JOSE MARIA COLLEGE

Philippine-Japan friendship Highway, Sasa, Davao City

COLLEGE OF ENGINEERING EDUCATION

I. Subject Code: CES413S

II. Subject Description: BRIDGE ENGINEERING
III. Topics: CHAPTER 4 - BRIDGE TYPE AND SELECTION
IV. Learning Objectives

Main Structure below the Deck Line:

1. Understand the significance of the main structure below the deck line in bridge design.
2. Explore the various components and engineering considerations related to the substructure of
bridges.
3. Examine how the substructure influences the stability and longevity of different bridge types.
Main Structure above the Deck Line:
1. Comprehend the role of the main structure above the deck line in bridge construction.
2. Investigate the superstructure components and their impact on the bridge's functionality.
3. Analyze how the superstructure affects the load-bearing capacity and flexibility of different bridge
designs.
Main Structure Coincides with the Deck Line:
1. Learn about bridge designs where the main structure coincides with the deck line.
2. Explore the advantages and disadvantages of this design approach.
3. Understand how this design choice influences construction methods and costs.
Selection of Bridge Type:
1. Discuss the process of selecting an appropriate bridge type for a specific project.
2. Examine the factors and criteria that engineers and planners consider when choosing a bridge
type.
3. Explore the importance of aligning the selected bridge type with the project's objectives and
requirements.
Factors to Be Considered:
1. Identify and evaluate the key factors that play a pivotal role in bridge type selection.
2. Discuss how factors like location, budget, traffic volume, and environmental conditions impact
decision-making.
3. Consider safety, aesthetics, and sustainability as essential factors in the selection process.
Bridge Types Used for Different Span Lengths:
1. Explore the relationship between bridge span lengths and the choice of bridge types.
2. Examine the suitability of various bridge types for short, medium, and long spans.
3. Understand why certain designs, such as arch, suspension, or cable-stayed bridges, are preferred
for specific span lengths.

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

V. Discussions:

Main Structure below the Deck Line

Substructure Elements

❖ Piers - Vertical or inclined supports that extend from the foundation level to the underside of the
bridge deck.
❖ Abutments - The support structures at the ends of the bridge.
❖ Foundations -The structures below the ground that support the piers and abutments.
❖ Bearings - Devices placed between the bridge superstructure (deck) and substructure (piers or
abutments) to allow for movement.
❖ Wing Walls - Extensions of abutments and are used to guide and direct water flow under the
bridge.
❖ Retaining Walls - In cases where a bridge crosses uneven terrain, retaining walls may be used as
part of the substructure to support the embankment or roadbed leading up to the bridge.
❖ Pile Caps - For bridges supported by piles, pile caps are horizontal structures that distribute the
load from the superstructure to the piles.
Substructure Type of Bridges
❖ Arch Bridges
❖ Masonry Arch

❖ Reinforced Concrete Arch

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

❖ Steel Arch

❖ Truss-Arch Bridges
❖ Steel Truss-Arch

❖ Steel Deck Arch

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

Main Structure above the Deck Line

Superstructure Elements

❖ Girders and Beams - These horizontal elements provide support for the bridge deck and distribute
the loads to the vertical supports, such as piers or abutments.
❖ Trusses - Truss bridges use a framework of interconnected diagonal and vertical members to
support the deck.
❖ Deck - The deck is the top surface of the bridge that carries the traffic and provides a platform for
vehicles and pedestrians to cross.
❖ Parapets and Railings - Parapets and railings are safety features installed along the sides of the
bridge to prevent vehicles from accidentally going off the sides.
❖ Expansion Joints - Designed to accommodate thermal expansion and contraction of bridge
components due to temperature variations.
Superstructure Types of Bridges
❖ Suspension Bridges

❖ Cable Stayed Bridges

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

❖ Through-Truss Bridges

Main Structure Coincides with the Deck Line

Girder bridges of all types are included in this category. Examples include slab (solid and voided),
T-beam (cast-in-place), I-beam (precast or prestressed), wide-flange beam (composite and noncomposite),
concrete box (cast-in-place and segmental, prestressed), steel box (orthotropic deck), and steel plate girder
(straight and haunched) bridges. Illustrations of concrete slab, T-beam, prestressed girder, and box-girder
bridges are shown in Figure 4.7. A completed cast-in-place concrete slab bridge is shown in Figure 4.8.
Numerous girder bridges are shown in the section on aesthetics.

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

Among these are prestressed girders (Fig. 3.32), concrete box girders (Figs. 3.10, 3.23, and 3.34),
and steel plate girders (Figs. 3.27, 3.35, and 3.36). Girder-type bridges carry loads primarily in shear and
flexural bending. This action is relatively inefficient when compared to axial compression in arches and to
tensile forces in suspension structures. A girder must develop both compressive and tensile forces within
its own depth. A lever arm sufficient to provide the internal resisting moment separates these internal forces.
Because the extreme fibers are the only portion of the cross section fully stressed, it is difficult to obtain an
efficient distribution of material in a girder cross section. Additionally, stability concerns further limit the
stresses and associated economy from a material utilization perspective. But from total economic
perspective slab–girder bridges provide an economical and long-lasting solution for the vast majority of
bridges. The U.S. construction industry is well tuned to provide this type of bridge. [As a result, girder
bridges are typical for short- to medium-span lengths, say <250 ft (75 m).]
In highway bridges, the deck and girders usually act together to resist the applied load. Typical
bridge cross sections for various types of girders are shown in Table 4.1. They include steel, concrete, and
wood bridge girders with either cast-in-place or integral concrete decks. These are not the only
combinations of girders and decks but represent those covered by the approximate methods of analysis in
the AASHTO (2010) LRFD Specifications.

CLOSING REMARKS ON BRIDGE TYPES

For comparison purposes, typical ranges of span lengths for various bridge types are given in Table
4.2. In this book, the discussion is limited to slab and girder bridges suitable for short to medium spans. For
a general discussion on other bridge types, the reader is referred to Xanthakos (1994).

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

SELECTION OF BRIDGE TYPE

One of the key submittals in the design process is the engineer’s report to the bridge owner of the
type, size, and location (TS & L) of the proposed bridge. The TS & L report includes a cost study and a set
of preliminary bridge drawings. The design engineer has the main responsibility for the report, but opinions
and advice will be sought from others within and without the design office. The report is then submitted to
all appropriate agencies, made available for public hearings, and must be approved before starting on the
final design.

FACTORS TO BE CONSIDERED
The discussion herein follows the outline presented by ACI-ASCE Committee 343 (1988) for concrete
bridges, but the factors should be the same, regardless of the construction material.

GEOMETRIC CONDITIONS OF THE SITE

The type of bridge selected often depends on the horizontal and vertical alignment of the highway route
and on the clearances above and below the roadway. For example, if the roadway is on a curve, continuous
box girders and slabs are a good choice because they have a pleasing appearance, can readily be built on a
curve, and have a relatively high torsion resistance. Relatively high bridges with larger spans over navigable
waterways will require a different bridge type than one with medium spans crossing a floodplain. The site
geometry will also dictate how traffic can be handled during construction, which is an important safety
issue and must be considered early in the planning stage.

SUBSURFACE CONDITIONS OF THE SITE

The foundation soils at a site will determine whether abutments and piers can be found on spread footings,
driven piles, or drilled shafts. If the subsurface investigation indicates that creep settlement is going to be a
problem, the bridge type selected must be one that can accommodate differential settlement over time.
Drainage conditions on the surface and below ground must be understood because they influence the
magnitude of earth pressures, movement of embankments, and stability of cuts or fills. All these conditions
influence the choice of substructure components that, in turn, influence the choice of superstructure. For
example, an inclined leg rigid frame bridge requires strong foundation material that can resist both
horizontal and vertical thrust. If this resistance is not present, then another bridge type may be more
appropriate. The potential for seismic activity at a site should also be a part of the subsurface investigation.
If seismicity is high, the substructure details will change, affecting the superstructure loads as well.

FUNCTIONAL REQUIREMENTS
In addition to the geometric alignment that allows a bridge to connect two points on a highway route, the
bridge must also function to carry present and future traffic volumes. Decisions must be made on the
number of lanes of traffic, inclusion of sidewalks and/or bike paths, whether width of the bridge deck should
include medians, drainage of the surface waters, snow removal, and future wearing surface. In the case of
stream and floodplain crossings, the bridge must continue to function during periods of high water and not
impose a severe constriction or obstruction to the flow of water or debris. Satisfaction of these functional
requirements will recommend some bridge types over others. For example, if future widening and
replacement of bridge decks is a concern, multiple girder bridge types are preferred over concrete box
girders.

AESTHETICS
Chapter 3 emphasizes the importance of designing a bridge with a pleasing appearance. It should be the
goal of every bridge designer to obtain a positive aesthetic response to the bridge type selected. Details are
presented earlier.

ECONOMICS AND EASE OF MAINTENANCE

A general rule is that the bridge with the minimum number of spans, fewest deck joints, and widest spacing
of girders will be the most economical. By reducing the number of spans in a bridge layout by one span,
the construction cost of one pier is eliminated. Deck joints are a high maintenance cost item, so minimizing
their number reduces the life-cycle cost of the bridge. When using the empirical design of bridge decks in
the AASHTO (2010) LRFD Specifications, the same reinforcement is used for deck spans up to 13.5 ft
(4100 mm). Therefore, little cost increase is incurred in the deck for wider spacing of girders, and fewer
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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

girders means less cost although at the “expense” of deeper sections. Generally, concrete structures require
less maintenance than steel structures. The cost and hazard of maintenance painting of steel structures
should be considered in type selection studies (Caltrans, 1990).
One effective way to obtain the minimum construction cost is to prepare alternative designs and allow
contractors to propose an alternative design. The use of alternative designs permits the economics of the
construction industry at the time of bidding to determine the most economical material and bridge type. By
permitting the contractor to submit an alternative design, the greatest advantage can be taken of new
construction techniques to obtain less total project cost. The disadvantage of this approach is that a low
initial cost may become the controlling criterion and life-cycle costs may not be effectively considered.

CONSTRUCTION AND ERECTION CONSIDERATIONS

The selection of the type of bridge to be built is often governed by construction and erection considerations.
The length of time required to construct a bridge is important and varies with bridge type. In general, the
larger the prefabricated or precast members, the shorter the construction time is. However, the larger the
members, the more difficult they are to transport and lift into place. Cast-in-place concrete bridges are
generally economical for grade separations unless the falsework supporting the nonhardened concrete
becomes a traffic problem. In that case, precast prestressed girders or welded steel plate girders would be a
better choice. The availability of skilled labor and specified materials also influences the choice of a
particular bridge type. For example, if no precast plants for prestressed girders are located within easy
transport, a steel fabrication plant is located nearby that could make the steel structure more economical.
However, other factors in the construction industry may be at work. The primary way to determine which
bridge type is more economical is to bid alternative designs. Designers are often familiar with bid histories
and local economics and have significant experience regarding the lowest first cost.

DESIGN–BUILD OPTION
In the early years of bridge building in the United States, the design–build option was traditional. An owner
would express an interest in having a bridge built at a particular location and solicit proposals from
engineers for the design and construction of the bridge. On other occasions an engineer may see the need
for a bridge and make presentations to potential owners of the merits of a particular design. Such was the
case in the building of the Brooklyn Bridge (McCullough, 1972). John Roebling convinced influential
people in Manhattan and Brooklyn to charter the New York Bridge Company to promote and finance his
design for a great suspension bridge across the East River. The company hired his son, Washington
Roebling, as chief engineer responsible for executing his father’s design, preparing drawings and
specifications, and supervising the construction. All services for designing and building the bridge were the
responsibility of one entity.
This design–build practice of single-source responsibility faded somewhat at the end of the nineteenth
century. The conventional approach became the design–bid–build model where an owner commissions an
engineer to prepare drawings and specifications and separately selects a construction contractor by
competitive bidding. The objective of the design–bid–build approach is to obtain the quality product
defined by the drawings and specifications at a reasonable price. The approach works well with the checks
and balances between the engineer and contractor when the separate parties work well together. Difficulties
can occur when things go wrong on the job site or in the design office. There can be a lot of “finger pointing”
that the other entity was responsible for the problem. This adversarial situation can increase the financial
risk for all involved.
To alleviate some of the problems of unclear lines of responsibility, there has been a trend in recent years
toward a return to the design–build option. One company is selected by the owner to prepare the engineering
design and to be the construction contractor. This approach almost assures that the design group will possess
the three essential mentalities: creative, analytical, and knowledge of construction techniques. If there is a
question about the quality of the work or are construction delays, only one entity is responsible. One
objection to the design–build option is the absence of checks and balances because the same party that
supplies a product approves it. It is important that the owner has staff people who are knowledgeable and
can make independent judgments about the quality of the work provided. This knowledgeable staff is
present in state DOTs, and more and more states are giving approval of the design–build option for
construction of their bridges.

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

LEGAL CONSIDERATIONS
In Figure 3.1, a model of the design process was presented. One of the components of the model was the
constraint put on the design procedure by regulations. These regulations are usually beyond the control of
the engineer, but they are real and must be considered. Examples of regulations that will determine what
bridge type can be built and where it can be located include: Permits over Navigable Waterways, National
Environmental Policy Act, Department of Transportation Act, National Historic Preservation Act, Clean
Air Act, Noise Control Act, Fish and Wildlife Coordination Act, Endangered Species Act, Water Bank Act,
Wild and Scenic Rivers Act, Prime and Unique Farmlands, and Executive Orders on Floodplain
Management and Protection of Wetlands. Engineers who are not conscious of the effect the design of a
bridge has on the environment will soon become conscious once they begin preparing the environmental
documentation required by these acts. In addition to the environmental laws and acts defining national
policy, local and regional politics are also of concern. Commitments to officials or promises made to
communities often must be honored and may preclude other nonpolitical issues.

Bridge Types Used for Different Span Lengths

Once a preliminary span length has been chosen, comparative studies are conducted to find the bridge type
best suited to the site. For each group of bridge spans (small, medium, and large), experience has shown
that certain bridge types are more appropriate than others. This experience can be found in design aids
prepared by associations, state agencies, and consulting firms. The comments that follow on common
bridge types used for different span lengths are based on the experience of ACI-ASCE Committee 343
(1988), Caltrans (1990), and PennDOT (1993).
Small-Span Bridges [up to 50 ft (15 m)]
The candidate structure types include:
- single or multicell culverts
- slab bridges
- T-beam bridges
- wood beam bridges
- precast concrete box-beam bridges
- precast concrete I-beam bridges
- and composite rolled steel beam bridges.
Culvert
Culverts are used as small-span bridges to allow passage of small streams, livestock, vehicles, and
pedestrians through highway embankments. These buried structures are often the most economical solution
for short spans. They are constructed of steel, aluminum, precast or cast-in-place reinforced concrete, and
thermoplastics. Either trench installations or embankment installations may be used. Minimum soil cover
to avoid direct application of wheel loads is a function of the span length and is not less than 12 in. (300
mm). It is often cited that there are 577,000 bridges over 20 ft (6 m) long in the National Bridge Inventory.
What is seldom mentioned is that 100,000 of them are structural culverts.
Slab
Slab bridges are the simplest and least expensive structures that can be built for small spans up to 40 ft (12
m). These bridges can be built on ground-supported falsework or constructed of precast elements. Their
appearance is neat and simple, especially for low, short spans. Precast slab bridges constructed as simple
spans require reinforcement in the topping slab to develop continuity over transverse joints at the piers,
which is necessary to improve the riding quality of the deck and to avoid maintenance problems.
T-Beam
These bridges usually are constructed on ground-supported falsework and require a good finish on all
surfaces. Formwork may be complex, especially for skewed structures. The appearance of elevation is neat
and simple, but not as desirable from below. The greatest use is for stream crossings, provided there is at
least 6-ft (2- m) clearance above high water (floating debris may damage the girder stem). Usually, the T-
beam superstructure is constructed in two stages: first the stems and then the slabs. To minimize cracks at
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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

the tops of the stems, longitudinal reinforcement should be placed in the stem near the construction joint.
To ease concrete placement and finishing, a longitudinal joint within the structure becomes necessary for
bridges wider than about 60 ft (20 m).
Wood Beam
Wood beam bridges can be used for low volume truck loads. The minimum width of roadway shall be 24
ft (7.2 m) curb to curb. The deck may be concrete, glued/spiked panels, or stressed wood. All wood used
for permanent applications shall be impregnated with wood preservatives. Wood components not subject
to direct pedestrian contact shall be treated with oil-borne preservatives. Main load-carrying members shall
be precut and drilled prior to pressure treatment. For a waterway crossing, abutments and piers shall be
aligned with the stream and piers shall be avoided in the stream if debris may be a problem.
Precast Concrete Box Beam
These bridges are most suitable for locations where the use of falsework is impractical or too expensive.
The construction time is usually shorter than that needed for cast-in-place T-beams. Precast box beams may
not provide a comfortable ride because adjacent boxes often have different camber and dead-load
deflections. Unreinforced grout keys often fail between adjacent units, allowing differential live-load
deflections to occur. A reinforced topping slab or transverse posttensioning can alleviate this problem. The
appearance of the spread-box beam is like a T-beam while the butted-box beam is like a cast-in-place box
girder. For multiple spans, continuity should be developed for live load by casting concrete between the
ends of the simple-span boxes.
Precast Concrete I-Beam
Precast prestressed concrete I-beam bridges can be used for spans from 30 to 150 ft (10 to 50 m) and are
competitive with steel girders. They have many of the same characteristics as precast concrete box-beam
bridges including the problems with different camber and rideability. The girders are designed to carry dead
loads and construction loads as simple-span units. Live-load and superimposed dead-load design should
use continuity and composite action with the cast-in-place deck slab. Appearance is like that of the T-beam:
The elevation view is nice, but the underside looks cluttered. As in all concrete bridges, maintenance is low
except at transverse deck joints, which often may be eliminated.
Rolled Steel Beam
Rolled steel wide-flange beam bridges are widely used because of their simple design and construction.
These bridges are economical for spans up to 100 ft (30 m) when designing the deck as composite and
using cover plates in maximum moment regions. The use of composite beams is strongly recommended
because they make a more efficient structure. Shear connectors, usually in the form of welded studs, are
designed to resist all forces tending to separate concrete and steel surfaces. The appearance of the
multibeam bridge from underneath is similar to that of the T-beam, but the elevation is slenderer.
Medium-Span Bridges
Spans up to 250 ft (75 m). The candidate structure types include precast concrete box-beam bridges, precast
concrete I-beam bridges, composite rolled steel wide-flange beam bridges, composite steel plate girder
bridges, cast-in-place concrete box-girder bridges, and steel box-girder bridges.

COMPOSITE ROLLED STEEL BEAMS

According to Troitsky, 1994 :
- Characteristics of composite steel rolled steel beams were discussed under small bridges.
- Composite construction can result in savings of 20-30 percent for spans over 50ft (15m)
Adding cover plates and providing continuity over several spans can increase their economic range to span
100ft (30m)
- Composite steel plate girders can be built to any desired size and consist of two flange plates
welded to a web to form an asymmetrical I-section. These bridges are suitable for spans from 75
to 150 ft (25 to 50 m) and have been used for spans well over 300 ft (100 m).

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

- Girders must be braced against each other to provide stability against overturning and flange
buckling, to resist transverse forces, and to distribute concentrated vertical loads. Construction
details and formwork are simple. Transportation of prefabricated girders over 115 ft (35 m) may
be a problem.
CAST-IN-PLACE REINFORCED CONCRETE BOX GIRDER
- No prestressed reinforced concrete box-girder bridges are adaptable for use in many locations.
These bridges are used for spans of 50–115 ft (15–35 m) and are often more economical than steel
girders and precast concrete girders.
- Formwork is simpler than for a skewed T- beam, but it is still complicated. Appearance is good
from all directions. Utilities, pipes, and conduits are concealed. High torsional resistance makes it
desirable on curved alignment. They are an excellent choice in metropolitan areas.
- Pre- stressed concrete box-girder bridges afford many advantages in terms of safety, appearance,
maintenance, and economy.
- These bridges have been used for spans up to 600 ft (180 m). Because longer spans can be
constructed economically, the number of piers can be reduced, and shoulder obstacles eliminated
for safer travel at over- passes.
- High torsional resistance makes it desirable on curved alignment. Because of the prestress, the
dead-load deflections are minimized. Long-term shortening of the structure must be
accommodated.
- Maintenance is very low, except that bearing and transverse deck joint details require attention.
Addition of proper transverse and longitudinal post-tensioning greatly reduces cracking.
- Post-tensioned concrete box girders can be used in combination with conventional concrete box
girders to maintain constant structure depth in long structures with varying span lengths. In areas
where deck deterioration due to deicing chemicals is a consideration, deck removal and
replacement is problematic.
COMPOSITE STEEL BOX GIRDER
- Composite steel box-girder bridges, are used for spans of 60–500 ft (20–150 m). These bridges
are more economical in the upper range of spans and where depth may be limited.
- The boxes may be rectangular or trapezoidal and are effective in resisting torsion. They offer
an attractive appearance and can be curved to follow alignment.
- Generally, multiple boxes would be used for spans up to 200 ft (60 m) and a single box for
longer spans.
COMPOSITE STEEL PLATE GIRDER
- Characteristics of composite steel plate girder bridges are presented in medium span bridges.
CAST-IN-PLACE POSTTENSIONED CONCRETE BOX GIRDER
- Characteristics of cast-in-place posttensioned concrete box-girder bridges are presented in
medium-span bridges.
CONCRETE ARCH AND STEEL ARCH
- Concrete arch bridges are usually below the deck, but steel arch bridges can be both above and
below the deck, sometimes in the same structure. T. Arch bridges are pleasing in appearance and
are used largely for that reason even if a cost premium is involved.
STEEL TRUSS
- Steel truss bridges can also be below the deck and sometimes both above and below the deck in
the same structure as seen in the through-truss Sydney Harbour Bridge
- Truss bridges are not addressed in this book, but they have a long history and numerous books,
besides those already mentioned, can be found on truss design and construction. Few trusses are
being designed and constructed now because of economic reasons.

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 JOSE MARIA COLLEGE
Philippine-Japan friendship Highway, Sasa, Davao City
COLLEGE OF ENGINEERING EDUCATION

CLOSING REMARKS
In the selection of a bridge type, there is no unique or “correct” answer. For each span length
range, more than one bridge type will satisfy the design criteria. Regional differences and
preferences because of available materials, skilled workers, and knowledgeable contractors are
significant. For the same set of geometric and subsurface circumstances, the bridge type selected
may be different in Pennsylvania than in California. And both would be a good option for that
place and time.
Because of the difficulties in predicting the cost climate of the construction industry at the time of
bidding, a policy to allow the contractor the option of proposing an alternative design is prudent.
This design should be made whether the owner has required the designer to prepare alternative
designs. This policy improves the odds that the bridge type being built is the most economical.
In Section 3.2 on the design process, de Miranda (1991)
was quoted as saying that for successful bridge design three “mentalities” must be present: (1)
creative and aesthetic, (2) analytical, and (3) technical and practical. Oftentimes a designer
possesses the first two mentalities and can select a bridge type that has a pleasing appearance and
whose cross section has been well proportioned. But a designer may not be familiar with good,
economical construction procedures and the third mentality is missing. By allowing the contractor
to propose an alternative design, the third mentality may be restored, and the original design(s) are
further validated, or a better design may be proposed. Either way, incorporating the three
mentalities enhances the design process.

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