| 1. |
- Blomfors, Martin, et al.
(författare)
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Reliability analysis of corroded reinforced concrete beam with regards to anchorage failure
- 2019
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Ingår i: Life-Cycle Analysis and Assessment in Civil Engineering. - : CRC Press/Balkema. - 9781138626331 - 9781351857574 ; , s. 337-344, s. 337-344
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Konferensbidrag (refereegranskat)abstract
- Reinforcement corrosion is a common problem in reinforced concrete infrastructure today, and it is expected to increase in the future. To simply replace the corroded structures with new ones requires large resources, both in financial and environmental terms. Therefore it is important that existing structures are used to their full potential, also after the onset of corrosion. This paper presents a reliability study of the anchorage capacity of a reinforced concrete beam including reinforcement corrosion. The sensitivity of the different input parameters is also studied. As expected, the results show that the reliability is reduced with corrosion; the magnitude depends to a large extent on the modelling uncertainty used for the bond model for corroded reinforcement. The sensitivity analysis shows an influence of corrosion also on the sensitivities of the input parameters, which is expected based on the properties of the underlying bond model. This paper demonstrates that probabilistic evaluations give valuable insight of the reliability, which can be used to prolong the service-life of existing infrastructure and save both money and the environment.
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| 2. |
- Gotame, Milan, et al.
(författare)
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Finite element analyses of FRP-strengthened concrete beams with corroded reinforcement
- 2022
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Existing deteriorated reinforced concrete (RC) structures need strengthening to extend service life. Fibre reinforced polymer (FRP) has been widely used to strengthen sound structures, but its application on damaged concrete structures still needs to be investigated. This paper presents non-linear finite element analyses conducted to assess the flexural behaviour of corrosion-damaged RC beams strengthened with externally bonded FRP. Beams in four different categories were analysed: a reference beam, a corroded but non-strengthened beam, and corroded beams strengthened with glass FRP (GFRP) and carbon FRP (CFRP) respectively. Furthermore, the strengthened beams were modelled with different modelling choices to investigate the effectiveness of FRP applied to the beam soffit and as U-jackets. Pre-loading and corrosion-induced cracks were incorporated by reducing the tensile strength of concrete elements at crack locations. Average and pitting corrosion were incorporated by reducing the cross-sectional area of the reinforcement corresponding to the measured corrosion levels. Interface elements were used to simulate the bond between FRP and concrete. The modelling methods were validated against experimental results. It was found that modelling of pitting corrosion, especially the location of pits, lengths and number of pits considered, were influential in predicting the load and deformation capacity of beams. A CFRP plate at the beam soffit, combined with inclined U-jackets at its ends of the CFRP plate provided sufficient flexural strengthening. Thus, intermediate U-jackets did not further increase the load-bearing capacity for the studied beam geometry and corrosion damages. However, with a GFRP sheet at the beam soffit, both inclined and intermediate U-jackets were needed to provide full utilisation of the GFRP sheet for the studied beam geometry. In further studies of the effectiveness of the strengthening methods, it is recommended to investigate beams of varying dimensions, corrosion patterns and levels, and FRP spacing and dimensions.
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| 3. |
- Lundgren, Karin, 1968, et al.
(författare)
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Ta hänsyn till korrosionsskador vid reparation och förstärkning av betongkonstruktioner!
- 2022
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Ingår i: Bygg och teknik. - 0281-658X. ; 22:6, s. 40-42
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Vår byggda miljö består till stor del av armerade betongkonstruktioner, varav många har hunnit bli ganska gamla. Till exempel förvaltar Trafikverket nästan 20 000 broar, och merparten är byggda i armerad betong. Av dessa har många skador i form av korroderad armering. Kommande klimatförändringar förväntas öka på skadetakten. För broar ökar dessutom kraven på lastkapacitet med tiden. Samhället står därför inför en stor utmaning att kunna garantera säkerheten i det åldrande beståndet med begränsade ekonomiska resurser. Att kunna reparera eller förstärka konstruktioner gör att livslängden för många gamla och kulturellt värdefulla broar kan förlängas, vilket ger stora ekonomiska besparingar, minskade koldioxidutsläpp och mindre störningar i trafiken. Vi kommer därför att i en ökande omfattning behöva reparera och förstärka konstruktioner med befintliga korrosionsskador. Vi har studerat lämpliga metoder för slakarmerade balkar i ett doktorandprojekt och två examensarbeten på Chalmers, se [9], [6], [3]. Resultaten från dessa arbeten presenteras kort i denna artikel.
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| 4. |
- Blomfors, Mattias, 1990
(författare)
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Assessment of Concrete Structures Including Corrosion and Cracks
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reinforced concrete (RC) structures constitute a major proportion of the built environment and society relies continuously on their service. Many of these structures were built in the era following the Second World War and are thus approaching the end of their intended service life. The likelihood of deterioration increases with time and so damage caused by, say, corrosion is not uncommon. Also, increased demands are often laid on the load-carrying capacity of existing bridges, aimed at increasing utilisation of the road network by allowing heavier vehicles. Simply dismantling and re-constructing all bridges at the end of their designed service life, or taking needless strengthening measures, is unsustainable. Rather, improved methods of assessing the capacity of existing infrastructure are needed. The current work has aimed to develop improved, reliable assessment methods. Its focus areas were structures with reinforcement corrosion and structures with cracks from previous loading. Both simplified and advanced methods of evaluating anchorage capacity were developed for concrete structures with corroded reinforcement. The simplified method modifies the bond stress-slip relationship and is calibrated against a large database of bond tests, with the safety margin ensured by deriving partial safety factors. The advanced method is based on finite element (FE) analysis, with tensile material properties altered for elements positioned at the splitting cracks along the reinforcement. The latter method was also investigated for RC without corrosion damage but with cracks from previous loading. Design results from advanced nonlinear FE analyses (meaning results with a proper safety margin) are obtained by applying a “safety format”. The current work investigated whether safety formats available in fib Model Code 2010 also ensured reliable design capacities for structures with somewhat complicated load application and geometry; in this case, a concrete frame subjected to vertical and horizontal loads. The results indicate that the anchorage capacity may be reasonably well estimated by using the simplified method. The proposed partial safety factors also provided sufficient safety margin. Furthermore, in the advanced anchorage assessment, the capacity could be estimated solely from weakened tensile properties located at the position of the splitting cracks and without input concerning the corrosion level. Moreover, by including cracks from previous loading in advanced modelling, improved predictions of the failure mode, ultimate capacity and ductility were demonstrated. Lastly, in the investigation of safety formats for nonlinear FE analysis, the method of estimating a coefficient of variance of resistance (ECOV), did not reach the intended safety level. However, the global resistance factor method (GRF) and partial factor method (PSF) did. This work has the potential to improve both simplified and advanced assessment methods, providing more sustainable infrastructure management in the future.
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| 5. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Development of engineering assessment method for anchorage in reinforced concrete
- 2016
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Ingår i: Nordic Concrete Research. ; 2/2016:55, s. 63-78
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Konferensbidrag (refereegranskat)abstract
- There is an increasing need for reliable methods to assess load-carrying capacity and remaining service life of existing infrastructure. Several previous research projects have resulted in a verified, simple 1D model for assessment of anchorage in corroded reinforced concrete structures. Current research aims to extend the 1D model to comprise more practical situations. To verify the 1D model for various cases appearing in practice, such as multiple layers and bundled reinforcement, 3D analyses were carried out. The size of 3D NLFE models required to capture the bond behaviour between corroded reinforcement and concrete is investigated, this to enable efficient analyses. Beam-end models and models of sub-sections with varying sizes and boundary conditions were studied, and the results in terms of bond stress and crack pattern compared. Good agreement was found for several section models; however the choice of boundary conditions largely influence the results and can lead to overestimation of the capacity.
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| 6. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Digitala tvillingmodeller underlättar bedömning av risker
- 2019
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Ingår i: Samhällsbyggaren. - 2000-2408. ; , s. 24-25
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Digitala tvillingmodeller är digitala simuleringar som kombinerar information om en fysisk verklighet med avancerade beräkningsmodeller. I ett pågående samarbete mellan Chalmers och Stanford utvecklas digitala tvillingmodeller av broar, vilket kommer att leda till förbättrade tillståndsbedömningar och beslutsunderlag i framtiden; se digitaltwinslab.com.
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| 7. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Engineering Assessment Method for Anchorage in Corroded Reinforced Concrete
- 2016
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Ingår i: IABSE Congress Stockholm 2016. - : IABSE c/o ETH Hönggerberg. - 9783857481444 ; , s. 2109-2116
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Konferensbidrag (refereegranskat)abstract
- There is an increasing need for reliable methods to assess load-carrying capacity and remaining service life of existing infrastructure. Several previous research projects have resulted in a verified, simple 1D model for assessment of anchorage in corroded reinforced concrete structures. Previous verification has involved both experiments and detailed 3D NLFE analyses. To further develop the 1D model it needs to be extended to comprise more practical situations. In order to facilitate an efficient extension procedure in the future, the size of 3D NLFE model that is required to capture the bond behaviour between corroded reinforcement and concrete is investigated. Beam-end models and models of sub-sections were studied, and the results in terms of bond stress and crack pattern were compared. Preliminary results indicate good agreement for some situations; however for some cases a section model seems to overestimate the capacity.
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| 8. |
- Blomfors, Mattias, 1990, et al.
(författare)
-
Engineering bond model for corroded reinforcement
- 2018
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 156, s. 394-410
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion of the reinforcement in concrete structures affects their structural capacity. This problem affects many existing concrete bridges and climate change is expected to worsen the situation in future. At the same time, assessment engineers lack simple and reliable calculation methods for assessing the structural capacity of structures damaged by corrosion. This paper further develops an existing model for assessing the anchorage capacity of corroded reinforcement. The new version is based on the local bond stress-slip relationships from fib Model Code 2010 and has been modified to account for corrosion. The model is verified against a database containing the results from nearly 500 bond tests and by comparison with an empirical model from the literature. The results show that the inherent scatter among bond tests is large, even within groups of similar confinement and corrosion level. Nevertheless, the assessment model that has been developed can represent the degradation of anchorage capacity due to corrosion reasonably well. This new development of the model is shown to represent the experimental data better than the previous version; it yields similar results to an empirical model in the literature. In contrast to many empirical models, the model developed here represents physical behaviour and shows the full local bond stress-slip relationship. Using this assessment model will increase the ability of professional engineers to estimate the anchorage capacity of corroded concrete structures.
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| 9. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Evaluation of safety formats for non-linear finite element analyses of statically indeterminate concrete structures subjected to different load paths
- 2016
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Ingår i: Structural Concrete. - : Wiley. - 1751-7648 .- 1464-4177. ; 17:1, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- To increase the efficiency of new structures and perform safety evaluations of existing structures, it is necessary to model and analyse the non-linear behaviour of reinforced concrete. The applicability of the safety formats in present design codes is unclear for indeterminate structures subjected to loading in several directions. The safety formats in fib Model Code 2010 have been evaluated for a reinforced concrete frame subjected to vertical and horizontal loading and the influence of load history studied. Basic reliability methods were used together with response surfaces to assess the failure probabilities and one safety format did not meet the intended safety level. The results indicate the importance of load history and it is concluded that more research is required regarding how load history influences the safety level of complex structures.
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| 10. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Incorporation of cracks in finite element modelling of existing concrete structures
- 2019
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Ingår i: Structural Health Monitoring 2019: Enabling Intelligent Life-Cycle Health Management for Industry Internet of Things (IIOT) - Proceedings of the 12th International Workshop on Structural Health Monitoring. - Lancaster, PA : DEStech Publications, Inc.. ; 1, s. 1611-1618
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Konferensbidrag (refereegranskat)abstract
- Transport infrastructures are fundamental in society and interruption in their service leads to large economic losses. However, inspection and maintenance work of said infrastructures need to be performed to ensure their safety, which traditionally involves limitation or interruption of their use. This paper treats the finite element modelling part of a framework for non-intrusive assessment of existing structures. In practice, the load history of a structure is rarely known in detail. Here, existing cracks due to previous loading is included from the start of the finite element (FE) analysis to circumvent this issue. The focus is on comparing the choice of different shear retention factors for discrete cracks based on comparison to experimental test results. The results indicate that the shear retention factor used for the discrete cracks does not influence the capacity, which remains the same for all considered values. It appears the anchorage force development of the bond-slip reinforcement does not rely on shear transfer in the discrete crack in the adopted FE model. Moreover, the results showed that combining both discrete cracks and abond-slip relation implicitly including the loss of confinement due to corrosion-induced splitting cracks leads to excessively low capacity compared to experimentalresults. From the present study it can be concluded that the shear retention factor is of little importance for the considered FE model. However, it is emphasized that other modelling choices may entail other findings.
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