Ultimate Behavior of Precast Segmental Box Girders With External Tendons


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Title: Ultimate Behavior of Precast Segmental Box Girders With External Tendons

Author(s): J. Muller and Y. Gauthier

Publication: Special Publication

Volume: 120


Appears on pages(s): 355-374

Keywords: bending moments; box beams; bridges (structures); computer programs; moment-curvature relationship; post-tensioning; precast concrete; prestressing steels; segmental construction; serviceability; stress-strain relationships; structural design; unbonded p

Date: 6/1/1990

The concept of precast segmental construction with external tendons has been developed extensively since 1978, starting with the construction of the Long Key Bridge (Florida). Since this first experience, many other structures (more than 5,500,000 ftý of deck) have been designed and successfully built using the same method. The performance of all bridges now in operation has been excellent. However, some questions were raised in the minds of engineers, unfamiliar with the method, regarding the behavior of structures prestressed with external tendons beyond the range of design loads (serviceability limit state). Because continuous reinforcement is not usually provided across the match cast joints between segments, concern was expressed that adequate ultimate behavior and sufficient strength could not be obtained. To provide a satisfactory answer to these legitimate questions, a special computer program (DEFLECT) has been developed to analyze accurately the response of the structures prestressed by external tendons. Moreover, several tests are available to confirm the behavior of such structures while verifying the validity of the DEFLECT computer program. This design tool has been used to predict the structural behavior of simply supported and continuous structures beyond joint opening, up to ultimate capacity of the girders with and without thermal loads. Several different prestressing methods have been analyzed with different bonding conditions at the point of deviation of the external tendons. It was found systematically that structures prestressed with either internal or external tendons behave essentially the same way at all loading stages up to ultimate.