U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Sr. Structural Engineer
Resource Center – Structures TST
ABC-PBES offers significant advantages over Cast-in-place construction. ABC-PBES results into:
The foremost barrier perceived identified was the lack of education, training and experience, followed by lack of standard details and specifications, then lack of connection details and their durability. It is generally perceived that prefabrication will tend to higher costs in compare to usual cast-in-place construction methods. And finally, construction industry not equipped to handle large loads to transport and erect prefabricated bridge elements.
Needs related to those barriers were competitive costs and additional funding, appropriate projects that require speed, and fabrication and construction equipment and methods for use in prefabricated construction.
These responses provided the basis for the development of the decision-making framework for the effective use of prefabricated bridges.
The framework addresses the need for education and training on prefabricated bridges. It also includes discussions related to the other identified barriers and needs.
The framework was developed for use by the representatives of the owner agency and the contractor. The anticipated users include the decision makers for the bridge type as well as those developing and implementing the details, including designers and project managers.
The framework consists of an introduction, a one-page flowchart, a one-page "Yes-Maybe-No" matrix, and a more in-depth section that is in a question-and-discussion format with references.
In general, we know that prefabricated bridge systems have good quality because of the offsite or near-site fabrication that is off the critical path and in a more controlled environment. We know that it is faster than onsite because more of the work is done prior to final installation. Because it is faster onsite, we know that it is safer for both the traveling public and the construction crews. We also know that prefabricated bridge systems can have lower initial costs due to the significantly reduced traffic control, risks, environmental impacts, and user delay costs due to the reduced number of days of onsite exposure.
So we know that prefabricated bridges are in general better, faster, and safer. But, is a prefabricated bridge the best solution for the specific project under consideration? The framework was developed to help you answer that question.
The one-page flowchart allows decision-making at a glance, for example, for a high-level decision-maker who wants a high-level tool for a quick decision without getting into the technical details of a project.
Note the color-coded categories. The blue diamonds are related to rapid construction issues (factors). The tan diamond is related to other issues that may drive a project. The green rectangle and diamond are related to cost issues. These three categories are consistent throughout the framework.
Let’s take a look at the rapid onsite construction issues. As you can see, these relate to such factors as whether the bridge will experience high traffic volumes, or is an emergency project, or would cause a significant negative impact to commerce, or is on the critical path of the construction project. Such considerations drive the need for rapid onsite construction, which makes prefabrication the preferred solution.
If rapid onsite construction isn’t required, do other factors such as worker safety, environmental issues, or the efficiency of similar sections make prefabrication the preferred solution?
If rapid construction isn’t needed, and other factors don’t make prefabrication the preferred solution, what about initial construction costs? Is prefabrication anticipated to be less expensive because of the high daily expenses for traffic control through the work zone? Or are user delay costs a concern? Is liability or risk to the agency or contractor reduced with prefabrication due to the significantly reduced number of days of exposure? If so, then prefabrication is most likely the best choice.
So that’s how to use the flowchart to quickly decide whether prefabrication is the best solution for the specific project under consideration. You just follow the arrows depending on whether your answer is "Yes" or "No," and you will end at either "Use Conventional Construction" or "Use Prefabrication."
|High traffic volume?|
|Worker safety concerns?|
|High daily traffic control costs?|
The one-page "Yes-Maybe-No" matrix may be used in conjunction with the flowchart or as an alternative to the flowchart. It includes the same color-coded categories as the flowchart, with additional factors in each of the categories. You simply go down the questions and respond with a "Yes," a "Maybe," or a "No."
One or two factors may warrant the use of prefabrication. For example, the fact that the bridge is on an evacuation route may make prefabrication the preferred choice independent of other considerations.
Alternatively, you may want to assign weights to the factors to come up with the decision of whether or not to use prefabrication.
In any case, a majority of "Yes" responses indicates that a prefabricated bridge offers advantages for the specific location under consideration.
The third section is in a question-and discussion format that is broken into the same three categories of considerations as shown by color-coding on the flowchart and the matrix, i.e., rapid onsite construction, other factors, and costs. This section consists of the same questions as in the flowchart and the matrix, plus additional ones.
Let’s go over the categories in more detail.
The "Rapid Onsite Construction7quot; category includes questions related to...
The first category of questions and discussion is "Rapid Onsite Construction." This category is followed by the second category of "Other Factors," which is broken into subcategories of "Safety Concerns," Environmental Issues," "Standardization," and "Site Issues."
The "Other Factors" category includes questions related to safety concerns and environmental issues. Questions related to environmental issues include...
Environmentally sensitive area? (e.g. wetlands, air quality, and noise)
Natural or endangered species? (e.g. fish passage, or peregrine falcon nesting)
Also included in the "Other Factors" category are questions related to standardization. Questions related to standardization include...
The last group of questions in the "Other Factors" category relate to site issues. Questions related to site issues include...
The third and final category is "Costs," which is broken into the subcategories "Maintenance of Traffic," "Contractor’s Operations," "Owner Agency’s Operations," and "Service Life."
The framework ends with a brief conclusion paragraph and a listing of available online resources.
The final category is "Costs." This category includes questions related to maintenance of traffic and contractor’s operations. Questions related to maintenance of traffic include...
Questions related to the contractor’s operations include...
Also included in the "Costs" category are questions related to the owner agency’s operations, including...
The last subcategory under "Costs" is service life, which includes references to available life-cycle cost evaluation models.
See the Utah Case Study Example in the Student Handbook.
A performance goal is for States to include the decision-making framework into their project development process to evaluate ABC-PBES as early in the process as possible, similar to what the State of Utah has done.
Available online resources are listed at the end of the framework for use in obtaining additional information, including completed prefabricated bridge projects with contact information, publications, research, and a calendar of upcoming events.
The framework is available at this website, which is continually being populated with additional information. We encourage you to visit it often to stay current with the latest developments related to prefabricated bridges.
Select the items that are ABC Viable Concepts.
Select the obstacles to installing PBES in hours or days.
Select the major components of the PBES decision making framework.
Select the items that are onsite construction factors.
If rapid onsite construction is not required for a project, select the other factors that may make prefabrication the preferred solution.
Use PBES Decision-Making Framework to help accelerate bridge construction and help change America’s driving experience and meet the customers’ needs.
Claude Napier, Senior Structural Engineer
Resource Center, Structures TST