For those who think that precast bridges are less expensive than steel bridges, think again!

In a cost comparison of two nearly identical short span bridges in Missouri, a bridge engineering consultant found that Steel Bridge 411 in AudrainCounty saved over 25 percent—with an overall 19.3 percent savings in the total cost of the structure—when compared with its precast twin, Concrete Bridge 336. The bridges were both built in 2012, have the same location and topography, with nearly identical roadway length and width, abutments, structural depth and guardrail systems. They even had the same local work crew.

The unique aspect of this report is that a detailed side-by-side comparison of construction square footage costs from the beginning of design to the end of construction was put together, the first time that such an analysis of very similar concrete and steel structures had been conducted. The analysis was conducted by Missouri bridge engineering consultant John Mann, P.E. and Michael G. Barker, P.E., a professor in the College of Engineering and Applied Sciences at the University of Wyoming. All costs were considered, even the cost of using rented cranes.

The study also identified additional potential cost savings that could have saved Audrain County engineers even more, such as the use of simple, easy-to-install Geosynthetically Reinforced Soil (GRS) bridge abutments to handle lighter loads; elastomeric bearings; weathering or galvanized steel; accelerated bridge construction; and the free web-based steel bridge design tool eSPAN140.

What is the significance of this report for cost-conscious, time-constricted county engineers? Some prefer working with precast bridges because they think it saves money. But with this new information, plus the ability to design a short span steel bridge for free with the interactive design tool eSPAN140, steel becomes the better buy.

To read the full case study, click here.