ODOT BRIDGE LOAD RATING

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ODOT BRIDGE LOAD RATING
A basic how and why overview
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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
• AND
• 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)

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)

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The Load aspectof Bridge Load Rating
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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

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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

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
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AASHTO HS 25 Truck
(current Ohio design load)
HS 25
10k
40k
40k
14
Varies (14-30)
8
AASHTO HS 20-44 Truck
(still to be used for Ohio load ratings)
HS 20-44
8k
32k
32k
14
Varies (14-30)
9
Ohio Legal Loads (2F1)
2F1
2F1
20k
10k
10
10
Ohio Legal Loads (3F1)
3F1
17k
12k
17k
10
4
11
Ohio Legal Loads (4F1)
4F1
14k
12k
14k
14k
10
4
4
12
Ohio Legal Loads (5C1)
5C1
17k
12k
17k
17k
17k
31
12
4
4
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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
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Basic Equation for Calculating the Rating Factor
(RF)
A load rating can be expressed in terms of a
rating factor for a particular vehicle.
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
How to calculate the rating factor (RF)
C A1 D
RF
A2 L(1 I)
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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

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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
Every bridge in Ohio has six different load
rating factors calculated.
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Factors for LFD Load Rating
Ref AASHTO Manual for Condition Evaluation of
Bridges 2000
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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
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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

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Why do we rate structures?
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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.
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Why do we rate structures? (2)
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

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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

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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).
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.
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A Superload equals
any vehicle or combination of loads having a
gross weight in excess of 60 tons (or 120 kips).
27
Vehicle Categories based on weight
1.50 40
Gross weight of heaviest Ohio Legal Load (5C1)
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How many vehicle permits are issued each year?
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Of those permits issued, how many are for
Superload vehicles?
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How many Superload routes does the OSE check each
year?
31
Computer programs to assist in load rating ODOT
bridges

• AASHTO BARS-PC (SHALL be used where possible)
• (http//www.dot.state.oh.us/srg/download.ht
  m)
• BRASS (SHALL be used for buried structures)
• (http//www.dot.state.wy.us/generic/brass/i
  ndex.html)

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Additional Computer programs to assist in load
rating ODOT bridges

• DESCUS I (www.opti-mate.com)
• STAAD III/Pro (www.reiusa.com)
• GT STRUDL (Finite Element based)
• (www.gtstrudl.gatech.edu)
• SAP 90 / SAP 2000 (Finite Element based)
• (www.csiberkeley.com)

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Why is BARS desirable to ODOT?

• Can run Batch routines (useful for fast analysis
  of superload routes)
• Fast, free, and doesnt 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

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BARS on the Internet

• The program and instruction manuals can be
  downloaded for free at
• http//www.dot.state.oh.us/srg/download.htm
• An introductory tutorial can be downloaded at
• http//www.dot.state.oh.us/srg/bars-pc.htm

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ODOT Customization of BARS

• Custom.std file at
• http//www.dot.state.oh.us/srg/download.htm
• Ohio adopted custom allowable stresses
• ODOT BDM Tables 904 905
• Ohio legal vehicles

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BDM Section 900 Structure Load Rating
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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

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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.

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BDM Section 900 (3)

• NON-BURIED STRUCTURES
• ALL bridges ( 10) with 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

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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

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
• (OR DESIGN BUILD) PROCESS
• 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

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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

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BDM Section 900 (9)

• WHAT DO YOU PUT IN THE REPORT?

361.38 49.8
201.3827.7
Smallest 100 308
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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

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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,

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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

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ODOT Bridge Load Rating References

• ODOT (2004), Bridge Design Manual Section 900
• http//www.dot.state.oh.us/se/BDM/BDM2004/bdm2
  004.htm
• ODOT Structural Rating Groups http//www.dot.sta
  te.oh.us/srg/

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Questions??
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Appendix 1 Rating Equations
Reference BARS Manual 1
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STEEL RATING FACTORS (1)
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STEEL RATING FACTORS (2)

• RATING FACTORS BASED ON SHEAR CAPACITY
  (non-composite)

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STEEL RATING FACTORS (3)
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STEEL RATING FACTORS (4)
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Composite Steel Conc. Rating Factors (1)
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Composite Steel Conc. Rating Factors (2)
OPERATING (composite, based on Moment Capacity)
whichever is smaller
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Composite Steel Conc. Rating Factors (3)
RATING FACTORS BASED ON SHEAR CAPACITY
INVENTORY
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Composite Steel Conc. Rating Factors (4)
RATING FACTORS BASED ON SHEAR CAPACITY
OPERATING where Vp shear yielding strength of
the web
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Composite Steel Conc. Rating Factors (5)
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Composite Steel Conc. Rating Factors (6)
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Reinforced Concrete Rating Factors (1)
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Reinforced Concrete Rating Factors (2)
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Prestressed Concrete Rating Factors (1)
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Prestressed Concrete Rating Factors (2)
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Appendix 2 Load Rating Example
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Single-span slab bridge
Bridge SEN-23-0934 Over Branch of Wolf
Creek SFN 7401590 Clear Span 16-0 Slab
thickness 11.5 Slab Width 40.5 ft Overlay 3
asphalt on ¾ soil Long. Bottom Steel 7s _at_ 4
½ Transverse Bottom Steel 5s Analysis
Software BARS-PC Input filename R740159.DAT
67
(No Transcript)
68
Live load distribution factor
AASHTO Standard Specification for Highway Bridges
2002 3.24.3.2 CASE B Main Reinforcement
Parallel to Traffic
69
Impact load (Impact factor)
AASHTO Standard Specification for Highway Bridges
2002 3.8.2 Impact Formula
70
Superimposed Dead Load
((3 / 12) 1 ft 145 pcf) ((3/4 /12) 1 ft
120 pcf) 12 plf guardrail 55.8 lb/ft
Rebar distance to top of slab
(11.51 clear due to delamination- 5/8(7/8)
/ 2 ) 9.4375
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Interactive Bridge Data Entry
AA NEW X 99740159 01 082103DMH -
BN LF
POST 03 1SPEC0512.0 12 17.0 4
17.0 31 17.0 4 03 2SPEC
17.0 02740159DMH - BN 111
26 00161108 0040060001 05740159 7401590BSEN 23
0934
LF 067401591SEN-23-0934 OVER BRANCH OF WOLF
CREEK, SFN 7401590 067401592SINGLE SPAN CONCRETE
SLAB BUILT IN 1926, 16 FOOT CLEAR
SPAN 0674015933" ASPHALT W.S. (DATE N/A) ON
0.75" OF SOIL, 40.5' SLAB WIDTH 08740159S01 01
00161108 RC32000
0.199 10740159S01 01 W55.80
00161108 11740159S01 0101 0016110801 13740159S01
01 11.50 12.00 01 1.5999.4375
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Load Rating Summary
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APPENDIX 3 Where to get more help ?

• BARS Manuals
• Limited support from Structure Rating Section
• Amjad Waheed, PE 614-752-9972 (amjad.waheed_at_dot.s
  tate.oh.us)
• Shelton A. Howard, PE 614-752-9975
  (shelton.howard_at_dot.state.oh.us)
• Richard C. Irwin, PE 614-752-9977
  (richard.irwin_at_dot.state.oh.us)
• Cindy Wang, PE 614-466-1973 (cindy.wang_at_dot.state
  .oh.us)