Page 284 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 6 APPLICATIONS OF BRIDGE DESIGN AND RATING METHODS 259

• Floor beam analysis:
1. Floor beam moments
2. Maximum SF
• Rating of main girder:
1. For one loaded: Multiple presence factor m 3 1.2
Distribution factor DF 3 g1 LRFD 3.6.1.1.2
2. For both lanes loaded: DF 3 g2

3. Nominal flexural resistance of section LRFD C6.10.4 -1
4. Classify section LRFD 6.10.3.3.2
Non-composite symmetric section, D 3 0.5 8 D w
cp
5. Check web slenderness for compact section LRFD 6.10.4.1.2
3.76 (E/f )½ 2D /t
yc cp w

6. Check compression flange slenderness at midspan LRFD 6.10.4.1.4
1 / 1 /
b /2 t 1.38 (E/f ) 2; where f 3 (2D /t ) 2
yc
yc
f
c w
f

7. Check compression flange bracing LRFD 6.10.4.1.9
1 /
L 1.76 r (E/F ) 2
b t yc
8. Compute I yc

Compute A (compression flange area at midspan)
c
r 3 (I /A )½
yc
c
t
• Check flexural resistance and non-compact section LRFD 6.10.4.2.4

Load shedding factor, R LRFD 6.10.4.3.2a
b
Flexural resistance:
F 3 R R F , R 3 1.0
n b h yf h
Compute 2D / t
c w
3 5.76 when compression fl ange area tension fl ange area
b
1 /
Compute (E/ f ) 2
b c
1 /
R 3 1 6 [ a / (1200 4 300 a )] [2D / t 6 (E/f ) 2]
b r r c w b c
a 3 2D t / A
r c w c
• Using general load rating Eq. (6-1) Section 6.4.2
• Evaluation factors for strength limit states
– Resistance factor )
() ) 3 () ) 3 1.0 for fl exure and shear
v
f
– Condition factor ) 3 1.0 Section 6.4.2.3
c
– System factor ) s
) 3 0.90 for flexure of riveted two-girder system Section 6.4.2.4

s
) 3 1.0 for shear Section 6.4.3
s
• Strength I limit state Section 6.6.4.1
Flexural stress at midspan (unfactored):
f 3 (M )/S
DC4DW DC4DW
f LL4 IM 3 (M LL4IM )/S
Flexural resistance at midspan: F
n
Inventory RF
Operating RF
• Service II limit state