Coupling beam is an important member of the lateral force-resisting system in a structure. Consequently, it couples or combines the two independent systems like shear walls. Types, advantages and design of coupling beam as per ACI 318- 11 is discussed.
Types of Coupling Beam used in Structure
There are two types of coupling beams used in structure:
1- Conventionally reinforced concrete coupling beams
2- Diagonally reinforced concrete coupling beams
1- Conventionally Reinforced Concrete Coupling Beam
This type of coupling beam is similar to normal reinforced concrete with bottom and top reinforcement in addition to shear stirrups. It is employed when the beam is quite long compared with its depth. Such beams develop moment hinge at its ends and failure type will be a ductile failure.
2- Diagonally Reinforced Concrete Coupling Beam
When the ratio of coupling beam length is similar to its depth, the design of the beam is governed by shear and the failure is brittle. Diagonal reinforcement is provided to avoid brittle failure and resist shear. This reinforcement arrangement leads to a decrease in the amount of shear reinforcement.