Post-tensioned stress ribbon systems in long-span roofs : Case study: Västerås Travel Center

University essay from KTH/Betongbyggnad; KTH/Betongbyggnad

Abstract: The stress ribbon system has numerous advantages, that includes but are not limitedto: increasing overall stiffness, control deflections and reduction of materialsconsumption, which in turn, reduces the load and the cost. Nevertheless, its use isusually limited to bridges, in particular, pedestrian bridges; this can be attributedto the insufficient space that buildings’ usually have for end supports, or/and backstayedcables, that can accommodate the expected high pull-out forces occuring atthe cables’ ends. In this work, the roof of Västerås Travel Center, which will become one of the longestcable suspended roofs in the world, was chosen as a case study. The aim was toinvestigate the optimal technique to model the post-tensioned stress ribbon systemfor the roof structure using SAP2000, and to assess any possible reduction in thepull-out forces, deflections and concrete stresses. Subsequently, a conventional cablesuspended roof was simulated, using SAP2000, and compared to the post-tensionstress ribbon system in order to examine the potential of the latter. Moreover,the effects of temperature loads and support movements on the final design loadswere examined. Based on the study, a few practical recommendations concerningthe construction method and the iterative design process, required to meet thearchitectural geometrical demands, are stated by the authors. The results showed that the post-tensioned stress ribbon system reduces the concretestresses, overall deflections, and more importantly, reduces the pull-out forces by upto 16%, which substantially reduces the design forces for the support structures.The magnitude of these reductions was found to be highly correlated to the appliedprestressing force, making the size of the prestressing force a key factor in the design.

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