Coupling beams are typically added to a structure to improve its lateral force resistance. They bridge two separate, independent items together (like shear walls) to add stiffness to the overall system. They are usually short and thick, similar to deep beams. In concrete buildings, in particular, they take the form of concrete beams, which are often one of the most critical elements.
Coupling beams have two roles in most buildings. Firstly, the beam couples two shear walls to increase the moment of resistance. If you have two uncoupled shear walls, the force exerted from the side of one wall would not influence the second wall because they are not connected by beams with a typical rectangular cross section. This means that the force exerted will affect only one wall, which might cause movement to occur independently of the other one. This significantly decreases the structural integrity of the building. By contrast, by coupling the two, you reduce the stress each wall attracts by distributing the forces from one wall to the other through the beam system. Coupling beams also distribute the lateral force across the length of the second wall, which further spreads the tension along the element and enhances the overall resistance of the structural elements.
The second role of a coupling beam is to act as a source of energy dissipation during extreme stress. For example, if there is an earthquake, a building has to be resilient against pressure. To be resilient, a structure cannot be too rigid. Otherwise, if there were an earthquake (for example), that building would break at the wall pier and collapse. By contrast, a slight amount of flexibility under extraordinary pressure means that the structure is much more able to maintain essential structural integrity under pressure.
A coupling beam then both strengthens the design of a building as a whole and is designed to yield first to preserve more vital parts of a building if it experiences extreme stress. By accommodating a building’s motion in beam design, structural engineers make more stable and safe structures.
