BOX GIRDER BRIDGE DESIGN
ρmin=0.03f'c/fy
Working Stress Design Formula
• Z= jd = d-(x/3) = d-(kd/3) =d(1-(k/3)) = dj
 j=1-(k/3), k = nfc/(nfc+fs), n=Es/Ec=modular ratio
• The moment resistance is, M=T*Z=As*fs*j*d
 As = M/(fs*j*d)
No of
Bars
Diam.
(mm)
As
(mm2)
d'
(m)
Rect.
a=
Beam
d =D-d'
Asfy/(0.85fc' Rect. or
ØMn
p=As/bd
(m)
b)
T-beam =Ø*Asfy(d
(mm)
-a / 2 )
(KNm)
T-beam
No of Bars
a=(AsM2
Asf=0.85fc
ØMn
M1=Asf.fy(d-hf/2) Asf)fy/(0.85*fc'*b =(As-Asf)fy
(b-bw)hf/fy
=Ø ( M1 +
(KNm)
w)
(d -a / 2 )
(mm2)
M2 )
(mm)
(mm)
SkinReinforcement
If the depth of side face of a member exceeds 3ft,
longitudinal skin reinforcement shall be uniformly distributed
along both side faces of the member for a distance d/2
nearest the flexural tension reinforcement.
Area of skin reinforcement, Ask > = 0.012*(d - 30) in2 / ft
(on each side face)
Maximum spacing, Smax, lesser of d/6 or 12"
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