Changing bridge fabrication and inspection practices
of analysis “can greatly over estimate strength and reliability of a damaged bridge if all factors are not considered,” Wright explained.
So, Wright and Conner are working to create a more comprehensive approach. The release notes that they want to develop an all-inclusive systems method that would reliably predict the fatigue and fracture limit states of steel, the ultimate strength of the connections in the structure, the stability of the system, the overall condition, and the value of having an in-service inspection.
They believe a significant cost savings could be achieved through their approach. If states will pay a modestly higher, up front cost for better materials, the financial burden of lifetime inspections can be reduced, Wright said.
“The bridges we build today present a much lower risk of fracture compared to those built prior to about 1980. The reasons are the higher quality standards for fracture critical member fabrication, greatly improved knowledge about fatigue design and detailing to prevent in-plane fatigue as well as distortion cracking issues, and improved material quality. However, there is little evidence that fatigue critical in-service inspection contributes significantly to this improvement,” Wright said.
Due to these advancements in engineering, new bridges should have less need for inspection for fatigue issues when compared to the older vintage bridges.
As Wright investigates this fracture critical analysis system for the Transportation Research Board, he is simultaneously working on a multi-state pooled fund project administered by the Indiana Department of Transportation to develop improved fracture toughness specifications for structural steels used in critical members. His goal is to design and fabricate standards to eliminate fracture critical concerns in low redundancy structures, such as two-girder bridge systems.
Working with a host of partners including the Commonwealth of Virginia, the Army Corps of Engineers and the Federal Highway Administration, Wright suggests the results of this study “will be transformative for the steel bridge industry. For the first time, material selection, design, and inspection will be rationally integrated to eliminate fracture concerns. This can result in significant cost savings for medium and long-span bridges and facilitate the introduction of modular concepts for short-span bridges.”
The highway administration has the authority to allow the owners of bridges to forego fracture fatigue critical inspection for low-redundancy bridge structures on a case by case basis. This reprieve, however, rarely occurs since there is little guidance to insure bridge safety, Wright said.
“This project will establish guidance that provides a high level of bridge safety that can then form the basis for in-service inspection decisions,” Wright said.
The release reports that throughout his career, Wright’s primary research interests have involved development and experimental evaluation of new, innovative bridge systems that can meet three critical requirements: rapid construction, life cycle durability, and cost effectiveness. He has targeted this “Bridge of the Future” goal as the overriding principal guiding the Federal Highway Administration research program. The current research on fracture critical bridge systems is an enabling technology for the “Bridge of the Future.”
