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Structural Concrete - Hassoun

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Review Problems on <strong>Concrete</strong> Building Components 953<br />

First stirrup at face of support<br />

Second stirrup at s/2 = 9/2 = 4.5 in.<br />

Seven stirrups at 9 in.→ 67.5 in.<br />

c. Check development length<br />

Calculate the development length for tension bar l d<br />

Check if conditions for spacing and cover are met to select an equation: (ACI Code,<br />

Section 25.4.2.2)<br />

d b = 1in.<br />

clear cover = 3in.>d b<br />

clear spacing = 10 − 7 − 1 = 2in.>d<br />

1<br />

b<br />

Conditions are met, use l d = Ψ t Ψ e f y<br />

20λ √ d b<br />

f c<br />

′<br />

Determine the multiplication factors: (ACI Code, Section 25.4.2.4)<br />

Ψ t = 1.0 (bottom bars)<br />

Ψ e = 1.0 (no coating)<br />

Ψ t Ψ e < 1.7 OK<br />

λ = 1.0 (normal − weight concrete)<br />

√ √<br />

f<br />

′<br />

c = 3000 = 54.8psi< 100 psi<br />

Calculate l d : (ACI Code, Section 25.4.2.2)<br />

l d = Ψ t Ψ e f y<br />

20λ √ d b =<br />

f c<br />

′<br />

(1)(1)(60, 000)<br />

20(1) √ (1) =54.8in. = 55 in. ≥ 12 in.<br />

3000<br />

Example 23.3<br />

A simply supported beam has a 25 ft span and carries a service uniform dead load of 3 K/ft (including<br />

self-weight) and a uniform live load of 1 K/ft.<br />

Given: b = 12 in., d = 20 in., d ′ = 2.5in.,f ′ c = 3ksi,f y = 60 ksi.<br />

a. Design the section for flexural reinforcement.<br />

b. Design for shear reinforcement.<br />

c. Check development length.<br />

Solution:<br />

a. Design the section for flexural reinforcement<br />

Check for minimum thickness to satisfy the deflection criterion: (ACI Code, Section 24.2.3.1)<br />

Minimum thickness for simply supported beam = 25 = 25×12 = 18.75 in. ≤ 25 in. (OK)<br />

16 16

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