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Prefabricated Bridge Elements and Systems


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Slide 1. Modular Steel Bridge Concepts

Brian Raff – National Steel Bridge Alliance
Contact: 312.670.5415 ¦ raff@steelbridges.org

Dan Snyder – American Iron and Steel institute

Dan Snyder – American Iron and Steel institute
Contact: 301-367-6179 ¦ dsnyder@steel.org


Slide 2. Learning Objectives

  • Advantages of PBES
  • Family of ABC used in the US
  • Steel Bridge Substructures
    • Driven steel piles
    • Tubular steel bridge piers
    • Steel bent caps
  • Steel Bridge Super Structures
    • Precast deck on steel framing
    • Pre-decked girders
    • Inverset
    • Folded Plate Bridge System
    • Orthotropic Deck
  • Total Steel Superstructures

Slide 3. Advantages of PBES

  • Fast(er)
  • Minimizes traffic impacts
  • Improve construction work safety zones
  • Construction less disruptive on Environment
  • Improves constructability (Quality)
  • Increased quality leads to lower life cycle costs

Speaker Notes:

Using PBES can facilitate meeting several key needs:

Minimizes Traffic Impacts of Bridge Construction Projects

Using prefabricated bridge elements and systems means that time-consuming formwork, concrete curing, and other tasks associated with fabrication can be done offsite in a controlled environment without affecting traffic.

Improves Construction Zone Safety

Bringing prefabricated superstructures and substructures to the site ready for installation reduces disturbance to the land surface at the site, and it reduces the amount of time required onsite for heavy equipment. Keeping equipment out of sensitive environments is less disruptive for those environments

Improves Constructability

Many job sites impose difficult constraints on the constructability of bridge designs— heavy traffic on an Interstate highway that runs under the bridge being constructed, difficult elevations, long stretches over water, or restricted work areas due to adjacent properties, to name a few. Using prefabricated bridge elements and systems relieves such constructability pressures.

Increases Quality and Lower Life Cycle Costs

Prefabricating bridge elements and systems takes them out of the critical path of the project schedule: work can be done ahead of time, using as much time as necessary, in a controlled environment. This reduces dependence on weather and increases quality control of the resulting bridge elements and systems. All projects that use prefabricated bridge elements and systems increase the quality of their components; most also lower life cycle costs.


Slide 4. Family of ABC used in the US

Flow chart depicting the family of ABC elements used in the US.

Speaker Notes:

While there are many means that methods that contribute to ABC, we will mostly focus on Prefabricated elements such as deck panels and sub and superstructure assemblies. Look for the use of Self Propelled Modular Transporters in upcoming slides.


Slide 5. Steel Bridge Substructures

  • Driven Steel Piles
    • Can consist of H, box, and tubular sections
    • High load-carrying capacity
    • Extremely durable and resistant to lateral forces

Photos of Driven Steel Piles.

Speaker Notes:

Preformed steel piles can consist of H-sections, box sections, but also tubular sections, which usually are not filled with concrete after driving.

Driven steel piles have high load-carrying capacity for a given weight of pile, which can reduce driving costs.

Steel pilescan have a high carrying capacity, when driven to a hard stratum can withstand even hard driving without risk of damage can readily be cut down and re shaped for further driving cause relatively small soil displacement can be readily extended/spliced without much delay by welding or splicing, thus long piles can be installed without the need of a very long leader can be readily cut if not driven to full penetration, and the cut-off portions can be reused or have value as scrap material can be roughly handled without risk of damage can have good resistance to lateral forces and buckling can be easily combined with water jetting and grouting.


Slide 6. Steel Bridge Substructures

Diagram of Tubular Steel Bridge Piers.
  • Tubular Steel Bridge Piers
    • Successfully used under severe loading conditions:
      • Deep water, hurricane, seismic, and ice loading
    • Less steel tonnage compared to concrete reinforced piers
    • Combined with precast elements, tubular steel bridge piers can save motorists almost 90% of the typical user delay costs

Speaker Notes:

Proven technology:

Developed for Offshore Structures Industry: To meet the construction demands for deep water fixed offshore platforms, modular tubular steel braced frames proved successful. The full depth space frames are fabricated on shore, transported to the offshore site, launched from the construction barge, positioned on the seafloor, and piles are driven to fix the structure to the seabed.

Modular Tubular Steel Technology has been applied worldwide over 70 years on more than 5,000 fixed offshore platforms.

It has been successfully used in

  • Deep Water Platforms: North Sea
  • Hurricane Loads: Gulf Coast
  • Seismic Conditions: California Coast
  • Ice Loads: Arctic Locations

Tubular Steel Bridge foundations significantly reduce the overall bridge construction schedule. Combined with precast elements, it can save motorists almost 90% of the typical user delay costs.

Source: Introduction to Tubular Steel Piers by Will Reeves


Slide 7. Steel Bridge Substructures

Photo of prefabricated steel bent caps.
  • Prefabricated Steel Bent Caps
    • Reduce the amount of worker exposure time
    • Reduce construction time
      • No waiting for CIP curing and formwork installation and removal

Speaker Notes:

Substructure: Bent Caps:

Cast-in-place bent caps require sequential construction processes, including extensive formwork erection and removal, as well as concrete curing time. If they are fabricated offsite, these sequential processes are not a factor. As a result, bridge owners and contractors are turning to prefabricated bent caps:

For over-water bridges, they reduce the amount of time that workers need to operate over water.

For bridges over existing roadways, they reduce the disruption to traffic on the lower roadway.

For bridges with job-site constraints, such as power lines that affect work zone safety, they limit the amount of time that workers are at risk.


Slide 8. Steel Bridge Super Structures

Precast Decks on Steel Framing

Diagram of Precast Decks on Steel Framing.

Speaker Notes:

Superstructure: Decks

Prefabrication offers exceptional advantages for deck construction, particularly for removing deck placement from the critical path of bridge construction schedules, for cost to place the deck, and for quality of the deck.


Slide 9. Steel Bridge Super Structures, (Cont’d.)

Precast Concrete Panel Systems

Diagram of Precast Concrete Panel Systems.

Speaker Notes:

Full depth precast concrete panel system shown provides for the driving surface.

Longitudinal openings provide access for tensioning cables. As more and more panels are added, cables are tensioned to pull panels together. Once the tensioning strands reach the appropriate tensile stress, the openings are filled, engaging the shear studs, and locking the panels into place. Because the panels are pulled together, there is no need for grout within the transverse joints between panels.

For wider applications, a longitudinal closure pour is required.


Slide 10. Steel Bridge Super Structures, (Cont’d.)

Precast Decks on Steel Framing

Photo of Steel Bridge Super Structures, (Cont’d)

Speaker Notes:

Deck options: Steel Grid Decks, FRP Decks, Partial Depth Deck Forms (which remain in place)

Full-depth prefabricated bridge decks (shown here) facilitate and speed construction, and bridge designers are finding innovative ways to connect full-depth panels to ensure durable connection details.

Partial deck forms (not shown) remain in place indefinitely and provide a good working platform. Partial deck example is the Tapan Zee bridge in New York.


Slide 11. Pre-decked Systems

Picture of a Decked Girder. Top: Traditional girder. Bottom: Sub-deck or partial deck top flange.
  • Decked girders
    • Traditional girder
    • Sub-deck or partial deck top flange
    • Analogous to a bulb tee

Speaker Notes:

Instead of just laying girders and then a cast in place deck... Lay modules down and connect in place for faster construction. Modules can even come with barriers already in place


Slide 12. Pre-decked Systems, (Cont’d.)

  • I-95 over the James River (Virginia)
    • 11 I-95 bridges replaced between I-64 E+W replaced with Precomposite Units (PCUs)
    • 102 supserstructure spans replaced with no lane closures during peak traffic
I-95 over the James River (Virginia). 11 I-95 bridges replaced between I-64 E+W replaced with Precomposite Units (PCUs). I-95 over the James River (Virginia). 102 supserstructure spans replaced with no lane closures during peak traffic.

Speaker Notes:

Minimal impact on motorists was a project goal for replacement of the superstructure of the I-95/James River Bridge, which carries approximately 110,000 vehicles per day through the city of Richmond. After considering alternatives, the Virginia Department of Transportation opted for night-only construction, most of which occurred between 7 PM and 6 AM Sunday through Thursday nights. During nighttime construction, one lane of traffic was kept open in each direction. For most spans, bridge preconstructed composite units (PCU’s), which include an 8-¾-inch deck over steel plate girders, were precast at a nearby casting yard and then transported to the work site. Work crews cut out the old bridge span and removed it, prepared the gap for the new PCU, and set the new PCU in place.

Used preconstructed composite units consisting of precast 8-¾-inch deck over steel plate girders. Minimized traffic disruption by facilitating replacement of the bridge superstructure without ever closing the highway to rush hour traffic.


Slide 13. Pre-decked Systems, (Cont’d.)

MassDOT I-93 FAST 14 Project

  • 14 bridges replaced in 12 weekends in Medford, MA
  • Minimized project impact on travelers
  • Reduced construction time
Satellite images of the MassDOT roadways
Illustration of the MassDot I-93 FAST 14 Project

Speaker Notes:

By building the bridges in sections, at locations away from the roadways, MassDOT greatly reduced the duration of on-site construction. By erecting the bridges over weekends, MassDOT did not impact weekday rush-hour traffic. To lessen the impact on local communities, MassDOT timed the work so that only one local street was impacted each weekend. MassDOT worked with emergency responders to ensure that emergency services operated without interruption throughout the project. The project team also distributed the work schedule widely to advise visitors, residents and commuters on how to avoid delays and reach their destinations and businesses during construction.


Slide 14. Pre-decked Systems, (Cont’d.)

  • MassDOT I-93 FAST 14 Update

Photo: MassDOT I-93 FAST 14 Update.

Speaker Notes:

Inverset – system built upside down – only one company in the country can do it – grouted shear key – variable girder spacing.
Great system for low volume roads.
Simple precast deck on simple girders (unlike Inverset where slab is cast inverted) – details are essentially the same as traditional bridge construction.
Simple cast in place construction.
Emulating a traditional cast in place deck with precast.
High early-strength concrete.


Slide 15. Pre-decked Systems, (Cont’d.)

  • MassDOT I-93 FAST 14 Project

Photo: MassDOT I-93 FAST 14 Project.

Speaker Notes:

You’ll notice that the section shown in this slide looks very similar to what is called the "Inverset" system which we’ll look at on the next slide.

Threaded dowls are part of the Link-Slab technology concept in which structural beam spans are not continuous while the deck elements ARE continuous over the length of the bridge.

The key is that these elements are jointless.

MassDOT finished the last bridge this last weekend with a total of 10 55-hour closures (each bridge was completed in less than 48 hours!)

Learning/Cost curve that McMinimee talks about:

1st weekend – 200 workers on site (tons of labor) because it was risky – they had not constructed a bridge in this manner before. Cost a lot of money.

By week 4 – number of workers onsite went down to 30 as they became comfortable with the technique.

With lower labor costs and higher efficiencies, the marginal cost of each bridge installed went down dramatically.

This is a great, real, example on how ABC using PBES can be successful.

What’s important to take away from this slide is that just doing one bridge using ABC will make a positive difference, but states will get the most bang for their buck if they can work a multitude of ABC bridges into their portfolio.


Slide 16. Steel Bridge Superstructures

  • Steel beams and a concrete slab that act as a composite unit
  • Enhanced resistance to cracking
  • Pre-fabrication allows for minimal lane closure time even in the coldest winter months
  • Any width spanning 20’ to over 100’ and can be skewed or contain vertical curves.

Photo of Steel Bridge Superstructures.

Speaker Notes:

The Inverset system is a precast, pre-compressed concrete/steel composite superstructure made up of steel beams and a concrete slab that acts as a composite unit to resist its own dead load. The deck is cast upside down in forms suspended from steel girders, allowing the combined weight of the forms and the concrete to produce a prestressing effect on the girders. Also, when the units are turned over the concrete deck is then pre-compressed. The resulting compression in the concrete deck offers enhanced resistance to cracking. The fabrication of the units in a controlled environment allows for replacement of bridge sections even in the coldest winter months with minimal lane closure time. The systems can be fabricated in any width with a span ranging from 20’ to over 100’. When shipping on highways, the width of the units is generally limited to 8 feet. They can also be skewed or contain vertical curves as the site dictates.

It should be noted that this bridge type was first introduced and patented under the brand name "Inverset" a play on Inverse – set (i.e. casting the deck upside down). Since then this patent has expired and the system is no longer proprietary.

Source: http://www.fhwa.dot.gov/bridge/prefab/psbsreport03.cfm Image 1+2: Delta Engineers Prefabricated Bridges PDF


Slide 17. Steel Bridge Superstructures

  • Folded Plate Bridge System
    • Deck is placed with conventional equipment prior to site delivery
    • Stable configuration which eliminates all cross frames
    • Top flange can be used as a work platform reducing construction hazards
    • Open bottom making inspection extremely easy
Typical cross section for the Folded Plate Bridge System. Dimensions vary based on span length. Photo of a Folded Plate Bridge System.

Speaker Notes:

Great solution for short span bridges.

Length is limited by plant equipment capabilities (i.e. press break).

Mass Highway will be putting one into place this year.


Slide 18. Pre-decked Systems

Photo of a Decked girder with steel deck.
  • Decked girders with steel deck
    • Traditional girder, orthotropic deck
    • Analogous to a bulb tee
    • Lighter than tee with concrete flange
    • Improved durability

Slide 19. Steel Bridge Superstructures

Diagram of an orthotropic deck bridge.
  • What is an "orthotropic deck bridge?"
    • Deck plate with stiffening ribs to provide load distribution in 2 directions
    • All steel superstructure
    • Potential to provide very long service life

Speaker Notes:

In essence, the steel deck acts as the top flange for the steel girder supporting the section. Because concrete is cast on the deck, composite action is acquired through the finished assembly.

Orthotropic deck bridges make sense for large spans due to their light weight.


Slide 20. Steel Bridge Superstructures, (Cont’d.)

Photo of a Orthotropic Deck Girder Bridge Overview.
  • Orthotropic Deck Girder Bridge Overview
    • Improve safety performance of structures and long-term safety improvement
    • Reduce congestion during construction
    • Accelerating construction
    • Improving quality

Speaker Notes

Improve safety performance of structures and long–term safety improvement.
Light superstructure can be used to facilitate preassembly and rapid construction.
Closed girder sections can provide superior service life with less surface area subjected to weather.
Boxed girders or decked I-girders eliminates torsional failure modes during erection.
Conventional cross frames eliminated minimizing elevated assembly work.
Erected girders provide a safe working platform, essentially eliminating one source of construction worker fatalities.


Slide 21. Steel Bridge Superstructures, (Cont’d.)

  • Orthotropic Deck Girders
    • Deck serves as top flange of girder
    • Bolted splices in FBs and long. field weld for deck
    • Wearing surface can be shop applied
    • Nothing new here...it’s all been done before!

Pictures of Orthotropic Deck Girders.

Speaker Notes

The deck spans in two directions making it extremely stiff and able to carry the loads between girders.


Slide 22. Steel Bridge Superstructures, cont’d.

  • Orthotropic Deck Girder Advantages:
    • Rapid construction and durable
    • Very easy and safe erection
      • No LTB
      • Good working platform
    • Shallow superstructure
    • Wide girder spacing possible
      • No redecking to consider
  • "Off the shelf" design based on span

Slide 23. Steel Bridge Superstructures, (Cont’d.)

Approach span to self-anchored suspension unit of the Oakland Bay Bridge.

Approach span to self-
anchored suspension
unit of the Oakland
Bay Bridge

  • Potential advantages of orthotropic construction:
    • light weight
    • prefabricated/modular
    • redundancy
    • integration with bridge framing
    • few deck joints
    • durability
    • rapid construction
    • life-cycle economy

Speaker Notes:

This image shows one particular approach span to the self-anchored suspension unit of the Oakland Bay Bridge, the remainder of the bridge is concrete.


Slide 24. Steel Bridge Superstructures, cont’d.

Steel box beam with Orthotropic Deck

Photo of Steel box beam with Orthotropic Deck.

Speaker Notes:

Extreme example of a steel box beam with an orthotropic deck.

This is certainly considered a prefabricated bridge element.


Slide 25. Steel Bridge Superstructures, cont’d.

Carquinez Bridge b/w Crockett & Vallejo, CA.

Carquinez Bridge b/w
Crockett & Vallejo, CA

  • 1000s of successful applications worldwide
  • Successful U.S. projects
    • San Mateo Hayward (1967)
    • Fremont (1973)
    • Golden Gate (1985)
    • Carquinez (2005)
    • New Tacoma Narrows (2007)

Speaker Notes:

This image is of the Carquinez Bridge between Crockett and Vallejo, CA.

In San Francisco, 24 bridge segments (like the one shown here) weighing over 800 tons are installed using a heavy lift ship and strand jacks.


Slide 26. Steel Bridge Superstructures

  • Orthotropic Deck Bridge Conclusion
    • Orthotropic deck bridges have the potential to become the preferred solution for more U.S. bridges, where rapid construction or life cycle economy is required.
    • Volume will promote standardization, improving quality while reducing cost.
    • Designers must work towards providing more freedom for fabricator to develop acceptable welding techniques.

Speaker Notes:

There are a lot of slides on orthotropic decks, but it should not be taken that they are the most important or best solution. Fabricators and researchers are working tirelessly to make orthotropic deck fabrication more cost effective, modular, and more efficient for smaller projects. Economies of scale could be achieved if the proper standards are developed.


Slide 27. Total Steel Superstructures

  • Decks cast and bridges assembled off site
  • Transported and lifted into place
  • Improved constructability, reduced construction and equipment time.

I-80 State Street to 1300 East – Bridge Farm.
I-80 State Street to 1300 East – Bridge Farm

Speaker Notes:

I-80 State Street to 1300 East – Bridge Farm (UDOT)

Superstructure: Total Superstructure Systems

Increasingly, innovative bridge designers and builders are finding ways to prefabricate entire superstructures. Pre-constructed composite units may include steel or concrete girders prefabricated with a composite deck, cast off the project site and then transported and lifted into place in one operation. Truss spans also can be prefabricated. Prefabrication this scale offers tremendous potential advantages in terms of improved constructability, reduced onsite construction time, and reduced time that equipment is on the construction site.


Slide 28. Total Steel Superstructures, (Cont’d.)

An example photo of Total Steel Superstructures to show size and context.

Speaker Notes:

An example to show size and context.


Slide 29. Total Steel Superstructures, cont’d.

Photo example of Providence River Bridge Arch
Providence River Bridge Arch
Video Link: http://www.youtube.com/watch?v=vROwFWDNe1c

Speaker Notes:

Example: Providence River Bridge Arch

The bridge was assemble on the ground where girders were at worker eye level which made it very efficient. SPMTs move a fully pre-assembled network tied arch bridge onto (2) 300-foot barges.

Floated structure weighing 2500 tons 12 miles (3 hours) up Narragansett Bay Barges used the tide to slowly lower the bridge onto its piers.

Link to video: http://www.youtube.com/watch?v=vROwFWDNe1c&feature=player_embedded


Slide 30. Total Steel Superstructures, cont’d.

Acrow Panel Bridges

Example photo of Arroyo Malo – 2006. Acrow Panel Bridges.
Arroyo Malo Bridge – 2006

Speaker Notes:

Example: Arroyo Malo – 2006

Large orthotropic deck units are designed to handle heavy wheel loads such as those created by the American loadings of HS20, HS25 or HL93. Wheel loads from the bridge design standards of other countries can be accommodated also.

The plate deck surface readily accepts surface overlays, such as asphalt or epoxy aggregates.

They are easily transported using standard trucks or standard dry ocean containers and they are quickly and easily erected.

Acrow Bridges can be rolled in full cantilever (launched) from one side of a river gorge or they can be lifted into place.


Slide 31. Future of Prefabrication in US

  • ABC is gaining momentum
  • More bridges being built every year
  • Prefabricated composite decks continue to be the most common form of prefabrication
  • There is a need for research for pier connections in "High" Seismic Zones
  • Utah Department of Transportation Goal
    • Make accelerated bridge construction with prefabrication standard practice by 2010

Slide 32. Learning Outcome

You should now have a good understanding of:

  • Advantages of PBES
  • Family of ABC used in the US
  • Steel Bridge Substructures
    • Driven steel piles
    • Tubular steel bridge piers
    • Steel bent caps
  • Steel Bridge Super Structures
    • Precast deck on steel framing
    • Pre-decked girders
    • Inverset
    • Folded Plate Bridge System
    • Orthotropic Deck
  • Total Steel Superstructures

Slide 33. Questions

Brian Raff – National Steel Bridge Alliance
Contact: 312.670.5415 ¦ raff@steelbridges.org

Dan Snyder – American Iron and Steel institute
Contact: 301-367-6179 ¦ dsnyder@steel.org



Page last modified on August 15, 2013.
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