Design and 

Construction 

Specifications for

Bridges

by Keith L. Christiansen

Structural Engineer

BLM, National Science and

Technology Center

Background

Bureau of Land Management

Manual Section 9112, Bridges

and Major Culverts, provides

the responsibilities, policies, and

procedures for the planning,

design, construction, and maintenance of bridges and major

culverts. The objective of this

manual section is to provide

safe bridges and major culverts under a uniform system

of design, construction, and

maintenance management. The

manual requires that bridges and

major culverts be designed in

accordance with the latest edition

of the “Standard Specifications

for Highway Bridges”, published

by the American Association of

State Highway and Transportation Officials (AASHTO).

Additionally, the manual requires

the use of Federal Highway

Administration’s (FHWA)

“StandardSpecifications for Construction of Roads and Bridges

on Federal Highway Projects for

preparing construction or maintenance specifications for bridges

and major culverts.

Discussion

AASHTO’s Subcommittee on

Bridges and Structures meets

annually to revise and update the

standard design specifications.

Constant research and development in structures of all

types of construction materials

necessitate the continual

improvement of the design

specifications. During the 1999

Annual Meeting, a new bridge

design specification, which

will replace the Standard Specifications for Highway Bridges,

was officially adopted as the basic

specification. This new specification is AASHTO LRFD Bridge

Design Specifications, which has

been under development for 10

years under the National Cooperative Highway Research Program

(NCHRP Project 12-33). The

design provisions of the new

specification employ the load

and resistance factor design

(LRFD) methodology and are

intended for the design, evaluation, and rehabilitation of

highway bridges.

Load and resistance factor design

philosophy considers the variability in the properties of structural

elements. This is similar to the

philosophy of load factor design

(LFD) which reflects the variable

predictability of certain load

types, such as vehicular loads

and wind forces, through

adjustments to the design factors. LRFD methods will result

in improved bridge designs and

more accurate analysis methods.

This will lead to bridges exhibiting superior serviceability,

enhanced long-term maintainability, and more uniform levels

of safety.

As the implementation and use

of the new LRFD design specification proceed, the old design

specification will be gradually

phased out. AASHTO’s current

Standard Specifications for

Highway Bridges, Sixteenth

Edition, 1996 which allows

the use of either Working

Stress Design or Load Factor

Design methods, will not be

maintained after 1999. Any

errors discovered in the specification will be corrected, but

additional study or new

research to enhance the specification will not be undertaken.

Specifications used for construction of roads and bridges are

printed in FHWA’s Standard

Specifications for Construction

of Roads and Bridges on Federal Highway Projects. The

current edition is FP-96 which

was issued in 1996. The International System of Units (SI)

is used in this publication as

required by Public Law 100-418

(1988 Omnibus Trade and

Competitiveness Act) and

Executive Order 12770 (Metric Usage in Federal Government

Programs). The preceding edition, FP-92, was issued in

1992 and used Customary

U.S. (English) Units of measurement with metric equivalents in

parentheses. Presently, metric

designs by various state

departments of transportation

are declining because of the

reluctance of industry to make

changes and the enactment of

laws in some states prohibiting

metric designs. Only about 50

RESOURCE NOTES

NO. 41 DATE 08/17/00

Range

ENGINEERING
percent of the states are currently

designing roads and bridges in

metric units. Consequently,

FHWA plans to issue a revised

edition of its Standard Specifications in 2003. This edition

will be printed in two volumes,

one volume in the International

System of Units and one volume

in U.S. Units.

Conclusion

With the adoption of AASHTO’s

LRFD Bridge Design Specifications as the new design criteria,

eventually all new bridges will

be designed in accordance with

the load and resistant factor

methodology. However, as the

implementation of the new

specification proceeds, the

Sixteenth Edition of the Standard Specifications for Highway

Bridges will remain a viable standard to use for design until it

ultimately becomes obsolete.

FHWA’s Standard Specifications

for Construction of Roads and

Bridges on Federal Highway

Projects, FP-96, is the preferred

edition for use in the construction of roads and bridges until

the revised edition is issued in

2003. However, when FP-96 is

used, either design drawings

should bear soft metric equivalents unless metric units are

used exclusively or supplemental

specifications should be written

to convert the metric units

within FP-96 into U.S. Units.

The use of the older edition,

FP-92, although acceptable, is

discouraged. FP-96 has corrected some deficiencies in the

older specification, and copies

of FP-92 are out of print and

unavailable for purchase.

Contact

Keith L. Christiansen

Structural Engineer, BLM

National Science and 

Technology Center (RS-110)

Denver, Colorado

Telephone: (303) 987-6853

E-mail:

Keith_Christiansen@blm.gov

Range

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