| 1. |
- Aggestam, Emil, 1992, et al.
(författare)
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Optimisation of slab track design considering dynamic train–track interaction and environmental impact
- 2022
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails.
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| 2. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Incorporation of pre-existing cracks in finite element analyses of reinforced concrete beams without transverse reinforcement
- 2021
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- Cracking in reinforced concrete (RC) bridges and other structures is common and not necessarily detrimental. However, some cracks may grow past specified limits and, aside from aesthetic and durability aspects, may influence the ductility and structural capacity of an RC member. This is not generally reflected in current assessment methods and, therefore, improved methods are needed. The aim of the current work was to develop a modelling methodology to incorporate pre-existing cracks into finite (FE) analysis for improved structural assessments. Two different approaches were investigated: (1) weakening the continuum elements at the position of a crack and (2) introducing discrete crack elements with weakened properties. In both approaches, a total-strain based model was used in the continuum elements. These modelling approaches were applied to analyses of experiments, in which concrete beams had been pre-cracked and tested in four-point bending. The pre-existing cracks led to differing failures limiting the deformation capacity, plus varying ultimate capacity and ductility. In the current study the weakened-elements approach captured the failure characteristics, ultimate capacity and ductility more accurately than a standard FE analysis without cracks included; the discrete-crack approach, on the other hand, did not. Furthermore, the bending stiffness differed between the experimental tests and the FE analyses. Damaged bond properties and closure of cracks in the compressive zone were identified as probable causes. Moreover, the choice of shear retention used for the weakened elements was shown to noticeably affect the predicted capacity and ductility. In conclusion, the weakened-elements approach was the most straightforward to implement. It was less time-consuming and led to better agreement with experimental results, compared to the discrete-crack approach. Based on this study, the weakened-elements approach is regarded as a promising approach for the structural assessments of tomorrow.
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| 3. |
- Blomfors, Mattias, 1990, et al.
(författare)
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Incorporation of pre-existing longitudinal cracks in finite element analyses of corroded reinforced concrete beams failing in anchorage
- 2020
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Ingår i: Structure and Infrastructure Engineering. - : Informa UK Limited. - 1573-2479 .- 1744-8980. ; In press, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Transportation infrastructure is of fundamental importance and must be regularly assessed to ensure its safety and serviceability. The assessment of ageing reinforced concrete bridge stock may need to consider corrosion and cracks, as the likelihood of deterioration increases with age. This work accordingly investigates the incorporation of pre-existing anchorage zone corrosion cracks into the finite element modelling of reinforced concrete beam structural behaviour. Three methods of accounting for cracks were applied: (1) modifying the bond stress–slip relation, (2) weakening elements at the position of the crack, and (3) weakened discrete crack elements. The results show that modifying the bond stress–slip relation results in accurate predictions of the ultimate capacity when one-dimensional reinforcement bars are used in the model. Weakening elements at the position of the crack provides reasonable results when the anchorage is modelled with three-dimensional reinforcement bars and a frictional bond model. The implementation of discrete cracks was found to be unsuitable for the studied load situation, as compressive stresses formed perpendicular to the crack. It was concluded that the capacity of the studied case could be well estimated based on visual measurements, without knowledge of the exact corrosion level.
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| 4. |
- 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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| 5. |
- Fahimi, S., et al.
(författare)
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A novel method for implementation of corrosion-induced cracks in the finite element models of reinforced concrete structures
- 2021
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Ingår i: Scientia Iranica. - 1026-3098 .- 2345-3605. ; 28:3 A, s. 1079-1095
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Tidskriftsartikel (refereegranskat)abstract
- Currently, there is a clear need for reliable procedures for condition assessment and service-life evaluation of existing infrastructures. Advanced 3D Nonlinear Finite Element (3D NLFE) analysis has proven to be capable of describing the behavior of reinforced concrete provided that detailed and appropriate condition assessment data are available. The present study aims to review and compare different procedures for coupling 3D NLFE analysis with condition assessment data to model corrosion induced cracking, and, consequently to find a method with better accuracy, less computational cost, and improved robustness. This paper introduces a new method for adding cracked elements directly to the finite element model, called Re-FEM. The force-displacement response, ultimate crack pattern, and failure mode from this model are compared with four other methods for a pull out test case on specimens under an accelerated corrosion process. Using this method, the force displacement response for the corroded specimens was overestimated by about 70%. However, the trend was promising and the failure mode and crack pattern were correct. Moreover, the analysis continued after the peak point in the force-displacement curve, which makes it possible to monitor the behavior of the specimen in the softening regime.
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| 6. |
- Plos, Mario, 1963, et al.
(författare)
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Recommendations for Assessment of Reinforced Concrete Slabs: Enhanced structural analysis with the finite element method
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Reinforced concrete structures show a pronounced non-linear response, with cracking of concrete for service loads and reinforcement yielding and concrete crushing at ultimate load. With non-linear finite element (FE) analysis, the structural response can be captured, and such analyses have shown great potential to reveal higher load carrying capacity compared to simplified and linear analysis methods. A multi-level structural assessment strategy, developed in previous research, provides a framework for more advanced, successively improved analysis of reinforced concrete slabs. This report provides recommendations for practicing structural engineers on structural assessment using FE analysis. The focus is on enhanced assessment with non-linear FE analysis, and the scope is reinforced concrete slabs with limited membrane effects. The intention is to facilitate the use of non-linear analysis in engineering practice by providing detailed recommendations on how such analyses can be made to provide increased understanding of the structural behaviour and reliable estimations of the load-carrying capacity of concrete slabs. However, the framework presented is general, and the approach can in many aspects also be used for other types of reinforced concrete structures. The recommendations given here are based on previous research performed by the authors, information from literature and engineering judgement based on practical experience. They are intended to give conservative estimates of the load-carrying capacity, fulfilling the required safety level. The report includes a thorough description of the assessment strategy. The global safety format recommended for non-linear analysis is presented and its application for different assessment levels is described. Furthermore, recommendations on how to take deterioration into account are given. Non-linear FE analysis of concrete structures is presented together with general advices for its application. Furthermore, general recommendations are presented for simplified and linear analysis, corresponding to today’s practice. For assessment with non-linear FE analysis, detailed recommendations for use in engineering practice are presented. Advices are given on idealization of the structure, choice of material models, determination of material parameters, modelling and analysis. Furthermore, the evaluation of structural response, determination of load carrying capacity and response under service conditions are described. For non-linear analysis with shell elements, resistance models on higher Level-of-Approximation according to Model Code 2010 are used. Finally, examples are showing the application of the strategy on two slabs tested in laboratory and one bridge deck slab.
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| 7. |
- Pollmann, Nele, 1987, et al.
(författare)
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Modeling and computational homogenization of chloride diffusion in three-phase meso-scale concrete
- 2021
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 271
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Tidskriftsartikel (refereegranskat)abstract
- A computational homogenization technique for modeling diffusion in concrete is introduced with emphasis on the influence of the aggregate content and variability. The highly heterogeneous material is investigated on different scales by combining Variationally Consistent Homogenization on numerical microstructures with analytical techniques accounting for lower, unresolved, length scales. The concrete structure consists of the cement paste, the embedded aggregates, and the Interfacial Transition Zone (ITZ) in between the two. Diffusion takes place in the cement phase, as well as in the ITZ. Since the thickness of the ITZ is, typically, much smaller than the diameter of the aggregates, the effect of the ITZ can be modelled as a surface transport around the aggregates. The occurrence of different aggregate sizes is described via the Particle Size Distribution for given sieve curves, as described in design codes. The Particle Size Distribution curve is split into two parts. The effect of smaller aggregates is homogenized analytically using a mixture rule. This results in an effective matrix material consisting of cement paste and the smaller aggregates. Synthetic structures are then generated numerically to account for the larger aggregates. At first, a dense sphere packing is created based on the Particle Size Distribution. This information is used to generate a weighted Voronoi diagram, which is modified by a shrinking process. This procedure allows us to create periodic Representative Volume Elements for numerical investigations. The overall diffusivity of the concrete mixture is evaluated upon using Variationally Consistent Homogenization, in the context of Finite Element analysis, for the generated RVEs and compared with analytical homogenization results and experimental data. It is found that, depending on the Particle Size Distribution, the ITZ has a large effect on the effective properties.
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| 8. |
- Radbakhsh, Soheil Heidarian, et al.
(författare)
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Physics-Informed Neural Network for Analyzing Elastic Beam Behavior
- 2023
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Ingår i: Structural Health Monitoring 2023: Designing SHM for Sustainability, Maintainability, and Reliability - Proceedings of the 14th International Workshop on Structural Health Monitoring. ; , s. 744-751
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Konferensbidrag (refereegranskat)abstract
- This paper introduces a methodology that combines a physics-based model with observed data for accurately modeling the deflection of an elastic beam in the context of structural health monitoring. The challenges associated with physics-based and data-based methods such as computational time, simplifying assumptions, and seamless integration of sensor data with physics-based models are addressed. The presented method offers a promising approach by effectively fusing data with prior physical knowledge in a cost-effective manner. The proposed methodology is validated through comparisons with analytical and finite element analysis methods for beams with various irregularities such as point loads and supports. The results demonstrate the advantages of integrating sensor data into the model for faster convergence and improved accuracy.
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| 9. |
- Shu, Jiangpeng, 1987, et al.
(författare)
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Automated generation of FE mesh of concrete structures from 3D point cloud using computer vision technology
- 2021
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Ingår i: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations - Proceedings of the 10th International Conference on Bridge Maintenaince, Safety and Management, IABMAS 2020. - : CRC Press. ; , s. 3300-3303
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Konferensbidrag (refereegranskat)abstract
- To achieve real-time structural health monitoring (SHM), a concept of digital twin - a digital copy of a structure has been brought up and investigated. It provides an up-to-date virtual model of structures, with the integration of physical as well as data information. The goal of this research is to provide faster and more accurate procedures to capture the spatial information required by a digital twin of a concrete structure using 3D point cloud data. Given that the method is intended for real-scale structures, such as bridges, the work can be divided to 3 steps: (1) to segment and extract geometric information for structural components; (2) to convert the geometry information to FE mesh with consideration of element types; (3) to assign material property as well as boundary conditions based on extracted components type. Linear FE analyses have been carried out to evaluate the structural performance based on the FE model created from the point cloud. The automation of such a process is an essential part of the creation of a digital twin of infrastructures.
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| 10. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Ballastless Track – Minimizing the Climate Impact
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Railway transportation is becoming increasingly important for transport of passengers and goods in Sweden, Europe and many parts of the world. Ballastless (slab) railway systems are increasingly in use; however, their construction is known to cause a substantial climate impact. The objective of this study was to investigate possible methods to reduce greenhouse gas (GHG) emissions of slab tracks and to provide required knowledge to identify the methods with high potential for further development. The approach adopted in this study consists of two steps. First, a comprehensive literature study was carried out, including a survey of existing methods for reducing GHG emissions for slab tracks, and of those which require further research. These methods are presented and assessed with respect to criteria related to potential benefit, possibility to use in large volumes, quality assurance and cost. In the second step, recommendations are made on which of the different methods of reducing GHG emissions are suitable to further develop in future projects. Two uncertainties identified for all methods are related to quantification of potential benefits and the associated costs. Nonetheless, structural optimization of slab tracks is found to have potential to reduce the climate impact quite substantially, with the smallest risks associated. The most promising methods for structural optimization includes: geometry optimization to focus on the use of material where it is structurally most effective; stiffness optimization to reduce the energy consumption of trains; prestressing of concrete to minimize crack width; and employing steel fiber reinforced concrete to control cracks and reduce the use of traditional reinforcement. Three solutions combining these methods in different ways are suggested for future studies. Furthermore, methods related to the use of alternative binders & materials are also recommended to reduce the climate impact; however, it is noted that such methods in general exhibit larger uncertainties than structural optimization. Of the alternatives focusing on alternative binders & materials, the following were evaluated to be most promising: textile reinforcement, other cement types (e.g. CSA, BCSA & BYF cements) as well as optimized mix design of concrete. It is to be noted that the three suggested solutions based on structural optimization can also benefit from the use of alternative binders & materials. To sum up, combination of several methods is required to minimize the environmental impact, as in the suggested solutions. The needs for future investigation for each solution are also identified in the report. The project contributes to the overall goal of increasing consideration for the environment and climate by providing knowledge and road map on how GHG emissions can be reduced for slab tracks.
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