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Finita Element Metoden som verktyg för systemberäkning av Alnöbron: Möjligheter och begränsningar i modelleringen av spännarmerade konstruktioner
2013 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Over time people´s way of life has changed and thus the use of existing structures. There is a considerable value in continuing to use these structures and adapt them to today´s needs. In recent decades, the bike has a more significant role in everyday life, which requires a secure and highly available infrastructure. The town of Sundsvall has expressed a desire to explore the possibility of moving traffic lanes on Alnö Bridge to make way for a wider sidewalk. Transport Administration has ordered an investigation of the load carrying capacity of Alnö Bridge to evaluate if it is possible to adapt the existing bridge to today ´s needs as well as to check its current status.The Alnö Bridge was built in the 1960´s and connects the island Alnön with the mainland just north of Sundsvall. It is built as a Freivorbau bridge in prestressed concrete. Calculations are in this report performed to evaluate the sectional forces in the bridge. This is done using the finite element method, where the focus is on how the prestressed concrete is covered in a finite element model. Recently use of the finite element method has increased for analysis of structures because it provides a more accurate description of reality. For this reason it may be possible to increase the load carrying capacity of a structure, which is examined in this thesis by performing a comparison of the sectional forces calculated by the displacement method.For this reason it is possible to increase the resistance of a structure, which is examined in this thesis by performing a comparison of sectional forces calculated by the displacement method.The results demonstrate lower sectional forces in all the finite element models in comparison with the model performed with the displacement method. This indicates that a higher load carrying capacity can be achieved by using the finite element method. The results show up to 17 % lower results for bending moment, 13 % for lateral forces and 23 % regarding torque.Stress concentrations have been identified at the connection between the web and the bridge deck, where the longitudinal, transversal and vertical prestressed tendons interact. The results show that local stress concentrations occur in the concrete with tensile stresses up to 5,517 MPa, which is higher than the tensile strength of most concrete classes. The evaluation of these stress concentrations has been limited and a more thorough investigation is necessary before it may be possible to use them for designing purposes.The expectations when the thesis was started were to be able to take into account the large amount of prestressed tendons in a detailed manner. Due to the fact that the finite element programs was not built to calculate the time dependent prestress losses that occur in the prestressed tendons, time consuming manual calculations were required. This means that the effects of performing a detailed finite element model became less important. In summary, the finite element method is a good method to analyze prestressed concrete structures but the implementation was more difficult and time consuming than anticipated. It requires detailed work procedures for the model to reflect reality and it requires a good knowledge of the conditions that apply.

Place, publisher, year, edition, pages
Keyword [en]
Keyword [sv]
Teknik, Alnöbron, BRIGADE/Plus, finita elementmetoden, Freivorbau broar, förskjutningsmetoden, systemberäkning, spännkraftsförluster, spännstål, tidsberoende effekter
URN: urn:nbn:se:ltu:diva-56663Local ID: d6ab8ee6-f295-416e-ad55-00b157113eb7OAI: diva2:1030050
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Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20131008 (global_studentproject_submitter)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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Manneteg, KristoferJohansson, Therese

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