| 1. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Practical bond model for corroded RC bridges
- 2017
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Ingår i: High Tech Concrete. - Cham : Springer International Publishing. - 2617-4820. - 9783319594705 ; , s. 1793-1803
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Konferensbidrag (refereegranskat)abstract
- Corrosion of steel reinforcement is a common cause of deterioration in reinforced concrete bridges and many existing bridges are damaged to varying degrees. The rate of deterioration of the bridge stock has been shown to increase due to climate change. Unsympathetically, the demand for load-carrying capacity is however often increased with time. Therefore there is an increasing need for reliable methods to assess the load-carrying capacity and remaining service-life of existing infrastructure. A simple model for the assessment of Anchorage in corroded Reinforced Concrete structures (ARC) has previously been developed. It was originally based on fib Model Code 1990 and has been verified with experiments and three-dimensional nonlinear finite element (3D NLFE) analyses for both accelerated and natural corrosion as well as for different degrees of corrosion. The model was applied when assessing two road bridges in Sweden. The investigation demonstrated great cost savings but also areas for improvement, in particular regarding (a) applicability to practical cases and (b) incorporation of uncertainties in the assessment. The primary focal point of this paper is to present an overview of the development of the ARC model together with recent verifications against a large bond test database as well as foreseen future developments. It was found that the ARC model represents the physical behaviour reasonably well, and gives conservative values of bond strength compared to the bond tests database. In future works, among others, uncertainties of the input variables will be incorporated by means of probabilistic modelling, making way for implementation of the ARC model into semi-probabilistic safety concepts by extraction of modification factors. Overall, with more accurate and reliable assessment methods for corroded RC structures, environmental and economic savings are imminent as more of the potential of existing structures can be realized.
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| 2. |
- Coronelli, Dario, et al.
(författare)
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FIB model code 2020 - Structural models for existing concrete structures
- 2018
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Ingår i: FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger. - 2617-4820. ; , s. 3019-3040
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Konferensbidrag (refereegranskat)abstract
- The paper gives an overview of this ambitious project, which builds upon the achievements of fib MC2010, the previous edition of the fib Model Code. MC2020 will deal with both the design of new structures and all the activities associated with the through-life management and care of existing concrete structures, including matters such as inservice assessment and interventions to extend the life / improve the performance of these structures. Particular attention will be paid to issues specific to existing structures. Relevant structural models are planned for the determination of their load capacity / structural reliability, serviceability, remaining service life etc taking account of: • Load-carrying behaviour not considered in design, such as compressive membrane action and the increase in concrete compressive strength with time due to ongoing hydration effects. • Load-carrying behaviour in deteriorated members and structures, which is different to those members which have not experienced deterioration. The paper gives consideration to corrosion of reinforced concrete members and prestressed concrete members, as well as to the effects of other forms of deterioration such as alkali-aggregate reactions and frost damage. The paper also notes some of the differences between the approaches employed for Life Cycle Assessment and Design (LCA / LCD) based on deterioration models, and the assessment of the present condition of the structure (i.e. at a given moment in time) which utilise mechanical models to represent the influences of the deterioration processes which are active.
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| 3. |
- Coronelli, Dario, et al.
(författare)
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Structural modelling of the response of deteriorated rc and psc members: Levels of approximation for model code 2020
- 2021
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Ingår i: fib Symposium. - 2617-4820. ; , s. 283-292
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Konferensbidrag (refereegranskat)abstract
- The assessment of reinforced concrete structures affected by deterioration such as reinforcement corrosion involves the use of different models, according to different scientific and technical purposes. The paper presents a framework for structural modelling approaches previously developed by the authors to fit in the concept of Levels of Approximation for Model Code 2020. The concept is here extended to include different accuracy levels in deterioration modelling. The paper moves from simple strut and tie models to analytical models and finite element numerical studies. The possibility of an extension of the framework to modelling the freeze-thaw deterioration is highlighted. The conclusions highlight the available techniques and the needs for research developments.
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| 4. |
- Eik, Marika, et al.
(författare)
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Measuring and numerical modeling of behaviour of fibre concrete in a direct tensile test
- 2019
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Ingår i: Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures. - 2617-4820. - 9782940643004 ; , s. 423-429
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Konferensbidrag (refereegranskat)abstract
- Efficiency of fibre reinforced concrete in tension depends on the strength of contact between the fibre or aggregate and the cementitious matrix. The present study focuses on the measuring and numerical modelling of the behaviour of concrete and fibre concrete samples under tension. The device used in present study for tensile loading of concrete samples enabled to control and track the applied tensile load after the cracking of concrete in a sample with steel fibre. In case of pure concrete sample, the configuration of the device made possible to track the applied load until the sectional area of concrete was completely cracked. The numerical simulations of the tensile cracking load, as well as the tensile softening behaviour of the pure concrete sample demonstrated the dependence on the values of the fracture energies used.
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| 5. |
- Lundgren, Karin, 1968, et al.
(författare)
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A model for the anchorage of corroded reinforcement : Validation and application
- 2015
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Ingår i: Concrete - Innovation and Design. - : Technical University of Denmark. ; , s. 135-136, s. 135-136, s. 135-136
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Konferensbidrag (refereegranskat)abstract
- When reinforcement in concrete corrodes, splitting stresses around corroded bars may lead to cover cracking and even cover spalling, affecting the anchorage. The aim of this study was to validate an existing one-dimensional (1D) analysis for anchorage capacity, and to show how it can be applied in assessment of existing bridges. The 1D analysis was validated through comparisons to experiments and detailed 30 finite element analyses. The methodology is exemplified in assessment of two bridges built in the 1960s. The bridges exhibit systematic damage in the form of spalled concrete on the bottom side of the main beams at cast joints where large amounts of reinforcement are spliced. The anchorage length needed to anchor the yield force was calculated from the bond-slip response, using the one-dimensional bond-slip differential equation. The model proved to be easy to use in practical design work. Furthermore, the bridges could be shown to have sufficient capacity, and costly strengthening could be avoided. This work clearly demonstrates the potential to certify sufficient load-carrying capacity of corroded reinforced concrete structures through improved models.
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| 6. |
- Lundgren, Karin, 1968, et al.
(författare)
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What do we know about concrete, steel, and bond-slip relation for corroded bars?
- 2020
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Ingår i: Capacity Assessment of Corroded Reinforced Concrete Structures. Proceedings of the fib CACRCS DAYS 2020. - 2617-4820. - 9782940643103
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Konferensbidrag (refereegranskat)abstract
- Reinforcement corrosion influences the deformation and load capacity of steel rebars. Further, it generates splitting stresses that weaken the concrete and strongly affect the bond between reinforcement and concrete. Here, a recently published engineering model to determine the deformation capacity of rebars with pitting corrosion is described. Further, the effect of corrosion on bond is described in a systematic way, with an overview of the effect for various cases depending on reinforcement type, existence of transverse reinforcement, and confinement due to concrete and boundaries. Finally, an engineering model to determine bond-slip relationships for ribbed bars is presented.
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| 7. |
- Lundgren, Karin, 1968, et al.
(författare)
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What do we know about concrete, steel, and bond-slip relation for corroded bars? (key-note lecture)
- 2021
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Ingår i: fib Symposium. - 2617-4820. ; , s. 123-130
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Konferensbidrag (refereegranskat)abstract
- Reinforcement corrosion influences the deformation and load capacity of steel rebars. Further, it generates splitting stresses that weaken the concrete and strongly affect the bond between reinforcement and concrete. Here, a recently published engineering model to determine the deformation capacity of rebars with pitting corrosion is described. Further, the effect of corrosion on bond is described in a systematic way, with an overview of the effect for various cases depending on reinforcement type, existence of transverse reinforcement, and confinement due to concrete and boundaries. Finally, an engineering model to determine bond-slip relationships for ribbed bars is presented.
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| 8. |
- Mathern, Alexandre, 1986, et al.
(författare)
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Experimental study of time-dependent properties of a low-pH concrete for deposition tunnels
- 2018
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Ingår i: fib Symposium. - 2617-4820. ; , s. 1726-1735
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Konferensbidrag (refereegranskat)abstract
- The Swedish Nuclear Fuel and Waste Management Company developed a method for the final disposal of canisters for spent nuclear fuel in tunnels at depths of about 500 meters. The concept for closure of the deposition tunnels is based on a bentonite seal supported by a spherical concrete dome structure. In order to fulfil the requirements specific to the repository concept, a special mix of low-pH self-compacting concrete was developed. A series of large-scale castings and laboratory tests were conducted to gain experience on this low-pH concrete mix, in conjunction with the full-scale demonstration test of an unreinforced concrete dome plug in the underground hard rock laboratory in Äspö, Sweden. The laboratory tests aimed at studying the creep properties under high sustained compressive stresses of the low-pH concrete mix, its shrinkage properties and the properties of the rock-concrete interface. This paper provides an overview of these tests and analyses the latest results of the recently completed creep tests, which include 6 years of measurements. These results allow to improve understanding of the structural behaviour of the concrete plug and to assess the effects of the very high pressure acting on the plug on its deformations, cracking and water tightness.
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| 9. |
- Nanukuttan, S. V., et al.
(författare)
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Taking performance to practice – simplified in situ approach for specifying concrete for chloride environments
- 2016
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Ingår i: fib Symposium. - 2617-4820. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- The application of conservative structural codes such as EN1992 with high factors of safety and performance based compliance measures for concrete strength means that actual structural loading rarely exceeds the capacity and therefore has negligible influence on long term load carrying capacity. Majority of structures fail due to physical and chemical changes that concrete undergoes influenced by the exposure environment and subsequent reinforcement corrosion and loss of load carrying capacity. Lack of appreciation of concrete and its interactions with exposure environments, makes Designers and Engineers adhere more closely to prescriptive standards developed for relatively less aggressive environments. The data from exposure sites and real structures prove categorically that the prescriptive specifications are in adequate, especially for chloride environments. A performance-based approach similar to that followed for strength guarantee is proposed as a way forward for bringing durability into the forefront. For marine and de-icing salt environments, a handful of measurable parameters control the flow of chloride ions into concrete and such parameters form the core of most transport models. This article shows the scope of a simplified approach to chloride transport modelling using these core parameters for one chloride exposure environment. Further, the authors put forward a strong case for in situ measurements and the benefits it can have on assessing the whole structure. Examples for predicting the remaining service life as well as forming performance-based specification are also provided.
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| 10. |
- Robuschi, Samanta, 1991, et al.
(författare)
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Anchorage capacity of corroded smooth reinforcement bars in existing reinforced structures
- 2018
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Ingår i: Proceedings of the 12th fib International PhD Symposium in Civil Engineering. - : Czech Technical University. - 2617-4820. - 9788001064016 ; , s. 1039-1046
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Konferensbidrag (refereegranskat)abstract
- Concrete structures are strongly affected by reinforcement corrosion, the most common cause of deterioration. Most studies on structural effects of corrosion rely on artificial methods to obtain a corrosion level that would otherwise require years, but doubts on the soundness of the methods have been raised. Specimens taken from existing structures offer the chance of studying the effect of natural corrosion, however the choice of the test setup is challenging. Hence, pilot tests are carried out to investigate the optimal design for testing the anchorage capacity of specimens with smooth reinforcements. The outcome is an asymmetrically supported 3-point bending beam test. The benefits of using complementary tools as Digital Image Correlation (DIC), Non-Linear Finite Element Analysis (NLFEA), pull-out tests and tensile tests and 3D scanning of the bars are presented.
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