U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Benjamin Beerman, P.E.
FHWA Resource Center
Structures Technical Service Team
Going Greener Shortening Project Delivery
Accelerating Deployment Technology and Innovation
As many of you all know, there has been an increased and focused awareness on the benefits of using PBES by State and Local Transportation agencies throughout the U.S. as a result of the Every Day Counts program that was launched by our FHWA executive leadership in November of 2009.
To meet the objectives of the EDC program, there are 15 initiatives, of which 10 are focused on shortening project deliveryand 5 are focused on technologies that improve safety, reduce congestion, and keep America moving and competitive in the world market.
The EDC program is about taking effective, proven, and market-ready technologies that are ready for Agency implementation and putting them into widespread use.
So how does the EDC program impact the use of PBES, or from a more broader perspective, Accelerated Bridge Projects?
Over half of the EDC initiatives which fall under the "Shortening Project Delivery" category are planning strategies that are often used in conjunction with PBES to Accelerate onsite bridge constructionâ€“ either for a single, group, or entire program of bridge projects.
And because every one of the 15 initiatives from the EDC program has defined deployment goal that your leadership is committed to – the methods in which you and your Agency are procuring bridge construction projects in the future may be changing.
Why is their a need to Accelerate on-site construction???
As you already know, we are challenged by:
In the transportation infrastructure renewal program, impacts from increasing work zones is almost certain.
A study in 2003 reported the total number of highway work zones in the summer was estimated to be more than 6,400 – which corresponded to over 6,000 lane miles closed.
That amounts to 20% of the capacity reduction on our national highway network!
The American Truckers Association reports that by 2016 our highways will carry 1 million more trucks. This is caused by trucker’s hours-of-service regulations — which prevents haulers from operating their rigs for more than 11 hours/day and for more than 70 hours per eight-day period.
As quoted by B.J. Gorman, president of Tango Transport Inc. of Shreveport, LA. (ref. AASHTO Journal, September 15, 2006), One reason for trucks’ popularity is that they become de facto warehouses as the result of our modern inventory-control systems. This is a service other forms of transport can’t supply."
and ATA’s Chief economist Bob Castello reported that there are 2.7 million big rigs on U.S. Highways as of 2006.
One business at a time, and one commuter at a time – congestion robs our nation of productivity and quality of life.
Based on TTI 2007 Urban Mobility Report (437 urban communities) congestion translates to:
|CBC (v): does not seek out methods to significantly reduce onsite construction times.|
Before we discuss the definition of PBES, lets first discuss how ABC differs from conventional bridge construction (CBC).
We define Conventional Bridge Construction as construction methods that do not significantly seek out methods to reduce the onsite construction time that is needed to build, replace, or rehabilitate a single, or group of bridge projects.
Conventional construction methods require time consuming onsite activities which are typically weather dependent, impact the flow of traffic which may present driver distractions that can reduce the safety of the traveling public and the safety of contractor personnel.
An example of conventional construction includes onsite installation of substructure and superstructure forms, followed by reinforcing steel placement, concrete placement, and concrete curing, all typically occurring in a liner manner, oftentimes along side – or adjacent to ongoing traffic.
ABC (v): The use of innovative planning, design, materials, and construction methods to reduce onsite construction and mobility impact times
Alternatively – we define Accelerated Bridge Construction as bridge construction which use innovative planning, design, materials, and construction methods in a manner to specifically reduce the onsite construction time and mobility impacts that occur when building new bridges or replacing and rehabilitating existing bridges.
Onsite construction time: The period of time from when a contractor alters the project site location until all construction-related activity is removed. This includes, but is not limited to, the removal of Maintenance of Traffic, materials, equipment, and personnel.
Mobility impact time: Any period of time the traffic flow of the transportation network is reduced due to onsite construction activities.
To gauge the effectiveness of ABC, two time metrics is included in the definition of ABC:
The first is...
Onsite construction time: Which is The period of time from when a contractor alters the project site location until all construction-related activity is removed. This includes, but is not limited to, the removal of Maintenance of Traffic, materials, equipment, and personnel.
The second time metric is the...
Mobility impact time: This is Any period of time the traffic flow of the transportation network is reduced due to onsite construction activities. There are 5 mobility impact time categories as shown below...
A common reason to use ABC is to reduce the traffic impacts because the flow of the transportation network can be directly impacted by the disruptions caused by onsite construction related activities.
PBES are structural components of a bridge that are built offsite, or adjacent to the alignment, and includes features that reduce the onsite construction time and mobility impact time that occurs from conventional construction methods.
Use of prefabricated bridge elements and systems (PBES) is one strategy that can meet the objectives of accelerated bridge construction.
PBES are structural components of a bridge that are built offsite, or adjacent to the alignment – and includes features that reduce the onsite construction time and mobility impact time that occurs if conventional construction methods were used.
By building the structural elements, or the entire bridge offline, the onsite construction period can be condensed and the mobility impacts to the transportation network can be reduced – like in hours or in a weekend!
However, there are other common and equally viable reasons to use PBES which deal with site constructability issues. Oftentimes remote site locations, limited construction seasons, material availability, and consistent quality in workmanship present opportunities where the use of PBES can provide more practical and economical solutions over conventional construction methods.
Regardless of the reason(s) to choose PBES, On-site construction time and Mobility impact time are typically reduced in some manner relative to conventional construction methods.
Is there a difference between a prefabricated element and a prefabricated system??
Due to the influx of information received from our EDC quarterly surveys, we are finding that it would be useful to build upon the definitions that we have used in the past so that we can relate key words and terms to common technologies.
In addition, the ability to track what types of elements and systems are being used (and which was aren’t) would be useful so that we can easily identify trends and have the ability to get information such as plans, specifications, bid-tabs, and schedules for projects that have are been built using PBES.
Internally, the FHWA is developing a tracking tool to provide such information, so that Transportation Agencies can easily share and exchange information from one another.
Elements: single structural component of a bridge
Given the need to categorize our information better, we are defining single structural components of a bridge that are prefabricated in a manner and eliminates or reduces the onsite construction time that is needed to build a similar structural component using conventional construction methods as a Prefabricated Element.
Elements are typically built in a repeatable manner to offset costs thru the economies of scale. Because the elements are built under controlled environmental conditions, the influence of weather related impacts can be eliminated and improvements in product quality and long-term durability can be better achieved.
There are 5 categories of Prefabricated Bridge Elements which we will define in more detail and provide key words and examples, starting with the deck elements.
Prefabricated deck elements eliminate activities that are associated with conventional deck construction – which typically includes onsite installation of deck forms, overhang bracket and formwork installation, reinforcing steel placement, bid-well set up, concrete placement, and concrete curing.
Key words and examples of Prefabricated Deck Elements include:
Deck Beam Elements
Prefabricated beam elements are classified into two "sub" categories: "deck" beam elements" and "full-width" beam elements.
Deck beam elements eliminate conventional onsite deck forming activities, but do so in a different manner than the "deck" elements previously discussed. To reduce onsite deck forming operations, "deck" beam elements are typically placed in an abutting manner.
Key words and Examples of Deck Beam Elements include:
The second sub category is "Full-width" beam elements which eliminate conventional onsite beam placement activities and substructure construction by reducing the number of spans and pier units. Once placed, they make up the full-width cross section of the bridge and are typically rolled, slid, or lifted into place.
Examples of Full-Width Beam Elements include:
Given their size and weight, the entire deck is sometimes not included.
Moving down into the substructure, we have Prefabricated pier elements which eliminate activities that are associated with conventional CIP pier construction.
Examples of Pier Elements include:
We also have versions of Prefabricated abutments and wall elements.
Precast approach slab
In our last category, we have a "miscellaneous" prefabricated element group that consists of secondary structural components that are often used in conjunction with the major structural components previously discussed.
Examples of Miscellaneous Elements include:
Because of the ongoing evolvement of innovations, we also include "deck closure" methods and "overlay systems" in this category.
We discussed the various versions of prefabricated elements, so how do they differ from prefabricated systems?
Prefabricated Systems are defined as a category of PBES that consists of an entire superstructure, an entire superstructure and substructure, or a total bridge that is procured in a modular manner such that traffic operations can be allowed to resume after placement.
Prefabricated systems are typically rolled, launched, slid, lifted, or otherwise transported into place, and have the deck – and preferably the parapets in place.
Due to the manner in which they are installed, prefabricated systems often require innovations in planning, engineering design, high-performance materials, and unique Structural Placement Methods.
The benefits of using prefabricated systems include: Minimal utility relocation and right-of-way take (if any at all)
FDOT Graves Ave. over I-4 Bridge Replacement – 2006
143-ft long, 59-ft wide 1,300-ton replacement
spans built in adjacent staging area
Half-hour rolling roadblocks
on I-4 to remove
71-ft long, 30-ft wide, 250-ton spans
So what do successful projects that use PBES look like?
We can start with the Graves Avenue project which is an example of a Prefabricated superstructure "system".
A 143’ long, 59-ft wide structure was built in an adjacent staging area on Self Propelled Modular Transporters (or SPMTs).
Once complete, the existing spans over I-4 were removed using SPMTS (different set) using ½ hour rolling roadblocks.
FDOT Graves Ave. over I-4 Bridge Replacement – 2006 (Cont.)
Each new span installed in a few hours overnight
Once the existing bridge was removed, the new structures were transported and installed during night time operations in just a few hours.
George P. Coleman Bridge, VA – 1995
Another example of a Prefabricated Superstructure "system" is the Coleman Bridge, in which the entire deck and superstructure was constructed on barges and "floated" in place.
Note that it has the parapet already in place, as well as the overhead lights and signs!
Wells Street Bridge, Chicago – 2002
Shown here in the congested area of downtown Chicago, a 111-ft long, 425-ton truss span owned by the Chicago Transit Authority was fabricated near site and installed over a weekend timeframe.
This was done to avoid the loss in revenue impacts from transit riders using alternative modes of transportation while the bridge was out of service.
Virginia DOT I-95 Bridge over James River, 2002
|102 superstructure spans replaced in 137 nights...|
|...with no lane closures during rush-hour traffic|
In these photos here, prefabricated versions of "beam deck" elements were used to replace 102 superstructure spans in 137 nights with no lane closures during rush hour traffic.
Maryland SHA MD Rt. 24 Bridge over Deer Creek, 2001
10 week bridge closure before school started
122.5-ft long, 33-ft wide historic
Full Width prefabricated FRP "deck" elements were used to accelerate the onsite construction time needed to rehabilitate this thru truss located Maryland.
Baldorioty Castro Ave. – San Juan, Puerto Rico 1992
And in Puerto Rico, two bridges – 700 ft and 900 ft long, were installed in just 21 to 36 hours each using totally prefabricated bridge elements!
April 2004 International Prefabricated Bridge Scan
Europe has been installing bridges in hours for years, even multi-span bridges as shown here.
In this case, the bridge was placed in two hours, and the entire length of closure of the highway was limited to one weekend.
SPMTs Install Complete Multiple-Span Railroad Bridge
2,200 tons moved using SPMTs
To date, a "total" bridge system has not been moved in the United States. However, in Normandy, this multiple-span railroad bridge was built adjacent to the existing railroad tracks on the concrete slab where the truck is sitting.
The existing railroad tracks were closed for a short duration (usually several days) and the existing embankment was removed to accommodate the wider bridge opening.
Once ready, the prefabricated bridge (including the entire superstructure and substructure) was picked up and moved into place using SPMTs. The railroad tracks were connected and trains began using the new bridge soon afterwards.
The concrete struts used for lifting the bridge were latter removed in their entirety.
ABC / PBES reduces:
ABC/PBES can minimize:
ABC offers benefits to the traveling public.
However, ABC by itself can simply be a matter of providing more onsite labor, equipment, and contracting mechanisms (like I/D clauses) to meet the need to "get in/get out/stay out".
But when we use PBES to accelerate bridge construction – we not only meet the objectives of ABC, we do so in a more efficient manner and realize additional benefits as well. By replacing conventional on-site construction activities with prefabricated elements and systems, the benefits of ABC expand and compound.
For example, the safety of the traveling public in addition to the safety of the contractor’s personnel improves. Improvements in product quality and long term durability can be better achieved, the opportunity for weather related time delays become less, and the on-site project disruptions which can directly influence the existing roadway alignment, environmental impacts, ROW, and Utility disruptions can be minimized even further.
Using prefabricated bridge elements and systems means that time consuming onsite construction activities such as formwork construction, re-bar and concrete placement, concrete curing, formwork removal and other related tasks including the planning, coordination, and scheduling efforts for the on-site labor, material, and equipment can be done off-site and off the critical path.
US 59 under Dunlavy, TX I-59 and I-65 Interchange, AL
Prefabricated bridges minimize traffic impacts by reducing the amount of on-site construction time.
This reduces lane closures, detours, and traffic delays which results in improved safety for the traveling public.
Robin Hood Bridge, WV
Here is a project example where the use of PBES greatly reduced the permitting, utility, right-of-way, and maintenance of traffic involvement that is commonly associated with most transportation improvement projects during the Environmental process. In this particular site location, if a temporary alignment was placed to the right of the structure to maintain traffic, ROW impacts and the removal of a hillside would be needed. If placed to the left, Utility Relocations would be required, and a longer temporary bridge and longer temporary road alignment would have been an equally extensive activity to construct.
As an Owner, these impacts not only add costs to the project, but they also require time consuming resources to coordinate with the land owners, outside permitting agencies, and private utility companies – that oftentimes have conflicting priorities and agendas.
To circumvent the site constraints, public feedback was sought out during a "public meeting" to see if closing the bridge in it’s entirety – but for a limited timeframe, was an option. During the limited closure period, the public agreed to use an alternate detour, and coordination for emergency services and bus routes for the residences on either side of the structure was made.
To meet the time constraints established by the public, the substructure was built around the existing structure using drilled shafts while traffic operations resumed. Once the shafts were complete, the bridge was shut down entirely and the remaining structure was replaced in an accelerated manner using prefabricated bridge elements to minimize the closure period (prefabricated saddle cap is just a p/s box beam).
From the Owners perspective, the project was procured in a quicker manner, the site disruptions were less, the roadway alignment was preserved, and the total cost and resource allocation to the Agency was really no different (possibly less) than if a conventional procurement methods using a temporary alignment were used.
Because on-site construction times are reduced when PBES are used, work zone safety can be greatly improved upon. Construction workers spend less time near high traffic volumes, power lines, and over elevated work areas. The durations of exposure to extreme weather conditions which influence worker fatigue also becomes less. As shown in this slide, the bridge was totally prefabricated over land then rotated into place. The workers did not have to work over the water, and there were no impacts to navigational clearances during construction.
Other challenges could have been realized when we look at how this bridge could have been constructed:
For example, using prefabricated sections lifted from barges as a method of construction would require permitting and a biological impact assessment by multiple approving agencies – which is a time and resource consuming activity.
As an alternative method of construction, form travelers could be used; however, encroaching into the vertical clearance envelope of the navigational channel from above and assuring concrete delivery over the water way would be two issues that would have to be dealt with. Raising the vertical profile could be an option to address this issue, but to do so unnecessarily would introduce additional material costs to the project for the additional approach work and taller towers (or lower profile cable stays).
When we discuss the need to improve On-site Constructability, we speak of the project sites that impose constraints to the constructability of bridges. Examples include heavy traffic on an interstate highways, difficult elevations, long stretches over water, restricted work areas due to adjacent facilities such as utilities and buildings, and detour routes that aren’t feasible nor practical.
Areas that experience high traffic volumes, either with or without congestion in terms of ROW and utility impacts are common in urban and major metropolitan areas.
However, rural areas also experience their share of difficult site conditions.
For example, as shown in this picture we can see that the need to deliver material, equipment, and labor could be a challenge due to the site being in a remote location. (Dealing with remote site locations is actually a very common site issue throughout the U.S.)
In some parts of the country the Construction Season can be limited. Alaska for example, has only a 2-3 month construction season due to the long winters.
Another site that introduces 2 common constructability constraints is shown here.Â There is no feasible detour route to use if the existing bridge is taken out of service. In this case, the road wraps around a mountainside and there is there is only one way in and one way out.Â A temporary bridge would also be costly given that the existing bridge spans over a gore area with over a 150 foot vertical drop.
Construction using prefabricated bridge elements could be used to help address the site constraints in any of these examples.
Prefabricating the structural components of a bridge takes them off the critical path of the project schedule:
work can be done ahead of time, using as much time as necessary, and it can be done so in controlled environmental conditions.
This reduces the dependence on weather, and can improve the control of quality of the resulting elements and systems.
Here, we see the form work that is used set 30 feet in the air to conventionally construct this pier cap.
Whereas in this picture, we see a substructure pier cap being constructed off the critical path, where consistency in material and concrete curing is easily achieved.
As a result of the improved quality that can be expected from using prefabrication, we should also expect to see the additional benefits of lower life-cycle costs.
PBES becomes the standard method of bridge construction, and the use conventional construction methods – such as on-site CIP operations, are used in a limited manner.
Because the use of PBES offers so many benefits and it’s use is so versatile for many site situations, the FHWA’s goal is to shift the paradigm of our industry so that the use of PBES becomes the standard method of construction and the use of conventional construction methods, such as on-site CIP operations are used in a limited manner.
So let’s discuss the performance measures for PBES under the EDC initiative to see where we were and where we are headed.
Prior to the EDC program, a state survey on PBES implementation was conducted in 2003 thru NCHRP report 324.
The response at that time indicated that 40 states used PBES in 1 or more projects, while 3 have used PBES in 20 or more projects.
Also, during that timeframe, 11 states were actively pursuing the use of PBES as their standard practice.
This national map shows a breakdown of the implementation of PBES at that time. These are projects that have been designed or built using PBES in increments of 5, over the past several years prior to the implementation of the EDC deployment goals.
These projects don’t count!!!
This is a map showing how many Agencies that reported a commitment to using PBES as part of their EDC deployment goals.
44 out of 55 Agencies
Data validation may be further required.
These are the results of the 1st Quarterly EDC survey showing the number of PBES projects that are either designed or have been built using PBES.
The survey results represents the time period between October 2010 to about March/April 2011.
This graph shows what the Agencies are selecting. For example, 25 Agencies reported that they are using versions of prefabricated beams, 12 are using partial depth deck panels, and 16 are using full depth deck panels.
These are the deployment goals for PBES under the EDC initiative
More than 20 bridges have been designed and/or constructed using PBES in the past 3 years and a decision making framework that considers the use of PBES is incorporated in the design process.
To be fully implemented as an Agency, more than 20 bridges have been designed and/or constructed using PBES in the past 3 years and a decision making framework that considers the use of PBES is incorporated in the design process.
This concludes Training Module 1
To summarize, we discussed the...
Why are we championing the use of PBES technologies? It offers significant advantages.
The traveling public deserves a new driving experience with reduced user costs due to reduced work zones and congestion