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Title: Development of an Optimized Continuity Diaphragm for New PCBT Girders
Contact: Kevin K. McGhee
Associate Director for Pavements
Project No.: 64028
Target Date: 09/19/2005
Abstract: With the implementation in Virginia of the new prestressed concrete bulb-tee (PCBT) girders, the need arises for a well-detailed continuity diaphragm. Simple span girders made to be continuous for live load and superimposed dead loads are more efficient and inherently safer than ordinary simple span girders. Also, by casting the deck continuously, high maintenance joints are eliminated over interior supports and rider comfort is greatly improved. The elimination of joints not only enhances the durability of the deck but also prevents premature deterioration of other super- and sub-structure components, which can be caused by water and deicing salts leaking through faulty joints. The continuity diaphragm, however, must be properly analyzed, designed, detailed, and constructed. Improperly detailed or constructed continuity diaphragms can develop excessive cracking with time and themselves become a high-maintenance element of the bridge. The currently unresolved issues remain: 1. How much, if any, positive moment reinforcement should be provided in the continuity diaphragm? 2. If positive moment reinforcing is provided, how much restraint moment develops? 3. How effective is the diaphragm in maintaining continuity between the spans? NCHRP Project 12-53 is examining these issues and developing and testing details for standard AASHTO girder shapes. The project proposed here will build on the results of the NCHRP project, currently projected to be completed in the summer of 2002, and develop details for the new PCBT shapes.

     Carin L. Roberts-Wollmann
     Michael C. Brown

  • Pavements