Title: Bridge Girders:Strength at Transfer,Transmission & Development Length, De-bonding & Detailing

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Publication: CIA

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Date: 2/14/2011

Abstract:
Design of pretensioned prestressed concrete flexural members such as precast bridge girders has particular requirements that differ from post-tensioned prestressed concrete design. This paper examines strand transmission length, strand development length, de-bonding of strands and concrete strength at transfer in short-span applications as they relate to the achievement of flexural member capacity. The length required to develop the tensile capacity of strand is much greater than the transmission length nominated in earlier Australian design codes. Recognition of this fact is now provided for in the Bridge Design Code AS 5100.5 and the soon to be published revised AS 3600. It has also been shown that local de-bonding of strands for the purpose of controlling stress at transfer reduces both shear and moment capacity. This can result in cracks penetrating to the strand causing anchorage to be reduced or even destroyed. Presented also in this paper is guidance on a methodology for the rational design for de-bonding. With increasing size and complexity of precast prestressed concrete in infrastructure, it is timely to also revisit the subject of design detailing and its economic influence on the manufacture of precast elements.