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Strengthening of concrete structures by external prestressing
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.ORCID iD: 0000-0001-7799-5809
2006 (English)In: Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006 / [ed] Paulo J. S. Cruz; Dan M. Frangopol, London: Taylor & Francis Group, 2006, p. 1047-1048Conference paper, Meeting abstract (Other academic)
Abstract [en]

Rehabilitation and strengthening of existing concrete structures has become more and more in focus during the last decade. All over the world there are structures intended for living and transportation. The structures are of varying quality and function, but they are all ageing and deteriorating over time. Some of these structures will need to be replaced since they are in such a bad condition. However, it is not only the deterioration processes that make upgrading necessary, errors can have been made during the design or construction phase so that the structure needs to be strengthened before it can be used. The causes for repair and/or strengthening can be many, but normally deteriorated concrete, steel corrosion, change of use, increased demands on the structure, errors in the design or/and construction phase or accidents are governing factors. Many methods to repair or/and strengthen concrete structures exists such as concrete overlays, shotcrete, use of external prestressed tendons, just to mention a few. Prestressing is in particular interesting with several comparable advantages to other methods. In this paper the use of prestressing for repair and strengthening are briefly discussed and tests on concrete T-beams with external Prestressed tendons of steel or CFRP (Carbon Fibre Reinforced Polymer) are presented. The tests shown that prestressing is a very effective way to increase the existing load carrying capacity of existing concrete members. The presented project is a small part of a larger European funded project, the "Sustainable Bridges", where the aim is to evaluate the load carrying capacity and life of existing railway bridges with the purpose to increase existing load carrying capacity with 25% and the train speed to 350 km/h. The tests were carried out at Luleå University ofTechnology (LTU). The test specimens were concrete T-beams with a length of 6 meters, see figure 1. The beams were loaded under four-point bending, the load was applied with deformation control at 0.2 mm/s until failure or to a point where the beam no longer could carry any more load. A total of eight beams were tested during the series. The strengthening techniques used were externally prestressed steel rods, externally prestressed CFRP rods and Near Surface Mounted Reinforcement (NSMR) CFRP rods with and without prestress. For the steel tendons a traditional steel wedge anchor was used, but that was not possible for the CFRP tendons, as normal steel wedge anchors would crush the FRP tendons. For the tests an anchor was developed using a nylon wedge. To get better effect of the anchor, the tendons had quarts sand glued on them in the zone for anchoring. As those anchors would not be able to take as high forces as a steel anchor on a steel tendon six tendons were used instead of two. However, as the prestressing was applied it became clear that it would not be possible to achieve the same prestressing force as with the steel tendons. With the exception of the beam with external CFRP tendons all the tested beams behaved as expected. The strengthening effects for the prestressed beams were over 100% bom for concrete cracking and steel yielding. When looking at the post-steel yielding behaviour it is interesting to compare the beams strengthened with unbonded tendons and those with bonded tendons (Steel 3 and NSMR PS). The beams with bonded tendons and rods showed a better behaviour after steel yielding than those with (Graph Presented) unbonded tendons. The problems with the CFRP anchor during prestress continued during loading and the loads were much lower for that beam then predicted. In figure 2 the loads and displacements are shown. The tests show a large increase in crack and steel yielding loads. The increase in load for steel yielding can be very important for a constructions life, the fatigue behaviour will improve and as a consequence the crack widths will be smaller which can result in increased durability. Together with higher crack loads the cracks also go smaller, this should also indicate a more advantageous behaviour in the service limit state (SLS).

Place, publisher, year, edition, pages
London: Taylor & Francis Group, 2006. p. 1047-1048
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-28654Local ID: 28750940-7acc-11df-ab16-000ea68e967bISBN: 0-415-40315-4 (print)ISBN: 978-0-415-40315-3 (print)OAI: oai:DiVA.org:ltu-28654DiVA, id: diva2:1001856
Conference
International Conference on Bridge Maintenance, Safety and Management : 16/07/2006 - 19/07/2006
Note
Godkänd; 2006; 20100618 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-20Bibliographically approved

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Nordin, HåkanTäljsten, Björn

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