Deflection Prediction and Cracking of Beams Prestressed with Unbonded Tendons

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Title: Deflection Prediction and Cracking of Beams Prestressed with Unbonded Tendons

Author(s): O. Ozkul, H. H. Nassif, and F. Malhas

Publication: Special Publication

Volume: 225

Issue:

Appears on pages(s): 93-118

Keywords: beams; crack width; deflection; high strength concrete; serviceability; unbonded tendons

Date: 3/1/2005

Abstract:
With the introduction of high strength concrete and larger diameter strands, more emphasis is placed on developing new types of prestressing alternatives that would take advantage of these new developments. Moreover, the use of replaceable unbonded tendons allows future upgrade, maintenance, and rehabilitation of concrete structural elements. However, few researchers have addressed the behavior of beams with unbonded tendons under service loads. There is a need to adopt simplified and rigorous procedures for the prediction of deflection as well as the cracking behavior. This paper presents a new rigorous procedure for calculating the deflection of high strength concrete girders prestressed with unbonded tendons. The analysis is based on the “trussed-beam” analogy used to model the prestressed concrete girder and the unbonded tendons as trussed beam system. To validate the analysis, a total of twenty-two beams with various parameters were tested to failure. Results are presented in terms of load versus deflection as well as the stress in tendon.