to **ACI 18.10.7.3**, Coupling beams reinforced with two intersecting groups of diagonally placed bars symmetrical about the midspan should satisfy either of the two conditions given below;

Each diagonal bars group should be enclosed bu rectilinear transverse reinforcement having out-to-out dimensions of at least

in the**b**_{w}/2direction and**b**_{w}along the other sides. The transverse reinforcement should satisfy**b**_{w}/5**ACI 18.7.5.2**, and the minimum transverse reinforcement areais given below;**A**_{sh}

The transverse reinforcement spacing should satisfy

**ACI Eq. (18.7.5.3)**and not exceedingof the smallest diagonal bars, and the maximum spacing of crossties or legs of hoops is 14 inches.**6d**_{b}The transverse reinforcement should continue through the intersection of the diagonal bars. At the intersection, it is permitted to modify the arrangement of the transverse reinforcement provided the spacing and volume ratio requirements are satisfied. Additional longitudinal and transverse reinforcement should be distributed around the beam perimeter with a total area in each direction of at least

and spacing not exceeding 12 in.**0.002b**_{w}sThe transverse reinforcement should satisfy

**ACI 18.7.5.2**is given below;**A**_{sh}

Maximum longitudinal spacing of transverse reinforcement is the lesser of 6 in. and

of the smallest diagonal bars. Maximum Spacing of crossties or legs of hoops both vertically and horizontally in the plane of the beam cross-section should be 8 in. Each crosstie and each hoop leg shall engage a longitudinal bar of equal or greater diameter.**6d**_{b}