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- Bennitz, Anders, et al.
(författare)
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External prestressing of RC T-beams with CFRP tendons
- 2009
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Ingår i: Proceedings of the 9th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures. - Adeleide : University of Adelaide. - 9780980675504
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Konferensbidrag (refereegranskat)
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| 2. |
- Bennitz, Anders, et al.
(författare)
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Failure modes of prestressed CFRP rods in a wedge anchored set-up
- 2009
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Ingår i: Advanced Composites in Construction (ACIC) 2009 Conference Proceedings. - : ACIC. ; , s. 104-114
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Konferensbidrag (refereegranskat)abstract
- In the process of developing a new wedge anchorage to anchor prestressed CFRP rods, five different anchorage designs were manufactured. These designs have led to a constantly increased ultimate failure load of the prestressing system and an eventual load level above 95% of the ultimate failure load of the rod was achieved. If 100% efficiency is achieved the anchorage does not reduce the capacity of the system, but failure is then governed by the capacity of the rod itself, which is considered favourable and required by several guidelines. In the process seven different failure modes were identified: soft slip, power slip, cutting of fibres, crushing of rod, bending of fibres, frontal overload and intermediate rupture. In this paper the failure modes are discussed further. The failures are documented with explanatory figures and their backgrounds are found in the theory. Suggestions are given on how these failures can be avoided in theory and practice. From the experiences gained in the project, it is concluded that it is a challenging task to create a fully mechanical anchorage for CFRP tendons and that the failure margins are small between a successful and an unsuccesful anchorage system.
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| 3. |
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| 4. |
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| 5. |
- Bennitz, Anders, et al.
(författare)
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Strengthening of a railway bridge with NSMR and CFRP tubes
- 2008
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Ingår i: FRP Composites in Civil Engineering. - Dübendorf : EMPA-Akademie. - 9783905594508
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Konferensbidrag (refereegranskat)abstract
- Strengthening of structures with CFRP is considered today as an accepted method in the upgrading of concrete structures. This paper presents the use of two different CFRP strengthening systems combined to extend the service life of a Swedish double-trough-doubletrack railway bridge, constructed in concrete with a 10 meter span. One system is the reliable NSMR (Near Surface Mounted Reinforcement) while the other is new. They were used with the intention to strengthen the interior of a concrete structure using integrated CFRP tubes. Both systems were used to increase the tensile flexural strength of the slab transverse to the tracks. NSMR bars were positioned in the bottom concrete cover of the trough's bottom-slabs, while the new system was inserted in holes drilled through the bridge in the cross direction and located in the upper part of the slab. In connection with the strengthening monitoring was conducted in order to obtain an understanding of the bridge behaviour before and after strengthening, and to demonstrate any effects of the extra CFRP reinforcement. Results from these measurements are presented together with how the strengthening work was carried out. Sensors on bars and tubes show evidence of utilization of the CFRP while displacement sensors and strain gauges on the steel reinforcement show minor effect due to the small loads in the service limit state.
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| 6. |
- Bennitz, Anders, et al.
(författare)
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Undersökning av skjuvförband i trä : provning av bulttyper för Vasaskeppet
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Föreliggande rapport är resultatet av laboratorieförsök vilka utförts på avdelningen för byggkonstruktion vid Luleå tekniska universitet. Försöken har genomförts under slutet av 2007 och är en direkt fortsättning av tidigare försök från 2004 och 2005. De tidigare rapporterna pekade på ett behov av fortsatt provning. Föreliggande rapport är således en fortsättning av tidigare arbete, dock med vidareutveckling av möjliga bulltyper för Vasaskeppet. De testade bulltyperna har konstruerats och tillverkats i Statens Maritima Museer regi av Anders Ahlgren. Försöken har genomförts vid Luleå tekniska universitet och Complab, av Civ. Ing. Georg Danielsson samt forskarstuderande Anders Bennitz.
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| 7. |
- Bergström, Markus, et al.
(författare)
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Bro över Järpströmmen : kompletterande mätning av påkänningar vid tung överfart
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Kompletterande mätning på bron över Järpströmmen genomfördes då lasten vid föregående mätning ansågs för liten. Vid aktuell mätning bestod lasten av ett transportekipage med en totalvikt på cirka 400 ton fördelat på 20 hjulaxlar och en bit över 100 däck. Mycket låg påkänning i kolfibermaterial och stålarmering, i storleksordningen omkring 5 m/m. Den låga påkänningen härleds inte till en för låg last, då ekipagets tyngd är stor. Däremot kan mätresultaten förklaras i att tvärkraftsarmeringen och förstärkningen inte tar last förrän uppsprickning av brobetongen inträffar. Betongbrons spricklast förutsätts inte vara uppnådd vid aktuell lastnivå, vilket förklarar de små töjningarna på armering och kolfiber. Detta resonemang baseras på genomförda försök (Carolin, 2003). Erfarenhetsmässigt är tvärkraftsförstärkning med kolfiberlaminat en fungerande och effektiv metod för att uppgradera en konstruktion. Kolfiberförstärkningen har konsekvent en töjning omkring 5 με vid överfart, vilket visar att förstärkningen tar last och därmed fungerar. Ingen tendens av vidhäftningsproblem finns vid aktuell lastnivå, vilket stöds av att armeringen och kolfibermaterialet töjs lika mycket. Detta betyder att förstärkningen fortsätter ta mer last vid ökad belastning. Förstärkningen kan därför förutsättas bidra till en ökad kapacitet i brottgränstillstånd, då uppsprickning av betong inträffar, trots att effekterna är svåra att bestyrka i bruksgränstillstånd och utförd mätning.
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| 9. |
- 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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| 10. |
- Bergström, Markus, et al.
(författare)
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Failure load test of a CFRP strengthened railway bridge in Örnsköldsvik, Sweden
- 2009
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Ingår i: Journal of Bridge Engineering. - 1084-0702 .- 1943-5592. ; 14:5, s. 300-308
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Tidskriftsartikel (refereegranskat)abstract
- The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in Örnsköldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.
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