| 1. |
- Bergström, Markus, et al.
(författare)
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Degradation of structural performance : Experiment introduction and expected results
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 - 9780415403153 ; , s. 251-252
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Much effort has been put on investigating degradation of concrete structures, repair and upgrading separately, as can be read in numerous publications, i.e., Green et. al. (2003), Morgan (1995) and Täljsten (2004). However, an overall view has not been taken where the whole life cycle of a concrete structure is considered. In particular, no laboratory tests have been presented in the literature to the author's knowledge. A structure passes several stages during its life. Normally two major stages are discerned, the service limit state (SLS) and the ultimate limit state (ULS). Concrete structures are designed for both these stages. In the SLS normally the deformation and crack widths are controlled. Deformation due to comfort demands and crack widths due to durability demands. In the ULS the structure is designed for its ultimate capacity - which for civil and building structures almost never is reached. From a safety aspect the ULS is most important; however, for the client the SLS with regard to maintenance, repair and upgrading are most costly. If the SLS was better understood, in particular from a rehabilitation point of view, more robust and cost effective repair and upgrading system could be developed. (Figure Presented). This paper is also a part of "Sustainable bridges". "Sustainable bridges" is a European project which focus is to preserve bridges throughout Europe and create unanimous codes for all participating countries. The project presented in this paper, Degradation of Structural Performance (DOSP), will investigate the behaviour of concrete beams which will endure a simulated life cycle procedure. The test program will direct the beams from full strength of the intact beam through degradation, repair and upgrading with FRP plate bonding to its original strength again or near. The cross-sectional strain distribution will be monitored during the test using Fibre Bragg Grating (FBG) Strain Sensors as well as traditional strain gauges. This gives the possibility of comparing results in between the two monitoring techniques over proportionately long time span. An accelerated corrosion procedure is used to corrode the flexural tensile reinforcement. The cycle may be divided into seven stages, a to g, presented shortly in Figure 1, Horrigmoe (1998) and Sand 2001. This life cycle is possible in the real case scenario for bridges or other concrete structures which are subjected to chlorides, i.e. de-icing salt or sea water
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| 2. |
- Blanksvärd, Thomas, et al.
(författare)
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Mineral based bonding of CFRP to strengthen concrete structures
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 - 9780415403153 ; , s. 1057-1058
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Strengthening of concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has been proved to be a good strengthening technique. However, this strengthening technique with epoxy adhesives do contain some disadvantages such as diffusion closeness, thermal incompatibility to the base concrete, working environment and minimum application temperature. Some of these drawbacks can be overcome by substituting the epoxy to a polymer reinforced mortar as the bonding agent. This work presents a pilot study with CFRP strengthened concrete beams. In this case the epoxy bonded CFRP has been replaced with a mineral based composite (MBC). The results from the pilot study indicates that the MBC strengthening system do achieve very good composite action and strengthening effects. These results warrant for further research and improvement of the MBC strengthening system
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| 3. |
- Enochsson, Ola, et al.
(författare)
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Assessment and condition monitoring of a concrete railway bridge in Kiruna, Sweden
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor and Francis Group. - 0415403154
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Konferensbidrag (refereegranskat)abstract
- A two-span railway concrete trough bridge over Luossajokk in Kiruna in northern Sweden has been studied. The owner wanted to increase the axle loads from 250 to 300 kN in order to reduce freight costs for iron ore. Examples are given of methods used and results obtained from the assessment where bending, shear and fatigue were studied. Material properties, loads and load carrying capacity were evaluated using deterministic and probabilistic methods. It was shown that the bridge could carry the higher loads with a safety index β > 4.7 for reasonable assumptions of the load distributions. A measurement system was installed to check the actual level of critical strains and the worst positions of the train. Results are also given from a condition monitoring program 2001-2006, launched to periodically check the development of strains with time.
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| 4. |
- He, Guojing, et al.
(författare)
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Numerical modeling and dynamic behavior of a railway concrete bridge over the Vindel River in Sweden
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 ; , s. 104-111
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Konferensbidrag (refereegranskat)abstract
- The Vindel Railway Bridge in northern Sweden is composed of a concrete deck, columns and an arch with a span of 110 m and a height of 22 m. In order to check the possibility to increase the axle load from 225 kN to 250 kN, the properties of the bridge needed to be evaluated. Especially, the dynamic behavior of the bridge is an important factor as it is affecting the load bearing capacity and the serviceability. In this paper, two types of three-dimensional (3-D) finite element models have been developed. One uses shell elements and the other uses beam elements. Based on the 3-D FE models, the effects of nonstructural mass, side spans and connection between columns and deck on the dynamic behavior are discussed. Furthermore, field test data from passing through train are compared with the results calculated by the models. The numerical simulations of the dynamic response coincide reasonably well with the field test data.
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| 5. |
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| 6. |
- Nordin, Håkan, et al.
(författare)
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Strengthening of concrete structures by external prestressing
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 - 9780415403153 ; , s. 1047-1048
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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).
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| 7. |
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| 8. |
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| 9. |
- Plos, Mario, et al.
(författare)
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Structural assessment of railway concrete bridges : non-linear analysis and remaining fatigue life
- 2006
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Ingår i: Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost. - London : Taylor and Francis Group. - 0415403154 ; , s. 271-
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Konferensbidrag (refereegranskat)abstract
- For a sustainable development in Europe, there is a need to at least double the railway transports in the coming 20 years. In order to reach this, the residual service lives of existing concrete bridges need to be extended at the same time as they are subjected to higher axle loads, higher railway speeds and heavier traffic intensity. Today, many concrete bridges are replaced or strengthened because their reliability cannot be guaranteed based on the structural assessments made. The aim of the work presented here is to provide enhanced assessment methods that are able to prove higher load carrying capacities and longer fatigue lives for existing concrete railway bridges. One main objective is to facilitate the use of non-linear analysis for structural assessment. In addition to higher load carrying capacities, the methods give improved understanding of the structural response, forming a better basis for decisions in the assessment. Another main objective is to improve knowledge about the fatigue behaviour of concrete bridges and to develop realistic methods for the evaluation of remaining fatigue life of existing bridges. The emphasis here is on short-span bridges and secondary elements. The work presented is a part of the ongoing EU-project Sustainable Bridges. The results will be implemented in the Guideline for Load and Resistance Assessment of existing European Railway Bridges that is being developed
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| 10. |
- Rusinowski, P., et al.
(författare)
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Numerical analysis of two-way concrete slabs with openings strengthened with CFRP
- 2006
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Ingår i: Bridge maintenance, safety, management, life-cycle performance and cost. - London : Taylor & Francis Group. - 0415403154 - 9780415403153 ; , s. 1045-1046, s. 387-390
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Carbon Fibre Reinforced Polymers, CFRP, offer excellent corrosion resistance to environmental agents as well as the advantages of high stiffness-to-weight and strength-to-weight ratios when compared to conventional construction materials. Perhaps the biggest advantage of CFRP is its tailorability. One common application for CFRP sheets is to strengthen slabs and walls when openings are to be made. In spite of this, there have not been many studies reported on slabs with openings strengthened with CFRP and especially, not with distributed loading. This paper presents numerical analyses of simply supported two-way concrete slabs with openings strengthened with CFRP sheets. The finite element program ABAQUS is utilized for the analyses. The analyses are compared with full-scale laboratory tests and show a good agreement
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