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LTBP Tools and Products

Bridge Deterioration Models

Bridge Components Condition Forecast Models

Bridge condition forecast models are an essential component for implementing a data-driven bridge asset management program by optimizing the funding allocation that is associated with bridge replacement, rehabilitation, repairs, maintenance, or preservation. 

The LTBP Program developed three bridge components (deck, superstructure, and substructure) condition forecast models (Base Models, Survival Models, and Machine Learning Models) and implemented them in the January 2020 LTBP InfoBridge release. The models are updated annually to account for annual submittals of the National Bridge Inventory (NBI).

The three models represent three levels of modeling complexities. Base Models are statistically deterministic and compute the average time-in-condition for each bridge type from historical National Bridge Inventory (NBI) data and apply those to each bridge component condition forecasting. Survival models derive condition rating transition probabilities from survival-analysis curves and use Markov chain probabilistic methods to forecast future condition ratings. Machine-learning models are developed by mining the historical NBI and climate data using a deep learning approach. 

"The top of the screen is labeled, Long-Term Bridge Performance InfoBridge: Data. Underneath is the label, Bridge Information. The State Name is Connecticut. The Structure Number is 06562. A Data tab and Condition Forecast tab are underneath the State Name, and the Condition Forecast tab is active. The condition forecast graph that is shown on the Condition Forecast tab depicts two of three available forecasting models: the time in condition model and the deep learning model. Each of these models are shown to forecast the bridge condition from the year 2023 to 2069 and 2070, respectively."

Figure 1. InfoBridge showing the Bridge Deck (Component) Condition Forecast Modeling Tool (Source: FHWA)

Bridge Network Performance Forecast Models

Survival Models and Machine Learning Models were also extended to perform network-level forecasting of bridge conditions for a group of selected bridges.

Bridge Condition Transition Forecast

The Bridge Performance Transition Forecast tool in InfoBridge™ produces a list of bridges that may transition from one condition state to another over a user-specified time period. Under Performance Forecast, select the Bridge Condition Transition Forecast tab to access the tool. The tool can also be accessed from the Tools menu.

The starting year for the forecast is set to the latest year for which the National Bridge Inventory (NBI) data are available. For selected bridges, users can specify the condition in the start year and the desired condition in a later year. Users may also input the minimum probability of occurrence for the forecast. Users select one of two deterioration models—the proportional hazards deterioration model or the machine learning model—to perform the calculations.

The resulting list of bridges, and a few pertinent NBI items, are displayed on screen and can also be exported into an Excel® spreadsheet.

"Two tabs are shown: “Network Performance Forecast” and “Bridge Performance Transition Forecast.” Bridge Performance Transition Forecast is selected. In the top left corner, below the tabs, is a dropdown menu labeled “Performance Forecast Models.” There are also options to select condition states and years, which are shown as four dropdown menus labeled, from left to right, “Condition Going From,” “In Year,” “To,” and “In Year.” On the same line, there is a text box labeled “Probability of Occurrence (percent) Greater Than Or Equal To.” Next to these selections, there is a button labeled “Display Results.” There is a header that separates the selection area from the results. The heading reads “Bridge Performance Transition Forecast,” which corresponds with the name of the selected tab. In the same header, on the right side of the page, is an “Export Table” link. Below this heading is a display bar that shows the user selections in sentence form, including the selected year, condition state, and selected model. The main body of the screen capture shows a table containing the user-selected list of bridges. The table is arranged in columns and rows. The column headings correspond with various National Bridge Inventory (NBI) fields, and the rows contain the NBI records for each bridge. The following NBI fields are shown as column headings in this table: “State Name,” “Structure Number,” “Owner Agency,” “Deck Area (square feet),” “Year Built,” “Main Design Material Type Value,” “Main Construction Design Value,” and “Probability of Occurrence (percent).” Below the table, there are navigation controls to change the page numbers and to increase or decrease the number of rows per page."
Source: FHWA

Figure 2. InfoBridge showing the Bridge Performance Transition Forecast Tool (Source: FHWA)

Bridge Condition Transition History Tool

The Bridge Condition Transition History tool in InfoBridge™ produces a list of bridges that has transitioned from one condition state to another over a user-specified period. Under Performance History, select the Bridge Condition Transition History tab to access the tool. The tool can also be accessed under the Tools menu.

The starting year selection is limited to the year from which InfoBridge maintains condition data for all bridges; in most cases this year is 1985. The ending year must occur later than the starting year, and both the starting and ending years cannot occur later than the current NBI data year.

The tool generates a list of bridges meeting the user-specified requirements. The list includes a few pertinent NBI items. The bridge condition in terms of Good, Fair, and Poor is displayed for each year of the specified duration. The list can be exported into an Excel© spreadsheet.

This figure is a screen capture of the Bridge Condition Transition History tool on the Long-Term Bridge Performance InfoBridge™ website. In this screen capture, two tabs are shown: “Bridge Performance Measures” and “Bridge Condition Transition History.” Bridge Condition Transition History is selected. Just below the tab header, there are options to select condition states and years, which are shown as four dropdown menus labeled, from left to right, “Condition Going From,” “In Year,” “To,” and “In Year.” Next to these selections, there is a blue button labeled “Display Results.” There is a solid gray header that separates the selection area from the results. The heading reads “Bridge Condition Transition History,” which corresponds with the name of the selected tab. In the same header, on the right side of the page, is an “Export Table” link. Below this heading is a light blue display bar that shows the user selections in sentence form, including the selected years and condition states.

Figure 3. InfoBridge showing the Bridge Condition Transition History Tool (Source: FHWA)

Asset Valuation Tool

The asset valuation tool in InfoBridge provides an estimate of the replacement value, existing value (EV), and remaining value of user-selected bridges. 

The tool also provides a State-wise summary of the replacement value, EV, and remaining value of bridges in each State. 

Details of the calculations are available under the InfoBridge Library menu.

"The top of the screen is labeled Asset Valuation by State. Underneath is the label Group By with choices for All Bridges, which is selected, Interstate Bridges, National Highway System (NHS) Bridges (Includes Interstate), and Non-NHS Bridges. Below the Group By options is the Total Bridge Count for All Bridges (619,588), Total Deck Area for All Bridges (4,290,222,930.5 square feet), Total replacement Value for all bridges ($833,380,1923,216), Total Existing Value for all Bridges ($763,489,103,451), and Remaining Value for All Bridges (91.6 percent). At the center of the page is a map of the United States with Select Value to Plot on Map set to Replacement Value in dollars. Each State on the map is shaded to indicate the replacement value of bridges within each State. Below the map is a table that shows Total Bridge Count, Total Deck Area in square feet, Replacement Value in dollars, Replacement Unit Cost in dollars, Existing Value in dollars, and Remaining Value in dollars for each State. Only the top of the table is visible with data for Alabama and Alaska."

Figure 4. InfoBridge showing the Bridge Asset Valuation Tool (Source: FHWA)

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Historical Bridge Specification Changes

This tool documents the historical changes in bridge materials and design specifications in chronological order. It also provides an easy to use search feature.

"The top tabs are labeled Library and Historical Specification (Spec) Changes. Under the Library tab are the tabs InfoBridge Documentation, InfoBridge Update Notes, Long-Term Bridge Performance Documentation, Historical Spec Changes, and Student Data Analysis Contest. The Historical Spec Changes tab is active, and under the Historical Spec Changes label, the specification is set to Reinforcing Steel. Below the specification selection is a chronological listing of years, starting in 1991 and going up to 2015. The 2015 year is selected, and to the right of the listing of years is an entry for 2015 for ASTM A615/A615M revision to the specification adding grade 100 steel. Also shown are three changes in the year 2009; AASHTO MP18 was published, ASTM A706/A706M revised adding Grade 80 steel, and ASTM A615/A615M revised adding grade 80 steel."

Figure 5. InfoBridge showing the Historical Bridge Specification Tool (Source: FHWA)

LTBP Program Protocols

To ensure that LTBP Program data are collected in a consistent manner over the duration of the program, FHWA is developing data collection protocols for use by practitioners, LTBP Program researchers, and decisionmakers 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 6. Illustration. LTBP Program Protocol Hierarchy.

The 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 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.

The 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 InfoBridge™ 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.