ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/297009
42 | ASPIRE , Fall 2013 F H WA T his article is a follow-up to the article titled "Map-21 and Bridge Life-Cycle Cost Analysis" published in the Summer 2013 issue of ASPIRE.™ This article describes the project- level, life-cycle cost analysis using the Federal Highway Administration (FHWA) bridge life- cycle cost analysis (BLCCA) software tool. An example illustrates application of the tool to compare the life-cycle costs for rehabilitation versus replacement of a bridge. The FHWA BLCCA software tool is a powerful tool for performing various levels of project cost analysis and comparative studies. It is ideal in support of making project level strategic investment decisions. FhWA BlCCA Software Tool Bridge project engineers consider various investment strategies on a project level. The strategies primarily include: • investing in the repair of existing bridge deterioration, • preservation activities that extend service life and delay major investments, or • replacing a bridge that has advanced deterioration. For this purpose, FHWA offers the BLCCA software tool. This tool helps engineers perform an analysis of each strategy for a specific bridge so that, in comparison, the strategy that provides the desired performance with the best potential life-cycle cost scenario can be selected. Specifically, the BLCCA software calculates the present value of costs of alternative investment strategies applied over a specific time horizon. The BLCCA software tool is based in Microsoft Excel. It includes worksheets organized into four separate areas: summary, data, settings, and reports and models. Each group of worksheets provides specific details about the analysis. For example, the summar y worksheet provides a synopsis of the analysis results and hyperlinks to relevant worksheets. The worksheets in the data area display details about elements and costs for alternative strategies. To run the software, the analyst simply opens the file and selects the data set to link to, selects the bridge of interest from the list of bridges, and begins inputting the specifics about each alternative. It allows users to select data about a specific bridge along with its in-service condition ratings fr om either the National Bridge Inventory (NBI) or Pontis data set. S p e c i f i c l i f e - c y c l e a c t i o n s s u c h a s rehabilitation, deck repairs, or replacement can be selected for alternative strategies that the user identifies. Using these inputs, the software applies deterioration algorithms to each element associated with the bridge and displays a summary of the performance of each investment strategy over the user-specified time horizon. The element deterioration algorithms and costs were refined from data collected on bridges nationwide and provide recommendations of bridge performance for use by the analyst. Each attribute can be overridden or customized by the analyst by simply entering values in pertinent fields. In the absence of expert knowledge, the recommendations provide a good gauge. The user can revisit other specific aspects of the analysis and refine inputs such as costs, dates that actions occur, or add additional actions as necessary. Copies of the BLCCA software will be available for download from FHWA by request beginning in October 2013. It is placed on the local machine along with the specific (NBI) data set. FHWA provides access to NBI data sets on its webpage at http://www.fhwa.dot.gov/bridge/nbi/ ascii.cfm. Illustrative Example An example analysis using the software to compare the life-cycle costs for performing rehabilitation versus replacing a bridge is depicted in Figure 1, which shows the scenario for each strategy. The software estimates the agency costs for each of these activities needed to restore each affected element to acceptable performance levels. Specifically, it maps the selected actions (for example, heavy maintenance) to element level activities to calculate costs. The user can define the particular aspects of the new bridge by selecting relevant elements of the new bridge such as steel beams or prestressed concrete girders. The outcome of the analysis is depicted in Figure 2. The bar graph displays the present value of the total costs for the two alternatives. Costs are color delineated by direct agency costs for materials or construction, user costs, and vulnerability costs. Using Bridge Life-Cycle Cost Analysis tools for MAP-21 by Nathaniel Coley and M. Myint Lwin, Federal Highway Administration Figure 1: An example comparing the life-cycle costs for rehabilitation versus replacement of a bridge using the Federal Highway Administration bridge life-cycle cost analysis (BLCCA) software tool. Diagram: FHWA. Figure 2: The outcome from an example comparing the life-cycle costs for rehabilitation versus replacement of a bridge using the Federal Highway Administration bridge life-cycle cost analysis (BLCCA) software tool. Diagram: FHWA. Total present value of life-cycle cost ($000) 0 50,000 100,000 150,000 200,000 Rehab Replace 0 0 Agency User Vulnerability Start Screen Alternative #1: Rehab Scenario settings Summary results Rehabilitation Deck repairs Bridge replacement Deck repairs Heavy maintenance 2015 2025 2035 2045 2055 Treatment Year Life-cycle cost ($000) 94,589 8,278 27,973 130,840 Agency: User: Vulnerability: Total: Alternative #2: Replace Scenario settings Summary results Bridge replacement Deck repairs Heavy maintenance Rehabilitation Deck repairs 2015 2025 2035 2045 2055 Treatment Year Life-cycle cost ($000) 179,365 1,661 14,840 195,866 Agency: User: Vulnerability: Total: Book_Fall13ASPIRE.indb 42 9/6/13 12:05 PM