“Long-Term Analysis for Short-Span Bridges” – Modern Steel Construction
Excerpt from Modern Steel Construction: A recent life-cycle cost analysis compares steel and concrete short-span bridges.
There has historically been a healthy competition between material types for new bridge construction.
In personal discussions over the years with officials from state departments of transportation and local county engineers on effective and economical bridge construction, a frequent question that arises is the difference in life-cycle costs (LCC) between steel and concrete girder bridges.
Both the concrete industry and the steel industry cite various anecdotal LCC advantages using their assumptions on cost and maintenance for their materials. Even though owners want to consider LCC in bridge design decisions, they are unconvinced with anecdotal discussions—they want evidence.
This is where a life-cycle cost analysis (LCCA) comes in. An LCCA is an economical method to compare design alternatives over the entire life of the structure. It considers not only initial costs, but also future costs, their timing, and the service life of the bridge. An LCCA determines the “true cost” of bridge alternatives, considering the time value of money, for an equivalent monetary comparison.
For instance, if one alternative has a higher initial cost and no future costs, an LCCA can compare this to an alternative that has a lower initial cost and costly rehabilitation in the future, discounting future costs to equivalent today costs for a direct economic comparison.
When addressing the question of steel versus concrete, again, there are many assumptions but a lack of hard evidence, so the Short Span Steel Bridge Alliance (SSSBA) initiated a study to develop useful owner information on historical LCCs for typical bridges.
The study included a subset of the bridge inventory from the Pennsylvania Department of Transportation (PennDOT). It was narrowed down to five types of bridges:
- Simple- and multi-span steel rolled beam
- Steel plate girder
- Concrete box adjacent
- Concrete box spread
- Concrete I-beam bridges
This article from Modern Steel Construction explores the results (the full report, “Historical Life Cycle Costs of Steel and Concrete Girder Bridges”—including a detailed explanation of the criteria, calculations, and results—is available for a free download.)
Does steel provide an economical solution for bridge construction?
- Due to the light weight of steel, cost savings can be significant
- Studies show that weathering, A1010, and galvanized steel reduces both initial and life cycle costs.
- Steel can compete and even save costs when compared with nearly identical concrete structures. re.
- Steel bridges also have long lives, decreasing the need for replacement.
- Steel’s high strength permits longer spans, minimizing disruption to underlying habitats.
- Steel is highly resistant to extreme natural disasters such as earthquakes.
- Steel is the world’s most recycled material and is infinitely recyclable.
- Short span steel bridges can be designed with prefabricated elements which provide a simpler installation and cost savings.