Structural and Functional Characteristics of Decommissioned Bridges
“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 Caveat Reliance 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 State State
# 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 # Replaced 1000 900 800 700 600 500 400 300 200 100 0
876 658
13
34
47
57
64
80
100
113
State – 5320 County - 12860
# Replaced
Type of Main Span # Replaced 2 2 1 15
5
Frame Box Beam - Multi
18
Moveable - Bascule
97
Arch-Thru Moveable - Swing
22
Moveable - Lift Suspension Orthotropic
53
Stayed Girder
Type of Main Span # Replaced 574 785
534 226
1223
Stringer/Multi-Beam Truss- Thru Slab
1423
Girder & Floorbeam Tee Beam
3093
12428
Arch- Deck Box Beam - Single Other
Main Span Material # Replaced 707 847
641 220
Steel Wood or Timber
2902
Concrete Steel Continuous
10829 4046
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 # Replaced 5 2736
Urban Rural Unknown
17481
Rural Bridges Replaced # Replaced 231 648 Rural - Principal Arterial Interstate
1979
Rural - Principal Arterial Other Rural - Minor Arterial
2880 9854
Rural - Major Collector Rural - Minor Collector
1889 Rural -Local
Urban Bridges Replaced # Replaced Urban - Principal Arterial Interstate
384 618
109
Urban - Principal Arterial Other Freeways Urban - Other Principal Arterial
496 501
Urban - Minor Arterial Urban - Collector
628
Urban - Local
Age Mean 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 # Replaced 8000 7000
6985 5538
6000 5000 4000
3417 # Replaced
3000 1718
2000
1161
1199
1000
116
0 0 - 99
500 - 999
5000 - 9999
50,000 100,000
57
1
> 500,000
Median Age vs ADT 80 70 60 50
1 - 499
40
500- 999 1000 - 4999
30
5000 - 9999
20
10000 - 24999
10
> 24999
0 Concrete Slab
Concrete Continuous Slab
Concrete Tee Beam
Prestressed Concrete Box Beams
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% – 25% – .01 %
< 500 501 – 1000 > 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 38%
40% 34%
35%
32%
30% 25%
22%
22%
Deck Super
20% 15%
SD SE
12%
10%
10%
5%
7%
5% 0% Concrete
Steel
P/S Concrete
Functionally Obsolete Characteristics
QUESTIONS?
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 Caveat Reliance 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 State State
# 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 # Replaced 1000 900 800 700 600 500 400 300 200 100 0
876 658
13
34
47
57
64
80
100
113
State – 5320 County - 12860
# Replaced
Type of Main Span # Replaced 2 2 1 15
5
Frame Box Beam - Multi
18
Moveable - Bascule
97
Arch-Thru Moveable - Swing
22
Moveable - Lift Suspension Orthotropic
53
Stayed Girder
Type of Main Span # Replaced 574 785
534 226
1223
Stringer/Multi-Beam Truss- Thru Slab
1423
Girder & Floorbeam Tee Beam
3093
12428
Arch- Deck Box Beam - Single Other
Main Span Material # Replaced 707 847
641 220
Steel Wood or Timber
2902
Concrete Steel Continuous
10829 4046
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 # Replaced 5 2736
Urban Rural Unknown
17481
Rural Bridges Replaced # Replaced 231 648 Rural - Principal Arterial Interstate
1979
Rural - Principal Arterial Other Rural - Minor Arterial
2880 9854
Rural - Major Collector Rural - Minor Collector
1889 Rural -Local
Urban Bridges Replaced # Replaced Urban - Principal Arterial Interstate
384 618
109
Urban - Principal Arterial Other Freeways Urban - Other Principal Arterial
496 501
Urban - Minor Arterial Urban - Collector
628
Urban - Local
Age Mean 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 # Replaced 8000 7000
6985 5538
6000 5000 4000
3417 # Replaced
3000 1718
2000
1161
1199
1000
116
0 0 - 99
500 - 999
5000 - 9999
50,000 100,000
57
1
> 500,000
Median Age vs ADT 80 70 60 50
1 - 499
40
500- 999 1000 - 4999
30
5000 - 9999
20
10000 - 24999
10
> 24999
0 Concrete Slab
Concrete Continuous Slab
Concrete Tee Beam
Prestressed Concrete Box Beams
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% – 25% – .01 %
< 500 501 – 1000 > 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 38%
40% 34%
35%
32%
30% 25%
22%
22%
Deck Super
20% 15%
SD SE
12%
10%
10%
5%
7%
5% 0% Concrete
Steel
P/S Concrete
Functionally Obsolete Characteristics
QUESTIONS?
