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Tools for Quantifying Risk in Bridge Management Systems

Description:

The Moving Ahead for Progress in the 21st Century Act (MAP-21) requires the development by each state of a risk-based asset management plan and declares that “it is in the vital interest of the United States … to use a data-driven, risk-based approach and cost-effective strategy for systematic preventative maintenance, replacement, and rehabilitation of highway bridges and tunnels to ensure safety and extended service life.” Bridge Management Systems (BMS) such as American Association of State Highway and Transportation Officials (AASHTO)Ware Bridge Management (BrM) are increasingly incorporating software capabilities to consider risk in priority setting and life cycle cost analysis.

National Cooperative Highway Research Program (NCHRP) Project 20-07 / Task 378 is preparing a literature review and synthesis of existing risk assessment methods that may be adaptable for use with BMS software. The risks under consideration include earthquakes and other types of earth movement, hurricanes and tornadoes, floods and scour, fires, vehicular or vessel collisions, fatigue, and advanced deterioration. These hazards have consequences that are beyond the normal deterioration and functional deficiencies already assessed in bridge management systems. The probability of each hazard, and the ability of each structure to resist the hazard, is not always consistently and quantitatively assessed at the current state of the practice.

The NCHRP Project 20-07 / Task 378 work is uncovering significant gaps in the current state of the practice. Although data sources exist for many of the relevant types of risk, many transportation agencies may have difficulty in analyzing these data sets to objectively characterize the likelihood and consequences of adverse event scenarios on the individual bridges in an inventory using readily available data. Rather than asking each state individually to perform research and analyze data to quantify risks, there may be considerable value in developing national research-based quantitative likelihood and consequence models that any agency can use without additional research effort.

Objective:

The objective of this research is to develop a set of tools (mathematical formulas) to quantitatively estimate the likelihood (probability) and consequences (cost in dollars) of transportation service disruption related to specific types of risk, by analyzing existing data sets obtained from FEMA, NOAA, USGS, FHWA, and state agencies. The research should be resourceful in gathering relevant data for analysis, but the resulting models should be capable of being applied in BMS by transportation agencies using just the data items currently defined in the National Bridge Inventory and the AASHTO Manual for Element Level Bridge Inspection. Such data would include for example location (county, latitude/longitude, etc.), structure type, clearances and load ratings, navigation features, and element composition and condition. If any new data items are required from the inspection process (such as scour information or fatigue details), the tools should include strategies to minimize the amount of such data required.

Since risk models deal with fundamentally uncertain phenomena, the tools should be accompanied by information on the degree of uncertainty in estimates, to the extent that this can be developed. The usage of these tools in BMS would primarily be as a means of consistently considering asset-based risk in priority-setting for replacement and risk mitigation projects. So broad coverage and consistency are more important than precision in these estimates. Specific models of interest include:

  • Probability and recovery cost of over-height truck collisions as a function of bridge vertical clearance.
  • Probability and recovery cost of bridge overloads as a function of bridge load ratings.
  • Probability and recovery cost of seismic and earth movement events as a function of location and other relevant bridge characteristics.
  • Probability and recovery cost for hurricanes and other weather events involving high winds, storm surge, and/or tsunamis.
  • Probability and recovery cost of failure of structural elements due to advanced deterioration and/or fatigue.

Proposers are asked to offer creative approaches to risk quantification and to suggest additional hazards and data sources beyond what is discussed here. The mathematical formulas developed in the research may be demonstrated using spreadsheets or other types of calculations, but no software development is expected under this project. Owner agencies will want to incorporate the models into their existing bridge management systems using the functionality of those systems.

Benefits:

Transportation agencies currently lack objective, quantitative methods to assess risks for bridge management systems. The research will fill in gaps identified in NCHRP Project 20-07 / Task 378 to provide tools to objectively prioritize risk mitigation actions. The development of these tools will enable many agencies to reduce the necessary effort on data collection and analysis in order to implement risk management.

With these tools, agencies will be able to allocate resources efficiently with bridge-level risk fully considered, and will have a means of compiling and maintaining a detailed risk register. The public and stakeholders will be in a better position to understand the trade-offs among risk, funding, and other aspects of transportation system performance.

Related Research:

The National Bridge Inventory provides minimal opportunities for risk assessment. AASHTO provides more relevant data items in its Element Inspection Manual and in the AASHTOWare Bridge Management software. However, many of the available items are largely unused due to lack of guidance on how to use them in asset management analysis and decision making. NCHRP Project 20-07 / Task 378 documented methods for incorporating risk into BMS, but some of these methods require considerable additional analysis of national data sources.

A very comprehensive vulnerability assessment process is documented in a series of manuals in New York. Florida DOT has completed research on estimating likelihood of a variety of natural and man-made hazards, and has demonstrated one method of incorporating this information in a bridge management system. Minnesota’s Bridge Replacement and Improvement System demonstrates a process where risk assessment is used for prioritizing projects for inclusion in the STIP. NCHRP Report 590 documents some alternative methods for combining risk with other performance measures in a multi-objective bridge management analysis. Transportation Asset Management Plans in all 50 states are starting to develop concepts for incorporating risk into the highest levels of decision making in each agency.

The emerging field of geotechnical asset management, where risk is a primary performance concern, is developing methods for routinely assessing the geological and hydraulic risks to each section of road, and quantifying the effects of slopes, embankments, retaining walls, culverts, and other constructed facilities in resisting these hazards. The methods often adopt a level of service perspective, where the “service” is the reduction of event likelihood or the increase in road section resilience. This experience may provide some useful ideas for bridge management.

Tasks:

It is envisioned that the research will involve at least the following tasks:

  1. Augment and update, as needed, the NCHRP Project 20-07 / Task 378 literature review on risk assessment and risk management. Of particular interest are data sets available from national, state, and international sources that can help in quantifying the likelihood and consequences of hazard scenarios. Contact researchers and practitioners in a selected group of state DOTS to identify existing research studies which might have helpful data sources. Identify potential sources of anecdotal records of extreme events that may fill in gaps where systematic automated data sets are unavailable.

  2. Document an analysis plan as a set of models and alternative approaches to each type of hazard, which the researchers believe may be capable of being developed using the available data sets. Document the hazard scenarios to be considered. Identify potential problems and limitations of different approaches to quantifying likelihood and consequence of transportation service disruption. This analysis should especially consider the extent of national coverage, the ability to reflect state-specific and local conditions, the ability to work with data already found in bridge management systems, and the potential for future validation and improvement of models.

  3. After approval of the analysis plan, carry out the plan by gathering data sets, performing statistical data analysis and model estimation, performing validation of statistical models, and evaluating the coverage, quality, and usefulness of the models. Multiple alternative approaches are encouraged in order to find the approaches that provide the most useful insight for priority setting in risk management applications.

  4. Prepare a Final Report (draft and final) to document the research. The Final Report should contain a User Guide chapter capable of being extracted and implemented by transportation agencies in conjunction with the products of NCHRP Project 20-07 / Task 378.

Implementation:

This research is envisioned to feed directly into existing efforts to develop multi-objective optimization models in bridge management systems. It will provide default models and methods each agency can use as it customizes BMS models for its own use. Continued FHWA and AASHTO support for bridge management systems, and in general for asset management and performance management, will help to ensure successful and widespread implementation.

Sponsoring Committee:AKT50, Bridge and Structures Management
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Paul D Thompson
Source Info:AHD35, Bridge Management
Date Posted:01/22/2016
Date Modified:02/23/2016
Index Terms:Asset management, Risk management, Bridge management systems, Data files, State of the practice, Geological events, Atmospheric phenomena, Metrics (Quantitative assessment),
Cosponsoring Committees: 
Subjects    
Highways
Data and Information Technology
Maintenance and Preservation
Planning and Forecasting
Bridges and other structures

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