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Elfgren, Lennart, Senior ProfessorORCID iD iconorcid.org/0000-0002-0560-9355
Publications (10 of 308) Show all publications
Popescu, C., Täljsten, B., Blanksvärd, T. & Elfgren, L. (2019). 3D reconstruction of existing concrete bridges using optical methods. Structure and Infrastructure Engineering
Open this publication in new window or tab >>3D reconstruction of existing concrete bridges using optical methods
2019 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980Article in journal (Refereed) Epub ahead of print
Abstract [en]

Routine bridge inspections usually consist of visual observations. These inspections are time-consum-ing and subjective. There is a need to identify new inspection techniques for infrastructure that reducetraffic disturbance, and improve the efficiency and reliability of the acquired data. This study comparedthe performance of three different imaging technologies for the three-dimensional (3D) geometricmodeling of existing structures: terrestrial laser scanning, close-range photogrammetry, and infraredscanning. Each technology was used to assess six existing concrete railway bridges. The technologieswere compared in terms of geometric deviations, visualization capabilities, the level of the inspector’sexperience, and degree of automation. The results suggest that all methods investigated can be usedto create 3D models, however, with different level of completeness. Measurements such as spanlength, deck widths, etc. can be extracted with good accuracy. Although promising, a full off-siteinspection is currently not feasible as some areas of the bridges were difficult to capture mainly dueto restricted access and narrow spaces. Measurements based on terrestrial laser scanning were closerto the reality compared to photogrammetry and infrared scanning. The study indicates the no specialtraining is needed for photogrammetry and infrared scanning to generate a 3D geometric model.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
3D geometric modeling, terrestrial laser scanning, photogrammetry, infrared scanning, bridge inspection, remote sensing
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-73644 (URN)10.1080/15732479.2019.1594315 (DOI)
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-16Bibliographically approved
Duvnjak, I., Damjanović, D., Sabourova, N., Grip, N., Ohlsson, U., Elfgren, L. & Tu, Y. (2019). Damage Detection in Structures – Examples. In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management. Paper presented at IABSE Symposium 2019, Towards a Resilient Built Environment - Risk and Asset Management, March 27-29, 2019, Guimarães, Portugal.
Open this publication in new window or tab >>Damage Detection in Structures – Examples
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2019 (English)In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management, 2019Conference paper, Published paper (Refereed)
Abstract [en]

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 𝑙1-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.

Keywords
mode shape damage detection, finite element model updating, 𝑙1-norm regularization
National Category
Engineering and Technology Mathematics Other Civil Engineering
Research subject
Mathematics; Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-73334 (URN)
Conference
IABSE Symposium 2019, Towards a Resilient Built Environment - Risk and Asset Management, March 27-29, 2019, Guimarães, Portugal
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-15Bibliographically approved
Sabourova, N., Grip, N., Ohlsson, U., Elfgren, L., Tu, Y., Duvnjak, I. & Damjanović, D. (2019). Detection of Sparse Damages in Structures. In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management. Paper presented at IABSE Symposium 2019, Towards a Resilient Built Environment - Risk and Asset Management, March 27-29, 2019, Guimarães, Portugal.
Open this publication in new window or tab >>Detection of Sparse Damages in Structures
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2019 (English)In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management, 2019Conference paper, Published paper (Refereed)
Abstract [en]

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 the compressed sensing 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 (1) 𝑙2-norm regularization was used to solve the ill-posed inverse problems, such as damage identification. However, using (2) already well established 𝑙1-norm regularization or (3) our proposed 𝑙1-norm total variation regularization and (4) 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 structure. The validity of the proposed methods is demonstrated using simulations on a Kirchhoff plate model. The pros and cons of these methods are discussed.

Keywords
sparse damage, 𝑙2-norm, 𝑙1-norm, total variation, dictionary-based regularization, sensitivity
National Category
Engineering and Technology Mathematical Analysis Other Civil Engineering
Research subject
Mathematics; Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-73335 (URN)
Conference
IABSE Symposium 2019, Towards a Resilient Built Environment - Risk and Asset Management, March 27-29, 2019, Guimarães, Portugal
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-15
Nilimaa, J., Sabau, C., Bagge, N., Puurula, A., Sas, G., Blanksvärd, T., . . . Elfgren, L. (2018). Assessment and Loading to Failure of Three Swedish RC Bridges. In: Eva Lantsoght and Pinar Okumus (Ed.), Evaluation of Concrete Bridge Behavior through Load Testing: International Perspectives (pp. 8.1-8.18). Faarmington Hills, MI: American Concrete Institute, 323, Article ID SP-323-8.
Open this publication in new window or tab >>Assessment and Loading to Failure of Three Swedish RC Bridges
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2018 (English)In: Evaluation of Concrete Bridge Behavior through Load Testing: International Perspectives / [ed] Eva Lantsoght and Pinar Okumus, Faarmington Hills, MI: American Concrete Institute, 2018, Vol. 323, p. 8.1-8.18, article id SP-323-8Chapter in book (Refereed)
Abstract [en]

Current codes often underestimate the capacity of existing bridges. The purpose of the tests presented here has been to assess the real behaviour and capacity of three types of bridges in order to be able to utilize them in a more efficient way.

The three studied bridges are: (1) Lautajokk – A one-span trough bridge tested in fatigue to check the shear capacity of the section between the slab and the girders; (2) Övik – A two span trough bridge strengthened with Near Surface Mounted Reinforcement (NSMR) of Carbon Fibre Reinforced Polymers (CFRP) tested in bending, shear and torsion; and (3) Kiruna – A five-span prestressed three girder bridge tested to shear-bending failures in the girders and in the slab.

The failure capacities were considerably higher than what the code methods indicated. With calibrated and stepwise refined finite element models, it was possible to capture the real behaviour of the bridges. The experiences and methods may be useful in assessment and better use of other bridges.

Place, publisher, year, edition, pages
Faarmington Hills, MI: American Concrete Institute, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-69992 (URN)978-1-64195-007-7 (ISBN)
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-08-10Bibliographically approved
Täljsten, B., Blanksvärd, T., Sas, G., Bagge, N., Nilimaa, J., Popescu, C., . . . Häggström, J. (2018). Bridges tested to failure in Sweden. In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: . Paper presented at IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark.
Open this publication in new window or tab >>Bridges tested to failure in Sweden
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2018 (English)In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Five bridges of different types have been tested to failure and the results have been compared to analyses of the load-carrying capacity using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. There 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 five bridges were: (1) a strengthened one span concrete road bridge - Stora Höga ; (2) a one span concrete rail trough bridge loaded in fatigue – Lautajokk; (3) a two span strengthened concrete trough railway bridge - Övik; (4) a one span railway steel truss bridge -Åby; and (5) a five span prestressed concrete road bridge - Kiruna. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy and shortcomings/potentials of different codes and models for safety assessment of existing structures

Keywords
Test to failure, bridges of concrete and steel, Assessment, Strengthening, Monitoring, Bending, Shar, Torsion, Bond, Fatigue, Carbon Fibre Reinforced Polymers (CFRP)
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72378 (URN)
Conference
IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2018-12-28
Nilforoush, R., Nilsson, M. & Elfgren, L. (2018). Experimental Evaluation of Influence of Member Thickness, Anchor-Head Size, and Orthogonal Surface Reinforcement on the Tensile Capacity of Headed Anchors in Uncracked Concrete. Journal of Structural Engineering, 144(4), Article ID 04018012.
Open this publication in new window or tab >>Experimental Evaluation of Influence of Member Thickness, Anchor-Head Size, and Orthogonal Surface Reinforcement on the Tensile Capacity of Headed Anchors in Uncracked Concrete
2018 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 144, no 4, article id 04018012Article in journal (Refereed) Published
Abstract [en]

Cast-in-place headed anchors with different head sizes embedded in plain and reinforced concrete members of various thicknesses were subjected to pullout tests. The influence of member thickness, size of the anchor head, and orthogonal surface reinforcement on the tensile capacity and performance of anchor bolts was evaluated. The member thickness varied from 1.5 to 3.0 times the anchor embedment depth and headed anchors with small, medium, and large heads were tested.

The experimental results of the present study showed that increasing member thickness and/or the use of orthogonal surface reinforcement lead to increased anchorage capacity and anchorage ductility, whereas the anchorage stiffness decreases slightly. In contrast to the anchorage ductility, the tensile breakout resistance and the anchorage stiffness increase significantly with increasing size of the anchor head.

The experimental results corresponded closely to numerical results from a previous study (Nilforoush et al. 2016 a & b), which suggested a modified model incorporating several modification factors for improving the predictive capability of the Concrete Capacity (CC) method. In the present study, these factors yielded improved prediction of the tensile breakout capacity of the tested headed anchors.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2018
Keywords
headed anchor; anchor bolt; concrete cone breakout; concrete splitting; member thickness; anchor head; surface reinforcement.
National Category
Civil Engineering Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-66332 (URN)10.1061/(ASCE)ST.1943-541X.0001976 (DOI)000425620500004 ()2-s2.0-85040823012 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-01-23 (andbra)

Available from: 2017-10-31 Created: 2017-10-31 Last updated: 2018-09-25Bibliographically approved
Bagge, N., Popescu, C. & Elfgren, L. (2018). Failure tests on concrete bridges: Have we learnt the lessons?. Structure and Infrastructure Engineering, 14(3), 292-319
Open this publication in new window or tab >>Failure tests on concrete bridges: Have we learnt the lessons?
2018 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 3, p. 292-319Article in journal (Refereed) Published
Abstract [en]

Full-scale failure tests of bridges are important for improving understanding of bridges’ behaviour and refining assessment methods. However, such experiments are challenging, often expensive, and thus rare. This paper provides a review of failure tests on concrete bridges, focusing on lessons from them. In total, 40 tests to failure of 30 bridges have been identified. These include various types of bridges, with reinforced concrete or prestressed concrete superstructures, composed of slabs, girders and combinations thereof. Generally, the tests indicated that theoretical calculations of the load-carrying capacity based on methods traditionally used for design and assessment provide conservative estimates. It can also be concluded that almost a third of the experiments resulted in unexpected types of failures, mainly shear instead of flexure. In addition, differences between theoretical and tested capacities are often apparently due to inaccurate representation of geometry, boundary conditions and materials

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65060 (URN)10.1080/15732479.2017.1350985 (DOI)000423625400002 ()
Note

Validerad;2018;Nivå 2;2017-12-20 (andbra)

Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2018-02-16Bibliographically approved
Huang, Z., Lu, Z., Song, S., Tu, Y., Blanksvärd, T., Sas, G. & Elfgren, L. (2018). Finite element analysis of shear deformation in reinforced concrete shear-critical beams. Structure and Infrastructure Engineering, 14(6), 791-806
Open this publication in new window or tab >>Finite element analysis of shear deformation in reinforced concrete shear-critical beams
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2018 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 6, p. 791-806Article in journal (Refereed) Published
Abstract [en]

The objective of this paper was to study the contribution of shear deformation in reinforced concrete (RC) shear-critical beams. A 2D concrete material model based on smeared fixed crack was presented and incorporated into a commercial finite element (FE) software. A method of calculating shear and flexure deformation separately out of total deformation in the shear span was presented and implemented into the FE analysis. Several experiments of RC shear-critical beams were simulated and good agreement between the experimental and numerical results was obtained in terms of total deformation, flexure deformation, shear deformation and crack patterns. The results show that after shear cracking, the contribution of shear deformation to total deformation increases rapidly. The shear span-to-depth ratio, the longitudinal reinforcement, the shear reinforcement and the load level could be the critical factor to influence the contribution of shear deformation. It appears that for RC shear-critical beams without shear reinforcement, the deformational behaviour is governed by flexure deformation. However, for RC beams with shear reinforcement, the contribution of shear deformation is not negligible after shear cracks develop. Moreover, the measuring method could also affect the measured shear deformation. Finally, future work on experimental investigation into this topic is recommended.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65169 (URN)10.1080/15732479.2017.1360915 (DOI)000429038000009 ()
Note

Validerad;2018;Nivå 2;2018-04-10 (andbra)

Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2018-04-19Bibliographically approved
Duvnjak, I., Bartolak, M., Nilimaa, J., Sas, G., Blanksvärd, T., Täljsten, B. & Elfgren, L. (2018). Lessons Learnt from Full-Scale Tests of Bridges in Croatia and Sweden. In: IABSE Symposium, Nantes 2018: Tomorrow's Megastructures. Paper presented at 40th IABSE Symposium, 19-21 September 2018, Nantes, France.. International Association for Bridge and Structural Engineering, Article ID S23-127.
Open this publication in new window or tab >>Lessons Learnt from Full-Scale Tests of Bridges in Croatia and Sweden
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2018 (English)In: IABSE Symposium, Nantes 2018: Tomorrow's Megastructures, International Association for Bridge and Structural Engineering , 2018, article id S23-127Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
International Association for Bridge and Structural Engineering, 2018
Keywords
Load testing, proof loading, collapse, deformations, serviceability limit state (SLS), numerical modelling, stiffness
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72381 (URN)2-s2.0-85059365622 (Scopus ID)9783857481611 (ISBN)
Conference
40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Funder
EU, Horizon 2020
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2019-01-14Bibliographically approved
Coric, I., Täljsten, B., Blanksvärd, T., Sas, G., Ohlsson, U. & Elfgren, L. (2018). Railway Bridges on the Iron Ore Line in Northern Sweden– From Axle Loads of 14 to 32,5 ton. In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: IABSE Reports, Vol 111. Paper presented at IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark. , 111
Open this publication in new window or tab >>Railway Bridges on the Iron Ore Line in Northern Sweden– From Axle Loads of 14 to 32,5 ton
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2018 (English)In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: IABSE Reports, Vol 111, 2018, Vol. 111Conference paper, Published paper (Refereed)
Abstract [en]

The Iron Ore Railway Line was built around 1900 and has more than 100 bridges. It has a length of ca 500 km and runs from Kiruna and Malmberget in northern Sweden to the ice-free harbour in Narvik in Norway on the Atlantic and to Luleå in Sweden on the Baltic. The original axle load was 14 ton. The axle load has gradually been increased to 25 ton in 1955, to 30 ton in 1998 and to 32,5 ton in 2017.The increases in axle loads have been preceded by monitoring and assessment studies of the bridges. The capacity and need for strengthening or replacement of the bridges have been evaluated. Many of the bridges could carry a higher load than what it was designed for. Experiences from studies before the axle load was increased in 1998 and 2017 are presented and discussed.

Keywords
Railway bridges, foundations, steel, reinforced and prestressed concrete. Assessment, Strengthening, Fatigue
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72379 (URN)
Conference
IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2018-12-28
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ORCID iD: ORCID iD iconorcid.org/0000-0002-0560-9355

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