About the research
Adjacent concrete box beam bridges constitute more than 15% of the bridges built or replaced each year. This type of bridge is generally constructed by placing box beams next to one another, grouting adjoining shear keys, applying a transverse post-tensioning force, and then, perhaps, placing either a thin wearing surface or a thick (~6-in.) structural deck. Historically, these and other similar adjacent precast elements have suffered from differential displacements, which cause cracking in adjoining joint material (or, in some cases, in the cast-in-place topping material). Until recently, the addition of a structural deck has been the only nearly guaranteed way to eliminate problematic cracking. However, the structural deck adds significant cost, construction time, and bridge dead load. More recently, a new joint detail was developed and tested by the Federal Highway Administration (FHWA). The only potential drawback to the developed system is that its performance requires the use of so-called Ultra High Performance Concrete (UHPC). While UHPC provides many qualities that are far superior to conventional concretes, the cost of the material is up to ten times greater. Additionally, UHPC requires special mixing equipment and is best placed by experienced field staff.
Ending in 2017, the Iowa State University Bridge Engineering Center developed and tested an innovative adjacent box beam joint connection detail that does not use UHPC and, in the laboratory, exhibited performance levels that matched and/or exceeded the FHWA UHPC joint detail.
The objectives of the research are to design, construct, and evaluate the performance of a yet-to-be-constructed box beam bridge in either Delaware or Dubuque County.