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Structural Concrete - Hassoun

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22.7 Design for Shear (AASHTO 5.8) 911<br />

Flexural<br />

compression zone<br />

θ<br />

s x<br />

sin θ<br />

s x = d v<br />

(a)<br />

s x<br />

sin θ<br />

A S > 0.003b x s x<br />

s x = d v<br />

θ<br />

(b)<br />

Figure 22.11 Definition of crack spacing parameter s x<br />

.(a) Member without transverse<br />

reinforcement and with concentrated longitudinal reinforcement and (b) member without<br />

transverse reinforcement but with well-distributed longitudinal reinforcement. AASHTO<br />

LRFD Bridge Design Specifications, 2014. Used by permission.<br />

The value of θ shall be calculated as follows:<br />

θ = 29 + 3500ε s (22.21)<br />

where ε s is the calculated longitudinal strain at the middepth of the member when the section<br />

is subjected to N u , M u and V u . Longitudinal strain, ε s , can be calculated using the following<br />

equation:<br />

ε s =<br />

(|M| u )<br />

d v<br />

+ 0.5N u + |V u − V p | − A ps f po<br />

(E s A s + E p A ps )<br />

(22.22)<br />

According to AASHTO, ε s should not be greater than 6 × 10 −2 . Two different approaches are suggested<br />

when the value of ε s is negative: ε s can be taken equal to zero in the design procedure to be

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