March/April 2001
Steel
Fabrication Technologies Observed in Japan and Europe
by
Krishna K. Verma
In the United States, there is a need to modernize structural steel
bridge fabrication and erection technologies and upgrade fabrication
shops.
Recognizing the benefits that could result from an examination of
international practices, a team of steel bridge experts visited leading
steel fabrication facilities in Japan, Italy, Germany, and the United
Kingdom in May and June 1999. The team members represented the Federal
Highway Administration (FHWA), state departments of transportation,
academia, associations, and the private sector. The industry representatives
included fabricators, a manufacturer of welding equipment and consumables,
and a steel producer.
The Steel Bridge Fabrication and Erection Technology Scan was sponsored
by FHWA's Office of International Programs and was led by representatives
of the Office of Bridge Technology. The team identified several practices
that may have current or future value to transportation agencies in
the United States.
|
Computer-aided
design of girder bridge and cross frames used by Fairfield-Mabey
in the United Kingdom. One of the highest priority goals of U.S.,
European, and Japanese fabricators is the development of a computer-integrated
manufacturing software package. |
CAD/CAM
All of the fabricators had computer-aided drawing (CAD) and computer-aided
manufacturing (CAM) software. These systems also included three-dimensional
(3-D) bridge modeling that was used to verify assembly/field erection
location and elevation checks. The software was purchased from a variety
of vendors or developed in-house. None of the software was completely
integrated, and the results of one package were manually input into
the next.
The generation of a digital representation of the structure is crucial
to a modern fabrication shop. The information is used to verify the
geometry input and simultaneously produces manufacturing numerical
control data. The computer numerical control (CNC) data can be sent
directly to the machine using a local area network.
The U.S. practice is evolving along similar lines in a few of our
larger fabrication shops. Fully integrated systems are planned, and
cooperative development among fabricators seems desirable. Shop detail
drawings are unnecessary in the modern automated shop. Shop drawings
appear to be unnecessary because the dimensional checks can identify
necessary deviations on the design drawing for review by the owner.
The accuracy of the fabricated pieces reduces the need for shop assembly
and allows virtual assembly to be done based on measured section dimensions
in the 3-D modeling program. One of the highest priority goals of
U.S. and foreign fabricators is the development of a computer-integrated
manufacturing (CIM) software package.
Automated Recording
Automated recording of fabrication was employed by some of the fabricators
visited. Automated and digitally recorded ultrasonic inspection using
both pulse?echo and time?of?flight diffraction were employed in shop
and field ultrasonic inspection in Japan. However, this system is
still in its infancy, and its reliability has not been established.
One fabricator employed continuous monitoring and recording of welding
variables for quality control.
Various geometric measurement systems were employed by the fabricators
to determine the conformance of the geometry. These ranged from simple
digital surveying equipment to the more sophisticated computed assembling
test system (CATS) to measure the structure and compare it with the
geometry generated in the computer drawing and manufacturing system.
The virtual assembly provided a complete geometric record of the structure.
The detailed records and information, as well as the improved accuracy,
reduce the need for and the cost of the owner's quality control measures.
Owners in all of the countries visited are accepting work without
shop assembly to varying degrees. This ranged from 10 to 20 percent
in Japan and Italy to most of the fabrication in Germany and England.
High-Performance Steels and Coatings
The steels used for bridges around the world are governed either by
individual country specifications or by the new Eurocode. The yield
strength levels are very similar to those used in the United States,
and 50 kips per square inch (ksi) (345 megapascals [MPa]) is the most
common strength grade except in Germany where 36 ksi (248 MPa) is
used. All of the countries have a steel grade in the 65- to 70-ksi
(448- to 482-MPa) strength range and report growing interest in its
use.
Thermo-mechanical control processing (TMCP) is used by all countries
for higher strength levels and is aggressively used in Japan to improve
weldability and toughness. Quench and temper (Q&T) processing is used
for steels from 70 to 100 ksi (482 to 689 MPa) although steels greater
than 70 ksi are rarely used. Weathering steel is used in all countries
visited, and there are initiatives to increase its use.
Japan has developed several new higher alloy "seaside" weathering
steels for areas close to the coast. For painted bridges, zinc-rich
primers are commonly used in all countries, and the United Kingdom
is using aluminum metallizing instead of primer. Tapered plates have
been used in several countries, but it is not clear if this practice
is economical.
Cutting and Joining
Field welding in Europe and Japan is not only considered to be an
acceptable alternative to bolted connections, but in some countries,
it is the only joining method permitted. Enclosed shelters are employed
that allow the use of gas-shielded welding - gas metal arc welding
(GMAW), flux cored arc welding-gas (FCAW?G), and electrogas welding
(EGW). Field welding of webs employed automated EGW, FCAW?G or GMAW?P
(pulsed). Field welding of flanges used automatic submerged arc welding
(SAW) or GMAW. The prevalent shop and field welding with gas-shielded
processes use solid, metal?cored and flux cored wire electrodes. These
processes were employed in semi?automatic, automatic and robotic welding
by most Japanese and European fabricators. The benefits resulting
from such use included high production, lower rejection rates, and
low hydrogen weld deposits. Welding through a special wash primer
with flux cored welding was done in Japan. Preheating was not employed
in most of the shops. The need for preheating was eliminated by the
use of steels with low carbon content and low carbon equivalence,
in addition to the use of low hydrogen and high heat input processes.
All of the fabricators employed robots for welding stiffeners and
other plate attachments to plate girder webs and box girder webs and
flanges. Wrapping around the ends of stiffeners and plate attachments
was the standard practice in all of the countries. Robots were also
used for some cutting and corner grinding where necessary. A new high-speed
rotating-arc technique developed at NKK in Japan provided enhanced
weld tracking for robotic fillet welds. One?sided, high-deposition
welds with ceramic backing bars were used both in the shop and in
the field for groove welds in webs and thin flanges. This method eliminates
turning the plate and back-gouging followed by welding. More flexible
specification requirements are needed to allow the implementation
of these methods.
Internal quality assurance and quality control (QA/QC) was relied
on in the shops. The owner's inspectors normally audited the shops
at the beginning of the job and at the end. Radiographic inspection
has been phased out in the United Kingdom. Japan used ultrasonic inspection
for most welds, while Germany only allowed radiographic inspection.
The substitution of ultrasonic inspection (with record- producing
capability) for radiography provides faster inspection and interpretation
as well as increased worker safety. Procedure qualifications were
generally accepted by all owners and had an unlimited life. The ISO
9001 accreditation was accepted by the owners as proof that the fabricators'
quality control procedures were adequate and did not require the owner's
agent for constant supervision.
Extensive use of cold bending of components before and after welding
was employed to maintain the desired straightness. Laser cutting of
plates was widespread in Japan. All fabricators employed numerically
controlled cutting equipment using laser, plasma, or oxygen?fueled
torches. This equipment was often allowed to run unattended with direct
programming from the CAM software. The same equipment was used for
marking, cutting, and fit-up. The larger fabricators in the United
States employ similar equipment. The highly automated plants in Japan
were set up to make thin-plate rectangular box girders with stiffened
flanges and webs. These boxes were fabricated into short shipping
lengths because of weight and dimensional constraints.
Scan Team Members |
NAME |
ORGANIZATION |
Krishna
K. Verma (Chair) |
FHWA,
Washington, D.C. |
Ralph
E. Anderson |
Illinois
Dept. of Transportation (DOT) |
Hardy Campbell |
American
Welding Society |
Milo
Cress |
FHWA,
Lincoln, Neb. |
John
W. Fisher (Reporter) |
Lehigh
University |
Karl
H. Frank (Reporter) |
University
of Texas, Austin |
James
Hamilton |
Utah
Pacific Bridge |
Robert
Kase |
High
Steel Structures |
Kathleen
Linehan |
FHWA,
Washington, D.C. |
Pat
Loftus |
High
Steel Structures |
William McEleney |
National
Steel Bridge Alliance, R.I. |
Ronald Medlock |
Texas
DOT |
Dennis
Mertz |
University
of Delaware |
Randy
Sathre |
PDM
Bridge, Wasau, Wis. |
Arun
Shirole |
National Steel Bridge Alliance, Minn. |
Jerry
Uttrachi |
ESAB Welding and Cutting Products |
Alexandar D. Wilson |
Bethlehem
Steel Corp. |
William J. Wright |
FHWA, McLean, Va.
|
Certification and Contracting
All of the fabricators visited were certified in accordance with ISO
9001. The clients accept this accreditation and do not have the expense
of having their own inspectors in the shops. Shop certification of
U.S. fabricators may be enhanced by including appropriate parts of
the ISO 9001 accreditation. In most of the countries, the contract
with the fabricator includes both fabrication and responsibility for
the erection of the structure. This type of contract eliminates the
conflict between the fabricator and the erector concerning fit-up
and paint damage. This allows the fabricator to choose whether or
not shop assembly is required and to determine the most efficient
method of erection. Often the erector is a subcontractor to the fabricator.
This method of contracting should be tried in the United States. Design?build?finance?operate
and transfer projects are currently favored in the United Kingdom.
Partial payment for material and progress is typically included in
contracts for large projects in both Japan and Germany.
Design Innovation
The design practice in all of the countries visited is not encumbered
by the restrictions placed on fracture-critical members in the United
States. Two?girder systems, tied arches, and other structural systems
that use two lines of support are considered acceptable throughout
Europe and Japan. Tied arches are used for both road and railroad
bridges. Their high stiffness with orthotropic steel decks also makes
them suitable for high?speed rail. Welded field splices are considered
throughout Europe and Japan to be an acceptable design alternative
to the traditional bolted field splices. Erection by launching allows
the field welding to be performed without interfering with traffic.
Box girders, both open (i.e., tub girders) and closed, are more evident
in Europe and Japan than in the United States. Standardization of
design details such as installing stiffeners and attachments on one
side of the plates allows for automation in fabrication for both box
and plate girders. Throughout Europe, probability?based load and resistance
factor design (LRFD) is the design method in use. Japan continues
to use allowable stress design (ASD), and fatigue is not presently
considered in the design of highway bridges.
Back Home
In April 2001, FHWA's Office of Bridge Technology, the American Association
of State Highway and Transportation Officials (AASHTO), and the National
Steel Bridge Alliance (NSBA) will sponsor a follow-up workshop on
computer-integrated steel bridge design, fabrication, and construction.
The workshop will be hosted by Edison Welding Institute in Ohio and
will include speakers from the foreign fabricators visited on the
tour.
After the tour, the team members produced a final report entitled
Steel Bridge Fabrication Technologies in Europe and Japan. The report
is available online at www.international.fhwa.dot.gov,
and in hard copy by e-mailing the Office of International Programs
at international@fhwa.dot.gov,
or calling (202) 366-9636.
Krishna K. Verma is a senior welding engineer with FHWA's
Office of Bridge Technology in Washington, D.C. He is responsible
for policies regarding bridge welding, fabrication, fatigue, fracture,
and bridge painting. He is currently serving as a member of the AASHTO
T-17 Committee on Welding, the AASHTO-AWS-D-1.5 Bridge Welding Code
Committee, the TRB Committee on Fabrication and Inspection of Metal
Structures (A2F07), the AASHTO-NSBA Steel Bridge Collaboration, and
the International Institute of Welding's Commission V on Quality Control
and Quality Assurance of Welded Products and Commission XIII on Fatigue
Behavior of Welded Components and Structures. Verma has a bachelor's
degree from Benares, India; a master's degree in structures from the
University of Calgary, Canada; and a master's degree in materials
engineering from the Rensselaer Polytechnic Institute of Troy, N.Y.
Verma is a registered professional engineer in Pennsylvania.
Recommendations
for Implementation in the United States
Computer-Aided Design/Computer-Aided Manufacturing
Establish a task group of owners and fabricators to develop
a documentation standard.
Promote development of a computer-integrated manufacturing
(CIM) software package.
Carry out a pilot project using digital fabrication shop
documents in lieu of shop drawings.
Develop a storage protocol for archiving as-built documents.
Automated Recording
Evaluate existing measurement technologies.
Explore the feasibility of digital geometric measurements
of fabricated components for virtual assembly in lieu of preassembly.
Carry out a pilot project.
High-Performance Steels and Coatings
Study applicability of "seaside" weathering steels for
U.S. marine environments.
Promote development of a 50-ksi (345-MPa) high-performance
steel for improved weldability and toughness.
Cutting and Joining
Develop a workshop on gas-shielded welding and new methods
of welding for shop and field fabrication for fabricators and
owners.
Explore the use of the high-speed rotating arc technique
with enhanced tracking for fillet welding.
Promote the use of ultrasonic inspection with record-producing
capability in lieu of radiography.
Explore the development of weld qualification procedures
by electrode producers in place of fabricators.
Certification and Contracting
Set up a task group to develop a qualification program
for fabricators that allows them to be responsible for quality.
Explore incorporating appropriate parts of ISO 9001 in
the American Institute of Steel Construction (AISC) Certification
Program.
Explore providing fabricators with contractual responsibility
for both fabrication and erection.
Design Innovation
Reexamine the design practice, FHWA directives, and AASHTO
specifications related to two lines of support and fracture-critical
members considering modern materials, joining, and quality control
developments.
Continue national programs such as the Steel Bridge Collaboration
to develop standard design details. |
Other
Articles in this Issue:
DOT's Comprehensive Truck Size
and Weight Study — A Summary
Giving
Freight a Voice
FORETELL
— Finally, someone is doing something about the weather!
Steel
Fabrication Technologies Observed in Japan and Europe
Reliability
of Visual Bridge Inspection
For the Common Good: The 85th
Anniversary of a Historic Partnership
Telecommunications
— Getting More for Your Money
Celebrating
National Transportation Week, May 13-19