Papers by Lennart Elfgren
The European objective of a modal shift of freight transports to railways will require extensive ... more The European objective of a modal shift of freight transports to railways will require extensive upgrading of existing railway lines since very few dedicated freight railways are currently being built and existing lines were built for traffic demands at the time of construction. A transition to increased and enhanced railway freight operations can therefore be costly and complicated. To minimize negative effects, a guideline for upgrading was developed within the Capacity4Rail project. The current paper presents the major findings from this guideline. In particular it outlines different upgrading possibilities and their implications, and details structured approaches to upgrading analyses. Setting out from the Capacity4Rail handbook, the current paper discusses possibilities for upgrading of substructures, bridges, tunnels, and the track structure. In these areas, an overview of challenges and possibilities is presented together with examples of experience from operational upgrading. The paper concludes that freight line upgrading using a more streamlined approach as outlined in the guideline is a necessity if EU objectives on modal shifts in transportation are to be met. Further, it demonstrates why a political drive is necessary to increase efforts to upgrade freight lines.
Structure and Infrastructure Engineering, Apr 13, 2019
Routine bridge inspections usually consist of visual observations. These inspections are time-con... more Routine bridge inspections usually consist of visual observations. These inspections are time-consuming and subjective. There is a need to identify new inspection techniques for infrastructure that reduce traffic disturbance, and improve the efficiency and reliability of the acquired data. This study compared the performance of three different imaging technologies for the three-dimensional (3D) geometric modeling of existing structures: terrestrial laser scanning, close-range photogrammetry, and infrared scanning. Each technology was used to assess six existing concrete railway bridges. The technologies were compared in terms of geometric deviations, visualization capabilities, the level of the inspector's experience, and degree of automation. The results suggest that all methods investigated can be used to create 3D models, however, with different level of completeness. Measurements such as span length, deck widths, etc. can be extracted with good accuracy. Although promising, a full off-site inspection is currently not feasible as some areas of the bridges were difficult to capture mainly due to restricted access and narrow spaces. Measurements based on terrestrial laser scanning were closer to the reality compared to photogrammetry and infrared scanning. The study indicates the no special training is needed for photogrammetry and infrared scanning to generate a 3D geometric model.
Lennart Fransson has written most of chapter 3, Björn Täljsten has written most of chapter 4, and... more Lennart Fransson has written most of chapter 3, Björn Täljsten has written most of chapter 4, and Lennart Elfgren has written most of the other chapters. We express our sincere thanks to all in Russia, Finland and Sweden who have contributed to this pre-feasability study.
Construction and Building Materials
When in use, reinforced concrete bridge structures not only experience high-frequency fatigue loa... more When in use, reinforced concrete bridge structures not only experience high-frequency fatigue loading caused by passing vehicles, but also suffer from the effects of a corrosive environment. In addition to fatigue damage to reinforcement, long-term fatigue loading also causes concrete cracking and deterioration of pore structures, thereby accelerating the ingress of external corrosive substances and reducing concrete durability. Long-term exposure to a corrosive environment also reduces the performance of concrete and causes corrosion of reinforcement materials, affecting the fatigue performance of the structure. Therefore, there is a combined effect between fatigue loads and corrosion on concrete. This paper is a review of the current literature from a material perspective on the performance degradation of concrete under the combined action of fatigue loading and corrosion, that is, carbonation, chloride ion attack, freeze-thaw cycles, and sulphate attack. The paper includes (1) a description of a test method for examining the combined action of fatigue loading and corrosion, (2) a summary of performance degradation of concrete under the combined effect of fatigue loading and corrosion, and (3) an introduction to durability deterioration models considering fatigue damage, and fatigue models that can account for corrosion. Finally, potential future research on concrete under the combined effect of fatigue loading and corrosion is described.
IABSE Symposium, Prague 2022: Challenges for Existing and Oncoming Structures
A prestressed concrete bridge was built in 1963 with BBRV cables. It has three spans and a total ... more A prestressed concrete bridge was built in 1963 with BBRV cables. It has three spans and a total length of 134.8 m. Due to mining activities the bridge was loaded with trucks with a total weight of 90 ton during 2012-2014 and from 2019. Crack development has been monitored manually and from 2020 with strain gauges and LVDTs. Cracks normally vary between 0.1 to 0.3 mm in width and grow in length with time. In November 2020 some of the strain gauges on the concrete showed alarming growth and the bridge was closed for traffic. Additional strain gauges were installed on vertical reinforcement bars and an assessment was carried out of the fatigue capacity of the bridge. It was found that the new strain gauges did not indicate any growth in strain and that the fatigue capacity was sufficient. The bridge could be opened again for traffic after being closed for five weeks. Monitoring drift in the strain gauges and fatigue are discussed.
IABSE Symposium, Prague 2022: Challenges for Existing and Oncoming Structures
At least 20% of existing railway bridges in Sweden are reinforced concrete (RC) trough bridge tha... more At least 20% of existing railway bridges in Sweden are reinforced concrete (RC) trough bridge that consist in a slab carried by two longitudinal main beams. As these bridges are getting old, there is an urging need to assess their remaining capacity with the aim of prolonging their service lives. The limited literature on the topic has pointed out that there is a significant difference between the capacity predicted by available codes and that obtained experimentally. In this paper, a review of the Bridge and Tunnel Management database (BaTMan) of railway infrastructure in Sweden, is carried out to gain an overview of the current state of the Swedish railway bridge, with focus on trough bridges. Then, a non-linear finite element model is calibrated using the experimental results of the previous testing of a decommissioned trough bridge. The model is used in a parametric study where the effect of key mechanical parameters on the capacity of trough bridges is studied.
Report, 2020
Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of ... more Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of the structure. This property of damage has not been utilized in the field of structural damage identification until quite recently, when the sparsity-based regularization developed in compressed sensing problems found its application in this field. In this paper we consider classical sensitivity-based finite element model updating combined with a regularization technique appropriate for the expected type of sparse damage. The validity of the proposed methods is demonstrated using simulations on a bridge. The pros and cons of these methods are discussed.
High Tech Concrete: Where Technology and Engineering Meet, 2017
Three Swedish concrete bridges have been tested to failure and the results have been compared to ... more Three Swedish concrete bridges have been tested to failure and the results have been compared to assessment using standard code models and advanced numerical methods. The three tested and assessed bridges were: (1) Lautajokk, a 29 year old one span (7 m) concrete trough bridge tested in fatigue to check the concrete shear capacity. (2) Ӧrnskldsvik, a 50 year old two span trough bridge (12 + 12 m) strengthened to avoid a bending failure. (3) Kiruna Mine Bridge, a 55 year old five span prestressed concrete road bridge (18 + 21 + 23 + 24 + 20 m) tested in shear and bending of the beams and punching of the slab. The main results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy of different codes and models. In all three cases the bridges had a considerable hidden capacity.
To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests were ca... more To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests were carried out on a 55 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Bot ...
IABSE Symposium, Nantes 2018: Tomorrow’s Megastructures, 2018
Load testing is a way to control the capacity and function of a bridge. Methods and recommendatio... more Load testing is a way to control the capacity and function of a bridge. Methods and recommendations for load testing are described and examples are given form tests carried out in Croatia and Sweden. In order not to damage the bridge being tested, the load must be limited, often to be within the serviceability limit state (SLS). Numerical models can be calibrated by load tests and then be used to check the carrying capacity for higher loads than what has been tested. Need for further work and recommendations are discussed. By effective planning, costs can be saved and a more sustainable use of bridges can be obtained.
IABSE Symposium, Guimarães 2019: Towards a Resilient Built Environment Risk and Asset Management, 2019
Damage assessment of structures includes estimation of location and severity of damage. Quite oft... more Damage assessment of structures includes estimation of location and severity of damage. Quite often it is done by using changes of dynamic properties, such as natural frequencies, mode shapes and damping ratios, determined on undamaged and damaged structures. The basic principle is to use dynamic properties of a structure as indicators of any change of its stiffness and/or mass. In this paper, two new methods for damage detection are presented and compared. The first method is based on comparison of normalised modal shape vectors determined before and after damage. The second method uses so-called 𝑙l-norm regularized finite element model updating. Some important properties of these methods are demonstrated using simulations on a Kirchhoff plate. The pros and cons of the two methods are discussed. Unique aspects of the methods are highlighted.
IABSE Symposium, Guimarães 2019: Towards a Resilient Built Environment Risk and Asset Management, 2019
Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of ... more Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of the structure. This property of damage has not been utilized in the field of structural damage identification until quite recently, when the sparsity-based regularization developed in compressed sensing problems found its application in this field.In this paper we consider classical sensitivity-based finite element model updating combined with a regularization technique appropriate for the expected type of sparse damage. Traditionally, (I), 𝑙2- norm regularization was used to solve the ill-posed inverse problems, such as damage identification. However, using already well established, (II), 𝑙l-norm regularization or our proposed, (III), 𝑙l-norm total variation regularization and, (IV), general dictionary-based regularization allows us to find damages with special spatial properties quite precisely using much fewer measurement locations than the number of possibly damaged elements of the s...
The main objective of the COST Action TU1406 is to develop a guideline for the establishment of Q... more The main objective of the COST Action TU1406 is to develop a guideline for the establishment of Quality Control plans for roadway bridges by integrating the most recent knowledge on performance ass ...
Four bridges of different types have been tested to failure and the results have been compared to... more Four bridges of different types have been tested to failure and the results have been compared to the load-carrying capacity calculated using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. Here it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way. The four bridges were: (1) a one span steel truss railway bridge; (2) a two span strengthened concrete trough railway bridge; (3) a one span concrete trough bridge tested in fatigue; and (4) a five span prestressed concrete road bridge. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy of different codes and models.
Some examples are given of assessment of fastenings to concrete structures and the work started b... more Some examples are given of assessment of fastenings to concrete structures and the work started by Rolf Eligehausen in fib Task Group 2.9 “Fastenings to structural concrete and masonry”. Studies ha ...
IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, 2016
Starting in 2003 the European Union has funded three consecutive research projects dealing with m... more Starting in 2003 the European Union has funded three consecutive research projects dealing with maintenance, life length, capacity and repair/strengthening of railway bridges. The main results are that many bridges are capable of carrying increased loads and can have an increased service life if up to date technologies are used for assessment, monitoring, maintenance and strengthening.In order to obtain good value for the money spent in the projects, it is important to plan, coordinate and manage the projects in an efficient way. Long range projects of four years seem to be more effective than shorter projects of two and three years.
IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, 2016
The dynamic response of a concrete railway arch bridge is studied through a case study of the bri... more The dynamic response of a concrete railway arch bridge is studied through a case study of the bridge over Kalix River, situated at Långforsen on the railway line between Kalix and Morjärv in northern Sweden. A simplified beam-element model, a spatial grillage-beam model and a refined shell-element model were built to analyze the bridge structure. A methodology was applied where measured static and dynamic responses were used to update finite element models of Långforsen Bridge. A multi-response objective function was presented, and the finite element method was proved feasible by comparison of predicted and measured response. In the paper comparative analyses were made of the time history displacement of three finite element models under three measured load cases. A standard train model from EUROCODE, HSLM-A 1, was applied and the dynamic responses under different speeds were studied. The results showed that a refined shell element model could accurately analyze dynamic responses of...
IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, 2016
Examples are given from comparisons of analyses based on (1) code models, (2) finite element mode... more Examples are given from comparisons of analyses based on (1) code models, (2) finite element models and (3) full scale tests to failure of three bridges. The analyses based on the code models gave very conservative results, while the finite element models could better predict the real behaviour.
IABSE Symposium, Vancouver 2017: Engineering the Future, 2017
Four bridges of different types have been tested to failure and the results have been compared to... more Four bridges of different types have been tested to failure and the results have been compared to the load-carrying capacity calculated using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. Here it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.The four bridges were: (1) a one span steel truss railway bridge; (2) a two span strengthened concrete trough railway bridge; (3) a one span concrete trough bridge tested in fatigue; and (4) a five span prestressed concrete road bridge.The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy of different codes and models.
IABSE Congress Reports, 2021
In this paper, experiences on the development of an assessment method for existing bridges are pr... more In this paper, experiences on the development of an assessment method for existing bridges are presented. The method is calibrated using the results of full-scale testing to failure of a prestressed bridge in Sweden. To evaluate the key parameters for the structural response, measured by deflections, strains in tendons and stirrups and crack openings, a sensitivity study based on the concept of fractional factorial design is incorporated to the assessment. Results showed that the most significant parameters are related to the tensile properties of the concrete (tensile strength and fracture energy) and the boundary conditions. A finite element (FE) model in which the results of the sensitivity analysis were applied, was able to predict accurately the load-carrying capacity of the bridge and its failure mode. Two additional existing prestressed concrete bridges, that will be used to improve further the method, are also described, and discussed.
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Papers by Lennart Elfgren