Strengthening of Two Bridges
PULLMAN performed the following:
- A carbon fiber system was designed to restore the flexural strength of the beams.
- Deck was waterproofed
- New wearing course was placed on the bridge.
- All the deteriorated concrete was removed and replaced with a polymer-modified repair mortar
- Exposed mild steel was coated with an anticorrosion coating.
The Innovative Bridge Research and Construction (IBRC) Program of the Federal Highway Administration (FHWA) selected two bridges in the Upper-Midwest for rehabilitation using advanced composite materials and structural health monitoring.
Due to the significant deterioration of the prestressed strands in the bridge, coupled with extensive cracking and spalling of the concrete, a carbon fiber system was designed to restore the flexural strength of the beams. However, to optimize the high strength of the carbon fibers and replace the strands, of which approximately 25% were lost in the selected beams, it was decided to use an innovative method of post-tensioning the carbon fibers. This was the first time this post-tensioning system was utilized in the United States.
The main advantages of using a post-tensioned, carbon fiber system for structural strengthening were the high tensile capacity of the plates, the noncorrosive nature of the fibers, the ability to relieve strain in the existing tendons, and the ability to attach the plates to the concrete beams both by mechanical and chemical means to ensure a safe and long-lasting repair.
PULLMAN was selected to install the post-tensioning system and repair area of the bridges that had become damaged. In addition to strengthening all the affected beams, the bridge bearings were repaired and aligned, the deck drainage was redesigned and replaced, the deck was waterproofed, and a new wearing course was placed on the bridge. All the deteriorated concrete was removed and replaced with a polymer-modified repair mortar and the exposed mild steel was coated with an anticorrosion coating.
These repairs will enable the two bridges to be serviceable for many more years to come, and the cost of repairs was a fraction of what it would have cost the state for removal and replacement.