Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
About the research
The objective of this study was to determine the economic impact of designing pre-tensioned prestressed concrete beam (PPCB) bridges utilizing the continuity developed in the bridge deck as opposed to the current Iowa Department of Transportation (DOT) method of utilizing standardized spans treated as simply supported. This work consisted of a literature search and review, survey of other highway agencies, design comparisons, and cost-benefit analysis.
The design review consisted of comparisons of the standard design practices in terms of material use and cost from a review of electronically published design manuals, standards, and practices for state DOTs. Furthermore, the design review examined design cost, as determined by design hours spent to produce final bridge plans using the different design methodologies from state DOT survey respondents.
The cost-benefit analysis was based on construction costs from the Federal Highway Administration (FHWA) National Bridge Inventory (NBI) (with corrections to account for the different years the costs were recorded and the different regional bridge locations) and material and design costs from the design review.
Based on the evidence included in the final report for this project, the researchers concluded that simple span designs have a lower initial cost compared to continuous designs, in terms of construction cost and design time.
The lower construction cost demonstrated by the simple span designs in contradiction to theoretical material efficiencies in continuous design is an indicator that many of the continuous designs utilized are not optimized to the extent possible. While significant recent research has been completed on optimization methods for prestressed concrete bridge design, the majority of them remain undeveloped for practical application.
Due to the lack of strong evidence in favor of either design method in terms of long-term cost and performance, the research team concluded that simple span designs are preferable at this time.
Iowa Department of Transportation
Iowa Highway Research Board ($75,395.00)
Midwest Transportation Center
Contract Number: DTRT13-G-UTC37