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/297030
50 | ASPIRE , Summer 2012 S A F E T Y A N D S E R V I C E A B I L I T Y The factors involved in deciding how and when to replace substandard and functionally obsolete bridges can be more complex than the decision to build a new structure. These factors also impact whether accelerated bridge construction (ABC) methods can be used to complete construction quickly to improve safety and minimize costs. A new software analysis tool can help decision makers assess alternatives with more confidence that their choices will be the safest, fastest, and most cost effective. T h e t o o l wa s d e v e l o p e d i n a n O r e g o n Department of Transportation (ODOT) pooled- fund study, TPF 5(221). Based on the analytical hierarchy process (AHP), it determines the best alternative using specific weighted criteria (Saaty & Vargas 2001). The various criteria are compared two at a time to develop ranked priorities and a final decision. The process compares criteria and set s priorities and weights for each criteria based on the relative importance of one criterion to another. Matrices of weighted priorities are used to create utility values for specific bridge replacement alternatives. The weighted numerical result s are compared for each alternative and used to identify a preferred alternative. T h e p r o c e s s c a n a l s o b e u s e d t o h e l p designers decide among material as well as design choices. By comparing various cast-in- place concrete designs, precast concrete designs, or steel designs, the user of the tool can identify the best alternative, based on the criteria included in the hierarchy for a particular bridge replacement or rehabilitation project. A simple example of how the matrices and weighting can be applied to a decision can be seen at http://www.fhwa.dot.gov/publications/ publicroads/11novdec/02.cfm. Application to Bridges O D O T 's t e c h n i c a l a d v i s o r y c o m m i t t e e developed a two-level hierarchy of criteria relevant to determining the best construction methods to apply to bridge replacement and r eha bilitation project s. The highest lev el consist s of five criteria, each of which is specified by two to nine sub-criteria (Figure 1). One of the projects used to test the tool was the U.S. 52 Bridge over the Mississippi River ABC tool Weighs Alternatives by Benjamin Tang, Oregon Department of Transportation and Toni L. Doolen, Oregon State University Figure 1: Decision criteria for bridge replacement or rehabilitation projects. Matrix compares preferences two at a time to create ultimate priority listing for bridge designs ABC Decision- Making Criteria Schedule Constraints Indirect Costs Direct Costs Site Constraints Customer Service Calendar or Utility or RxR or Navigational Marine and Wildlife User Delay Construction Bridge Span Conﬁguration Public Perception Freight Mobility MOT Horizontal/Vertical Obstructions Resource Availability Revenue Loss Design and Construct Detour Environmental Livability During Construction Right of Way Historical Road Users Exposure Project Design and Development Construction Personnel Exposure Essential Services Maintenance Construction Engineering Inspection, Maintenance, and Preservation Toll Revenue Archaeological Public Relations Direct Costs Schedule Constraints Indirect Costs Site Constraints Customer Service Goal Shifted Same Alignment Alternatives Alternatives Utility [%] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Figure 2: Overall priority for two replacement alternatives for Sabula Bridge. ASPIREBook_Sum12_R02.indb 50 6/29/12 12:39 PM