Institute for Transportation

About the research

The team proposes to design and construct the first bridge in the United States to use a novel concrete mix referred to as ultra high performance concrete (UHPC) in an optimized shape referred to as a Pi girder (i.e., a double tee cross section). Due to the serviceability issues that were identified early on in the conduct of a previous project using UHPC, a modification of the optimized Pi shape will be utilized, but the general cross section shape will be retained. This project will develop and build on experience in Iowa in the design and construction of bridges using advanced materials. To accomplish this, the team proposes to complete the design using only Iowa-based engineers working at various levels (state, local, academia) and, where possible, to use local companies for the construction of the bridge (note: fabrication of the Pi shape girder will likely be done out of state due to specialty formwork issues). The team will also test a reduced-scale beam specimen in the laboratory and test the completed field bridge.

About the research

The state of Iowa currently has approximately 25,000 bridges and ranks No. 5 in the United States. About 80% of these bridges are on low volume roads (LVRs) which are the responsibility of the County engineers. Recent National Bridge Inventory data by FHWA reports that about 22% of the bridges in Iowa are structurally deficient while 5% of them are functionally obsolete. Since many of these bridges are on rural county roads, funding is limited to replace the deficient bridges. Performance of substructure components (i.e., abutment and foundation soils) is believed to play a major role in the overall performance of the bridges. Use of geosynthetic reinforced soil (GRS) abutment systems with flexible facing (i.e., using wrapped geosynthetics, concrete blocks, etc.) can potentially be a cost-effective and structurally efficient alternative for supporting LVR bridge abutments; however, there are no documented case studies in Iowa and there is limited long-term performance monitoring data using this method. The feasibility of this method has to be properly investigated and documented for local conditions and materials with regard to several aspects including design, internal and external stability during and after construction, construction methods, and performance monitoring.

The objectives of this project are to:

1. Develop an instrumentation and monitoring plan to evaluate performance of newly constructed GRS bridge abutment systems.
2. Develop a design approach and construction guidelines for GRS bridge abutment systems with shallow spread footings on LVR bridges.
3. Document and evaluate the cost and construction aspects associated with construction of GRS bridge abutment systems from detailed field observations on project sites.
4. Produce a research report and technology transfer materials that provide recommendations for use and potential limitations of GRS bridge abutment systems

About the research

With the assistance of the Iowa DOT and the Bridge Engineering Center, Buchanan County will construct a bridge made of ultra high performance concrete. The BEC will assess the behavior of the individual elements during construction, their long-term performance, and the long-term performance and overall behavior of the completed bridge. This project directly addresses the FHWA’s Innovative Bridge Research and Construction program’s goal of demonstrating and documenting the effectiveness of innovative materials and construction techniques for for new bridge structures.