| 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. |
- Akbarian, Mehdi, et al.
(författare)
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LCA+: Moving LCA into the Pavement Design Space
- 2012
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Ingår i: Proceeding of ACI International Convention.
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Konferensbidrag (refereegranskat)abstract
- The construction, operation, and maintenance of the United States roadway system are responsible for substantial energy and resource consumption. The current system of paved roads in the United States handles a volume of traffic on the order of 8 billion vehicle-miles per day. Due to high energy demand, road transport contributed the most greenhouse gases (GHGs) of any transportation mode in 2007, accounting for 83% of emissions from the transportation sector and 27% of all emissions in the United States. Improving the sustainability of this network requires better technical and decision making strategies starting with the design stage of pavements.While the Mechanistic-Empirical Pavement Design Guide (MEPDG) is being adopted as a design tool throughout the U.S. it lacks the ability to take into account the environmental impacts of pavement systems. Hence, it is necessary to incorporate the performance designs of MEPDG with an environmental assessment tool to merge the structural and environmental aspects of pavement design.The environmental impact of pavements throughout their lifetime is calculated using the life cycle assessment (LCA) technique. Conventional environmental assessments of pavements often overlook use phase related emissions, leading to conclusions based on incomplete results. Studies have empirically shown that an important factor in the life cycle assessment of pavements is the pavement-vehicle interaction (PVI) which describes the effect of pavement properties on vehicle fuel consumption. However, the results of these studies are not conclusive and cannot be generalized to all pavement designs.This research uses a mechanistic approach to rationalize PVI and creates a link between pavement properties and their impacts on fuel consumption. Moreover, a network-level analysis has been performed using the Long Term Pavement Performance (LTPP) program’s databases to calibrate and validate this model. Finally, life cycle assessment is taken into the design space by incorporating MEPDG designs with LCA principles, taking into account the effect of PVI over the pavement’s lifetime. Moreover, evaluation of high performance sustainable pavement systems is enabled by extending the realm of MEPDG to model-based LCA principles. Through this approach, pavement design is enhanced structurally and environmentally constructing the necessary foundations for LCA+.
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| 3. |
- Berg, F., et al.
(författare)
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Anchorage capacity of naturally corroded reinforcement in an existing bridge
- 2012
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Ingår i: Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management, IABMAS 2012, Stresa, Lake Maggiore, 8-12 July 2012. - : CRC Press. ; , s. 2800-2807
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Konferensbidrag (refereegranskat)abstract
- Corrosion of reinforcement is one of the most common causes of deterioration in reinforced concrete bridges. Anchorage, prior to shear and bending moment resistance, is the main uncertainties in the evaluation of the structural behavior of corroded reinforced concrete bridges. Thus, to assess the remaining load-bearing capacity of deteriorated existing bridges, models to estimate the remaining bond and anchorage capacity are needed. Most of our knowledge on the structural behavior of corroded reinforced concrete structures is based on experimental investigations of artificially corroded concrete specimens. In this study, the anchorage capacity of naturally corroded steel reinforcement was investigated experimentally. The test specimens were taken from edge beams of a bridge, Stallbackabron, in Sweden. Since the dimensions and the amount of reinforcement were given on beforehand, it was only the test set-up which could be chosen freely. A test set-up consisting of a four point bending test indirectly supported with suspension hanger was considered to be the best alternative with the least disturbance and influence of the natural damages. Detailed design was done by using a non-linear finite element method. It was seen that the edge beams needed to be strengthened with transverse reiforcement, else they would have failed in a local failure at the suspension hole or in shear. The technique adopted for the strengthening was an internal mounting of steel reinforcement using epoxy as adhesive. The bond and anchorage behavior was examined in tests through measurements of applied load, free-end slip and mid-span deflection. A first test showed that additional measures were needed to ensure anchorage of the strengthening bars. In subsequent tests, they were therefore anchored at the top of the beam with hexagonal nuts and flat steel plates. In two following tests, the beams failed in a splitting induced pull-out failure, i.e. anchorage failure was achieved as wanted.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Blomfors, Mattias, 1990, et al.
(författare)
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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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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