Table of Contents

SummaryHanger bars in beams shall be equipped with concrete that backs secondary beams. Reinforcement shall be equipped in the primary beam, and they shall be kept around the joint of the two beams. |

** 1. Design Technique **

Normally, we equip primary beams to reinforce the secondary beams.

The load of the secondary beams is held by the primary beam.

We usually design the primary beams for the load of the secondary beams, and most of the time multiple engineers ignore the design at the joint.

The joint should be well prepared to hold the reaction of the secondary beam.

Hanger reinforcement is provided at the joint, in the primary in addition to the normal shear reinforcements.

The requirement of hanger reinforcement can bypass if the shear force at the edge of the primary beam is less than 3(√f’c)b_{w2}d_{2} as the inclined cracking is not fully formed at this shear.

**Where,**

b_{w2} is the width of the secondary beam and d_{2} is the effective depth of the secondary beam. The method of design and detailing are as per ACI guidelines.

The depth of the primary and secondary beams are taken as h1 and h2 respectively. Here, h_{b} is the vertical distance between the bottom of the primary beam to the secondary beam.

** ϕA _{h}f_{yt} ≥ (1-h_{b}/h_{1}) V_{u2}**

**Where,**

ϕ = 0.75

A_{h }= area of hanger reinforcement adjacent to one face of the supporting beam

f_{yt}= Yield Strength of Reinforcement

V_{u2}= Factored Shear at the End of Supporting Beam

** 2. Design Example of Hanger Bars in Beam **

Factored shear force at end of the supporting beam V_{u2 }= **200 kN**

Yield strength f_{yt }= **460 N/mm ^{2}**

Primary beam height= **600 mm**

Secondary beam height= **400 mm**

**Now,**

h_{b }= 600 – 400 = 200 mm

**From the above equation,**

0.75x460x A_{h} ≥ (1-200/600) (2x200x1000)

A_{h} ≥773 mm^{2}

Provide 4 Φ 12 mm bars

Here, **area of reinforcement** = 113x2x4 = **904** mm^{2}

Here 4 links are sufficient.

There are a few additional methods as well for developing hanger reinforcements. The textbook, “Design of Concrete Structures” authored by H. Nilson, David Darwin, and Charles W. Dolan also provided a method to compute the requirement of reinforcements.

They suggested using the ratio of the beam height to calculate the required shear force.

V_{d} = (h_{secondary} / h_{primary} ) **(Shear force)**

For this shear force, we can calculate the hanger **reinforcements**. If we employ the exact idea above, we can note the area of reinforcements as follows.

ϕA_{h}f_{yt} ≥ V_{d} |

Read Also: Alignment Design |