1. ODOT BRIDGE LOAD RATING
Greeting
I would like to discuss the next part of this course which will cover ODOT Bridge Load Rating.
In the next ½ hour, I would like to discuss.
-What a load rating is
-Why we perform bridge load ratings
-What ODOT expects in a bridge load rating submittal
A basic how and why overview

2. What is a Bridge? Federal Highway Administration (FHWA) Definition:
A Bridge is ANY structure that…
1.) is erected over a depression or obstruction
(water, highway, railway, etc.)
AND
2.) has a track or passageway for carrying traffic or
moving loads
3.) has an opening greater than 20’-0” (measured along centerline of roadway between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening)
What is a Bridge?
Let’s start with the first term of the phrase “Bridge Load Rating”…
ON THE SIDE
FHWA definition based on the National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3)
FHWA: "The National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3) give the following definition: A structure including supports erected over a depression or an obstruction, such as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet* between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening. * (6.1 meters)"

3. What is a Bridge? (cont.)
Ohio Department of Transportation (ODOT) Definition (based on the Ohio Revised Code):
A Bridge is ANY structure that…
1.) is on, above, or below a highway
AND
2.) Is greater than or equal to 10’-0”
(measured the same way as in the FHWA definition)
A 9’ diameter round pipe culvert on a skew could be considered by ODOT to be a bridge)
It should be noted that these definitions include: Railroad Pedestrian, and Bikeway bridges.
The differences between these definitions is important when it comes to things like…
inventory
inspection &
load rating…
…ODOT self imposes a greater range of structures than is actually required of them.
ON THE SIDE:
ORC: "a bridge is defined as: any structure, including supports, of 10 feet  or more clear span or 10 feet or more (clear opening) in diameter on, above, or below a highway."

4. The “Load” aspect of “Bridge Load Rating”

5. There are Two Primary Types of Loads used in Load Ratings?
Permanent or Dead Loads
Structure self weight
Superimposed dead loads (barriers, overlays, utilities, etc.)
Transient or Live Loads
Vehicular loads
Impact loads
Next let’s look at the “Load” aspect of “Bridge Load Rating”

6. Three Types of Live Loads in Ohio
Design or inventory loads
HS20-44, HS25, HL-93
Ohio Legal Loads
2F1, 3F1, 4F1, 5C1
Permit Loads & Superloads
Design or inventory loads = Truck configurations developed by design codes such as AASHTO
Ohio Legal Loads = Truck configurations developed by ODOT that are used exclusively for load rating. The feds impose live load limitations based on a formula they call the “Federal Bridge Gross Weight Formula”. These Ohio Legal Loads are intended to cover the limits of this formula.
And finally…
Permit and Superloads are the extra heavy loads that require special permission to travel Ohio highways.
IT SHOULD BE NOTED that the feds only require us to use highway loads for load ratings. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated.
Note: The Feds only require highway loads to be used for load rating. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated

7. AASHTO HS 25 Truck (current Ohio design load) HS 25 40k 40k 10k
Varies (14’-30’)
14’

8. AASHTO HS 20-44 Truck (still to be used for Ohio load ratings)
Varies (14’-30’)
14’

9. Ohio Legal Loads (2F1)
2F1
2F1
10k
20k
10’

10. Ohio Legal Loads (3F1)
3F1
12k
17k
17k
10’ 4’

11. Ohio Legal Loads (4F1)
4F1
12k
14k
14k
14k
10’ 4’ 4’

12. Ohio Legal Loads (5C1)
5C1
12k
17k
17k
17k
17k
12’ 4’
31’ 4’

13. What Is Bridge Load Rating?
The safe live load carrying capacity of a highway structure is called its load rating.
It is usually expressed as a (rating) factor (RF) of a defined vehicle OR as a gross tonnage for a defined vehicle axle configuration
So, after all the dead loads are in place, we are basically asking “How much Live Load can this structure safely take?”

14. Basic Equation for Calculating the Rating Factor (RF)
A load rating can be expressed in terms of a “rating factor” for a particular vehicle.
How to calculate the rating factor (RF)
A1 = Factor for dead loads
A2 = Factor for live load
C = Capacity of the bridge
D = Dead load effect
I = Impact factor
L = Live load effect
C – A1 * D
The factors A1 and A2 depend on which Method and Type of Load rating you are doing.
RF =
A2 * L*(1 + I)

15. Three Different Load Rating Methods
Allowable Stress (ASD)
Also known as Working Stress (WSD)
Used for ODOT steel trusses and timber structures
Load Factor (LFD)
ODOT Preferred
FHWA Preferred
Load & Resistance Factor Rating (LRFR)
NCHRP Project 12-46
Currently, 95% of all ODOT bridges have been load rated using the LFD method.
Although the feds are requiring LRFD for design in 2007, ODOT is still planning to require that all load ratings be done using the load factor method. I am told that the feds are still going to REQUIRE Load Factor load ratings for the next 4-6 years.

16. Two Types of Ohio Load Ratings
Inventory Rating (Design Level)
1.) HS20-44
Operating Rating (Service Level)
2.) HS20-44
3.) 2F1
4.) 3F1
5.) 4F1
6.) 5C1
There are TWO types of load ratings
Inventory &
Operating Ratings
The A1 and A2 factors used for Inventory ratings are based on a design level
The A1 and A2 factors used for Operating ratings are more based more on an in service condition.
Every bridge in Ohio has six different load rating factors calculated.

17. Factors for LFD Load Rating
Ref: AASHTO Manual for Condition Evaluation of Bridges 2000

18. What components of a bridge is ODOT interested in Load Rating
All primary superstructure components of a bridge shall be load rated.
Unless specified in a scope, this excludes the following:
Decks (unless bridge is a deck slab type)
Bearings
Substructures
Field splices
Railing / Parapets

19. When Should a Load Rating be Revised?
The load rating of a bridge should be revised
when:
there is a change in the dead load on the structure
there is a physical change in any structural member of the bridge.
there is a change in the proposed live loading
A different method of analysis is required
Examples of #1
addition or removal of
wearing surfaces
Sidewalks
Parapets
Railings
Utilities
Examples of #2
when there is an alteration in the structure
when a new beam or a girder is placed
when a new deck is added
when there is rusting or damage to a beam, girder or other structural element that has resulted in section loss
when there is structural damage to the bridge members due to accidents (i.e. a vehicular collision)
when excessive deflection or elongation is observed under temperature or highway loads
when there is excessive structural damage (i.e. spalling or salt related damage to concrete)
Examples of #3:
Permit loads
Superloads
Example of #4:
When codes change (i.e. ASD to LFD and then eventually to LRFR)

20. Why do we rate structures?

21. Why do we rate structures? (1)
The Silver Bridge Collapse
The Dec. 15, 1967, collapse of the Silver Bridge at Point Pleasant, Ohio killed 46 people. The failure of the 39 year old eye bar suspension bridge across the Ohio River prompted US Congress to pass National Bridge Inspection Standards (NBIS) in 1968.
This collapse prompted the feds to require ORGANIZED inspection departments.
It was at this time that ODOT established their Inspection and Load Rating Departments
Since the collapse occurred in Ohio, the state felt obligated to stay ahead of these newly established fed requirements…
1.) while the feds required inspections every 2 years, ODOT established annual inspection requirements
2.) while the feds defined a bridge starting at 20’ in length, ODOT defined bridges starting at 10’

22. Why do we rate structures? (2)
Required by Federal government (NBIS)
To monitor safety of structures over time
To help determine when rehabilitation or replacement is needed

23. Why do we rate structures? (3)
To determine if a bridge needs to be posted for a load restriction as required by the Ohio Revised Code
To have a consistent summary of load carrying capacities of all state bridges
To assist Office of Permits in their processing of Permit and Superloads
Tab #1: Actually, the OHIO Revised Code (ORC), Section doesn’t specifically require load rating. It requires us to post warning signs when a structures capacity drops below a specified threshold. But it is the load rating analysis gives us the needed information to comply with the posting requirement.
Tab #2: Different design vehicles have been used in the past for the design of bridges ( e.g., H-15, HS20,  HS25, etc.). Some bridges have aged,  deteriorated or become structurally deficient during the course of their life. To have a consistent summary of the load carrying capacities of all the bridges in the state of Ohio, all bridges are rated using a standard set of vehicles, called Ohio Legal Loads.
Tab #3: ODOT has an internal need to load rate structures for the purpose of assisting the Office of Permits in their processing of Superload (vehicles > 120 kips) permits. The Office of Structural Engineering will check all structures along the desired Superload route against the proposed vehicle loading configuration. They will utilize batch routines to re-run already generated models where possible.

24. What is a Permit or Superload Vehicle?

25. A Permit* load equals…
any vehicle or combination of loads having a gross weight in excess of 40 tons (or 80 kips).
The 40 tons limit was established, because it is the maximum gross weight of the four Ohio Legal Loads (5C1 truck).
* = Permits are also required for over-SIZED vehicles. But, for the purposes of load rating, we are referring to permits that are required due to over-weight only.

26. A Superload equals…
any vehicle or combination of loads having a gross weight in excess of 60 tons (or 120 kips).
The top picture is from Diamond Heavy Hauling company. The transporter is about 205' long and weighs about 200,000 pounds. It is manufactured in Shandon, Ohio.
The bottom picture was from a gas turbine transport in The gross weight is 673 kips.

27. Vehicle Categories based on weight
1.50 * 40
NO PERMIT REQUIRED (<= 40 tons)
You and me driving our cars on the bridge
PERMIT LOAD VEHICLES (40 tons <weight <= 60 tons)
- 60 ton limit is based on 150% times 40 tons (the gross weight of the heaviest Ohio Legal Load, 5C1)
SUPERLOAD VEHICLES
Gross weight of heaviest Ohio Legal Load (5C1)

28. How many vehicle permits are issued each year?

29. Of those permits issued, how many are for Superload vehicles?

30. How many Superload routes does the OSE check each year?
You can see from this chart that the trucks traveling our highways are getting heavier and heavier.
This clearly illustrates the importance of knowing the live load limits of each bridge on the inventory.
It is also easy to see that there is a need for tools that allow engineers to quickly load rate structures.

31. Computer programs to assist in load rating ODOT bridges
AASHTO BARS-PC (SHALL be used where possible) (
BRASS (SHALL be used for buried structures) (
BARS (REQUIRED WHERE POSSIBLE)
Steel beams/girders
Prestressed and Reinforced Concrete beams/girders
Concrete Decks
Steel Trusses
BRASS
Cast-in-place or precast box or frame type buried structures (2’-0” or more of fill on top)

32. Additional Computer programs to assist in load rating ODOT bridges
DESCUS I (
STAAD III/Pro (
GT STRUDL (Finite Element based) (
SAP 90 / SAP 2000 (Finite Element based) (
DESCUS
Curved Steel beams/girders
STAAD
Fairly comprehensive general analysis program. Can do most anything (steel, concrete,
prestressed, post tensioned, trusses, etc.)
GT STRUDL and SAP 2000
Finite element analyses.

33. Why is BARS desirable to ODOT?
Can run Batch routines (useful for fast analysis of superload routes)
Fast, free, and doesn’t require a lot of resources
Tested and used over the last 20+ years
Provides output in rating format
Supports both Mainframe and PC computers
Custom vehicles can be easily defined
Useful for reviewing new designs

34. BARS on the Internet
The program and instruction manuals can be downloaded for free at…
An introductory tutorial can be downloaded at…
(An AASHTOWARE Product)

35. ODOT Customization of BARS
Custom.std file at…
Ohio adopted custom allowable stresses
ODOT BDM Tables 904 & 905
Ohio legal vehicles

36. BDM Section 900 Structure Load Rating

37. BDM Section 900 (1) BURIED STRUCTURES
ALL bridges (> 10’) with fill > 2’-0” shall be considered “buried” and shall be load rated
EXCLUDING…
Circular Steel pipes
Circular Plastic pipes
Circular Concrete pipes
Buried Metal Boxes
Buried Metal Frames
Junction Chambers
Manholes
Inlets

38. BDM Section 900 (2) BURIED STRUCTURES (cont.)
All buried structures that are a part of new construction, replacement, or rehabilitation projects shall be load rated as follows…
CIP Concrete bridges shall be load rated by the designer using BRASS-Culvert.
Precast concrete frames, arches, Conspans, and Bebo type structures shall be load rated by the manufacturer.
Precast boxes will be load rated by OSE using BRASS-Culvert.

39. BDM Section 900 (3) NON-BURIED STRUCTURES
ALL bridges (> 10’) with fill < 2’-0” (or no fill at all) shall be considered “non-buried” and shall be load rated
BARS-PC SHALL BE USED when possible
BRASS-Culvert SHALL BE USED for concrete boxes and three-sided culverts
OSE MUST be contacted if any other software is going to be used

40. BDM Section 900 (4) MISCELLANEOUS INFORMATION
Only load rate spans or portions of buried structure that will experience live load
Load ratings of new or rehabilitation bridge projects shall be based on final design plans and shall show results that meet or exceed the design loading
No FWS shall be included in load ratings
TAB #2: Even though the load rating uses an HS20 vehicle, the rating in gross tons for a new project should have results of HS25 or greater since HS25 is now being used as the design load.

41. BDM Section 900 (5) WHEN DO YOU SUBMIT YOUR ANALYSIS?
MAJOR OR MINOR PLAN DEVELOPMENT
(OR DESIGN BUILD) PROCESS
Include load rating report with STAGE 2 submittal **
MINIMAL PLAN DEVELOPMENT
Include load rating report with STAGE 3 submittal **
**Revise and resubmit load rating to District Project
Manager if design plans change after Stage 2
(or Stage 3) and prior to contract sale

42. BDM Section 900 (7) WHEN DO YOU SUBMIT YOUR ANALYSIS?
VALUE ENGINEERING CHANGE PROPOSAL (VECP)
Include load rating analysis with the Final VECP submission to the District Construction Engineer

43. BDM Section 900 (8) WHAT DO YOU PUT IN THE REPORT?
A full project description
Printouts of analysis software input/output
Explanation of how material properties were determined (for existing structures)
All hand calculations
A table summarizing the following rating factors for each live load truck…
Inventory & Operating ratings for each main bridge member analyzed (Beam 1, Beam 2, Interior, Exterior, etc.)
Overall ratings of each structure unit (mainline,
ramps, etc.)
Overall ratings of entire bridge
Full Project Description would include:
PID#
Bridge #
SFN
Bridge Description
Methods used
Assumptions made
All ratings shall be expressed in terms of specific truck tonnages and rounded to the nearest single digit decimal point
i.e… RF*20 for HS or
RF*(gross vehicle weight in tons for Legal loads)

44. BDM Section 900 (9) WHAT DO YOU PUT IN THE REPORT? 36*1.38 = 49.8
Loading
Gross Vehicle
Weight
(Tons)
Rating
Factor
Member
Location
Inventory
HS-20-44 36
1.38
49.8 tons
(HS27.7)
Girder 2
Midspan
Operating
2.31
83 tons
(HS46.1)
Ohio Legal
Loads (%) -
3.08
308%
2F1 15
4.87
73.1 tons
3F1 23
3.41
78.4 tons
4F1 27
3.09
83.5 tons
5C1 40
123.3 tons
20*1.38=27.7
(Mouse click to get circles)
You will notice that even though the gross weight of an HS20 truck is 36 tons the HS rating is 20*1.38 or HS27.7
The Inventory rating in this example is 49.8 tons which is equal to the 1.38 rating factor * 36 tons.
The 308% summary rating for the Ohio Legal Loads is equal to the smallest rating factor of all four legal loads times 100.
Smallest * 100= 308

45. BDM Section 900 (11) WHAT DO YOU SUBMIT TO ODOT?
2 - Printed copies of load rating report
(signed and sealed by an Ohio PE)
1 - Electronic copy of load rating report
1 – Electronic copy of input data files
BARS -
LISTA.LIS, RATE2.LIS, SUMMARY.LIS,
and FLEX.LIS files
BRASS -
Files with the following extensions:
DAT, CUS, and XML
Electronic copy can be either a CD or an attachment

46. AASHTO Load Rating References
AASHTO (2002), Standard Specifications for
Highway Bridges, 17th ed.,
AASHTO (2000), Manual for Condition
Evaluation of Bridges, 2nd Edition. (Section 6)
AASHTO (1995), Bridge Analysis and Rating
System, BARS-PC, Release 5.5, Mod 3.3,
Users Manuals I and II,

47. AASHTO Load Rating References (cont.)
AASHTO (1989), Guide Specifications for
Strength Evaluation of Existing Steel and
Concrete Bridges
AASHTO (1978), Guide Specifications for
Fracture Critical Non-Redundant Steel Bridge
Members

48. ODOT Bridge Load Rating References
ODOT (2004), Bridge Design Manual – Section 900
ODOT Structural Rating Group’s

49. Questions??

50. Appendix 1 – Rating Equations
Reference: BARS Manual 1

51. STEEL RATING FACTORS (1)

52. RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)
STEEL RATING FACTORS (2)
RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)

53. STEEL RATING FACTORS (3)

54. STEEL RATING FACTORS (4)

55. Composite Steel & Conc. Rating Factors (1)

56. Composite Steel & Conc. Rating Factors (2)
OPERATING (composite, based on Moment Capacity)
* whichever is smaller

57. Composite Steel & Conc. Rating Factors (3)
RATING FACTORS BASED ON SHEAR CAPACITY
INVENTORY

58. Composite Steel & Conc. Rating Factors (4)
RATING FACTORS BASED ON SHEAR CAPACITY
OPERATING
where Vp = shear yielding strength of the web

59. Composite Steel & Conc. Rating Factors (5)

60. Composite Steel & Conc. Rating Factors (6)

61. Reinforced Concrete Rating Factors (1)

62. Reinforced Concrete Rating Factors (2)

63. Prestressed Concrete Rating Factors (1)

64. Prestressed Concrete Rating Factors (2)

65. Appendix 2 – Load Rating Example

66. Single-span slab bridge
Bridge #: SEN
Over: Branch of Wolf Creek
SFN:
Clear Span: 16’-0”
Slab thickness: 11.5”
Slab Width: 40.5 ft
Overlay: 3” asphalt on ¾” soil
Long. Bottom Steel: 4 ½”
Transverse Bottom Steel: 5’s
Analysis Software: BARS-PC
Input filename: R DAT

68. Live load distribution factor
AASHTO Standard Specification for Highway Bridges 2002
CASE B – Main Reinforcement Parallel to Traffic
S = Effective Span length in feet
(AASHTO )
For wheel loads, the distribution width
E = *S  7’
S = 16+1 = 17 feet
E = *17 = 5.02 feet
BARS Dist. = 1/5.02= 0.199

69. Impact load (Impact factor)
AASHTO Standard Specification for Highway Bridges 2002
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 / ( ) = 0.352
Use I = 0.3

70. Superimposed Dead Load
((3” / 12)* 1 ft* 145 pcf) + ((3/4” /12) * 1 ft * 120 pcf) +
12 plf guardrail = lb/ft
Rebar distance to top of slab
(11.5”–1” clear due to delamination- 5/8”–(7/8”) / 2 ) =
9.4375”

71. Interactive Bridge Data Entry
AA NEW X
DMH - B&N *LF* POST
SPEC
SPEC 17.0
DMH - B&N
BSEN LF
SEN OVER BRANCH OF WOLF CREEK, SFN:
SINGLE SPAN CONCRETE SLAB BUILT IN 1926, 16 FOOT CLEAR SPAN
" ASPHALT W.S. (DATE: N/A) ON 0.75" OF SOIL, 40.5' SLAB WIDTH
S RC
S W S S

72. Load Rating Summary Loading Gross Vehicle Weight (Tons) Rating Factor
Member
Location
Inventory HS-20-44 36
0.58
20.90 tons
(HS11.61)
Conc.
Deck
Midspan
Operating HS-20-44
0.97
34.85 tons
(HS19.36)
Ohio Legal Loads (%) -
1.07
107%
2F1 15
1.55
23.2 tons
3F1 23
1.19
27.4 tons
4F1 27
29.0 tons
5C1 40
47.7 tons

73. APPENDIX 3 – Where to get more help ?
BARS Manuals
Limited support from Structure Rating Section
Amjad Waheed, PE
Shelton A. Howard, PE
Richard C. Irwin, PE
Cindy Wang, PE