A coupled shear wall in terms of its strength and stiffness can be imagined as lying halfway between a large unpenetrated wall and two individual walls whose combined lengths equal that of the single wall (Fig. 5.21). Envisage a coupled shear wall as two or more walls coupled or connected by deep coupling beams, or alternatively as a highly-penetrated single wall. For maximum structural effectiveness the depth of the coupling beams is normally greater than half their clear span, much deeper than conventional beams. Coupling beams force the walls to work together to resist seismic forces. Where walls are coupled by shallow beams or merely tied together by floor slabs they can be considered as independent walls that are considerably more flexible and weaker than if joined by coupling beams.
The architecturally defining feature of coupled shear walls is their squat coupling beams usually at each storey. They are readily identified during construction by their characteristic diagonal reinforcing bars which provide the system with its high level of ductility (Fig. 5.22). Where coupled reinforced concrete walls are designed in accordance with the Capacity Design approach structural fuses form in the coupling beams
and at the base of each wall before any shear or foundation damage occurs. Although fuses suffer structural damage when they absorb earthquake energy, thanks to the concrete confinement provided by closely-spaced ties they maintain their strength and are repairable after a damaging quake.
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