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DESIGN PRINCIPLES AND CALCULATIONS (SAMPLE CALCULATION)<br />
FLEXURAL CALCULATIONS - COMPOSITE<br />
Joist = H1207<br />
F y = 50 ksi<br />
Clear Span = 21’-0”<br />
Bottom Chord A s = 0.72<br />
y = 0.44”<br />
b = lesser of 16 t, L / 4, Joist Spacing<br />
= 40”<br />
f’ c = 3,000 psi<br />
t = Slab = 2.5”<br />
Dead Load = 60 psf<br />
Live Load = 40 psf<br />
Total Load = 100 psf<br />
OVERALL DEPTH<br />
DESIGN SPAN<br />
Doal = D + t<br />
= 12” + 2.5”<br />
= 14.5”<br />
L = Clear Span + 4”<br />
= 21.33’<br />
a =<br />
=<br />
A s x F y<br />
0.9 x 0.85 x f’ c x b<br />
0.72 x 50<br />
0.9 x 0.85 x 3 x 40<br />
= 0.392”<br />
LEVER ARM<br />
t<br />
D<br />
WORKING LOAD<br />
d u = Doal - y - a/2<br />
= 14.5 - 0.44 - 0.392/2<br />
= 13.86”<br />
y<br />
b<br />
Fig. 11<br />
W s = A s x F y x d u x 8,000<br />
1.7 x L 2 x 12<br />
= 430 lb./ft.<br />
a<br />
d u<br />
= 0.72 x 50 x 13.86 x 8,000<br />
1.7 x 21.33 2 x 12<br />
13
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