| 1. |
- Björnsson, Ivar, et al.
(författare)
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Decision support framework for bridge condition assessments
- 2019
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730 .- 1879-3355. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- An essential aspect in the maintenance of existing bridges is the ability to adequately and accurately assess and evaluate the condition of the structure. Condition assessments, which can be carried out in any number of ways, provide valuable information concerning the actual state of a bridge, including the severity of potential damages, and form the basis for further maintenance decisions. Any decision support concerning the management of existing structures thus requires attention towards the uncertainties associated with the assessment methods when applied in practice as well as the maintenance actions these support. These uncertainties cannot be solely described as model uncertainties but are also a result of the variation in engineering performance observed in practice. In the current paper a rational and systematic framework is presented which provides practical decision support concerning whether condition assessments are necessary, what assessment methods are recommended, if invasive actions are needed, or if some other non-invasive option may be more appropriate. The framework takes into account three main attributes of an enhanced condition assessment, namely, modelling sophistication, considerations of uncertainties and risks, and knowledge/information content. Increasing the level of one or more of these attributes may be advantageous only if the expected benefits or added value of information is considered appropriate in relation to the cost of implementation in practice. A decision making model, based on Bayesian decision theory, is adopted to evaluate this problem. Two case studies, in which the framework is applied, are provided for illustrative purposes; the first is a generic numerical example and the second a decision scenario related to the fatigue assessment of an existing railway bridge.
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| 2. |
- Björnsson, Ivar, et al.
(författare)
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Suitable degree of crudeness in engineering practice
- 2019
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Ingår i: IABSE Symposium, Guimaraes 2019. - : International Association for Bridge and Structural Engineering (IABSE). - 9783857481635 ; , s. 1592-1599
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Konferensbidrag (refereegranskat)abstract
- Practicing structural engineers may be familiar with the main principles of structural reliability but may not necessarily be experts in using such methods. This may lead to a lack in understanding the effect of uncertainties on the ensuing structural safety and to sub-optimization of more traditional structural engineering aspects. The aim of the current paper is to highlight the importance of considering risks and uncertainties in design and to improve the awareness of practicing engineers to such considerations. The importance of a consistent treatment of uncertainties in structural engineering is brought to attention with focus on the modelling approaches which often underlie decisions. Different aspects discussed are: decision making in light of uncertainty, principles of consistent crudeness and the influence of engineering performance in practice on the safety of structures. A simplified model, considering strategies for improving engineering models, is considered and examples, based on simplified decision models, are also provided.
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| 3. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Partial safety factors for the anchorage capacity of corroded reinforcement bars in concrete
- 2019
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 181, s. 579-588
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Tidskriftsartikel (refereegranskat)abstract
- Many reinforced concrete bridges in Europe and around the world are damaged by reinforcement corrosion and the annual maintenance costs are enormous. It is therefore important to develop reliable methods to assess the structural capacity of corroded reinforced concrete structures and avoid unnecessary maintenance costs. Although there are advanced models for determining the load carrying capacity of structures, it is not obvious how they should be used to verify the performance of existing structures. To confidently assess the bond of corroded reinforcement in concrete, for example, the calculation model must give a sufficient safety margin. When designing new structures, semi-probabilistic approaches (such as the partial safety factor method) are adopted to achieve the target reliabilities specified in structural design codes. This paper uses probabilistic methods to develop partial factors for application in an existing bond model, to assess the safety of corroded reinforced concrete structures. The response of the bond model was studied using Monte Carlo (MC) simulations for several design cases, with probability distributions fitted to the results. Partial factors were then derived, based on these distributions. Furthermore, an MC-based simulation technique called “importance sampling” was used to study the reliability of several deterministic bond assessments conducted using these partial factors. The results show that deterministic assessments which use the proposed partial factors lead to a safety level at least equal to the target value. The results presented in this paper will support the assessment of reinforced concrete structures with anchorage problems and give a reasonable approximation of the anchorage capacity with sufficient safety margin. When generalised to cover other failure modes and structural configurations, this will enable better utilisation of damaged structures and lead to major environmental and economical savings for society.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Reliable engineering assessments of corroded concrete structures
- 2017
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Ingår i: Nordic Concrete Research : Proceedings of the XXIII Nordic Concrete Research Symposium, Aalborg, Denmark, 21-23 August, 2017 - Proceedings of the XXIII Nordic Concrete Research Symposium, Aalborg, Denmark, 21-23 August, 2017. ; , s. 245-248
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Konferensbidrag (refereegranskat)abstract
- Corrosion of steel reinforcement is a large and increasing problem for reinforced concrete structures. Simple and reliable assessment methods are required to use the full capacity of existing infrastructure. In this paper, a reliable engineering assessment method is outlined. A model for anchorage has been developed and verified against a large database of bond tests. Also the influence of corrosion on the bending and shear capacity is to be included, and a probabilistic model will be established. The outcome of this work will enable practising engineers to perform reliable assessments of concrete structures with corroded reinforcement.
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| 7. |
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| 8. |
- Gottsäter, Erik, et al.
(författare)
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Comparison of Models for the Design of Portal Frame Bridges with Regard to Restraint Forces
- 2017
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Ingår i: Structures Congress 2017, Denver, United States, 6-8 April 2017. - Reston, VA : American Society of Civil Engineers. - 9780784480403 ; , s. 326-339
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Konferensbidrag (refereegranskat)abstract
- In the design of concrete bridges an important aspect is limiting crack widths, since large cracks can lead to e.g. corrosion and affect the bridge functionality. Restraint forces caused by thermal loads and shrinkage will likely constitute a large part of the total forces acting on the bridge in crack width design. In this paper, restraint stresses in portal frame bridges are calculated according to Eurocode with simple hand calculation models, 2D frame models and linear elastic 3D FE-models. The results are then compared and used in Eurocode crack width design methods. Large tensile restraint stresses were found in the transverse direction close to the frame corners, and the required reinforcement amount significantly exceeded the minimum reinforcement prescribed by codes. The results are however unrealistic since the thermal load distribution is simplified, and the crack width formula does not take the reduction of restraint stresses due to cracking into account. Future studies shall therefore determine a more realistic thermal load distribution and the effects of cracking, in order to create a more accurate linear elastic 3D FE design method.
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| 9. |
- Gottsäter, Erik, et al.
(författare)
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Crack widths in base restrained walls subjected to restraint loading
- 2019
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 189, s. 272-285
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Tidskriftsartikel (refereegranskat)abstract
- Cracks in concrete structures can have a negative impact on durability and aesthetic appearance. It is therefore important to estimate crack widths before construction, and to use suitable reinforcement amounts to limit crack widths. Crack widths are however hard to predict in restrained structures, as cracking reduces the stiffness, which in turn reduces the restraint and thereby the amount of cracking. In this paper, nonlinear finite element analyses of cracking are performed on base restrained walls mainly subjected to shrinkage. A non-linear material model for concrete and a bond-slip relation for concrete – reinforcement interaction are used. The model does not include the hardening process of concrete but instead applies the load effects on mature concrete, and is validated by comparisons with test results from full scale tests performed in previous research. Additionally, a sensitivity study is made to investigate the influence of certain parameters on crack widths and crack patterns. The intention is to use the model in the development of a model to be used in design of concrete structures which takes restraint effects into account in an improved, yet a simplified way. The results show that the model gives realistic crack patterns, but that it tends to overestimate crack widths and the number of cracks obtained. Therefore, the model is considered to be acceptable.
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| 10. |
- Gottsäter, Erik, et al.
(författare)
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Crack widths in portal frame bridges subjected to restraint effects
- 2019
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Ingår i: 20th Congress of IABSE, New York City 2019: The Evolving Metropolis - Report. ; , s. 1101-1105, s. 1101-1105
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Konferensbidrag (refereegranskat)abstract
- Restraint stresses appear in structural parts which are prevented from adjusting their shape when subjected to e.g. shrinkage or thermal actions. If the restrained stresses are large, cracking might occur, which can affect the durability of the structure. In the case of restraint effects, the reinforcement required in a bridge to limit the crack widths can be difficult to determine, as the magnitude of the restraint stresses depend on the stiffness of the structure. If cracking occurs, the stiffness is reduced and thereby also the stresses. For this reason, in structural parts affected by restraint effects, it can be hard to estimate both the number of cracks that will appear and the resulting restraint stress that governs the crack widths. In this study, crack widths in a portal frame bridge subjected to thermal actions and shrinkage were investigated using non-linear FE analysis. A bond-slip relation was used for concrete-reinforcement interaction, as the resulting crack spacing was unknown. Corresponding analysis was performed using linear elastic material models and hand calculations of crack widths, for two different thermal load cases, and relations between the results from the different methods are presented. The result can lead to the development of a more accurate design model, which would lead to more efficient use of reinforcement.
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