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Structural Concrete - Hassoun

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22.9 Deflections (AASHTO 5.7.3.6) 919<br />

3. Check Minimum Thickness (AASHTO 5.14.1.2.2)<br />

The thickness of any part of precast concrete beams shall not be less than:<br />

Top flange = 2.0 in.<br />

Web, non-posttensioned = 5.0 in.<br />

Bottom flange = 5.0 in.<br />

if (t top_flange ≥ 2in., “OK”, “NG”) =“OK”<br />

if (t bottom_flange ≥ 5in., “OK”, “NG”) =“OK”<br />

if (t web ≥ 5 in., “OK”, “NG”) = “OK”<br />

4. Effective Flange Width (Ref. (Section 22.5.3.5) & AASHTO 4.6.2.6.1)<br />

Interior Girder<br />

where<br />

b eff_int = min<br />

OH = 3.915 ft<br />

(Length of overhang)<br />

( (<br />

Leff<br />

4 , 12t s + max t web , t ) )<br />

top_flange<br />

, S<br />

2<br />

L eff = L = 100 ft<br />

t s = 8 in.<br />

t web = 6in.<br />

S = 9 ft<br />

t top _flange = 3.5 ft<br />

Effective span length<br />

Average depth of the slab<br />

Web thickness<br />

Centerline-to-centerline spacing of interior girders<br />

Width of the top flange of the girder<br />

Therefore, effective flange width of the composite section for an interior girder is<br />

computed as<br />

( (<br />

Leff<br />

b eff_int = min<br />

4 , 12t s + max t web , t ) )<br />

top_flange<br />

, S<br />

2<br />

Exterior Girder<br />

where<br />

= min<br />

b eff_ext = min<br />

( 100 ft<br />

, 12 (8in.) + max<br />

4<br />

(<br />

6,<br />

3.5 in.<br />

2<br />

) )<br />

, 9ft = 8.5ft<br />

( (<br />

Leff<br />

8 , 6t s + max tweb<br />

2 , t ) )<br />

top_flange<br />

, OH<br />

4<br />

OH = 3.915 ft<br />

(length of overhang)<br />

Therefore, effective flange width of the composite section for an exterior girder is<br />

computed as<br />

( (<br />

Leff<br />

b eff_int = min<br />

8 , 6t s + max tweb<br />

2 , t ) )<br />

top_flange<br />

, OH<br />

4<br />

( ( 100 ft<br />

6<br />

= min , 6 (8in.) + max<br />

8<br />

2 , 3.5in. ) )<br />

, 3.915 ft = 3.915 ft<br />

4<br />

5. Select Resistance Factors (AASHTO 5.5.4.2)<br />

For tension-controlled prestressed concrete sections 1.0<br />

For shear and torsion (normal-weight concrete) 0.9<br />

For compression in anchorage zones (normal-weight concrete) 0.8<br />

For tension in steel in anchorage zones 1.0

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