U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Brian Raff – National Steel Bridge Alliance
Contact: 312.670.5415 ¦ firstname.lastname@example.org
Dan Snyder – American Iron and Steel institute
Dan Snyder – American Iron and Steel institute
Contact: 301-367-6179 ¦ email@example.com
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
Many job sites impose difficult constraints on the constructability of bridge designsâ€” 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.
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.
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.
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
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
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.
Precast Decks on Steel Framing
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.
Precast Concrete Panel Systems
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.
Precast Decks on Steel Framing
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.
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
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.
MassDOT I-93 FAST 14 Project
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.
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.
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.
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
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.
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.
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.
The deck spans in two directions making it extremely stiff and able to carry the loads between girders.
Approach span to self-
unit of the Oakland
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.
Steel box beam with Orthotropic Deck
Extreme example of a steel box beam with an orthotropic deck.
This is certainly considered a prefabricated bridge element.
Carquinez Bridge b/w
Crockett & Vallejo, CA
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.
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.
I-80 State Street to 1300 East – Bridge Farm
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.
An example to show size and context.
Providence River Bridge Arch
Video Link: http://www.youtube.com/watch?v=vROwFWDNe1c
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.
Acrow Panel Bridges
Arroyo Malo Bridge – 2006
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.
You should now have a good understanding of: