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Prefabricated Bridge Elements and Systems

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Slide 1. Multi-State ABC Decision Tool and Economic Modeling

Toni Doolen, PhD

August 2011
School of Mechanical, Industrial, and Manufacturing Engineering
Oregon State University

 

Slide 2. FHWA-sponsored pool funded study, TPF 5(221), Technical Advisory Committee

State Members and Titles
Oregon Benjamin Tang, P.E., Br Preservation Manager
Steve Soltesz, Research Coordinator
Dawn Mach, Bridge Fin. Analyst
Holly Winston, Sr. Local Bridge Standards Engineer
FHWA Mary F. Huie, Highways for LIFE, Program Coordinator
Tim Rogers, P.E., Division Bridge Engineer
Nat Coley, Asset Manager
California Paul Chung, Sr. Bridge Engineer
Iowa Ahmad Abu-Hawash, Chief Structural Engineer
Minnesota Kevin Western, Bridge Design Engineer
Montana David Johnson, Bridge design Engineer
Texas Courtney Holle, Transportation Engineer
Utah Daniel Hsiao, P.E., S.E., Sr. Project Manager
Washington Bijan Khaleghi, Design Engineer
DeWayne Wilson, Bridge Management Engineer

Speaker Notes:

8 states + federal highways

 

Slide 3. Overall Project Objective

  • What: A tool to help analyze different alternatives and determine which construction approach for a specific bridge project is preferred. Focus is on being able to compare conventional and accelerated construction approaches.
  • Who: Transportation specialists and decision-makers

Speaker Notes:

Account for characteristics of bridge project, e.g. bridge length, complexity, road user characteristics, environmental requirements, traffic levels, existing levels of congestion, and construction site attributes

 

Slide 4. Project Goals and Target Users

  • Goals of Project
    • Bring Accelerated Bridge Construction (ABC) to ordinary (bread and butter) bridges
    • Create a tool that can communicate decision rationale
    • Assist users of ABC elements in making ABC standard process (standardization)
  • Target User Population
    • Project managers
    • Engineers
    • Project owners
    • Program planners

Speaker Notes:

User-friendly and flexible to accommodate a range of construction situations, transparent as to the method of calculation, and customizable to maintain future relevance.
Engineers who can use the tool to create detailed estimates for recommendations.

 

Slide 5. Agenda

  1. Identification and organization of decision criteria
  2. Defining decision-making criteria
  3. Multi-criteria decision-making
  4. Examples
  5. Software to assist with analysis
 

Slide 6. Criteria Identification

TAC team members along with research team developed a comprehensive list of criteria that are relevant to the decision of when to use ABC tools/methods for a project. Each criteria was defined and sub-criteria were defined, as appropriate.

 

Slide 7. Criteria Organization

Flow Chart illustrating the Criteria Organization.


 

Slide 8. Defining Criteria (Example)

Criteria Definitions and Examples


 

Slide 9. Multi-Criteria Decision-Making

  • AHP (Analytic Hierarchy Process) is a decision- making technique designed to select the best alternative from a set of alternatives evaluated against several criteria.
  • The decision maker performs pair-wise comparisons that are used to develop an overall priority ranking for each alternative

Shows the pair-wise comparisons that are used to develop an overall priority ranking for each alternative.


Speaker Notes:

Key Resources on AHP
Saaty, T.L. (1980) The Analytic Hierarchy Process, McGraw Hill.
Saaty, T.L. and Vargas, L.G. (1984) .Comparison of eigenvalue, logarithmic least squares and least squares methods in estimating ratios., Mathematical Modelling, 5, 309-324.

 

Slide 10. Analysis Details

  • The hierarchy organizes the decision-making process
    • The factors affecting the decision, i.e. criteria and sub-criteria, progress from general to particular
    • A decision maker can insert or eliminate levels and elements. Less important criteria and sub-criteria can be dropped from further consideration.
As shown in this Criteria Organization Chart, A decision maker can insert or eliminate levels and elements. Less important criteria and sub-criteria can be dropped from further consideration.
 

Slide 11. AHP Analysis Details

  • Comparisons between criteria and between sub-criteria are performed using data from actual measurements or using a qualitative scale.

Chart illustrating comparisons between criteria and between sub-criteria are performed using data from actual measurements or using a qualitative scale.


 

Slide 12. AHP Analysis Details, cont’d.

  • Comparisons are also used to assess the extent to which one alternative satisfies a criteria over another alternative.

Chart illustrating comparisons assessing the extent to which one alternative satisfies a criteria over another alternative.


 

Slide 13. AHP Analysis Details, cont’d.

Criteria Direct Costs Indirect Costs Site Constraints
Direct Costs 1 0.5 3
Indirect Costs 2 1 4
Site Constraints 0.33 0.25 1
  • To obtain the priorities (relative weights) of criteria, importance levels are normalized.
  • Priority of each criterion is determined by averaging normalized weights.
Criteria Priority
Direct Costs 0.320
Indirect Costs 0.558
Site Constraints 0.122
 

Slide 14. AHP Analysis Details, cont’d.

  • Overall priorities are calculated for each alternative after weighting normalized priorities for each criteria and after weighting the extent to which each alternative satisfies each criteria and sub criteria.
Alternative Utility Level
Alt A 0.665
Alt B 0.335
  • Select the alternative with the highest utility level (overall priority).
 

Slide 15. Example: Copano Bay Bridge in Texas

  • Connecting the cities of Rockport/Fulton and Lamar
  • 11,010 feet long, with a 129’ wide and 75’ tall navigation channel
  • Data for this project was obtained from Texas DOT
  • Alternatives Compared: Cast in Place (Conventional method) versus Pre-Cast Caps (ABC method)
  • Best Alternative: ABC is highly preferred
  • Critical Factors: Schedule Constraints and Site Constraints

Speaker Notes:

The Copano Bay Bridge: The Copano Bay Bridge replaces the existing causeway on SH 35 at the mouth of Copano Bay. The bridge connects the cities of Rockport/Fulton and Lamar, on the Gulf Intracoastal Waterway. Copano Bay is home to oyster colonies and migratory birds, attracting birdwatchers year-round. Two peninsulas frame the bay opening, limiting ROW and dictating phased construction. The bridge is 11,010 feet long, with a 129’ wide and 75’ tall navigation channel. The existing structure suffers severe corrosion from marine exposure, such that some piling members have failed and required extensive repair. As such, providing corrosion protection – in the form of high-performance concrete, stainless reinforcing steel, and cylinder pile foundations – was of high importance. The superstructure is 100’, 120’, and 150’ long prestressed concrete girders. A majority of the piers consist of cast-in-place caps on trestle piles, with the tallest piers around the navigation channel being CIP bent caps on CIP columns and waterline pile caps. Contractors may elect to propose precast bent caps as alternate construction, thus reducing the duration of construction activities over open water.

 

Slide 16. Results

Graphs depicting the results of the Copano Bay Bridge Construction Project. Bar chart showing the comparison of goals between conventional and ABC projects. Indicates the utility levels of the two alternatives being compared.


 

Slide 17. Results

Graphs depicting the results of the Copano Bay Bridge Construction Project in terms of goals. Pie Pie Chart showing site showing the weights for each of the following sub-categories: site constraints, schedule constraints, indirect costs, direct costs, and customer service.


 

Slide 18. Example: Clear Creek Bridge in Oregon

  • Located on Clear Creek, Gulick Lane
  • Existing Bridge length: 29’ steel girders on concrete vertical abutments
  • Data for this project was obtained from Oregon DOT
  • Alternatives Compared: Conventional construction versus ABC
  • Best Alternative: Conventional
  • Critical Factor: Direct Costs

Bridge info:
Existing Bridge is on Clear Creek, Gulick Lane
Existing Bridge length: 29ft steel girders on concrete vertical abutments
The bridge is on a rural local road.
ADT: 90
Detour length: 1 mile
The new bridge will be 80-100 ft in length

 

Slide 19. Results

The MMS (Moveable Scaffold System) underslung modular deck forming , span by span cast in place self launching form traveler, when there is insufficient room for casting yards or transport of segments is improbable. Photo Courtesy of Harsco Infrastructure Americas.Graphs depicting the results of the Clear Creek Bridge in Oregon Project. Graphs depicting the results of the Copano Bay Bridge Construction Project in terms of goals. Pie Chart showing site showing the weights for each of the following sub-categories: site constraints, schedule constraints, indirect costs, direct costs, and customer service. Bar graph showing the comparison of goals between conventional and ABC projects. Indicates the utility levels of the two alternatives being compared.


 

Slide 21. Software

Screenshot of software being used for analysis. The first tab is associated with constructing a decision hierarchy. In this tab, the user has access to all necessary functions to support loading, saving, and modifying a decision hierarchy.


Speaker Notes

The first tab is associated with constructing a decision hierarchy. In this tab, the user has access to all necessary functions to support loading, saving, and modifying a decision hierarchy. The user has the option to disable a decision category either temporarily or permanently for every hierarchy. The second tab is associated with conducting pairwise comparisons. The user can save the state of an analysis at anytime and later return to that specific position, without losing any data. After finishing all pairwise comparisons, the user can review the results in the third tab.

For each node, existing in the decision model, the tool will generate a set of two plots: a bar chart indicating the utility levels of the two alternatives being compared and a pie chart showing the weights for each of the sub-categories. The last tab provides the user with the option of completing an additional cost-weighted analysis. This tab may be used only after all cost criteria have been eliminated from the decision model constructed using the first (left most) tab.

 

Slide 22. Criteria Comparisons

Screenshot of software being used for analysis. The second tab is associated with conducting pairwise comparisons. The user can save the state of an analysis at anytime and later return to that specific position, without losing any data.


Speaker Notes:

Pairwise comparisons are used to determine the relative importance of each criterion and the preference for each alternative when a set of criteria is considered. Each choice is a linguistic phrase. Some examples of linguistic phrases that can be used are: "A is more important than B", or "A is of the same importance as B", or "A is a little more important than B", and so on. In the pairwise comparison window, the user still has visibility to the decision hierarchy (in read-only mode) on the right hand side of the window. By clicking on each item in the hierarchy listing on the right, all pairwise comparisons associated with that level of the hierarchy will be displayed. Prior to viewing the results, the user must save the entire sets of comparisons by clicking on the "Save Comparison" button at the bottom of the window.

The user can compare criteria in two ways. For qualitative criteria, the user can use the scales provided on the form to rate the relative importance of criteria. If the criteria are quantitative (and accurate values or estimations are available) or the user wishes to use even scale numbers, text entry boxes are provided next to each comparison. The value entered in this box will represent the relative importance of the criterion on the left, over the criterion on the right. If the user uses both the radio buttons and manually enters a rating or a ratio in the text box, the value entered in the text box has the priority and will override the value entered using the scale.


 

Slide 23. Results

Screenshot of software being used for analysis. The user can review the results in the third tab. The last tab provides the user with the option of completing an additional cost-weighted analysis. This tab may be used only after all cost criteria have been eliminated from the decision model constructed using the first (left most) tab.


Speaker Notes:

From the results tab, the user can review the results of the AHP analysis completed using the pairwise comparisons or ratios entered by the user. At the center of the page, the overall preference for the two alternatives being compared is presented using percentages. The alternative with higher percentage value has the highest preference (i.e. utility).

These plots are dynamically generated for each hierarchy node. In other words, every time the user selects a node or category from the decision hierarchy on the right, the associated plots are drawn automatically. The bar chart represents the preference or utility level, calculated for the alternatives, by only considering the criteria within that specific node. In other words, when the user selects the "Schedule Constraints" node from the hierarchy, the stacked plot will show the utility level by only considering the weights and preferences associated with calendar and schedule constraints. By default, the software will display the plots for the overall results (plots associated with the "Goal" node) when the user moves on to the results tab. At the "Goal" node level, every generated bar is aggregated based on the utility values calculated using every subcategory. The pie chart shows the synthesized weight for every sub-criterion in a selected category. If the user selects a third-level criterion, the pie chart will show the user entered preference for different alternatives. The criterion with the highest weight in pie chart has the greatest contribution towards the total utility displayed in the stacked bar chart.

 

Slide 24. Contact Details

Toni L. Doolen, PhD
Oregon State University
doolen@engr.orst.edu
541-737-5641

Benjamin Tang, P.E.
Oregon DOT, Technical Services
Benjamin.M.Tang@odot.state.or.us
503-986-3324

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Page last modified on August 15, 2013.
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