Bridges, Tunnels and other Transportation Structures
Full Session without Abstracts
This session will be led by several experts in the field of Post Tensioned Bridge Design and Construction.
Post tensioned bridges have become a significant part of the nation's infrastructure over the last 50-75 years. The technology became a common solution to the full spectrum of solutions for Bridge Design during the reconstruction of Europe following World War II. This type of construction was introduced into the United States in the 1960's during the construction of the Interstate Highway system. Since that time this type of construction has become a valuable part of the inventory of bridges in the US.
Post Tensioning is the life blood of these types of bridges and a method of protecting this essential structural element was developed using cementitious grout to protect the prestressing steel from the elements. Thousands of bridges have been constructed using this system and the vast majority have performed well. Grouting failures have been rare as a percentage of the overall inventory of this type of structure. Because the protection of the prestressing reinforcement is so critical to the durability and performance of these bridges is essential, significant concerns have been raised about the potential for failure of this system.
In a small number of isolated incidents, the tendon corrosion protection system has not performed as intended and the results have been disturbing which has called this very successful method of bridge construction into question.
This presentation will present a factual review of the nature and extent of problems that have been encountered. It will also describe the history of the development of the system, advances in the technology, issues related to specific projects, a detailed overview current testing methods used to identify issues and successful examples of methods to construct, repair and restore these structures to their intended service condition.
A panel of experts including a design engineer, a nationally recognized forensic expert, a former State Bridge engineer and the previous director of the American Segmental Bridge Institute will be presenting the material described above.
History of Tendon Grouting, How it Works and Repairs of Selected Projects with Corrosion Issues
Randall W. Poston, PhD, PE, SE, NAE
The use of cementitious grout in post tensioned bridge construction has worked well to protect the prestressing steel from corrosion while creating a potentially bonded connection to the final structure. The basic elements and chemistry of the system and how it is intended to work will be presented. A short discussion of select projects that had corrosion issues, the nature of the problems and solutions that were developed will follow based on the presenter’s extensive experience in the repair of concrete structures.
The ABC’s of Grouting Operations, What’s Involved in Doing it Right
Gregg Freeby, PE
The basics of Post Tensioned grout material choices, planning of operations, proper procedures for mixing and installing grout in the field and inspecting operations will be presented. The Do’s and Don’t’s of mixing, installation and evaluation of field operations for this important part of a Post Tensioned structure will be described. The focus of this presentation will be to inform the audience of what it takes to “Do it Right” and insure a good outcome.
The Development of Model Specifications M50 and M55 and Other Resources for Engineers Working with Grouted Post Tensioned Structures.
Miroslav Vejvoda, PE, SE
The Model Specifications M50 and M55 and other Technical Resources and References that have been developed by PTI for the Engineering and Construction Community will be described in detail. The history of how these resources were developed and refined will be presented. Recommendations on how these references may be used and the training that is available for personnel involved in Design and Construction will be summarized.