During the design process of members post-tensioned with unbonded tendons, deformations of the whole structure between anchorages, having impact on ultimate value of prestressing force, shall be considered. The conducted researches enabled the separation of several parameters influencing the stress increase in unbonded tendons – i.a. the loading pattern in multi-span members. This paper presents selected codes are shown and compared.
The design of multi-span structures post-tensioned with unbonded tendons may differ from the assigned one for reinforced structures or structures post-tensioned with bonded tendons. In some cases Ultimate Limit State can be reached by different loading patterns to which we got used to i.e. load cases which result in maximum values of bending moments in spans and at supports. This behaviour is related to the lack of bond between concrete and strands and the assumption that the force in tendons has a uniform value between anchorages.
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