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Modern Bridge Construction and
E· · ~ ~
ng~neer~ng Services
JUAN A. MURILLO
In fiscal year 1988 the Federal Highway Administration (FHWA) appor-
tionment for bridge replacement and rehabilitation amounted to $1.4 billion,
which, when combined with local and state funds, makes up the $3 billion
per year industry in bridge design and construction in the United States. This
level of expenditure on bridge design and construction represents a surge in
bridge activity in the United States brought on by the aging of existing
structures and increased traffic demands on the U.S. highway system.
From a global perspective the United States has been relatively slow in
applying innovation now available mostly from European sources to bridge
design and construction. As discussed later in this paper, the demand for
postwar reconstruction in Europe stimulated innovation and transformed Eu-
ropean bridge design and construction practice. America, during the 1950s
and 1960s, however, felt no comparable urgency. As a result, there has been
a noticeable lag in innovation and the transfer of technology from Europe
to the United States and there are many opportunities for improvements in
the efficiency of design and construction methods in the United States. It is
crucial that suppliers and buyers of bridge design and construction services
in the United States recognize that innovation is necessary and that the barriers
to enriching daily practice with the new technology lie not in technology
itself but in the limited roles and expectations that have become traditional
to bridge designers, contractors, and owners
In particular, in the United States a contractor building a bridge works
under the supervision of the engineer responsible to the owner for compliance
of the work with the contract documents and the design intent. This U.S.
practice is not universal. In Europe, bridge work is usually handled using
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JUAN A. MURILLO
the design/build concept. Under this arrangement, the owner/agency specifies
the project requirements and calls for bids for design and construction. This
approach has the advantage of promoting innovation at all stages of design
and construction by allowing the design engineer to consider both the type
of structure most suited to the site as well as the cost and time of construction.
If U.S. bridge design and construction teams are going to innovate in
analytical and construction techniques (or be more effective at adopting
innovations that originate elsewhere), adjustments are needed in the ways
that clients, legal counselors, insurance carriers, contractors, and engineers
conduct their professional and business activities. Moreover, the engineering
community, regulating agencies, government, and universities must recon-
sider their respective roles if the United States is to produce the required
innovation. Finally, the local, state, and federal agencies that buy bridges
have the responsibility of identifying and managing procurement procedures
that promote the best bridge design and efficient construction.
It is worth examining the postwar experience in Europe an experience
that created substantial innovation in bridge design and construction for
lessons applicable to U.S. policy.
THE EUROPEAN EXPERIENCE
Europe's dominance in bridge engineering and construction emerged dur-
ing reconstruction efforts after World War II, when hundreds of major struc-
tures had to be replaced rapidly under tough economic and industry conditions.
Steel fabricators were not ready to roll structural steel for bridge applications,
so as concrete substituted for steel as the dominant material for bridge build-
ing, the combined design/build concept was adopted to encourage competition
and reduce design and construction time.
The postwar European experience can be divided into two distinct historical
decades, each with its own special character. In the 1950s Ulrich Finster-
walder introduced cast-in-place, segmental balanced cantilever prestressed
concrete construction, and the structures built between the introduction of
this technology and 1962 have been generally labeled as the first generation
of modern bridge development.
In the 1950s it was demonstrated that by using the "balanced cantilever"
method of erection, precast or cast-in-place concrete segments could be joined
together progressively on top of a pier to form half of a bridge span on each
side of the pier. In similar fashion and simultaneously, concrete segments
erected on another pier, opposite the first, could be used to close the center
span. This method of erection, used repetitively, created multispan bridges
with very long center spans as long as 750 feet (230 meters). Balanced
cantilever construction also offers the advantages of eliminating ground-
supported formwork over deep valleys, navigable channels, and congested
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MODERN BRIDGE CONSTRUCTION kD ENGINEERING SERVICES
167
urban or industrial areas; minimal disturbance to the surrounding terrain,
allowing overhead construction while maintaining traffic; and construction
that could proceed regardless of weather conditions.
The design of balanced cantilever bridges is complex and involves con-
struction procedures that require specialized casting and erection equipment.
But since most European governmental contractual arrangements permit de-
sign and construction firms to work together to develop innovative and cost-
saving bridge designs, the casting and erection equipment designs were, and
still are, considered at the same time as cost/design proposals. Thus, joint
ventures between design firms with engineering excellence and construction
firms with experience and equipment encouraged the development of in-
house engineering expertise by contractors.
In such an atmosphere of engineering competition, new innovative designs
and construction practices advanced rapidly. The state of the art of designing
and constructing segmental prestressed concrete box girder bridges advanced
in response to the need for more productivity in the construction of bridge
structures. During the l950s new prestressing systems and alternative meth-
ods for constructing segmental prestressed concrete bridges were developed,
and design and construction procedures were refined. However, in the 1960s
a major slowdown in the development of concrete bridge technology took
place when some of the first structures built in the l950s showed signs of
distress. The Federal Republic of Germany took drastic measures banning
several of the newly developed schemes.
Engineers, builders, and owners wanted to know what was happening,
how to take care of the problems, and how to retrofit these distressed struc-
tures for service. Intensive investigations identified specific problem areas;
and predictably, as in most technological developments, the problems oc-
curred in areas where theoretical assumptions had substituted for factual
experience. Time-dependent effects on concrete structures proved to be highly
uncertain, with their true magnitude revealed only as the years passed. Fur-
the~nore, the newly introduced construction schemes overwhelmed existing
analytical bookkeeping methods, which were both cumbersome and prone
toi computational errors.
For example, to mathematically simulate the construction and stress history
of a balanced cantilever bridge, computations must be updated at each stage
of construction to reflect changes in the structural behavior of the bridge.
Every time a segment is added or a tendon is tensioned, the structural system
must be reanalyzed. Moreover, time causes the concrete and prestress to
creep, shrink, and relax. Furthermore, when the statical scheme changes or
when two adjoining cantilevers are made continuous, stress redistribution
takes place and must be recalculated. This redistribution is not only the effect
of the staged sequence of construction but also of time-dependent effects
that keep taking place in concrete and in prestressing steel long after con-
struction ends.
1
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JUAN A. MURILLO
In summary, the problem turned out to be a lack of understanding about
time-dependent effects on concrete and prestressing steel. Repair procedures
developed to restore the structural integrity of the distressed bridges also
promulgated new and more conservative guidelines to regulate design and
construction of bridges using this technology.
This major historical event clearly defines the transition to what has been
called the second generation of modern bridges.
By the 1960s long-span, segmental bridges had established their compet-
itive position. The industry addressed the problems encountered in the first
generation of bridges through more research and advanced computational
methods. Also, contractors started allowing better plant quality control in
concrete production, plus getting the benefit of reducing creep and shrinkage
in the finished structure, by letting segments undergo their natural and un-
restrained strain changes during storage in the casting yards before they were
finally incorporated in the structure.
Construction methods advanced rapidly, and segmental bridges were used
in a wide range of erection schemes. In addition to the balanced cantilever
method, span-by-span, incremental launching, progressive placing, and var-
ious combinations or modifications of these basic schemes were used.
Also, cable-stayed bridges in steel and concrete became the solution for
spans longer than 700 feet, the limit for girder bridges. They were developed
as an extrapolation of the balanced cantilever scheme: the cables replaced
the post-tensioning tendons projecting outside the structure causing a gain
in moment capacity due to the increased moment arm.
The development of cable-stayed bridges, inhibited at first by the analytical
complexity and stay-cable fatigue, moved forward with developments in
computer hardware and software and with developments in modern materials
technology and advanced testing facilities.
Almost simultaneous with the development of the second generation of
European bridges were major developments in segmental bridges and cable-
stayed bridges taking place in South America, Canada, and Mexico. Today
there are more segmental bridges in South America and Canada than in the
United States, and more cable-stayed bridges in South America, Canada,
and Mexico than in Europe. In South America the demands for new roads
to develop virgin areas and to solve traffic problems in the growing and
congested urban areas have produced record bridge construction rates and
started important trends. Figures 1 and 2 show construction on a modern
cable-stayed bridge and the final product.
THE U.S. EXPERIENCE
Based on recent bridge inventory and inspection programs, the United
States has recognized the need to replace or to rehabilitate approximately 50
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MODERN BRIDGE CONSTRUCTION AND ENGINEERING SERVICES
FIGURE 1 Construction in progress on modem cable-stayed
bridge.
169
percent of the major bridges in the country. Funds for this work are being
generated by new local and federal gasoline taxes, but the U.S. practice of
bridge building has not advanced or incorporated the European formula, in
which designers, contractors, and owner/agencies work together to meet the
common objective of building bridges that are more time and cost efficient.
If we look back, it is clear that while major developments in European
bridge technology were taking place, no similar efforts were under way in
the United States. Not until the European market was saturated did the
Europeans try to export their technology.
The major obstacle to ready acceptance of the European experience was
the U.S. construction industry's structure, which clearly allotted the respon-
sibilities and functions for design and for construction to two different services
groups. Those in design services were not involved with contractors, and
contractors in turn did not consider engineering functions as part of their
construction contract responsibilities. The process that could have combined
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JUAN A. MURlLLO
the two functions, the design/build bidding approach, particularly in the field
of bridge and highway work, was not their standard practice. Figure 3 il-
lustrates the traditional structure of the U.S. bridge design and construction
industry.
The first bridges built in the United States based on the European expe-
rience were the Pine Valley Creek Bridge in California in 1969, using cast-
in-place segmental construction with traveling forms, and the JFK Memorial
Causeway Bridge, which opened to traffic in 1973. The precast segmental
box girder for the JFK bridge was built in Corpus Christi, Texas, as a pilot
project following a comprehensive model test program at the University of
Texas at Austin. After concluding that the segmental bridge model safely
carried the service and ultimate loads for all critical moment and shear loading
configurations established by the analysis, a clean bill of health was given
to proceed with actual construction. Moreover, theoretical calculations agreed
with experimental results and actual construction.
After this major event took place, engineers, specialized material suppliers,
and contractors saw the business opportunity and imported this technology
when the economic conditions of the early 1970s demanded it. By the end
of the 1970s the FHWA issued a directive requiring competing, alternative
designs for steel and concrete for any major bridges in the United States.
This opened the doors for major changes in bridge technology.
FIGURE 2 Cable-stayed bridge.
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MODERN BRIDGE CONSTRUCTION AND ENGINEERING SERVICES
~""1
V., ,... a,.., ,[~ ,,, ,; A;,)`
~3~ art ~ ,. ;~ ~,~,,,p,,,, . .-.? f- Alp..; .1
^~.+=A - Too Y Review of Construction for Compliance with Desion; ...t, ENGINEER ':-;.3
FIGURE 3 Functional relationship in a typical bridge project
in U.S. practice.
171
Successful innovation came first in concrete bridge construction, followed
by improvements in steel bridges. Small and new design firms rushed in
to take control of the concrete bridge design market. To match the com-
petitive success of concrete bridges, the steel industry had to offer free
engineering to design firms to improve the analytical capabilities of the
designers. In addition, the steel industry had to lobby extensively to modify
the established design criteria and the controlling policies to pave the way
for new design concepts in steel. Research and development also improved
national applications for steel, including the improvement of site assembly
by using steel erectors that duplicated the effective erection schemes of
concrete segmental construction, as in the case of the Baytown Bridge
(bid in 1986).
The design competition requirement on all federally funded long-span
bridges (discussed in the next section) forced changes in material use by
demanding plant control tolerances, for example, reducing field fabrication
to a minimum, which improves quality, and stricter quality controls overall.
Such requirements enabled both more and better construction control and
improved fabrication techniques, and encouraged engineers and contractors
to use more sophisticated analytical methods under more demanding quality
control conditions.
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JUAN A. MURILLO
CURRENT TRENDS AND BARRIERS
Two aspects of the procurement process for bridge design and construction
are especially important to stimulating innovation in the U. S. bridge industry.
First, current bridge design and construction procedures require that alter-
native steel and concrete designs compete on all major federally funded
projects. This is more than a legal requirement the "extra" design oppor-
tunity is a challenge to incorporate the innovative techniques that can give
a competing design an important advantage in performance or constructibility.
Second, after the design phase is completed, but before a bridge project
begins, price competition among contractors drives innovation in the means
and methods of construction, factors that can dramatically affect the price
tag on a structure.
The alternative design requirement also means that the contractor has
alternatives under redesign clauses in the bidding documents. These redesign
clauses fall into two categories: (1) the construction options allowed within
the general design and (2) more significant changes made according to the
"value engineering" concept.
Required alternative designs are not new. In the 1 950s prestressed concrete
structures had to be presented as alternatives to conventional designs. In 1978
the FHWA issued a directive to encourage alternative design on all major
bridges in an attempt to fight inflation and a then-current trend of bids coming
in 5 percent over the engineer's estimate. The alternative design program in
effect since then has produced very competitive bids, reversing the previous
trend and producing more projects bid at or under the engineer's estimate.
In the state of Florida the cost of major bridges in the 1980s has remained
constant because of improved designs and construction schemes that offset
the rising costs of materials and labor.
However, innovation in bridge design and construction has been sharply
curtailed by legal and professional liability concerns spawned by the openness
in the contract documents that allows contractors more flexibility. Liability
concerns have also changed the nature of the relationship between the en-
gineer and the contractor.
The future success of alternative designs will depend on the structuring
of the contract documents to preserve the contractor's high degree of flex-
ibility in those optional details and construction methods that do not modify
the design intent. Contracts must also keep the responsibility and liability
separate and under the two distinct categories of design intent and contractor
ways and means. Properly structured contract documents must provide clarity
without restricting freedom; that is, true performance specifications must
preserve the basic design requirements without precluding further develop-
ment within these requirements. Also, policy changes in the functions en-
gineers perform must be adequately addressed.
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MODERN BRIDGE CONSTRUCTION AND ENGINEERING SERVICES
173
The current policy as laid out in "Alternate Bridge Designs" prepared by
the U.S. Department of Transportation FlIWA Technical Advisory (T 5140.12)
is a start, but many of the other lessons learned still need to be incorporated.
Even though the closer relationship between design and construction activities
has clearly established closer ties between engineers and contractors, two
major issues continue to inhibit the acceptance of contractor alternative de-
sign/build proposals.
These two issues are the twin questions of who pays for design modifi-
cations and who takes ultimate responsibility for the design. In a traditional
design relationship the owner backs up the engineer unless he or she is found
to be negligent. On a contractor design/build alternative the owner does not
want to cosign on the design. In some instances, owners have taken the stand
that if the contractor's alternative design will cost more than the client's or
require modifications, then the contractor should abandon the alternative and
build the client's design for the alternative bid price. From an insurance and
legal point of view, this scenario has resulted in various claims, lawsuits,
and increased professional liability premiums.
Antagonistic positions definitely do not help improve efficiency. There-
fore, an effort to cooperate in defining mutually acceptable new standards
will require a joint effort between the client's policymaking agencies, and
the construction industry and design services groups. Clients must embrace
better alternative design procedures to lift the barriers that restrict and could
eventually stop the entire practice of alternative design. They need to look
at alternative design as an economic solution to rising costs based on com-
petitive bidding, and then be objective and open to reasonable changes re-
quired by state-of-the-art technology. Insurance carriers need to consider
departures from existing practice as risks that are insurable, with broader
premium ranges based on case-by-case assessments of practices developed
to allow innovation. The current claims atmosphere is definitely an obstacle
to innovation.
Current practices suggest that although the roles of engineers and con-
tractors are still separate, alternative designs are emerging despite the re-
duction in the range of contractors' options for design modifications. For
example, the engineer now produces schematic erection drawings that define
the range of construction loads and the types of erection methods by spec-
ifying-the structural behavior of the permanent structure; then the contractor,
operating within this limited range, takes full responsibility for the design
and sizing of equipment and temporary works. Technical specifications are
written to be more performance-oriented, with strict tolerance requirements
to achieve the trimmed-down designs.
The role of the engineering community in this field is clear. We need to
further clarify the design intent and responsibility of all three parties involved
in a bridge project in the contract documents. The current procedure for
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JUAN A. MURlLLO
preparing these documents, for example, a linear process in which the de-
signer drafts the contract according to the owner's procurement guidelines
for construction contractors' bids, is still a big problem.
POLICY LESSONS FOR THE UNITED STATES
In an atmosphere where the cost pressures on public works projects such
as bridge construction continue, efficiency gains are most likely to come
only through innovation, and, in policy, from lessons learned from European
experience. In particular, closer relationships between the design function
and the construction function appear to be a better formula for innovation
than the separation typically practiced in the United States. Although neither
the legal nor insurance environment is likely to change much in the near
future, it is the bridge owner's procurement guidelines something that is
amenable to modification-that currently force designers and builders into
separate roles. There is much room for improvement in the owner's guidelines
for considering innovation and technical advances in design and construction
methods as an ongoing process. The designer, in turn, will also need to
reflect this process in construction specifications that leave room for the
contractor's innovations. Today, the major obstacle slowing the evolution in
bridge engineering is the limited importance accorded innovation. This is
reflected in current design specifications that do not recognize new design
and construction schemes and standard construction specifications that fall
short of the level of development in design, construction techniques, and
materials. If we are to incorporate new bridge technology into U.S. practice,
the owner, designer, and contractor must each be free to innovate and to
work together toward achieving one objective rather than adopting adversarial
roles that have made the most successful projects a lawsuit paradise.
Representative terms from entire chapter:
bridge construction
