Page 297 - Bridge and Highway Structure Rehabilitation and Repair

272 SECTION 2 STRENGTHENING AND REPAIR WORK

Analysis: Main reinforcement perpendicular to traffic. Analyze as a strip of unit width
continuous over beam fl anges.

Deck thickness: It is based on live load deflection control, which is a function of girder spac-
ing, s/h 20 where s is girder spacing, h min 3 (s 4 3000) / 30 175 (Table A2.5.2.6.3-1)
Structural depth 9 7 in (for thinner slabs and wide girder spacing, transverse prestressing
may be used to prevent crack formation).
Dead load moments: Dead load bending moments can be evaluated by the moment distri-

bution method, stiffness matrix method, or by coefficients given in handbook.
Highest positive and negative moments are in end spans of a continuous deck and less in
middle spans. The greater the number of beams, the higher the redundancy.
Equal spacing of girders is assumed.
2
Transverse dead load bending moments, for repeated beams, M max 3 4wL /12 and
2
6wL /8
2
2
For four beams, M max 3 4wL /10 and 6wL /10
st

For five or more beams (use influence lines at 0.4 L of 1 span), M 3 0.0744 wL 2

2
Adjust for overhang moment 6wl /2
For scond span, M 3 40.0471wL and 60.1141wL 2
2
For analysis, external actions due to load must balance internal actions: $M 3 0
Hence M 3 )M 3 A f (d 6 a /2); a 3 A f / 0.85 f 1 b
u
s y
s
y
n
c
A 3 (M /)) / f j.d)
u
y
s
For Design, )M M Note: Sign ( ) is to ensure minimum requirements and results in
u
n
higher overall safety factor for the bridge.
Check for shear $V 3 0 is not required.
• Check ductility: a 0.35 d
• Minimum reinforcement # 0.03 f 1/f (5.7.3.3.2)
y
c
1.2 M M or 1.33 $ M (factored moments)
cr u
M 3 f I/(y t)
cr
r
M 3 M DC 4 M DW 4 M LL4I
u
Rupture stress f 3 2.4 f 1
r
c
• Maximum spacing s max 3 450 mm or 1.5 h (5.10.3.2)
• Distribution reinforcement 3 3840/ S % (9.7.3.2) and (9.7.2.3)
e
where S is the effective span length
e
220/ s 67 percent (bottom distribution bars)
A 9 0.11A / f (top distribution reinforcement)
s
y
g
• Maximum reinforcement:
c / d 0.42 (5.7.3.3.1-1)
e