Tài liệu Material Usage and Condition of Existing Bridges in the U.S pptx

December 2004
Cover photos: T
op left:
IMG47095; Bottom left:
IMG48877; T
op right:
IMG12124; Bottom right:
Graph of bridges built, reference: 2003 NBI Data.
This document is intended SOLELY for use by PORFESSIONAL PERSONNEL who are competent to
evaluate the significance and limitations of the information provided herein, and who will accept total
responsibility for the application of this information. The Portland Cement Association DISCLAIMS
any and all RESPONSIBILITY and LIABILITY for the accuracy of the application of the information
contained in this publication to the full extent permitted by law.
Material Usage and Condition of
Existing Bridges in the U.S.
Based on NBI Data as of
December 2003
Prepared by
Shri Bhide
Program Manager, Bridges
TABLE OF CONTENTS
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The National Bridge Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Data Used in this Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Bridge Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Limitations of Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Overview of Data Presented in Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Observations on Market Share and Bridge Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix A: Summary of Market Share and Bridge Condition Data . . . . . . . . . . . . . . . . . . . . . . . . 8

Table A.1 – Number and Percent of Bridges with Main Span Material of
RC, PS, Steel and Timber for All Bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table A.2 – Deck Area and Percent of Bridges with Main Span Material
of RC, PS, Steel and Timber for All Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table A.3 – Number and Deck Area of Bridges with Main Span Material
of Concrete (RC and PS) for All Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table A.4 – Structurally Deficient Bridges with Main Span Material of
RC, PS, Steel and Timber for All Bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table A.4a – Structurally Deficient and Functionally Obsolete Bridges with
Main Span Material of RC, PS, Steel and Timber for All Bridges . . . . . . . . . . . . . . . . . . . . . . . . 14
Table A.5 – Number and Percent of Bridges with Main Span Material of RC,
PS, Steel and Timber for Bridges – Built from 1990 through 2003. . . . . . . . . . . . . . . . . . . . . . . . 15
Table A.6 – Deck Area and Percent of Bridges with Main Span Material of RC,
PS, Steel and Timber for Bridges – Built from 1990 through 2003. . . . . . . . . . . . . . . . . . . . . . . . 16
Table A.7 – Percent of Bridges with Main Span Material of Concrete
(RC and PS) – Built from 1990 through 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table A.8 – Structurally Deficient Bridges with Main Span Material of RC,
PS, Steel and T
imber for Bridges – Built fr
om 1990 through 2003 . . . . . . . . . . . . . . . . . . . . . . . 18
Table A.9 – Number and Percent of Bridges with Main Span Material of RC,
PS, Steel and T
imber by System and Year Built – All States + DC and PR . . . . . . . . . . . . . . . . 19
T
able
A.10 – Number and Percent of Bridges with Main Span Material of RC,
PS, Steel and Timber by System and Span Length – All States + DC and PR . . . . . . . . . . . . . . 20
Table A.11 – Deck Area and Percent of Bridges with Main Span Material of RC,
PS, Steel and Timber by System and Year Built – All States + DC and PR . . . . . . . . . . . . . . . . 21
Table A.12 – Deck Area and Percent of Bridges with Main Span Material of RC,

PS, Steel and Timber by System and Span Length – All States + DC and PR . . . . . . . . . . . . . . 22
Table A.13 – Percent of Structurally Deficient Bridges with Main Span Material of
RC, PS, Steel and T
imber by System and Year Built – All States + DC and PR. . . . . . . . . . . . . 23
T
able
A.14 – Per
cent of Structurally Deficient Bridges with Main Span Material of
RC, PS, Steel and Timber by System and Span Length – All States + DC and PR . . . . . . . . . . 24
Figure A.1 – Bridges Built . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure A.2 – Structurally Deficient Built . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
i
MATERIAL USAGE AND CONDITION OF EXISTING
BRIDGES IN THE U.S.
ABSTRACT
Data on the market share of the four major bridge construction materials used in the US (reinforced
concrete, prestressed concrete, structural steel, and timber) are summarized in this report. All
bridges carrying public roadways are considered. Data are extracted from the National Bridge
Inventory (NBI) as of December 2003. The NBI is maintained by the Federal Highway
Administration (FHWA). Tables and figures present information on both the number and deck area
of existing bridges. To focus on current trends, data are also presented for bridges built during 1999-
2003. The market share and performance (structural deficiency) of bridge materials are given by
year of construction. This report updates data published in a similar document in September 2001
1
.
The National Bridge Inventory
Following the tragic collapse of the Sliver Bridge in December 1967, Congress passed legislation that
required each state to inspect and maintain an inventory of all bridges on the Federal-aid system.
Inspection standards were issued in 1971 to satisfy this mandate of Congress. Most states completed
their inventory of bridges on the Federal-aid system by the end of 1973. In 1978, Congress passed

the Surface Transportation Assistance Act which expanded the law to require all highway bridges
on public highways to be added to the inventory. Biennial inspections of all bridges were also
required to ensure the safety of the traveling public.
The states are responsible for assuring that owners of all bridges on public roads perform the
required inspections. Each state then collects the inspection reports for all bridges in the state and
submits them annually to the FHWA, where they are entered into the National Bridge Inventory
(NBI) database. The NBI must be updated annually as existing bridges are reinspected, new bridges
are added, and old bridges are rehabilitated, replaced or abandoned.
The FHWA uses the NBI to identify bridges that are eligible for rehabilitation or replacement
under federal programs. The NBI is also used as the basis for a biennial report on the condition of
the nation’s bridges. The Secretary of Transportation is required by law to submit this report to
Congress
2
.
The format for the NBI data is defined in the “Recording and Coding Guide” published by
FHWA
3
. The current guide contains 116 data fields, some of which contain sub-fields. These fields
contain a wide range of data about each bridge, including:
• Location and highway designation
• Year built and year reconstructed, if applicable
• Ownership and maintenance responsibility
• Structure geometry: structure length, main span length, number of main and approach
spans, deck width, skew
• Material and structure type for main span and approach spans, if any
• Condition and appraisal ratings of structure
• Traffic data
1
Material Usage and Condition of Existing Bridges in the U.S.
The coding guide assists bridge inspectors in pr

eparing data for identification items, such as
bride location, and for rating items, such as substructure and superstructure condition. The guide is
intended to pr
ovide greater uniformity in reporting data.
Data Used in this Report
The NBI is a dynamic database. It is regularly updated to reflect the current status of the bridge
inventory. Therefore, any set of data taken from the NBI is a “snapshot” of existing bridges in the
US at one point in time. This market share report is based on data extracted from the inventory as
of December 2003. On that date, the NBI contained information for 699,898 structures. These struc-
tures included highway bridges (including culverts), railway bridges, tunnels, and other trans-
portation structures carrying or passing over a public highway. The NBI includes data for structures
located in all states plus Washington, DC, and Puerto Rico. The format of this report parallels that
of Reference 1.
The main purpose for creating and maintaining the NBI is to monitor the condition of bridges
carrying public highways. Therefore, for funding and reporting purposes, the FHWA considers only
structures meeting the following criteria:
• The structure must support a roadway with vehicular traffic
• The total structure length must be equal to or greater than 20 ft.
Based on the above criteria, there are 594,888 structures in the inventory as of December 2003.
Of the structures considered in this report, 474,515 are identified as bridges, and 120,373 as culverts.
Culverts have been excluded from data considered for this report because they are typically buried
structures. Therefore, the database of structures used for this report contains a total of 474,515 struc-
tures. This subset of the total NBI database, referred to as the report database in the following, is
used to generate all tables and figures contained in this report.
For this report, data for all structures in the report database are retained, even when the
structure has invalid or missing data in some data fields. The number of structures with invalid or
missing data in any given field is very small. For ease of data extraction, invalid data fields were
given null values. While importing data for the total of 699,898 structures, there were 1129 errors
associated with input format for the data fields. Some structures had multiple invalid data fields,
making the number of str

uctur
es with invalid data fields smaller than 0.16%. The missing and/or
invalid data fields may r
esult in minor discr
epancies between total numbers listed in dif
ferent
portions of the tables.
Data extracted from the NBI are often reported in terms of the number of bridges. Such an
appr
oach has limitations because it does not distinguish between dif
fer
ent size bridges.
A
bridge
may have a single or multiple spans. To address this limitation, data in this report are presented by
the number of bridges and by the bridge deck area (i.e., product of structure length and width of
bridge deck). Bridge deck area is more representative of the volume of construction, since large
projects with greater deck area will receive more weight in the comparisons.
Bridge Condition
Data contained in the NBI can be used to determine whether a bridge is deficient in structural
condition or function. The FHWA also requires that the time since construction (or reconstruction,
if applicable) must be 10 years or more for a bridge to be classified as structurally or functionally
deficient. This additional age requirement is ignored when assessing deficiency in this report.
2
Material Usage and Condition of Existing Bridges in the U.S.
The str
uctural condition of bridges is evaluated based on five major items. Each item is rated on
a scale of 0 to 9, from bridge closed to excellent condition, respectively. According to FHWA, a
bridge is classified as str
ucturally deficient if it meets any one of the following criteria:

• A condition rating of 4 or less for:
– deck (Item 58)
– superstructure (Item 59)
– substructure (Item 60)
• An appraisal rating of 2 or less for:
– structural evaluation (Item 67)
– water-way adequacy (Item 71)
The FHWA coding guide
3
describes a condition rating of 4 as “POOR CONDITION – advanced
section loss, deterioration, spalling or scour.” An appraisal rating of 2 is noted as a “Basically intol-
erable requiring high priority of replacement.” A structurally deficient bridge is restricted to light
vehicular traffic, requires immediate rehabilitation to remain open, or is closed.
Of the 474,515 structures considered in this report, 79,519 or 16.8% are classified as structurally
deficient.
A bridge may also be classified as functionally obsolete. This classification indicates that the
deck geometry, clearances, load carrying capacity (comparison of the original design load to the
current state legal load), or approach roadway alignment do not satisfy the current minimum
criteria for the system of which it is a part. A bridge is excluded from the functionally obsolete
category if it is classified as structurally deficient.
Of the 474,515 structures considered in this report, 81,953 or 17.3% are classified as functionally
obsolete.
A total of 161,472 structures, or 34.0%, are classified as either structurally deficient or func-
tionally obsolete. Note that culverts are excluded in this analysis.
The FHWA uses data in the NBI to compute a sufficiency rating for each bridge. This rating is
based on structural adequacy and safety, serviceability and functional obsolescence, and essentiality
for public use. A bridge may be eligible to receive federal funding for rehabilitation or replacement
if it has a low sufficiency rating, is structurally deficient or functionally obsolete, and meets the
minimum age r
equirement stated above.

Str
uctural deficiency pr
ovides an indication of bridge condition. Ther
efor
e, it can be used to
compare the relative durability and long-term performance of different US bridge materials.
However, for the comparisons to be meaningful, bridges must be of the same age. In this report, data
related to structural deficiency are based on the number of existing bridges. Deck area is not used
when reporting structural deficiency. Structural deficiency does not necessarily reflect the overall
condition of a bridge, but may only reflect the condition of a single element. It would be misleading
to r
epr
esent the entire bridge area as deficient if only a single element or span of the structure is the
sour
ce of the deficiency
.
The condition of bridges is not directly related to market share. It is included as a significant part
of this bridge market shar
e report for several reasons. The first reason is that bridge condition can
be used as a general indication of the potential size of the bridge r
eplacement market. The second
reason is that the NBI data reveal that concrete bridges, both reinforced and prestressed, have
demonstrated very good long-term performance. Further
, this performance is significantly better
than that of bridges built using other materials (see References 4 through 9).
3
Material Usage and Condition of Existing Bridges in the U.S.
Limitations of Data
It is important to note that the data presented in this report represent only bridges existing in the
inventory as of December 2003. The NBI does not provide information on every bridge built in a

given year, but only on those bridges that are still in service. If a bridge is demolished or totally
replaced, it is deleted from the inventory.
All new bridges must be inspected and added to the NBI. Data on all bridges built in 2001 and
2002 may not have been entered into the 2003 NBI. The delay may be due to a lag between
inspection and entry of data into the NBI. Therefore, data on bridges built during 2001 and 2002 may
be incomplete. The incomplete sample is reported because it is assumed to be representative of the
total population built during those years.
In this report, each bridge is categorized according to the FHWA definition, i.e. by the material
of the main span superstructure. In structures incorporating approach spans, the main span super-
structure material may differ from the approach span superstructure material. In this case, the
contribution of the bridge to the market share is not accurate, since the material of the approach
span is neglected. However, this situation occurs for less than 2.9% of all bridges. It is not possible
to eliminate this minor source of error because the length of main and approach spans is not given
in the NBI. Data reported on the basis of deck area are more strongly influenced by this situation
than data reported on the basis of number of bridges built.
The NBI lists the “Year Built” for each structure. Where applicable, the “Year Reconstructed” is
also given. If the superstructure of a bridge is replaced, but the substructure is reused, “Year Built”
remains the year of original substructure construction. “Year Reconstructed” would then indicate
the year the superstructure was replaced. Such a situation can lead to apparent inaccuracies in the
analysis of NBI data. For example, prestressed concrete bridges were first built in the US in 1950.
However, some bridges with prestressed concrete superstructures have a “Year Built” prior to 1950.
These bridges have probably been “reconstructed” using prestressed concrete superstructures. In
this report, all data are presented using “Year Built”. “Year Reconstructed” is ignored. Data
contained in the NBI do not identify if the superstructure has been replaced during reconstruction.
It is expected that any error introduced by reconstructed superstructures is minor.
Prior to introduction of legislation requiring the inventory and inspection of all bridges on
public highways, detailed records of construction were not always maintained. Therefore, the year
of r
econstr
uction is not known for many older bridges. When the inspection of all federal-aid

bridges was first mandated in 1968, and the requirement was extended to all bridges in 1978,
inspectors wer
e r
equir
ed to estimate the year of constr
uction for a bridge if the actual year was
unknown. It appears that these estimates were rounded to five- or ten-year increments. This is
particularly evident for the year 1900, for which the NBI records that 6,678 bridges were built. This
number rivals the number of bridges built during the peak years of interstate construction. These
estimated construction dates only affect bridges built prior to 1978 and have a minor impact on the
data reported, since this report focuses on more recent trends.
Overview of Data Presented in Appendix A
Tables A.1 through A.8 present a broad overview of market share and bridge condition (structural
deficiency) information for each state. Data for Washington DC and Puerto Rico are also reported.
Data based on the number and deck area of bridges are presented for all existing bridges and for
those built during the 1990-2003 period. Detailed data are given for the four most prevalent main
span superstructure materials: reinforced concrete, prestressed concrete, steel, and timber. Data for
reinforced and prestressed concrete bridges are also combined to reflect the total market share for
4
Material Usage and Condition of Existing Bridges in the U.S.
concr
ete. Data on structurally deficient bridges are provided as an indication of the overall condition
of bridges in each state. This information can be used to assess the potential bridge replacement
activity in a state. These numbers should not be used to compar
e performance of bridges
constructed using different materials because bridges of different ages are included in the data.
Data presented in Tables A.9 through A.14 and Figures A.1 & A.2 could be used to compare
performance of bridges of similar ages, built of different materials. The figures illustrate the
changing market share of main span superstructure materials for existing bridges built in the indi-
cated five- and ten-year periods since 1950. Data are presented in tables for the number, deck area

and structural deficiency of existing bridges by main span superstructure material for the total
inventory and for various highway systems: City Street, County Highway, Federal Lands Road,
Interstate Highway, Other Road, State Highway, State Lands Road, and U.S. Numbered Highway.
These data are further separated into ranges for year built and maximum span length. The data on
structurally deficient bridges may be used to evaluate the relative performance of bridges
constructed using different superstructure materials that were built during the same period of time.
Observations on Market Share and Bridge Condition
Many observations can be made from the information presented in this report. However, observa-
tions made here will be limited because the report is intended to present data rather than interpret
the data. Trends also vary widely between states, making it difficult to make general observations.
References 4 through 9 provide detailed evaluations of NBI data, including market share and
performance comparisons. Although these references are based on data from previous versions of
the NBI, the same trends hold true for data reported herein.
The most prominent observation is that reinforced and prestressed concrete make up an increas-
ingly larger share of the bridge market. This is evident from the Figure A.1. The combined market
share for reinforced and prestressed concrete bridges in the US is close to 70 % of bridges built in
recent years for both number and deck area of bridges. This is a significant increase from the period
1950-1959 where the market share was approximately 43% based on number of bridges and 35%
based on deck area of bridges.
The market share in each state may vary widely from the national trends. To illustrate the differ-
ences in current market conditions between states, the two states at the extremes of market share are
discussed here based on data from Table A.7. In Maryland, only 22.5% of existing bridges built
recently (1990-2003) were constructed using reinforced and/or prestressed concrete superstructures.
In Hawaii, during the same period, the share is 100%. In Maryland, only 11.3% of the bridge deck
ar
ea was supported on r
einforced and/or prestressed concrete superstructures. In Hawaii, the corre-
sponding percentage was 100%.
Condition and Material usage by various highway systems are shown in Tables A.9 through
A.14. Interstate and State Highways have the lar

gest shar
e of the total deck area of bridges (28% and
26%, r
espectively). While County Highways have the lar
gest number (45%) and the most str
uc-
turally deficient bridges (22%), they account for only 17% of the total deck area. County and State
Highways show high (75% and 70%, r
espectively) usage of concr
ete bridge deck ar
ea in r
ecent
years, up from about 36% and 39% respectively, in the 50s. Interstate Highways also demonstrate
similar increase in the concrete bridge deck area; but the share of concrete bridge deck area is only
58%.
Data for all structurally deficient bridges in the US are listed in Tables A.13 and A.14. These data
indicate that, for almost each road or highway system, reinforced and prestressed concrete bridges
have a significantly lower rate of structural deficiency than steel or timber bridges within each range
5
Material Usage and Condition of Existing Bridges in the U.S.
of years shown. In most cases, timber bridges have the highest rate of str
uctural deficiency by a
wide margin.
Data for maximum span length for all bridges in the US (Table A.10) indicate that only 2.5% of
all bridges have main spans of 150 ft. or longer. It can also be seen that steel is the more prevalent
superstructure material for spans in excess of 150 feet, although the use of concrete for long span
structures has been growing in recent years.
6
Material Usage and Condition of Existing Bridges in the U.S.
REFERENCES

1. “Material Usage and Condition of Existing Bridges in the U.S.,” Portland Cement Association,
Skokie, Illinois, SR342, September 2001.
2. “2002 Status of the Nation’s Highways, Bridges and Transit: Conditions and Performance, Report
to Congress,” Federal Highway Administration, Washington, DC, March 2003.
3. “Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s
Bridges,” Bridge Management Branch, Office of Bridge Technology, Federal Highway Adminis-
tration, Washington, DC, December 1995.
4. Dunker, K.F. and Rabbat, B.G., “Assessing Infrastructure Deficiencies: The Case of Highway
Bridges,” Journal of Infrastructure Systems, Vol. 1, No. 2, June 1995, pp. 100-119.
5. Dunker, K.F. and Rabbat, B.G., “Characteristics of the US Highway Bridge Population,”
Computing in Civil Engineering, Proceedings of the First Congress, ASCE, Washington, DC, June
20-22, 1994, pp. 1006-1013.
6. Dunker, K.F. and Rabbat, B.G., “Why America’s Bridges Are Crumbling,” Scientific American,
March 1993, pp. 66-72.
7. Dunker, K.F. and Rabbat, B.G., “Performance of Prestressed Concrete Highway Bridges in the
United States – The First 40 Years,” Journal of the Precast/Prestressed Concrete Institute, Vol. 37,
No. 3, May-June 1992, pp. 48-64. Also, Discussions and Closure in Vol. 38, No. 2, March-April
1993, pp. 94-97.
8. Dunker, K.F. and Rabbat, B.G., “Performance of Highway Bridges,” Concrete International, Vol.
12, No. 8, August 1990, pp. 40-43. Also Discussion and Closure in Vol. 13, No. 4, April 1991, p 10.
9. Dunker, K.F. and Rabbat, B.G., “Highway Bridge Type and Performance Patterns,” Journal of the
Performance of Constructed Facilities, Vol. 4, No. 3, August 1990, pp. 161-173.
7
Material Usage and Condition of Existing Bridges in the U.S.
APPENDIX A
Summary of Market Share and Bridge Condition Data
The following tables are included:
All Existing Bridges
Table A.1 2003 NBI Data for Selected Main Span Materials by State Based on Number of All
Existing Bridges

Table A.2 2003 NBI Data for Selected Main Span Materials by State Based on Deck Area of All
Existing Bridges
Table A.3 2003 NBI Data for All Concrete Bridges (RC+PS) by State Based on Number and Deck
Area of All Existing Bridges
Table A.4 2003 NBI Data for Selected Main Span Materials by State Based on Number of All
Existing Structurally Deficient Bridges
Table A.4a 2003 NBI Data for Selected Main Span Materials by State Based on Number of All
Existing Structurally Deficient and Functionally Obsolete Bridges
Existing Bridges Built 1990 through 2003
Table A.5 2003 NBI Data for Selected Main Span Materials by State Based on Number of Existing
Bridges Built 1990 through 2003
Table A.6 2003 NBI Data for Selected Main Span Materials by State Based on Deck Area of
Existing Bridges Built 1990 through 2003
Table A.7 2003 NBI Data for All Concrete Bridges (RC+PS) by State Based on Number and Deck
Area of Existing Bridges Built 1990 through 2003
Table A.8 2003 NBI Data for Selected Main Span Materials by State Based on Number of Existing
Structurally Deficient Bridges Built 1990 through 2003
All Existing Bridges
T
able
A.9
2003 NBI Data for
Y
ear Built by Highway System and Material Based on Number of
All
Existing Bridges - All States + DC and PR
Table A.10 2003 NBI Data for Maximum Span Length by Highway System and Material Based on
Number of
All Existing Bridges -
All States + DC and PR

Table A.11 2003 NBI Data for Year Built by Highway System and Material Based on Deck Area of
All Existing Bridges - All States + DC and PR
T
able
A.12 2003 NBI Data for Maximum Span Length by Highway System and Material Based on
Deck
Ar
ea of
All Existing Bridges - All States + DC and PR
Table A.13 2003 NBI Data for Year Built by Highway System and Material Based on Percentage of
Structurally Deficient Bridges - All States + DC and PR
T
able
A.14
2003 NBI Data for Maximum Span Length by Highway System and Material Based on
Percentage of Structurally Deficient Bridges - All States + DC and PR
8
Material Usage and Condition of Existing Bridges in the U.S.