Wall systems

According to Section 5, a system in which, according to the results of the analysis, 65% of the seismic base shear is (or rather should be) resisted by primary seismic walls is termed a wall system. Wall systems resist the overturning moment directly, through bending moments rather than through axial forces in the individual walls. Provided that they comprise walls fixed at the base and with sufficient stiffness and strength relative to the beams to behave as vertical cantilevers, wall systems resist horizontal seismic actions very efficiently: for the same total quantity of concrete and horizontal steel (determining the resistance to base shear), lateral stiffness (which is important for drift control) increases and the total required vertical reinforcement decreases, with increasing horizontal dimension /w of the walls of the system. The limiting value of/w is the one that gives a shear span ratio, Ls//W, not less than 2.5, ensuring flexure-controlled behaviour and enhancing wall ductility.

If more than 50% of the total wall resistance is provided by coupled walls, the system is considered to be a coupled-wall system. As coupled walls dissipate energy not only in plastic hinges at the base of the individual walls but also in the coupling beams, overall they have significantly larger dissipation capacity than uncoupled walls with the same shear force capacity at the base. So, unlike the systems of uncoupled walls, coupled-wall systems are entitled to the same basic values of q as the inherently ductile frame systems.

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