AASHTOWare BrM 5.2 - etouches · Multi-Criteria decision analysis is BrM works through utility....
14
AASHTOWare BrM 5.2.3 Multi-Criteria Decision Analysis for Bridge Management April 26, 2017 Mesa, Arizona
AASHTOWare BrM 5.2 - etouches · Multi-Criteria decision analysis is BrM works through utility. Each of the criterion go into the overall utility value, which\ഠis simply a weighted
Multi-Criteria Decision Analysis Multi-criteria decision analysis methods aid decision makers in logically reasoning through the advantages and disadvantages of decision alternatives.
- Saaty & Vargas, 2001
• Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Bridges have several attributes and therefore to manage them effectively decision makers need to be able to capture multiple criteria when making decisions. This was the message from the Pontis (now BrM) User Group and the reason for the changes in how the software does optimization for work
Decision Alternatives in Bridge Management
Factors that Effect the ‘Need for Work’
• Condition
• Functionality
• Risk
• Economics / Life Cycle Cost
• Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
In your organization how do you go about determining which structure to work on and what work to do? Is it condition driven? Who makes the decisions? An agency may determine a bridge’s eligibility for rehabilitation or replacement based on it being located within the limits of a roadway project, where the project is planned and included in the STIP by district personnel, and are indirectly based on pavement deficiencies. In other words the bridges may not be the driving factor for the project. Recently agencies have realized that they need to make bridges the driving factor and have developed state or district wide bridge projects. However there are significant shortcomings to solely utilize condition as a performance measure, and an approach uses multi-criteria analysis is much better for bridge management. One example of this is a way to determine inspection frequencies. Bridges that are more risk may require more frequent inspections. And the opposite is true bridges with low risk may require less frequent inspections.
Bridge Management Criterion • Isolate items used to form a single rating or index • Categorize them under distinct bridge management
Structural Condition - measures the structural adequacy of a bridge Mobility - evaluates how bridge attributes affect the traveling public Risk - evaluates how bridge attributes and external factors affect the vulnerability of a bridge LCC - evaluates the timing of when work occurs to provide the least cost over a given period of time.
• Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
An item could be a major or minor element of a bridge (e.g. deck, girder, column, etc.), a characteristic of the bridge (e.g. vertical clearance, span length, roadway width, etc.) or an external attribute that is associated with the bridge (e.g. seismic category, detour length, traffic volume, etc.). Some of the items may be included under multiple components with the purpose of addressing the specific goal for each component. For example, Posting may be included under both the Structural Condition and Mobility with the respective goals of quantifying how deficiencies influence a bridges structural adequacy and how it could affect the traveling public by inducing route restrictions on heavy vehicles.
Utility • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Multi-Criteria decision analysis is BrM works through utility. Each of the criterion go into the overall utility value, which is simply a weighted ‘score’ for a given bridge. As the bridge ages we model deterioration and the utility value will go down as the value for each of the criterion is reduced. And conversely as we model improvements the utility value will increase. The benefit part of cost/benefit analysis for doing work is calculated from the incremental increase in the utility value. NOTE: The out-of-the–box criterion show are an example only. Your agency needs to customize what criterion are used based on its particular policies, practices, and requirements.
To determine the weighted average utility value, each of the primary criterion are given a set of sub-criterion. The bottom level of the sub-criterion are where the actual scores are assigned. For example, deck elements will have a utility score based on their condition state. This score is then multiplied by the relative weight. Then the scores are added and multiplied again by the relative weight of the next higher level in the hierarchy, and so on until there is a total combined utility value. The relative weights don’t have to add up to 100 as the software will normalize the relative weights. The user can just assign any value to each of the criterion, however a recommended methodology for determining relative weights is the Analytic Hierarchy Process (AHP). This process requires the user do a series of pairwise comparisons and translates those comparisons to a normalized relative weight for each item. This method can easily be used by any agency to customize the relative weights to their particular needs.
Utility - Mobility • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Sub-criterion for mobility. These are items that typically effect the functional aspect of a bridge. Again these are an example and an agency needs to customize them to their specific needs.
Utility – Risk • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Sub-criterion for mobility. These are items that typically effect the bridges reliability and hazard resistance. Again these are an example and an agency needs to customize them to their specific needs.
Utility – Scaling • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Each criterion has 2 parts: the base value and the scaler. The base value can be from any field of your database, any element or group of elements, any specific type of risk assessment or even derived from a formula. The scaler will then dictate how intermediate values are weighted: this can be done by the graphs or scaling formulas. Used to get everything on a common 100 point scale. A few examples are the deck element (rated using the new NBE and is a 4 point scale), the inventory rating (simply a ratio value) and the deck (rated using the NBIS ratings is a 1-9 scale).
Objectives • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization • Bridge A requires preservation work per agency policies
• Bridge B would not require work per agency policies
• Bridge C requires preservation work per agency policies
Bridge Utility Condition LCCA Mobility Risk A 78 55 95 80 95 B 80 87 52 88 97 C 77 90 95 51 60
Relative Weights 35 25 20 20
Presenter
Presentation Notes
When using a multi-criteria decision analysis it is imperative that each criterion has a well defined goal or objective. Here are few hypothetical situations to illustrate how mutli-criteria can be utilized to address different objectives. Bridge A has a Utility below 80 which would indicate per the agencies policy that it needs preservation work. However the LCCA component has a rating of 95, indicating that there is minimal if any preservation work that could be done to improve the structure. Therefore, if they are going to invest money into the structure they need to focus on improving the structural condition or replace the structure. Bridge B has a Utility of 80 which normally would not indicate a need for work based on agency policies. However, notice that the LCCA component is 52 indicating that there is a need for preservation work. Drilling down further the agency finds that the reason for the low LCCA is that the deck overlay is in very poor condition indicating that the bridge is in need of deck preservation work. Bridge C similar to bridge A has a Utility below 80 indicating that the bridge needs preservation work. However, when looking at the condition and LCCA components, there is little preservation, rehab, or other typical bridge improvement work that will increase the overall utility. The reason for the lower utility score is that the mobility and risk components are low, indicating that there are functional and hazard resistant improvements needed and therefore the agency should focus on programming this bridge for that type of work.
Objectives • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
For different optimization runs, you can temporarily re-weight the Utility Tree to focus in on certain nodes. For example: For Rehab & Replacement programs, consider leaning more heavily on condition and lifecycle nodes. For preservation work, lean almost exclusively on the lifecycle node. For Scour, you will probably lean mostly on risk.
Potential Utilization • Contact • Multi-Criteria
Decision Analysis
• Decision Alternatives in Bridge Management
• Bridge Management Criterion
• Utility • Objectives • Potential
Utilization
Presenter
Presentation Notes
Using multiple criteria for trade off analysis for inspection. There are structures that are in good condition with low risk that potentially could be inspected in longer intervals. There are structures in poor condition and high risk that should be inspected at more frequent intervals. Finally using multiple criteria allows the agency to identify differences in bridges that may otherwise have a very similar condition. Note: This functionality is not currently in the software, but is for illustrative purposes.
