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Structural Concrete - Hassoun

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976 Chapter 24 Design and Analysis Flowcharts<br />

Given: M u , b, b w , d, t, f′ c , f y<br />

Required: A s<br />

Calculate M u,ft (total flange).<br />

No<br />

d is given<br />

Yes<br />

Assume a = t<br />

d = M u /ϕ(0.85f′ c bt) + t/2<br />

a = t<br />

C ft = 0.85ϕf′ c bt<br />

M u,ft = ϕC ft (d – t/2)<br />

A s = M u /[ϕf y (d – t/2)]<br />

Yes<br />

M u ≤ M u,ft<br />

No<br />

If steel is high, assume<br />

a < t or a ≈ t/2<br />

d = M u /(0.85ϕf′ c ba) + a/2<br />

A s = M u /[ϕf y (d – a/2)]<br />

Rectangular section<br />

design, a ≤ t<br />

R u = M u /bd 2<br />

ρ = (0.85f′ c /f y ) [1 – 1 – 2R u /0.85ϕf′ c ]<br />

A s = ρbd<br />

T-section design,<br />

a > t<br />

C f = 0.85f′ c t(b – b w )<br />

A sf = C f /f y<br />

M uf = ϕC f (d – t/2)<br />

M uw (web) = M u – M uf<br />

R uw = M uw /b w d 2<br />

ρ w = (0.85f′ c /f y ) [1 – 1 – 2R uw /0.85ϕf′ c ]<br />

A s = A sf + A sw<br />

A sw = ρ w b w d<br />

No<br />

A s,min ≤ A s ≤ A s,max<br />

or<br />

ε t = (d t – c)/c ≥ 0.005<br />

Yes<br />

Change section<br />

Flowchart 24.6<br />

Design of T- or L-sections.<br />

A s is OK

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