Ultimate limit state analysis of externally post-tensioned structures.

摘要

The UK Department of Transport (DoT) has recently encouraged the use of externallyudpost-tensioned structures for bridge construction. This is due to the durabilityudproblems encountered with the conventional internally bonded post-tensionedudstructures. However, due to the lack of bond between the concrete and the externaludtendons, the ultimate strength of these structures cannot be determined by justudperforming a sectional analysis at the section of maximum moment. Although severaludrecommendations have been made for the ultimate analysis of these structures, noneudwere considered satisfactory here. Hence the purpose of this investigation is to studyudthe flexural behaviour of these structures of all stages up to collapse, and to propose audpractical methodology for estimating their ultimate strength.udThe study introduces eight non-linear analytical models developed for the predictionudof the moment vs. deflection response of simply supported externally post-tensionedudbeams (with and without deviators located along their spans) up to ultimate. Theudmodels employ an iterative procedure that involves the application of loads to theudstructure in increments up to the collapse condition, where the curvature distributionudpredicted at each loading sequence is used to estimate the stress increase and variationudin eccentricity in the external tendons. Second-order effects due to variation inudeccentricity of external tendons and frictional behaviour of tendons at the deviatorsudare both taken into account in these models. The eight models were then verified byudcomparing the results derived from them with reported experimental data, wherebyudgood correlation was obtained. An extensive parametric study was subsequentlyudconducted using the proposed models applied to the various parameters that influenceudthe ultimate behaviour of externally prestressed structures Finally, theudrecommendations in the codes of practice for the ultimate design of these structuresudwere also investigated here