“structural and functional characteristics of …...box beam -multi moveable -bascule arch -thru...
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“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?