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Long-Term Bridge Performance (LTBP) Program Protocols

To ensure that LTBP Program data are collected in a consistent manner over the duration of the program, the Federal Highway Administration (FHWA) is developing data collection protocols for use by practitioners, LTBP Program researchers, and decision makers involved with the research, design, construction, inspection, maintenance, and management of bridges. The LTBP Program protocols are for research purposes and intended primarily for use within the LTBP Program.

The LTBP Program protocols are organized into a hierarchy based on the following chronology of a data collection effort for a single bridge: Previsit (PRE), Field Visit (FLD), and Postvisit (PST). This simple chronology was selected to make finding the required protocols intuitive for users. The first three levels of the proposed hierarchy are shown in figure 1.

This flow chart details the data collection efforts for a single bridge. The flow chart is comprised of four levels, each level in a different color. The top level (shown in gray) of the flow chart is the LTBP Protocols. The second level (shown in pink) of the flow chart shows the three stages of data collection:  the Previsit, Field Visit, and Postvisit. The third level of the flow chart (shown in green) starts to give details of the activities that are required to complete the Previsit, Field Visit, and Postvisit reporting. Under the Previsit heading are the following activities:  sampling and selection of the bridge, reviewing existing documentation, reviewing the necessary equipment, and reviewing the required planning and logistics. Listed under the Field Visit heading, are the onsite pretest activities, field data collection, and data storage. The Postvisit heading activities are the data reduction and processing, data interpretation, and archiving and reporting of the data. The fourth level (shown in lavender) of the flow chart shows more detailed activities that are required to complete the data collection and analysis.
Figure 1. Illustration. LTBP Program Protocol Hierarchy.

The Previsit (PRE) protocols focus on preparation and actions that occur prior to collecting data at the bridge. This group includes the following activities:

  • Sampling and Selection (SS): The process involved with bridge selection.
  • Existing Documentation (ED): The obtaining of existing bridge documentation from bridge owners and detailing legacy data mining for specific performance issues.
  • Equipment (EQ): Equipment related to structural testing, including sensors and data acquisition systems along with specific protocols related to each type of truck testing.
  • Planning and Logistics (PL): Preparation for a field data collection effort, from personnel safety to the processes for maintenance and protection of traffic and site-specific requirements.

The Field Visit (FLD) protocols focus on collecting research-quality data in a consistent manner to facilitate comparative analysis across structures and with time. This group contains the following activities:

  • Onsite Pretest Activities (OP): Segmentation, identification, and labeling of the various elements of a bridge so recorded findings of the field assessment and testing activities may be tied to specific elements and locations on the bridge.
  • Field Data Collection (DC): Data collection at the bridge, including photography, material sampling, NDE, visual inspection, instrumentation logistics, and various types of testing. (NOTE: this makes up the main portion of the protocols.)
  • Data Storage (DS): Proper storage of raw data immediately after collection to ensure no repeat field efforts are required and that no data are lost.

Postvisit (PST) protocols focus on actions taken after the data are collected at the bridge and how the collected data are used to draw conclusions and include the following activities:

  • Data Reduction and Processing (DR): Data interpretation methods and steps to evaluate and interpret the data and metadata.
  • Archiving and Reporting (AR): Consistency in reporting results as well as formatting data and metadata for inclusion in the LTBP Bridge Portal.

Released in January 2016, Report FHWA-HRT-16-007Long-Term Bridge Performance (LTBP) Program Protocols, Version 1, presents the first 51 protocols (selected PRE and FLD protocols) that will be used throughout the LTBP Program for data collection, mining of bridge legacy data, visual inspection, sampling and testing of concrete materials, and NDE of bridges, as well as data management and storage. Future versions of the protocols will be published and include additional protocols that will be implemented in the LTBP Program studies as well as any modifications deemed necessary to the protocols already published.

Nondestructive Evaluation (NDE) Web Manual

The NDE Web Manual (figure 2) was conceived and developed to fill a critical knowledge gap between the practitioners dealing with bridge performance challenges on a day-to-day basis and the researchers developing and refining NDE technologies serving them. Over the last decade, there has been an explosion of new assessment tools, but their documentation is fragmented (across refereed and non-refereed literature) and not supported by actual performance data for particular technologies and products. The NDE Web Manual's aim is to provide concise and unbiased guidance to help practitioners navigate their way through a complex and changing landscape to identify the technologies that can serve their specific need.

Through a simple interface, users can search for technologies relevant to specific materials, types of deterioration, and/or infrastructure elements and can easily find definitions and descriptions of unfamiliar terms through the comprehensive glossary.

The manual strikes a balance between treating technologies as "black boxes" and simply regurgitating the detailed technical literature that is largely irrelevant for end users. To accomplish this, the Manual provides concise descriptions of each technology, including the following:

  • The foundational physical principle.
  • Performance attributes and limitations.
  • "Best-practices" test procedures and protocols.
  • Sample applications and results, among others.

Figure 2. Screen capture. NDE Web Manual homepage. The screen shows the homepage of the NDE Web Manual web application. There is a revolving slide show at the top. Above the slide show, there are tabs for the different areas of the web manual: Home, Find Technology, NDE Technologies, Glossary, and Acronyms and Abbreviations.

Figure 2. Screen capture. Home page of the NDE Web Manual, Version 1.0.

RABIT™ Bridge Deck Assessment Tool

In the United States, the stewardship and management of approximately 600,000 bridges present ongoing planning, operational, maintenance, and economic challenges for Federal, State, and local transportation agencies. Bridge condition assessments help transportation agencies plan and prioritize structure rehabilitation plans. Collecting data on the health of these bridges, however, can be a time-consuming, labor-intensive, and costly process.

The FWHA's LTBP Program developed a multifunctional NDE platform to enhance assessment of bridge decks. The RABIT™ bridge deck assessment tool was developed to deploy a suite of NDE technologies to collect comprehensive data on surface and subsurface conditions automatically and simultaneously. Recently, a commercially-available model was developed, known as RABIT-CE™ (figure 3).

 The photo shows the RABIT-CE™ bridge deck assessment tool on a concrete bridge deck

Figure 3. Photo. View of the RABIT-CE™ bridge deck assessment tool

The following technologies are incorporated into the robot-assisted, remote-controlled RABIT™ bridge deck assessment tool as shown in figure 4:

  1. High-resolution industrial cameras to capture high-resolution images of the deck surface.
  2. Electrical resistivity (ER) to characterize the corrosive environment of the concrete.
  3. Accoustic array, including impact echo (IE) and ultrasonic surface waves (USW), to evaluate concrete delamination and concrete deck strength.
  4. Ground penetrating radar (GPR) to "map" rebar and other metallic objects below the surface using electromagnetic waves. GPR also provides a qualitative assessment of concrete deck deterioration.
  5. Global positioning system (GPS) to record and mark exact location data, making testing grids virtually obsolete.

What does the RABIT™ bridge deck assessment tool detect?

The unique combination of surface and subsurface condition assessment tools allow bridge managers and engineers to easily identify the anticipated future condition concerns of a bridge deck (figure 4). All of the data collected by the RABIT™ bridge deck assessment tool are tagged with exact GPS coordinates for precise location reference.

Corrosion occurs when moisture and salt penetrate the concrete. As a result, rebar starts to corrode and concrete begins to crack and disintegrate. The RABIT™ bridge deck assessment tool features two NDE technologies that can identify corrosive environments: ER and GPR.

Figure 4. Photo. An example of bridge deck deterioration. The photo shows a close up an area of concrete that shows an area of spalling in the center of the photo.
Figure 4. Photo. An example of bridge deck deterioration.

Figure 5. Photo. An example of bridge deck delamination. The photo shows a side view of concrete with reinforcing bars exposed. Delamination is visible.
Figure 5. Photo. An example of bridge deck delamination.

Concrete quality degradation is caused by many factors. USW and GPR can detect changes in the quality of the concrete deck, while high-resolution imaging provides visual documentation of deck surface conditions. Delamination (figure 5) is the beginning of the division and separation of layers of a concrete bridge deck, weakening the bridge deck and making it more susceptible to the environment and traffic loads. The RABIT™ bridge deck assessment tool's IE system, GPR, high-resolution imaging, and GPS capabilities precisely locate delaminated areas to enable bridge owners to make the right repair decisions.

How does the RABIT™ bridge deck assessment tool collect and analyze data?

The RABIT™ bridge deck assessment tool collects a wide range of data simultaneously—high-resolution photographic, electromagnetic, seismic, and electrical— on external and internal bridge deck conditions. The RABIT-CE™ is transported in a trailer designed and built specifically for it (figure 6). The trailer is towed by a pickup truck. These vehicles are known as the system operational control (SOC) truck and SOC trailer.

The SOC trailer also serves as a mobile command center (figure 7). The data collected by the RABIT™ bridge deck assessment tool is transmitted wirelessly to a computer in the trailer for processing and display. Inside the trailer, engineers and inspectors use the following four main displays: NDE data collection and imaging, data analysis, real-time deck condition data, and crack mapping. This allows engineers and inspectors to analyze and share photographic, seismic, and location data all at one time.

The  photo shows a large silver trailer with its rear door open. There is a ramp extending  from the trailer floor down to the ground that allows the RABIT-CE™ bridge deck  assessment tool to ride down to the surface being tested.
Figure 6. Photo. SOC trailer for the RABIT-CE™ bridge deck assessment tool.

The photo shows the inside of the trailer. There is a desk and chair, with four display monitors mounted on the wall.
Figure 7. Photo. Mobile command center inside the SOC trailer.

Is the RABIT™ bridge deck assessment tool safe for workers and vehicles?

The RABIT™ bridge deck assessment tool can use a high-accuracy GPS to examine a bridge deck on its own, eliminating the need for workers to spend time on the deck making grid markings required for manual NDE tools. Unlike traditional roadway vehicles, the tool's four omnidirectional wheels allow it to move smoothly at a zero radius, which allows the tool to take up less space on the deck and requires only one lane of traffic be closed at a time. Finally, a laser scanning system protects the RABIT™ bridge deck assessment tool against collision with barriers, curbs, vehicles, and people.

A printable brochure about the RABIT™ bridge deck assessment tool can be found here.

LTBP Bridge Portal

The LTBP Program collects data from a wide array of sources. On its own, the data will be of great value, but the Program will further integrate the information through data fusion techniques. By employing the LTBP Bridge Portal to store and extrapolate data from multiple sources (figure 8), data on the temporal condition of treated and untreated decks, bearing, joints, prestressing strands, and coatings can be correlated with superstructure and substructure condition to reveal unknown mechanistic properties that, when explored, may identify innovative approaches. Figure 8 shows the data sources and capabilities in the current version of the LTBP Bridge Portal as well as those planned for future versions.

Figure 8. Illustration. LTBP Bridge Portal components. This illustration shows the components currently available and that will be available in the future in the LTBP Bridge Portal. The center of the photo is a funnel-shaped figure labeled "LTBP Bridge Portal Data-Driven Tool" and has an arrow pointing down, out of the narrow end of the funnel. At the top of the funnel are six ovals with arrows pointing into the funnel, indicating the types of data that are input into the Portal. Green-outlined circles (indicating currently used in version 1 of the Portal) are labeled "LTBP Field Data (V1)" and "NBI & Element Level Data (V1)." Yellow-outlined circles (indicating items that will be used in version 2 of the Portal) are labeled "Traffic & Truck Data (V2)" and "Inspection Data (V2)." Circles outlined in orange (indicating items that will be used in future developments) are labeled "Maintenance & Preservation (FD)" and "Weather Data (FD)." Underneath the funnel are three rows of boxes showing the available (current and future) capabilities and outputs of the Bridge Portal. The top row of boxes are green (indicating currently available) and are labeled "Basic Deterioration Model," "Advanced Data & Statistical Analysis," "Bridge Performance Assessment," "GIS Mapping & Visualization," and "Custom Reporting & Data Extraction." The next row of boxes are yellow (indicating will be available in version 2 of the Portal) and are labeled "Cost Analysis," "Bridge Timelines (materials & design)," "Data-Driven Deterioration Model," and "NDE Web Manual Link." The bottom row of boxes are orange (indicating will be available in future developments) and are labeled "Tools for Asset Management,"  "Mobile Apps," and "3-D Visualization." To the left of the funnel is a list of acronyms used in the figure: "(V1) Version 1 (September 2015)," (V2) Version 2 (Expected 2017)," and "(FD) Future Development."
Figure 8. Illustration. LTBP Bridge Portal components.

The LTBP Bridge Portal (figure 9) is a centralized, national repository for efficiently and quickly accessing and querying bridge performance-related data, information, and data analysis tools. It was developed to provide storage, retrieval, dissemination, analysis, and visualization of data collected through LTBP Program efforts and to provide users with the ability to holistically assess bridge performance on a network or individual project basis.

Figure 9. Screen capture. Homepage of the LTBP Bridge Portal. The screen says, "Welcome to LTBP Bridge Portal" with a picture of part of a steel bridge in the background. There are blue buttons labeled "Simple Search" and "Advanced Search," with the U.S. Department of Transportation logo underneath. At the top of the screen, from left to right are the following: LTBP Program logo, "LTBP Bridge Portal" label, "Simple Search," Advanced Search," a dropdown menu for users to select saved filters, "Settings," and "Log Out."
Figure 9. Screen capture. Homepage of the LTBP Bridge Portal.

At the touch of a button, the Bridge Portal can provide a statistical summary almost instantly, whether for 100 or 600,000 bridges. The query summary provides information on the current average condition state for the deck, superstructure, or substructure, as well as how each condition state has changed from previous years. In addition, the following information summaries can be obtained:

  • Current traffic information (both average daily traffic and average daily truck traffic).
  • Total number of square feet of deck represented.
  • Number of posted and structurally deficient bridges.
  • Average age of all bridges.
  • A comparison between national highway system (NHS), State-owned, locally-owned, and non-NHS structures.

For the example shown in figure 10, a simple search was conducted to query all of the prestressed multi-girder bridges in the entire national bridge inventory. The results can then be exported, charted, and statistical analyses run on the subpopulation. The query results are easily mapped within the LTBP Bridge Portal through geographic information system (GIS) functionality, charted, or summarized. The color of the markers on the GIS map visualization can be set to a specific attribute as can the size of the marker; in this case, the color can signify deck condition (taken from the National Bridge Inventory).

Figure 10. Screen capture. LTBP Bridge Portal GIS map visualization capabilities. The screen shows a map of the United States with dots in various shades of yellow and green primarily concentrated in the eastern part of the country; there are other green dots scattered throughout the rest of the country. There is a legend on the bottom right of the screen that gives the condition of the deck based on the color of the dot. The colors shown indicate those on the map are primarily in "6-Satisfactory," 7-Good Condition," and "8-Very Good Condition." On the right of the screen, above the legend, is a section labeled "Marker Color Attribute" and the user has selected "Deck" as the attribute that they want to view on the map. At the top of the screen, from left to right are the following: LTBP Program logo, "LTBP Bridge Portal" label, "Simple Search," "Advanced Search," a dropdown menu showing that "Prestres. Conc. Multi.." has been selected, "Settings," and "Log Out." 
Figure 10. Screen capture. LTBP Bridge Portal GIS map visualization capabilities.

The LTBP Bridge Portal will be of particular interest to FHWA Division Bridge Engineers, their counterparts at State transportation departments, and local agencies interested in bridge performance-related information.

The LTBP Bridge Portal Version 1 is currently available for use. Employees of FHWA, State transportation departments and local agencies can access the LTBP Bridge Portal through the FHWA's User Profile Access Control System (UPACS). The UPACS site contains instructions for State transportation department and local agency employees to obtain Operational Research Consultants credentials. Other users will be required to register and request access.

Visit the Data Analysis page to see more examples of the Portal in action! For more information about the LTBP Bridge Portal, please contact Robert Zobel.

NDE Lab Field Test Bed

FHWA's Advanced Sensing Technology (FAST) NDE Laboratory located at Turner Fairbank Highway Research Center (TFHRC) is a world class facility for the development and testing of NDE technologies. To assist with ongoing research efforts, the FAST NDE Laboratory maintains an extensive specimen library that includes test beds from a bridge in Virginia and prestressed bridge girders removed from an active bridge on Maryland I–90.

Both of these test beds are available to researchers and vendors of NDE technologies to demonstrate and test their products and technologies. The LTBP Program has developed a memorandum of understanding (MOU) that provides a framework for researchers and vendors to conduct their tests and obtain research results.

Virginia Pilot Bridge Test Bed

In June 2016, the bridge carrying U.S. Route 15 over I–66 was demolished to make way for a new, diverging diamond interchange. This bridge, known in the LTBP Program as the Virginia Pilot Bridge, was subjected to NDE in 2009, 2011, and 2014, and it was also subject to testing under the Strategic Highway Research Program (SHRP2). Bridge deck deterioration knowledge gained through the program was too valuable to let the demolition eliminate this bridge deck from the LTBP Program.

Figure 11. Photo. Virginia pilot bridge slab test bed at TFHRC. The photo shows a large portion of the bridge deck from the Virginia pilot bridge. The slabs are horizontal across the photo. The slabs rest on top of two large concrete block piers situated at each end of the slabs. The slab has rails around it for the safety of workers.
Figure 11. Photo. Virginia pilot bridge slab test bed at TFHRC.

Instead, FHWA identified an opportunity to retain three sections of the bridge deck for continued research at the TFHRC (figure 11). Three sections from the areas previously tested by SHRP2 and the LTBP Program were cut from the deck; each section is 6 by 30 feet. Each section was attached to a strong-back system and transported to TFHRC where a test bed facility was designed and constructed. In addition to preserving the deck slabs for continuing research on deterioration, a research plan was developed for evaluating differential settlement of the test bed abutments.

The FHWA FAST NDE Lab is planning on using the test bed to evaluate NDE technologies that can scan decks with overlays to supplement information in the NDE Web Manual and direct the LTBP Program research on bridge decks with overlays.

Prestressed Concrete Girder Test Bed

The accurate assessment of embedded prestressing strands and tendons is one of the most pressing challenges facing the NDE research community within the civil engineering domain. Given the increased construction of prestressed concrete multi-girder and box girder bridges a half-century ago, and the more recent proliferation of segmental bridges, the deterioration of embedded strands and tendons represents a critical vulnerability to the U.S. bridge population. A key aspect of any mitigation strategy for this vulnerability is developing and validating cost-effective and accurate techniques for the assessment of embedded stands and tendons.

To help advance this development, FHWA has procured and maintains two decommissioned prestressed concrete girders as a testbed for the research community. It is envisioned that this testbed will achieve the following objectives:

  • Provide access to realistic, embedded strands to allow researchers to evaluate, validate, and ultimately refine their assessment techniques.
  • Facilitate comparative studies of a diverse set of assessment techniques to allow complementary strategies to be identified and integrated.
  • Serve as a benchmark of assessment techniques to instill confidence in end users and reduce the time from validation to implementation.

Like the Virginia Pilot Bridge Test Bed, the two American Association of State Highway and Transportation Officials (AASHTO) prestressed concrete girders (figure 12) are available to researchers and vendors to demonstrate and test technologies to evaluate the condition of these girders. Each girder is approximately 60 by 4 ft. The two girders are representative of bridges approaching 50 years of service and are characteristic of thousands of bridges in service today.

Figure 12. Photo. Two AASHTO prestressed concrete girders at TFHRC. The photo shows a front-side view of two prestressed concrete girders. Each girder is resting on two concrete block piers.
Figure 12. Photo. Two AASHTO Prestressed Concrete Girders at TFHRC.

For more information about the prestressed concrete girder test bed, please contact Robert Zobel.

Updated: Monday, December 2, 2019