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Structural Concrete - Hassoun

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592 Chapter 16 Continuous Beams and Frames<br />

and<br />

f y = yield strength of steel, ksi<br />

E s = modulus of elasticity of main steel<br />

ρ = percentage of main steel<br />

ρ s = percentage of steel fibers<br />

A plastic hinge in the maximum negative moment region.<br />

From Eq. 16.21, it is obvious that the plastic rotation of fibrous reinforced concrete is dependent<br />

upon the percentage of steel fibers and percentage of the main steel and its yield strength. Raising<br />

the yield strength of the main steel reduces the plastic rotation. Equation 16.21 also includes the<br />

effect of the plastic hinge length on rotation.<br />

A simplified form can be presented [14]:<br />

( ) 0.003<br />

θ p = λβ<br />

(16.23)<br />

λ<br />

For example, if ρ s = 0andf y = 60 ksi, then θ p1<br />

= 0.00289∕λ, andifρ s = 1.0%, ρ = 1.5%, and<br />

f y = 60 ksi, then θ p2<br />

= 0.01222∕λ. This means that the rotation capacity of a concrete beam may<br />

be increased by about four times if 1% of steel fibers is used.

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