1 ODOT BRIDGE LOAD RATING A basic how and why overview.

1

ODOT BRIDGE ODOT BRIDGE LOAD RATINGLOAD RATING

A basic how and why overview

2

What is a Bridge?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? What is a Bridge? (cont.)(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)

4

The “Load” aspectThe “Load” aspectofof

“Bridge Load Rating” “Bridge Load Rating”

5

There are Two Primary Types of There are Two Primary Types of Loads used in Load Ratings?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

6

Three Three Types of Live LoadsTypes of Live Loads in Ohio in OhioDesign or inventory loads

– HS20-44, HS25, HL-93

Ohio Legal Loads– 2F1, 3F1, 4F1, 5C1

Permit Loads & SuperloadsNote: 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 TruckAASHTO HS 25 Truck

14’Varies (14’-30’)

10k

HS 25

40k

40k

(current Ohio design load)(current Ohio design load)

8

AASHTO HS 20-44 TruckAASHTO HS 20-44 Truck

14’Varies (14’-30’)

8k

HS 20-44

32k

32k

(still to be used for Ohio load ratings)(still to be used for Ohio load ratings)

9

2F12F1

Ohio Legal Loads (2F1)Ohio Legal Loads (2F1)

20k

10k

10’

10

3F1


17k

12k

10’

17k

4’

11

4F1


14k

12k

10’

14k

4’

14k

4’

12

5C1

Ohio Legal Loads (5C1)Ohio Legal Loads (5C1)

17k

12k

12’

17k

4’

17k

17k

4’ 31’

13

What Is Bridge Load Rating? 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

14

Basic Equation for Calculating Basic Equation for Calculating the Rating Factor (RF)the Rating Factor (RF)

A load rating can be expressed in terms of a

“rating factor” for a particular vehicle.

RF = C – A1 * D

A2 * L*(1 + I)

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)

15

Three Different Three Different Load Rating MethodsLoad Rating Methods

Allowable Stress (ASD)•Also known as Working Stress (WSD)•Used for ODOT steel trusses and timber structures

Load Factor (LFD)Load Factor (LFD)•ODOT PreferredODOT Preferred•FHWA PreferredFHWA Preferred

Load & Resistance Factor Rating (LRFR)NCHRP Project 12-46NCHRP Project 12-46

16

Two Two TypesTypes of Ohio Load Ratings of Ohio Load RatingsInventory Rating (Design Level)

1.) HS20-44

Operating Rating (Service Level)2.) HS20-443.) 2F14.) 3F15.) 4F16.) 5C1

Every bridge in Ohio has six different load rating factors calculated.

17

Factors for Factors for LFDLFD Load Rating Load Rating

Ref: AASHTO Manual for Condition Evaluation of Bridges 2000

18

What components of a bridge is What components of a bridge is ODOT interested in Load RatingODOT 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 When Should a Load Rating be Revised?be Revised?

The load rating of a bridge should be revisedwhen:

1. there is a change in the dead load on the structure

2. there is a physical change in any structural member of the bridge.

3. there is a change in the proposed live loading

4. A different method of analysis is required

20

Why do we rate structures?Why do we rate structures?

21

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.

Why do we rate structures? Why do we rate structures? (1)(1)

The Silver Bridge Collapse

22

Required by Federal government (NBIS)

To monitor safety of structures over time

To help determine when rehabilitation or replacement is needed

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

23

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

Why do we rate structures? Why do we rate structures? (3)(3)

24

What is a Permit or What is a Permit or Superload Vehicle?Superload Vehicle?

25

A Permit* load equals…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.

26

A Superload equals…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 weightVehicle Categories based on weight

Gross weight of heaviest Ohio Legal Load (5C1)

1.50 * 40

28

How many vehicle permits are How many vehicle permits are issued each year?issued each year?

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

120,000

1990 1992 1994 1996 1998 2000 2002 2004

29

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

0

2000

4000

6000

8000

10000

12000

14000

1989 1991 1993 1995 1997 1999 2001 2003

30

How many Superload routes How many Superload routes does the OSE check each year?does the OSE check each year?

0

200

400

600

800

1000

1200

1400

1985 1987 1989 1991 1993 1995 1997 1999 2001 2003

31

Computer programs to assist Computer programs to assist in load rating ODOT bridgesin load rating ODOT bridges

AASHTO BARS-PC (SHALL be used where possible) (http://www.dot.state.oh.us/srg/download.htm)

BRASS (SHALL be used for buried structures) (http://www.dot.state.wy.us/generic/brass/index.html)

32

Additional Computer programs to Additional Computer programs to assist in load rating ODOT bridgesassist 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)

33

1) Can run Batch routines (useful for fast analysis of superload routes)

2) Fast, free, and doesn’t require a lot of resources

3) Tested and used over the last 20+ years

4) Provides output in rating format

5) Supports both Mainframe and PC computers

6) Custom vehicles can be easily defined

7) Useful for reviewing new designs

Why is BARS desirable to ODOT?Why is BARS desirable to ODOT?

34

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

BARS on the InternetBARS on the Internet

35

Custom.std file at…http://www.dot.state.oh.us/srg/download.htm

Ohio adopted custom allowable stressesODOT BDM Tables 904 & 905

Ohio legal vehicles

ODOT Customization of BARSODOT Customization of BARS

36

BDM Section 900BDM Section 900

Structure Load RatingStructure Load Rating

37

BDM Section 900 BDM Section 900 (1)(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


BURIED STRUCTURES (cont.)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


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


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


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


WHEN DO YOU SUBMIT YOUR WHEN DO YOU SUBMIT YOUR ANALYSIS?ANALYSIS?

VALUE ENGINEERING CHANGE PROPOSAL (VECP)

– Include load rating analysis with the Final VECP submission to the District Construction Engineer

43


WHAT DO YOU PUT IN THE REPORT?A full project descriptionPrintouts of analysis software input/outputExplanation of how material properties were

determined (for existing structures)All hand calculationsA 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

44


WHAT DO YOU PUT IN THE REPORT?WHAT DO YOU PUT IN THE REPORT?

Loading

Gross VehicleWeight(Tons)

RatingFactor Rating

Member Location

InventoryHS-20-44 36 1.38

49.8 tons(HS27.7) Girder 2 Midspan

OperatingHS-20-44 36 2.31

83 tons (HS46.1) Girder 2 Midspan

Ohio LegalLoads (%) - 3.08 308% Girder 2 Midspan

2F1 15 4.87 73.1 tons Girder 2 Midspan



5C1 40 3.08 123.3 tons Girder 2 MidspanSmallest * 100= 308

36*1.38 = 49.8

20*1.38=27.7

45


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 report1 – 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

46

AASHTO Load Rating ReferencesAASHTO 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 AASHTO Load Rating References (cont.)(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 ODOT Bridge Load Rating ReferencesReferences

ODOT (2004), Bridge Design Manual – Section 900 http://www.dot.state.oh.us/se/BDM/BDM2004/bdm2004.htm

ODOT Structural Rating Group’s http://www.dot.state.oh.us/srg/

49

Questions??Questions??

50

Appendix 1 –Appendix 1 –Rating EquationsRating Equations

Reference: BARS Manual 1

STEEL RATING FACTORS STEEL RATING FACTORS (1)(1)R A T I N G F A C T O R B A S E D O N M O M E N T C A P A C I T Y ( n o n - c o m p o s i t e )

I N V E N T O R Y

)(

)5

3(*)

3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

O P E R A T I N G

)(

)3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)

STEEL RATING FACTORS STEEL RATING FACTORS (2)(2)

IN V E N T O R Y

)_(

)5

3(*)

3.1(

IL

SDLDLP

VMAX

VVV

RFV

O P E R A T IN G

)_(

)3.1

(

IL

SDLDLP

VMAX

VVV

RFV

w h e re V p = sh e a r y ie ld in g s t r e n g th o f t h e w e b


R A T I N G F A C T O R S B A S E D O N M O M E N T - S H E A R I N T E R A C T I O N ( n o n -c o m p o s i t e )

I N V E N T O R Y

)3

5(*]*)(*625.0)(*[*3.1

]*)(*625.0)(*[*3.1**375.1

uILLIL

uT

DLuT

DLuu

MVVM

MVVMVMRF

O P E R A T I N G

]*)(*625.0)(*[*3.1

]*)(*625.0)(*[*3.1**375.1

uILLIL

uT

DLuT

DLuu

MVVM

MVVMVMRF


R A T I N G F A C T O R S B A S E D O N S E R V I C E A B I L I T Y S T R E N G T H ( n o n - c o m p o s i t e )

I N V E N T O R Y

)3

5(*)(

)**80.0(

IL

SDLDLy

M

MMSFRFS

O P E R A T I N G

)(

)**80.0(

IL

SDLDLy

M

MMSFRFS

Composite Steel & Conc. Rating Factors (1)

R A T I N G F A C T O R F O R S E C T I O N B A S E D O N M O M E N T C A P A C I T Y( c o m p o s i t e )

I N V E N T O R Y

)(

)5

3(*]*95.0[

3_

IL

nnCOMP

SDL

COMPNON

DLy

nnCOMP

M

S

M

S

MFS

RFMOM S DLDL

)(

)5

3(*)

3.1

)(_(

IL

SDLDLu

M

MMMStrengthUltimate

RFMOM

w h i c h e v e r i s s m a l l e r

Composite Steel & Conc. Rating Factors Composite Steel & Conc. Rating Factors (2)(2)

OPERATING (composite, based on Moment Capacity)

)(

]*95.0[3

_

IL

nnCOMP

SDL

COMPNON

DLy

nnCOMP

M

S

M

S

MFS

RFMOM SDLDL

)(

)3.1

)(_(

IL

SDLDLu

M

MMMStrengthUltimate

RFMOM

* whichever is smaller


RATING FACTORS BASED ON SHEAR CAPACITY

INVENTORY

)_(

)5

3(*)

3.1(

IL

SDLDLp

VMAX

VVV

RFV


RATING FACTORS BASED ON SHEAR CAPACITY

OPERATING

where Vp = shear yielding strength of the web

)_(

)3.1

(

IL

SDLDLP

VMAX

VVV

RFV


R A T I N G F A C T O R S O N M O M E N T - S H E A R I N T E R A C T I O N ( c o m p o s i t e )

I N V E N T O R Y

)3

5(*]*)(*625.0)(*[*3.1

]*)(*625.0)(*[*3.1**375.1

uILLIL

uT

DLuT

DLuu

MVVM

MVVMVMRF

O P E R A T I N G

]*)(*625.0)(*[*3.1

]*)(*625.0)(*[*3.1**375.1

uILLIL

uT

DLuT

DLuu

MVVM

MVVMVMRF


R A T I N G F A C T O R S O N S E R V I C E A B I L I T Y S T R E N G T H ( c o m p o s i t e )

I N V E N T O R Y

)3

5(*)(

]*95.0[3

_

IL

nnCOMP

SDL

COMPNON

DLy

nnCOMP

M

S

M

S

MFS

RFS SDLDL

O P E R A T I N G

)(

]*95.0[3

_

IL

nnCOMP

SDL

COMPNON

DLy

nnCOMP

M

S

M

S

MFS

RFS S D LD L

Reinforced Concrete Rating Factors (1)

R A T I N G F A C T O R B A S E D O N M O M E N T C A P A C I T Y

I N V E N T O R Y

)(

)5

3(*)

3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

O P E R A T I N G

)(

)3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

F l e x u r a l _ S t r e n g t h = p h i * M u

Reinforced Concrete Rating Factors Reinforced Concrete Rating Factors (2)(2)

R A T I N G F A C T O R S B A S E D O N S H E A R C A P A C I T Y

I N V E N T O R Y

)_(

)5

3(*)

3.1(

IL

DLu

VMAX

VV

RFV

O P E R A T I N G

)_(

)3.1

(

IL

DLu

VMAX

VV

RFV

w h e r e V D L = V D L + V S D L

V u = 0 . 8 5 * ( V c + V s )

Prestressed Concrete Rating Factors (1)

R A T I N G F A C T O R B A S E D O N M O M E N T C A P A C I T Y

I N V E N T O R Y

)(

)5

3(*)

3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

O P E R A T I N G

)(

)3.1

_(

IL

SDLDL

M

MMStrengthFlexural

RFMOM

F l e x u r a l _ S t r e n g t h = U l t i m a t e _ S t r e n g t h

Prestressed Concrete Rating Factors Prestressed Concrete Rating Factors (2)(2)

R A T IN G F A C T O R S B A S E D O N S H E A R C A P A C IT Y

IN V E N T O R Y

)_(

)5

3(*)

3.1(

IL

DLu

VMAX

VV

RFV

O P E R A T IN G

)_(

)3.1

(

IL

DLu

VMAX

VV

RFV

65

Appendix 2 –Appendix 2 –Load Rating ExampleLoad Rating Example

66

Single-span slab bridgeSingle-span slab bridgeBridge #:Bridge #: SEN-23-0934 SEN-23-0934

Over:Over: Branch of Wolf Creek Branch of Wolf Creek

SFN:SFN: 7401590 7401590

Clear Span:Clear Span: 16’-0” 16’-0”

Slab thickness:Slab thickness: 11.5” 11.5”

Slab Width: Slab Width: 40.5 ft40.5 ft

Overlay:Overlay: 3” asphalt on ¾” soil 3” asphalt on ¾” soil

Long. Bottom Steel: Long. Bottom Steel: 7’s @ 4 ½”7’s @ 4 ½”

Transverse Bottom Steel: Transverse Bottom Steel: 5’s5’s

Analysis Software:Analysis Software: BARS-PC BARS-PC

Input filename:Input filename: R740159.DAT R740159.DAT

68

AASHTO Standard Specification for Highway Bridges 2002

3.24.3.2 CASE B – Main Reinforcement Parallel to Traffic

S = Effective Span length in feet

(AASHTO 3.24.1)

For wheel loads, the distribution width

E = 4 + 0.06*S 7’

S = 16+1 = 17 feet E = 4 + 0.06*17 = 5.02 feet

BARS Dist. = 1/5.02= 0.199

Live load distribution factor

69

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 / (17 + 125) = 0.352 Use I = 0.3

Impact load (Impact factor)

70

((3” / 12)* 1 ft* 145 pcf) + ((3/4” /12) * 1 ft * 120 pcf) +

12 plf guardrail = 55.8 lb/ft

Superimposed Dead Load

Rebar distance to top of slab(11.5”–1” clear due to delamination- 5/8”–(7/8”) / 2 ) =

9.4375”

71

IInteractive nteractive BBridge ridge DData ata EEntryntryAA NEW X9974015901 082103DMH - B&N *LF* POST03 1SPEC0512.0 12 17.0 4 17.0 31 17.0 403 2SPEC 17.002740159DMH - B&N 111 26 00161108 004006000105740159 7401590BSEN 23 0934 LF067401591SEN-23-0934 OVER BRANCH OF WOLF CREEK, SFN: 7401590067401592SINGLE SPAN CONCRETE SLAB BUILT IN 1926, 16 FOOT CLEAR SPAN0674015933" ASPHALT W.S. (DATE: N/A) ON 0.75" OF SOIL, 40.5' SLAB WIDTH08740159S01 01 00161108 RC32000 0.19910740159S01 01 W55.80 0016110811740159S01 0101 001611080113740159S01 01 11.50 12.00 01 1.5999.4375

72

Load Rating SummaryLoad Rating SummaryLoading

GrossVehicleWeight(Tons)

Rating Factor Rating

Member Location

Inventory HS-20-44 36 0.58

20.90 tons(HS11.61)

Conc.Deck Midspan

Operating HS-20-44 36 0.97

34.85 tons(HS19.36)

Conc.Deck Midspan

Ohio Legal Loads (%) - 1.07 107%

Conc.Deck Midspan

2F1 15 1.55 23.2 tonsConc.Deck Midspan



5C1 40 1.19 47.7 tonsConc.Deck Midspan

73

APPENDIX 3 – APPENDIX 3 – Where to get more help ?Where to get more help ?

BARS Manuals Limited support from Structure Rating Section

Amjad Waheed, PE 614-752-9972 ([email protected])

Shelton A. Howard, PE 614-752-9975 ([email protected])

Richard C. Irwin, PE 614-752-9977 ([email protected])

Cindy Wang, PE 614-466-1973 ([email protected])

1 ODOT BRIDGE LOAD RATING A basic how and why overview.

Documents

odot bridge load rating

rating factor rf slide

current ohio design

highway loads

lfd load rating ref

different load rating

live load effect

live load c