Iowa Department of Transportation
Iowa Highway Research Board
Justin Dahlbergdahlberg@iastate.edu email >
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer
About the research
The primary goal for this project was to evaluate the efficacy of A709 Grade QST 65 steel for use in Iowa bridge projects. The objectives of the project were as follows:
- Identify the current state of use of A709 Grade QST 65 steel in bridge projects
- Identify the ductility and strength characteristics of A709 Grade QST 65 steel through full-scale laboratory testing
- Identify the fatigue characteristics of A709 Grade QST 65 steel through cyclic fatigue testing
- Observe and compare bridge construction similarities and differences to conventional steel construction using a new bridge planned over Sand Creek in Buchanan County, Iowa
- Compare relative costs of using A709 Grade QST 65 steel versus conventional steel
- Measure the live load response at various points in time on the Sand Creek Bridge, which was constructed using A709 Grade QST 65 steel
The ductility and strength of the steel was observed through the various laboratory tests completed for this project as well as the testing performed by others. Minimum requirements for this steel grade have been established, and the results of this study indicate that the requirements were met and surpassed.
The modified design of this first-in-the-nation bridge using Grade QST 65 steel over Sand Creek allowed for a reduction in beam size for this relatively short-span, low-traveled bridge due to the increased strength of the steel beams. The total steel cost for these beams resulted in a 20% material cost savings.
The results should give confidence to engineers considering use of this steel grade on bridge construction projects with longer spans and higher traffic counts.