Page 295 - Bridge and Highway Structure Rehabilitation and Repair

270 SECTION 2 STRENGTHENING AND REPAIR WORK

Using the greater of the two distances, L 3 30 ft
Effective width of slab E 3 4 4 0.06 S 3 4 4 0.06 8 25 ft 3 5.5 ft (AASHTO 3.24.3.2
Case B)
Dead load of slab and overlay 3 0.15 8 (18 in/12 4 2 in/12) 3 0.25 ksf
Manual of Condition Evaluation of Bridges (3.3.2.1 to 3.3.2.3)
Dead load of parapet and sidewalk to be distributed over 3 0.5 k/ft / (33.5/2) 4 0.15 8
8/12/(33.5/2) 3 0.030 4 0.006 3 0.036 ksf (Use 0.04 ksf.)
Total DL 3 0.25 4 0.04 3 0.29 ksf
2
2
Maximum DL negative moment at supports 3 6 wl /10 3 6 0.29 8 25 /10 3 618.13
kip-ft
Per ft. width 3 18.13/5.5 ft 3 4 3.3 kip-ft/ft
2
2
Maximum positive moment at 0.4 L 3 4wl /12 3 40.29 8 25 /12 3 15.1 kip-ft
Per ft. width 3 15.1/5.5 ft 3 42.75 k-ft/ft
Use HS-20 Truck with two axles of 32 kips each and one axle of 8 kips.
Two wheels/axle 3 16 kips/wheel; Imp. factor 3 1.33
Distance between back axles 3 14 ft; distance between front axles varies.
Using influence lines M L4I at midspan or support 3 1.33 8 (16 kip 8 k1 4 16 kip 8

k2) span
Positive moment at midspan with one wheel in negative moment region,
k1 3 0.175, k2 3 6 0.017 (Check coeffi cients from infl uence lines method and
STAAD. Pro output)
M 3 1.33 8 25 8 16(0.175 6 0.017) 3 532 8 0.158 3 84.1 kip-ft
L4I
Per ft. width 3 84.1/5.5 ft 3 4 15.28 k-ft/ft
Maximum positive moment occurs at 0.4 L of end span,
k1 3 0.204, k2 3 0
M 3 1.33 8 25 8 16(0.204) 3 532 8 0.204 3 108.53 kip-ft
L4I
Per ft. width 3 108.53/5.51 3 4 19.73 k-ft/ft
Negative moment at penultimate support,
k1 3 60.102, k2 3 60.09
M 3 1.33 8 25 8 16(60.102 6 0.09) 3 532 8 60.192 3 6102.14 kip-ft
L4I
Per ft width 3 6102.14/5.5 ft 3 618.57 k-ft/ft
Load factors: = 1.2; 3 1.3 (Section 3.3.4.1 and Table 2)
DL LL
Maximum total moment 3 1.2 8 3.3 41.3 8 19.73 3 29.61 kip-ft/ft
) 3 0.85 (Section 3.3.4.2 and Table 3a and 3b)
2
Reinforcement: ¾ in diameter bars at 8 in centers (0.66 in top) and 6 in centers
2
(0.89 in bottom)
a 3 A f /0.85 f 1 b
s
y
c
a 3 0.89 8 33.0 ksi / 0.85 8 2.8 ksi 8 12 in 3 1.03
M 3 )M 3 A f ( d 6 a/2 ) 3 0.85 8 0.89 8 33.0 8 (16 6 1.03/2) 3
s y
u
n
24.970 8 14.48 kip-inch
M 3 361.71 kip-in 3 30.14 kip-ft/ft 9 29.61 kip-ft
u
Hence okay.
Existing slab bridge has the capacity to carry HS-20 live load.