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Structural Concrete - Hassoun

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812 Chapter 20 Seismic Design of Reinforced <strong>Concrete</strong> Structures<br />

δ X + 1<br />

δX<br />

x + 1<br />

x<br />

δX – 1<br />

Δ x + 1<br />

x – 1<br />

Δ x<br />

Δ x – 1<br />

Figure 20.4<br />

Definition of drift.<br />

The stability coefficient, θ, should not exceed<br />

θ max = 0.5<br />

C d β<br />

≤ 0.25 (20.28)<br />

where β is the ratio of shear demand to shear capacity for the story between level x and (x–1).<br />

A conservative value of β = 1 can be used where the ratio is not calculated.<br />

If θ>θ max , then the structure is potentially unstable, and must be redesigned. For<br />

0.1

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