1. LOAD RATING BY MANUAL CALCULATIONS
RC_ SLAB BRIDGE RATING
Amjad Waheed, PE
Ohio Department of Transportation
Load Rating

2. Agenda – Day 1 8:00 am – 8:15 am Introductions and House Keeping
8:15 am – 8:45 am Session 1: Load Rating Basics
8:45 am – 9:30 am Session 2: Basic Load Rating Calculations
9:30 am – 9:45 am Break
9:45 am – 11:45 am Session 3: Example – Load Rating Concrete Slab Bridge
11:45 am – 12:00 pm Questions
12:00 pm – 1:00 pm Lunch
1:00 pm – 2:30 pm Session 4: Example – Load Rating Steel Beam Bridges
2:30 pm – 2:45 pm Break
2:45 pm – 3:45 pm Session 4: Example – Load Rating Steel Beam Bridges (Con’t)
3:45 pm – 4:00 pm Questions
Load Rating Seminar

3. What is Load Rating? RF = RF =
The safe live load carrying capacity of a highway structure is called its load rating.
How to calculate the rating factor (RF)
A1 = Factor for dead loads
A2 = Factor for live load
C = Capacity of the bridge
D = Dead loads
I = Impact loads
L = Live loads
Capacity for (L+I)
RF =
Actual (L + I)
C – A1 * D
RF =
A2 * (L + I)
Load Rating

4. Factors for LFR Load Rating
Rating Type
A1 = Factor for dead loads
A2 = Factor for live load
Inventory
* Design level
1.3
2.17
Operating
Ref: AASHTO Manual for Condition Evaluation of Bridges 1994
Load Rating

5. Rating Factor Equation
Inventory Rating
C – A1 * D
R.F. =
A1 = 1.3
A2 = = 1.3 * 1.67
A2 * (L + I)
C – 1.3 * D
R.F. =
1.3 * 1.67 * (L + I)
C/1.3 – D
R.F. =
1.67 * (L + I)
Load Rating Seminar

6. Rating Factor Equation
Operating Rating
C – A1 * D
R.F. =
A1 = 1.3
A2 = 1.3
A2 * (L + I)
C – 1.3 * D
R.F. =
1.3 * (L + I)
C/1.3 – D
R.F. =
(L + I)
Load Rating Seminar

7. Single-span slab bridge
Load Rating

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21. Live Load Distribution Factor
AASHTO Standard Specification for Highway Bridges
CASE B – Main Reinforcement Parallel to Traffic
For wheel loads, the distribution width
E = *S  7’
S = Effective Span length in feet
3.24.1
E = *13 = 4.78’
S = 13’
Load Rating

22. Load Rating Seminar

23. Impact Load (Impact Factor)
AASHTO Standard Specification for Highway Bridges
3.8.2 Impact Formula
The amount of impact allowance, I, as a fraction of the live load
I = 50 / (L + 125)  0.3
L = Effective Span length in feet
I = 50 / ( ) = 0.362
Use I = 0.3
Load Rating

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31. Summary of Rating Results
Load
Weight (GVW) Tons
M L+I
ft. k/ft
R.F. = (28.09/ M L+I)
Safe Load
Tons
% Ohio Legal
HS 20 36
14.1
1.992
71.20
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2F1 15
8.8
3.192
47.90
319%
3F1 23
10.4
2.700
62.10
270%
4F1 27
10.9
2.577
69.60
258%
5C1 40
108.00
POSTING NOT REQUIRED
Load Rating Seminar

32. Load Rating

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37. Material Strengths
BMD - Figure 904
Load Rating Seminar

38. Material Strengths
BMD - Figure 905
Load Rating Seminar

39. Learning Curve
Load Rating

40. ODOT Rating Contact Information
Amjad Waheed, PE
Shelton A. Howard, PE
Richard C. Irwin, PE
Cindy Wang, PE
Load Rating

41. That’s all folks
Load Rating