Advatages of Prestress Concrete

Advantages of Advantages of PrestressedPrestressedConcrete BridgesConcrete Bridges

FORWARD

Owners and designers Owners and designers

have long recognized have long recognized

the low initial cost, low the low initial cost, low

maintenance needs and maintenance needs and

long life expectancy of long life expectancy of

prestressed concrete prestressed concrete

bridges. This is bridges. This is

reflected in the reflected in the

increasing market share increasing market share

of prestressed concrete, of prestressed concrete,

which has grown from which has grown from

zero in 1950 to more zero in 1950 to more

than 55 percent today.than 55 percent today.

ADVANTAGES OF PRESTRESSED BRIDGES -- CASE STUDIES

Bridges BuiltBridges Built

Source: National Bridge Inventory Data

0

10

20

30

40

50

60

50 55 60 65 70 75 80 85 90 95 00

Year Built

% Built

S/S

R/C

P/C

T

FORWARDBACK

This growth This growth

continues very continues very

rapidly, not only for rapidly, not only for

bridges in the short bridges in the short

span range, but also span range, but also

for spans in excess for spans in excess

of 150 feet which, of 150 feet which,

heretofore, has been heretofore, has been

nearly the exclusive nearly the exclusive

domain of structural domain of structural

steel.steel.


FORWARDBACK

The following The following

examples illustrate examples illustrate

some of these key some of these key

advantages of advantages of

precast, prestressed precast, prestressed

concrete bridges: concrete bridges:

Cost EfficienciesCost Efficiencies

Structural/EngineeringStructural/Engineering

Design AestheticsDesign Aesthetics

PCI Certified QualityPCI Certified Quality


FORWARDBACK

Many bridge Many bridge

designers are designers are

surprised to learn surprised to learn

that precast, that precast,


bridges are usually bridges are usually

lower in first cost lower in first cost

than all other types than all other types

of bridges. of bridges.

Coupled with savings Coupled with savings

in maintenance, in maintenance,

precast bridges offer precast bridges offer

maximum economy.maximum economy.



FORWARDBACK




Fast and Easy ConstructionFast and Easy Construction

An old bridge located on An old bridge located on a main logging road in a main logging road in Idaho was replaced with Idaho was replaced with a prestressed concrete a prestressed concrete bridge. The bridge bridge. The bridge consists of integral deck consists of integral deck beams on precast beams on precast concrete abutments and concrete abutments and wing walls. The heavy wing walls. The heavy spring runoff dictated spring runoff dictated the need for a shallow the need for a shallow superstructure, and the superstructure, and the load capacity of the load capacity of the bridge had to be bridge had to be sufficient to carry off-sufficient to carry off-highway logging trucks highway logging trucks that weigh as much as that weigh as much as 110 tons each.110 tons each.

Cost Efficiencies andSpeed of ConstructionCost Efficiencies andSpeed of Construction


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The precast prestressed The precast prestressed

bridge system offered bridge system offered

two principal two principal

advantages: advantages:

it was it was economicaleconomical and it and it

provided provided minimum minimum

downtimedowntime for for

construction. Project construction. Project

duration was duration was

three weeks.three weeks.



FORWARDBACK

The state of Minnesota The state of Minnesota

saved more than 16% - saved more than 16% -

a half a million dollars – a half a million dollars –

by planning for a by planning for a

prestressed alternate to prestressed alternate to

a steel bridge. a steel bridge.

The 700-foot-long The 700-foot-long

bridge is jointless up to bridge is jointless up to

the abutments and is the abutments and is

the longest continuous the longest continuous

bridge in the state. It bridge in the state. It

also contains the also contains the

longest single concrete longest single concrete

span.span.



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A Minnesota A Minnesota

transportation official transportation official

stated, “Originally, we stated, “Originally, we

didn’t think concrete didn’t think concrete

was suited to this… was suited to this…

bridge. However, the bridge. However, the

fabricator showed us fabricator showed us

it was a viable it was a viable

alternative. alternative.

Everything went Everything went

smoothly… we’re well smoothly… we’re well

satisfied…” satisfied…”



FORWARDBACK

Precast, prestressed Precast, prestressed

concrete bridge concrete bridge

components are components are easy easy

to erectto erect, particularly , particularly

when the tops of the when the tops of the

units comprise the units comprise the

entireentire

deck slab to form an deck slab to form an

“integral deck” or “integral deck” or

“full-deck” beam. “full-deck” beam.

Easy to ErectEasy to Erect



FORWARDBACK

In a full-deck bridge, the In a full-deck bridge, the

formwork of the super formwork of the super

structure is eliminated. structure is eliminated.

Connections between Connections between

adjacent units often adjacent units often

consist of welding consist of welding

matching plates and matching plates and

grouting continuous grouting continuous

keyways. Carefully keyways. Carefully

planned details speed planned details speed

the construction process the construction process

and result in overall and result in overall

economy. economy.



FORWARDBACK

Substandard bridges Substandard bridges

are easily replaced are easily replaced

with precast with precast

prestressed sections. prestressed sections.

In some cases, In some cases,

existing abutments existing abutments

can be used… can be used…



FORWARDBACK

……but it may be easier but it may be easier and more economical and more economical to build new ones, or to build new ones, or to utilize precast to utilize precast abutments and wing abutments and wing walls supported on walls supported on cast-in-place footings. cast-in-place footings. Because precast Because precast concrete integral deck concrete integral deck bridges with precast bridges with precast abutments can be abutments can be erected without delay erected without delay in cold weather, they in cold weather, they can be opened to can be opened to traffic sooner. traffic sooner.



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Bridge departments Bridge departments

are challenged to are challenged to

maintain traffic flow, maintain traffic flow,

minimize traffic minimize traffic

interruptions, and interruptions, and

reduce or eliminate reduce or eliminate

detours during detours during

construction projects.construction projects.

This Florida bridge, This Florida bridge,

damaged in a tanker damaged in a tanker

fire, was completely fire, was completely

rebuilt and opened to rebuilt and opened to

traffic in 18 days.traffic in 18 days.


Fast ConstructionFast Construction


FORWARDBACK

The The fast constructionfast construction

of precast concrete of precast concrete

integral deck bridges is a integral deck bridges is a

key advantage. Precast key advantage. Precast

concrete bridges can be concrete bridges can be

installed during all installed during all

seasonsseasons and opened to and opened to

traffic more rapidly than traffic more rapidly than

any other permanent any other permanent

type of bridge, because type of bridge, because

of the availability of of the availability of

plant-produced sections plant-produced sections

and the speed of and the speed of

erecting and finishing erecting and finishing

construction. construction.


Fast ConstructionFast ConstructionAll SeasonsAll Seasons


FORWARDBACK

Replacing this bridge onReplacing this bridge on

US Route 95 in Idaho US Route 95 in Idaho

illustrates another illustrates another

example of the example of the

advantages of very fast advantages of very fast

construction:construction:

New Year’s Day: Rains New Year’s Day: Rains

and melting snow and melting snow

washed out this bridge washed out this bridge

over the Little Salmon over the Little Salmon

River linking the River linking the

northern and southern northern and southern

parts of the state.parts of the state.


FastFastConstructionConstruction


FORWARDBACK

January 4: The Idaho January 4: The Idaho Department of Department of Transportation contacted Transportation contacted the precaster to investigate the precaster to investigate solutions. They determined solutions. They determined that the fastest way to that the fastest way to replace the three spans was replace the three spans was to use a singleto use a single80-foot span comprised of 80-foot span comprised of bulb-tees with an integral bulb-tees with an integral deck. The top flange would deck. The top flange would be 8-inches thick and be 8-inches thick and 8'-6" wide. The end 8'-6" wide. The end diaphragms would also be diaphragms would also be precast onto the girder precast onto the girder ends.ends.

January 8: Engineers in the January 8: Engineers in the Bridge Section approved Bridge Section approved shop drawings and shop drawings and tensioning calculations.tensioning calculations.




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January 18: Bulb-tees January 18: Bulb-tees were shipped 240 miles were shipped 240 miles and set in place…just 17 and set in place…just 17 days after the flood! days after the flood! Included in the shipment Included in the shipment was intermediate steel was intermediate steel diaphragms, guard rail diaphragms, guard rail posts and guard rail…all posts and guard rail…all the components to the components to complete the structure.complete the structure.

January 25: The project January 25: The project was completed. The was completed. The bridge was in service bridge was in service just 24 days after the just 24 days after the flood!flood!




FORWARDBACK

As a result of a Winter As a result of a Winter flood, this single lane flood, this single lane bridge on a major forest bridge on a major forest road was washed out, road was washed out, cutting access to a U.S. cutting access to a U.S. highway for a half dozen highway for a half dozen residents…including one residents…including one with a senior needing with a senior needing continuing medical care.continuing medical care.

Within only 15 of receiving Within only 15 of receiving plans, the precaster had plans, the precaster had fabricated the 135-foot-fabricated the 135-foot-long spans with 7’-6”-wide long spans with 7’-6”-wide integral decks, and the integral decks, and the bridge was opened to traffic bridge was opened to traffic 3 days later – 18 days in all.3 days later – 18 days in all.


Simple SolutionSimple Solution


FORWARDBACK

In Ketchikan, Alaska a bridge In Ketchikan, Alaska a bridge on the only highway to the on the only highway to the north was washed out when north was washed out when an old dam gave way on an old dam gave way on October 26. Integral deck October 26. Integral deck girders were selected for the girders were selected for the 85-ft span. The 12 girders 85-ft span. The 12 girders were designed and precast in were designed and precast in the state of Washington, then the state of Washington, then shipped by rail and barge to shipped by rail and barge to Alaska. The girders were Alaska. The girders were installed and the bridge was installed and the bridge was completed and opened to completed and opened to traffic on December 19 - only traffic on December 19 - only 54 days after the washout - 54 days after the washout - despite the problems of despite the problems of design, remote location, design, remote location, great distances, and adverse great distances, and adverse weather conditions during weather conditions during the onset of an Alaskan the onset of an Alaskan winter!winter!


AdverseAdverseWeatherWeatherConditionsConditions


FORWARDBACK

To accurately compare To accurately compare

costs, consider a costs, consider a

bridge’s life-cycle: bridge’s life-cycle:

The initial cost of the The initial cost of the

structure must be structure must be

added to the total added to the total

operating cost.operating cost.

For stationary bridges, For stationary bridges,

the operating cost is the operating cost is

the maintenance cost.the maintenance cost.


Life Cycle Cost =

Initial Structure +

Total Operating Costs(Maintenance)

Life Cycle Cost =

Initial Structure +

Total Operating Costs(Maintenance)


FORWARDBACK

The durability of precast The durability of precast


bridges designed and built bridges designed and built

in accordance with in accordance with

AASHTO or AREMA AASHTO or AREMA

specifications means there specifications means there

should be little, if any should be little, if any

need for maintenance. need for maintenance.

One of the reasons One of the reasons

designers select integral designers select integral

deck prestressed concrete deck prestressed concrete

is the durability of the is the durability of the

precast, prestressed precast, prestressed

concrete and the resulting concrete and the resulting

low maintenance low maintenance

requirements.requirements.


DurableDurable


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Fatigue problems are Fatigue problems are

nonexistent because nonexistent because

only minor net only minor net

stresses are induced stresses are induced

by traffic loads. by traffic loads.


DurableDurable


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And of course, no painting And of course, no painting

is needed. Some bridge is needed. Some bridge

engineers estimate the engineers estimate the

life-cycle cost of re-life-cycle cost of re-

painting steel bridges to painting steel bridges to

be 15 to 25% of the initial be 15 to 25% of the initial

cost. Painting bridges is cost. Painting bridges is

environmentally environmentally

unfriendly and can be unfriendly and can be

especially dangerous or especially dangerous or

expensive when done expensive when done

over busy highways, over busy highways,

streams, railroad rights-streams, railroad rights-

of-way or in rugged of-way or in rugged

terrain.terrain.


Painting Steel BridgePainting Steel Bridge


FORWARDBACK

On the Illinois Toll Highway, On the Illinois Toll Highway, the superstructures of 224 the superstructures of 224 bridges are precast bridges are precast prestressed concrete prestressed concrete beams. These bridges, beams. These bridges, built during 1957 and 1958, built during 1957 and 1958, have withstood heavy have withstood heavy traffic and severe traffic and severe weathering and yet require weathering and yet require very little maintenance. very little maintenance. Other projects in all parts of Other projects in all parts of North America have North America have exhibited similar exhibited similar experience ‑ little or no experience ‑ little or no maintenance has been maintenance has been required on precast required on precast prestressed concrete prestressed concrete bridges.bridges.


Minimal MaintenanceMinimal Maintenance


FORWARDBACK

In addition to its cost In addition to its cost

efficiencies and efficiencies and

speed of speed of

construction, precast construction, precast

concrete provides concrete provides

important structural important structural

and and engineering engineering

advantagesadvantages as as

well. well.




FORWARDBACK



A common requirement A common requirement

of many bridges is that of many bridges is that

the superstructure be as the superstructure be as

shallow as possible in shallow as possible in

order to provide order to provide

maximum clearance with maximum clearance with

minimum approach minimum approach

grades.grades.

Through the technique of Through the technique of

prestressing, the prestressing, the

designer can utilize the designer can utilize the

maximum possible span-maximum possible span-

to-depth ratio. This to-depth ratio. This

superstructure occupies superstructure occupies

just 13 inches just 13 inches

of profile.of profile.

Structural/EngineeringAdvantagesStructural/EngineeringAdvantages

Shallow SuperstructureShallow Superstructure


FORWARDBACK

Span-to-depth ratios as Span-to-depth ratios as

high as 30:1 can be high as 30:1 can be

achieved with solid slabs, achieved with solid slabs,

voided slabs, box beams, voided slabs, box beams,

multi-stemmed units, or multi-stemmed units, or

bulb-tee sections. Even bulb-tee sections. Even

though deeper sections will though deeper sections will

require less prestressing require less prestressing

steel, the overall economy steel, the overall economy

of a project may dictate the of a project may dictate the

highest possible span-to-highest possible span-to-

depth ratio.depth ratio.

These HPC girders are These HPC girders are

4'-6" deep and span 157 ft. 4'-6" deep and span 157 ft.

A span/depth ratio of A span/depth ratio of

nearly 35!nearly 35!

Shallow SuperstructureShallow Superstructure



FORWARDBACK

Precast prestressed Precast prestressed concrete integral deck concrete integral deck girders were selected to girders were selected to provide a shallow provide a shallow superstructure for a superstructure for a bridge over a busy bridge over a busy urban highway in urban highway in Denver. Even though Denver. Even though the bridge must carry the bridge must carry frequent heavy truck frequent heavy truck traffic, the total depth traffic, the total depth of the girders is only 3 of the girders is only 3 feet, including the 3-feet, including the 3-inch wearing surface, inch wearing surface, for a span of 80 feet.for a span of 80 feet.

Adaptable to Many SituationsAdaptable to Many Situations



FORWARDBACK

This bridge illustrates This bridge illustrates

the high span-to-depth the high span-to-depth

ratios possible with ratios possible with

integral deck integral deck

prestressed concrete.prestressed concrete.


High Span-to-Depth RatioHigh Span-to-Depth Ratio


FORWARDBACK

Bridges are subjected to Bridges are subjected to an assortment of hostile an assortment of hostile environments as well as environments as well as repeated impact loadings. repeated impact loadings. Some must endure Some must endure intense sun, extreme intense sun, extreme temperatures and temperatures and brackish waters. Others brackish waters. Others must withstand not only must withstand not only the freezing and thawing the freezing and thawing provided by nature but provided by nature but also the potential for also the potential for damage through the use damage through the use of de-icer chemicals. of de-icer chemicals. Dense, high strength Dense, high strength prestressed concrete has prestressed concrete has excellent freeze-thaw and excellent freeze-thaw and chemical resistance. chemical resistance.



FORWARDBACK

Greater Greater fire fire

resistanceresistance is another is another

advantage. This timber advantage. This timber

bridge experienced a bridge experienced a

dramatic fire… dramatic fire…

Fire ResistanceFire Resistance



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……it was replaced by a it was replaced by a

low maintenance low maintenance


bridge erected without bridge erected without

falsework over an falsework over an

environmentally-environmentally-

sensitive area…sensitive area…



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Prestressed concrete Prestressed concrete bridges have bridges have excellent excellent riding characteristicsriding characteristics that minimize traffic that minimize traffic vibrations. The public will vibrations. The public will not only not only bebe safe but also safe but also feelfeel secure and secure and comfortable on a comfortable on a prestressed concrete prestressed concrete bridge. Traffic vibrations bridge. Traffic vibrations are held to an absolute are held to an absolute minimum. The owner will minimum. The owner will have a structure on which have a structure on which the deck is less likely to the deck is less likely to crack prematurely. crack prematurely. Continuous spans even Continuous spans even hold deck joints to a hold deck joints to a smooth minimum.smooth minimum.

Excellent Riding CharacteristicsExcellent Riding Characteristics



FORWARDBACK

Steel girder bridges frequently Steel girder bridges frequently exhibit noticeable vibrations. exhibit noticeable vibrations. The natural frequency of The natural frequency of vibration of these bridges often vibration of these bridges often coincides with the frequencies coincides with the frequencies of traffic and then resonance of traffic and then resonance occurs. Because of their mass occurs. Because of their mass and stiffness, the natural and stiffness, the natural frequency of vibration of frequency of vibration of prestressed girder bridges prestressed girder bridges rarely coincides with the rarely coincides with the vehicle frequencies. vehicle frequencies. Documented cases show that Documented cases show that light bulbs in fixtures installed light bulbs in fixtures installed on steel bridges burn out more on steel bridges burn out more rapidly as a result of such rapidly as a result of such vibrations. Reports are vibrations. Reports are surfacing that indicate decks surfacing that indicate decks on steel bridges are more on steel bridges are more prone to cracking and prone to cracking and deterioration. deterioration.


Excellent Riding CharacteristicsExcellent Riding Characteristics


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The clean, attractive The clean, attractive

lines of concrete lines of concrete

beams also help beams also help

bridge designers bridge designers

meet the meet the

most demanding most demanding

aesthetic aesthetic

requirements. requirements.




FORWARDBACK



Prestressed concrete Prestressed concrete

bridges can be bridges can be

attractive from above, attractive from above,

below, and from the below, and from the

side because of the side because of the

simple and clean simple and clean

shapes of the members shapes of the members

used. The high span-to-used. The high span-to-

depth ratios made depth ratios made

possible through the possible through the

use of prestressing, use of prestressing,

result in strong, tough, result in strong, tough,

durable and yet durable and yet

graceful bridges. graceful bridges.



FORWARDBACK

Prestressed concrete Prestressed concrete

is efficient because it is efficient because it

is a composite of is a composite of

high-strength steel high-strength steel

and high-performance and high-performance

concrete. To ensure concrete. To ensure

this efficiency and to this efficiency and to

comply with exacting comply with exacting

project specifications, project specifications,

precasting plants precasting plants

have developed have developed

sophisticated quality sophisticated quality

assurance programs. assurance programs.




FORWARDBACK



Precast, prestressed Precast, prestressed

concrete products are concrete products are

inspectedinspected both during both during

and following and following

production. production.

In fact, every operation In fact, every operation

in the manufacturing in the manufacturing

process provides a process provides a

point of inspection and point of inspection and

control. control.



FORWARDBACK

Today’s bridge designs Today’s bridge designs

use more high-use more high-

performance materials performance materials

and sophisticated and sophisticated

solutions than ever solutions than ever

before. More and more, before. More and more,

engineers are requiring engineers are requiring

only qualified sources only qualified sources

with certified with certified

technicians and technicians and

inspectors. inspectors.



FORWARDBACK

A plant that is PCI-certified A plant that is PCI-certified tells the engineer five tells the engineer five important things:important things:


Independent Auditors;Unannounced Audits

Audits Based onNational Standards

1.1. The production facility has The production facility has demonstrated its demonstrated its capability to produce capability to produce quality products to the quality products to the satisfaction of a nationally satisfaction of a nationally recognized, independent recognized, independent consulting engineering consulting engineering and inspection firm and inspection firm engaged by PCI for engaged by PCI for multiple, unannounced multiple, unannounced annual audits.annual audits.

2.2. The rigid audits the plant The rigid audits the plant undergoes are based on undergoes are based on published industry published industry standards – the standards – the PCI PCI Manual for Quality Manual for Quality Control for Plants and Control for Plants and Production of Precast Production of Precast Structural Concrete.Structural Concrete.


FORWARDBACK

Five important things cont.:Five important things cont.:

3.3. The plant practices a The plant practices a documented and PCI-documented and PCI-approved quality approved quality assurance program open assurance program open for review.for review.

4.4. The plant has PCI-certified The plant has PCI-certified QC personnel.QC personnel.

5.5. The producer has PCI The producer has PCI confirmed capabilitiesconfirmed capabilities. .


Independent Auditors;Unannounced Audits

Audits Based onNational Standards

Documented Quality System

Certified Personnel

Confirmed Capabilities


FORWARDBACK

To maintain PCI Certification, To maintain PCI Certification, producers are audited and producers are audited and graded semi-annually on more graded semi-annually on more than 150 items that include than 150 items that include an inspection of all raw an inspection of all raw materials; concrete mixing, materials; concrete mixing, placing, finishing and curing; placing, finishing and curing; tensioning and de-tensioning tensioning and de-tensioning of strands; temperature of strands; temperature controls; stripping, stockpiling controls; stripping, stockpiling and inspection of product. In and inspection of product. In addition, engineering, shop addition, engineering, shop drawings, record keeping, drawings, record keeping, purchasing, personnel purchasing, personnel training, and many other training, and many other practices related to quality practices related to quality production are examined. production are examined. Failure to maintain acceptable Failure to maintain acceptable standards makes loss of standards makes loss of certification mandatory. certification mandatory.



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Advatages of Prestress Concrete