“Structural and Functional Characteristics of

Decommissioned Bridges”

John M. Hooks, PE

J. M. Hooks and Associates

November 2011

Objectives

• To examine the the life span of bridges vs. material/design

type, traffic volumes, etc.

• To quantify the age, condition, and functional status of

bridges at the time they were replaced

• To develop insight into the reasons that bridges are

replaced and the expected service life of structures of

various material/design types

• To provide knowledge for engineers involved with bridge

preservation policy, bridge management, and life cycle cost

analysis of bridges.

Questions About Decommissioned Bridges

• Where?

• Owned/maintained by?

• Type, material, size?

• Age when replaced?

• Functional class of highway?

• Why were they replaced?

– What was their condition when they were replaced?

– Were they structurally deficient or functionally obsolete?

Studying a Population of Decommissioned

Bridges• Identify a significant number of bridges that have been

taken out of service (and probably replaced)

• Determine what year they were decommissioned, and

• Having completed steps (1) and (2), historical data from

the NBI can be used

– To answer the other aspects of the “what” question

– To provide clues that help answer the “why” question

This Study

• Resources:

– Historical NBI data – available for Years 1984 to 2009

– Bridge Portal – interface with LTBP database

• Study focus:

– 1992 to 2009

– Identified 20645 bridges in 42 states that were replaced

during that time span

– Culverts excluded

A CaveatReliance on NBI data should be tempered with

understanding that some NBI data may be in error. For

instance:

– Found a NJ DOT owned bridge located in Angola

– Age data obtained from the NBI can be problematic

• Results included some bridges that were replaced before they were

originally built

• In one case 288 years earlier; in two others over 1000 years earlier

Therefore, I eliminated some bridges with obvious age

errors, but really don’t know the extent of any other

errors

Replaced Bridges by StateState # Replaced State # Replaced State # Replaced State # Replaced

AL 74 IL 2 NV 35 TN 1443

AK 4 IN 2258 NH 137 TX 2487

AZ 317 IA 86 NJ 555 UT 32

AR 45 KS 1732 NM 1 VT 184

CT 164 LA 1324 NY 2459 VA 80

DE 44 ME 245 ND 218 WA 36

DC 2 MD 323 OH 21 WV 351

FL 4 MI 1176 OR 37 WI 24

GA 118 MS 392 PA 1106

HI 20 MT 414 RI 33

ID 1 NE 1764 SD 471

Bridges Replaced

Range:

Min 1

Max 2524

Mean # = 504

Median # = 130

Owner

13 34 47 57 64 80 100 113

658

876

0100200300400500600700800900

1000

# Replaced

# Replaced

State – 5320

County - 12860

Type of Main Span

97

53

22

18

155

2 2 1

# Replaced

Frame

Box Beam - Multi

Moveable - Bascule

Arch-Thru

Moveable - Swing

Moveable - Lift

Suspension

Orthotropic

Stayed Girder

Type of Main Span

124283093

1423

1223

785

574 534 226

# Replaced

Stringer/Multi-Beam

Truss- Thru

Slab

Girder & Floorbeam

Tee Beam

Arch- Deck

Box Beam - Single

Other

Main Span Material

10829

4046

2902

847

707 641220

# Replaced

Steel

Wood or Timber

Concrete

Steel Continuous

Concrete Continuous

Prestressed Concrete

Other

Other Includes 40 P/S Concrete

Continuous

Structure Type/Material vs. Median

Age

Structure Type/Material vs. Median Age

Structure Type/Material vs. Median

Age

Urban vs. Rural Bridges Replaced

2736

17481

5

# Replaced

Urban

Rural

Unknown

Rural Bridges Replaced

231 648

1979

2880

1889

9854

# Replaced

Rural - Principal Arterial -

Interstate

Rural - Principal Arterial -

Other

Rural - Minor Arterial

Rural - Major Collector

Rural - Minor Collector

Rural -Local

Urban Bridges Replaced

384109

496

628

501

618

# Replaced

Urban - Principal Arterial -

Interstate

Urban - Principal Arterial -

Other Freeways

Urban - Other Principal

Arterial

Urban - Minor Arterial

Urban - Collector

Urban - Local

AgeMean Age =

58.5

Median Age =

60

Age by Material Type

Material Range Mean Median

Concrete 8 - 110 61.1 64

Steel 8 - 110 62.8 64

P/S Concrete 8 - 80 39.3 37

ADT

6985

5538

1718

3417

1161 1199

116 57 10

1000

2000

3000

4000

5000

6000

7000

8000

0 - 99 500 - 999 5000 - 9999 50,000 -

100,000

> 500,000

# Replaced

# Replaced

Median Age vs ADT

0

10

20

30

40

50

60

70

80

Concrete Slab Concrete

Continuous Slab

Concrete Tee

Beam

Prestressed

Concrete Box

Beams

1 - 499

500- 999

1000 - 4999

5000 - 9999

10000 - 24999

> 24999

Median Age vs ADT

Conclusions• Sample Population – 20,222 bridges (no culverts)

• 86 % Rural

• Rural bridges – 56% local & 22% minor

• Urban bridges – 14% Interstate, 22% Principal Arterial

• Ownership – 26% State, 64% County

• ADT

– 62% < 500

– 25% 501 – 1000

– .01 % > 50,000

Conclusions• Main Span Type

– Girder/Girder-Floorbeam

– Thru truss

– Slabs, tee beams

• Main Span Material

– Simple span steel beam bridges - >50%

• Age when replaced – fairly normal distribution

• Age when replaced vs. traffic volumes – direct

correlation not evident

Inventory Rating (Metric Tons)

Sufficiency Rating

Mean SR = 58.4

Median SR = 60

Structural Deficiency

• Structurally Deficient (SD) - A highway bridge is classified as

structurally deficient if one of the following is rated in "poor"

condition or worse (4, 3, 2, 1, or 0 on the NBI rating scale

– Item 58 - Deck,

– Item 59 – Superstructure,

– Item 60 – Substructure or

– Item 62 – Culvert

• Or,

– Item 67 – Structural Evaluation Appraisal is coded 2, 1, or 0)

– Item 71 - Waterway adequacy for the feature below the bridge is coded 2 or

below

Functional Obsolescence

• Functionally Obsolete (FO) - Highway bridges classified as

functionally obsolete are NOT structurally deficient; classification as

Functional Obsolete would be triggered by a code of 3 or lower,

meaning basically intolerable and requiring high priority for

correction, for

– Item 68 – Deck Geometry Appraisal,

– Item 69 – Underclearances – Vertical & Horizontal, or

– Item 72 – Approach Roadway Appraisal;

• Or if

– Item 67 - Structural Evaluation Appraisal or

– Item 71 – Waterway Adequacy Appraisal are coded 3.

Deficient Bridges

Structural Deficiencies

Reasons for Rating of SD

Reasons for Rating of SD by Material

0%

5%

10%

15%

20%

25%

30%

35%

40%

Concrete Steel P/S Concrete

22%

32%

10%

34%

38%

5%

12%

22%

7%

Deck

Super

SD SE

Functionally Obsolete Characteristics

QUESTIONS?