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Elfgren, Lennart, Senior ProfessorORCID iD iconorcid.org/0000-0002-0560-9355
Biography [eng]

Lennart Elfgren was born on July 9, 1942, in Gothenburg, Sweden. He studied civil engineering at Chalmers University of Technology and obtained a M.Sc. in 1965 and a PhD in 1971 on torsion-shear-bending in rc structures.

After a post doc stay at University of California at Berkeley 1972-73 working with curved box-girder bridges he was appointed to a position as Associate Professor in Structural Engineering at the recently started Luleå University of Technology. In 1981-83 he worked as a Consulting Engineer with Jacobson & Widmark (now WSP) in Gothenburg and in 1982-83 as part time Researcher in the Swedish Research and Testing Institute (now RISE) in Borås.

He returned to Luleå as Full Professor in 1983 and has served as Department Head and Dean of the Faculty of Engineering Sciences. He has been the main supervisor for 14 PhDs and an associate supervisor for another 15.

Publications (10 of 315) Show all publications
Wang, C., Zhang, J., Tu, Y., Sabourova, N., Grip, N., Blanksvärd, T. & Elfgren, L. (2020). Fatigue Assessment of Reinforced Concrete Railway Bridge based on a Coupled Dynamic System. Structure and Infrastructure Engineering
Open this publication in new window or tab >>Fatigue Assessment of Reinforced Concrete Railway Bridge based on a Coupled Dynamic System
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2020 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980Article in journal (Refereed) Epub ahead of print
Abstract [en]

This paper proposes a fatigue damage assessment methodology of a reinforced concrete bridge based on a train bridge coupled dynamic analysis system. This coupling system is composed of a vehicle a ballasted track and a bridge structure to realize a coupled vibration analysis during train passages. This methodology adopts the Palmgren Miner rule to linearly accumulate fatigue damage, and accomplishes fatigue assessment based on recommended SN relationships for reinforced concrete from various criteria. In this paper, the dynamic performances of a bridge structure are analyzed with two different vehicle models, a moving load model (and a moving spring mass damper model). Calculated dynamic stresses areused to evaluate the fatigue damage of critical positions in a reinforced concrete bridge. A case study is carried out of a railway arch bridge with a span of 89 m, Långforsen Bridge. It runs over Kalix River on the railway between Kalix and Morjärv in northern Sweden The fatigue assessment is made by combining the presented methodology with measurements. Furthermore, the effects of train speed and axle load on fatigue damage are investigated. The results indicate that good estimations of the fatigue damage assessment are made for four measured cases based on a train-bridge coupled dynamic analysis. For low speeds and light loads no difference could be seen in the cumulative fatigue damage for the two vehicle models. But high speeds and/or heavy load ssignificantly affect the fatigue damage.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2020
Keywords
Train Bridge Coupling System, Fatigue Damage, Moving Load Model, Moving Spring Mass Damper Model, Reinforced Concrete Railway Bridge
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-76136 (URN)10.1080/15732479.2019.1671467 (DOI)000488187400001 ()2-s2.0-85074260959 (Scopus ID)
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-11-20
Popescu, C., Täljsten, B., Blanksvärd, T. & Elfgren, L. (2019). 3D reconstruction of existing concrete bridges using optical methods. Structure and Infrastructure Engineering, 15(7), 912-924
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 1744-8980, Vol. 15, no 7, p. 912-924Article in journal (Refereed) Published
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 Other Civil Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-73644 (URN)10.1080/15732479.2019.1594315 (DOI)000466668000001 ()2-s2.0-85064494122 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-07-12 (johcin)

Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-07-12Bibliographically 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
Elfgren, L., Täljsten, B. & Blanksvärd, T. (2019). Load Testing as Part of Bridge Management in Sweden.: Chapter 11 (1ed.). In: Eva O.L. Landsoght (Vol 13), Dan M. Frangopol (Series Editor) (Ed.), Load Testing of Bridges: Proof load Testing and the Future of Load Testing, Volume Editor Eva O. L. Landsoght: Series: Structures and Infrastructures, Vol. 13, Series Editor Dan M. Frangopol, (pp. 333-346). London/Leiden: Taylor and Francis Group
Open this publication in new window or tab >>Load Testing as Part of Bridge Management in Sweden.: Chapter 11
2019 (English)In: Load Testing of Bridges: Proof load Testing and the Future of Load Testing, Volume Editor Eva O. L. Landsoght: Series: Structures and Infrastructures, Vol. 13, Series Editor Dan M. Frangopol, / [ed] Eva O.L. Landsoght (Vol 13), Dan M. Frangopol (Series Editor), London/Leiden: Taylor and Francis Group , 2019, 1, p. 333-346Chapter in book (Refereed)
Abstract [en]

Load testing of new and existing bridges was performed regularly in Sweden up to the 1960ies. It was then abandoned due to high costs versus little extra information obtained. Most bridges behaved well in the serviceability limit range and no knowledge of the ultimate limit stage could be obtained without destroying the bridge. At the same time the methods for calculating the capacity developed and new numerical methods were introduced. Detailed rules were given on how these methods should be used. Some decommissioned bridges were tested to their maximum capacity to be able to study their failure mechanisms and to calibrate the numerical methods. In this paper some examples are given on how allowable loads have increased over the years and of tests being performed. Nowadays, load testing may be on its way back, especially to test existing rural prestressed concrete bridges, where no design calculations have been retained

Place, publisher, year, edition, pages
London/Leiden: Taylor and Francis Group, 2019 Edition: 1
Series
Structures and Infrastructures ; 13
Keywords
Load Testing, Bridges, Management, Sweden
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-76135 (URN)9780429265969 (DOI)9781138091986 (ISBN)
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-09-26
Haugum, D. (2019). Långtidsstudie av byggnader i trä i kallt klimat. Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Långtidsstudie av byggnader i trä i kallt klimat
2019 (Swedish)Other (Other (popular science, discussion, etc.))
Abstract [sv]

För 30 år sedan uppfördes en svensk forskningsstation, Wasa, i Antarktis. Huvudbyggnaden konstruerades utifrån erfarenheter från svenska fjällstugor. Ett av syftena var att visa att svensk träbyggnadsteknik fungerade väl i det arktiska klimatet. Initiala byggfysiska mätningar gjordes. Att använda en träkonstruktion till en forskningsstation i Antarktis var unikt vid denna tidpunkt. Under sydsommaren 2019-20 finns möjlighet att för första gången sedan 1990 göra en uppföljande undersökning av byggnadens påverkan av klimatet som kännetecknas av stora dygnsvariationer i temperatur och av stora vindlaster i kombination med stark kyla och drevsnö. Analys görs av byggnadens uttorkning/täthet och hur detta påverkar inträngning av fukt i form av drevsnö. Byggnadens utformning gör att vi kan jämföra olika konstruktionslösningar på plats. Jämförelse kommer att göras med den intilliggande finska stationen som är byggd enligt helt andra principersamt med motsvarande byggnader i Skandinavien.

Place, publisher, year, pages
Luleå: Luleå tekniska universitet, 2019. p. 1
Keywords
träbyggnad, energieffektivitet, kallt klimat, Antarktis
National Category
Building Technologies
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-76579 (URN)
Funder
Swedish Energy Agency, 47847-1
Available from: 2019-10-30 Created: 2019-10-30 Last updated: 2019-10-30
Sabourova, N., Grip, N., Tu, Y., Wang, C., Enochsson, O., Blanksvärd, T., . . . Elfgren, L. (2019). Railway Concrete Arch Bridge over Kalix River at Långforsen: Dynamic Properties and Load-Carrying Capacity. Luleå: Luleå University of Technology
Open this publication in new window or tab >>Railway Concrete Arch Bridge over Kalix River at Långforsen: Dynamic Properties and Load-Carrying Capacity
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2019 (English)Report (Refereed)
Abstract [en]

The concrete arch bridge over Kalix River at Långforsen was built in 1960 and has a mid-span of 89,5 m and a height of 13,7 m. The bridge owner, Trafikverket, wanted to increase its allowable axle load from 225 to 300 kN. Field tests were carried out under service condition and with ambient vibrations. The test results were used to update and validate Finite Element Models. At last, the refined models were used to check the possibility to increase the axle load.

According to earlier assessments, most parts of the bridge is capable of carrying an axle load of 330 kN. The only critical sections are located in the beams carrying the rail on top of the arch in the section where the beams are united with the arch. Here the stresses in the longitudinal bottom reinforcement are slightly too high.

These sections have been studied in a FEM model for different loads and results show maximum strains of about 50·10-6 corresponding to stresses of only about 10 MPa in the reinforcement in the critical sections. Live load vertical deflections of the crown of the arch is of the order of only ± 6 mm. Dynamic studies have also been made showing that fatigue is no issue. Altogether the studies show that the bridge is able to carry an increased axle load of 300 kN without problems.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019. p. 44
Series
Research report / Luleå University of Technology, ISSN 1402-1528
Keywords
Concrete Arch Bridge, Railway, Dynamic Properties, Load-Carrying Capacity
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-76116 (URN)978-91-7790-473-1 (ISBN)
Funder
Swedish Transport Administration
Available from: 2019-09-25 Created: 2019-09-25 Last updated: 2019-10-18Bibliographically approved
Bernander, S. & Elfgren, L. (2019). Stability of the North Spur at Muskrat Falls. In: Stephen Crocker (Ed.), Muskrat Falls Symposium: 28-29 September 2018, Memorial University. St. John’s, NL, Canada. Paper presented at Muskrat Falls Symposium, 28-29 September 2018, Memorial University. St. John’s, NL, Canada. St. John's, NL, Canada
Open this publication in new window or tab >>Stability of the North Spur at Muskrat Falls
2019 (English)In: Muskrat Falls Symposium: 28-29 September 2018, Memorial University. St. John’s, NL, Canada / [ed] Stephen Crocker, St. John's, NL, Canada, 2019Conference paper, Published paper (Refereed)
Abstract [en]

The paper presents the geotechnical background to one of the stability problems regarding the North Spur dam wall: This land was formed in the regression of the sea during and after the last ice age with deposits of multiple layers of silty sands and silty sandy clays that formed the valleys and plains that are now above sea level. Some of these layers, deposited thousands of years ago in post-glacial times, are vulnerable to liquefaction when they are disturbed. These conditions have in the past repeatedly caused slides along the banks of the Churchill river.

In the current paper, a specific type of possible progressive failure – the most dangerous one in respect of the safety of the North Spur – is discussed. This type of landslide development may be caused by the rising water pressure, when - or after - the dam is impounded. As will be explained, such a slide could force part of the North Spur ridge to slide along a failure surface sloping East-wards into the deep river whirlpool downstream of Muskrat Falls. 

In the following, we provide a brief overview of the geotechnical background behind our concerns, also discussing methods of mitigating the risk of the kind of slope failure in question. Hence, we propose measures such as compacting the soil by piling or by methods of grouting and drainage. We also suggest the need for an expert Advisory Panel to look further into the long-term safety of the North Spur.

Place, publisher, year, edition, pages
St. John's, NL, Canada: , 2019
Keywords
Landslide, Downhill Progressive Failure, Dam stability, Strain-softening soils, Metastable soils
National Category
Geotechnical Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-76680 (URN)
Conference
Muskrat Falls Symposium, 28-29 September 2018, Memorial University. St. John’s, NL, Canada
Available from: 2019-11-11 Created: 2019-11-11 Last updated: 2019-11-27
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: 2019-09-06
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0560-9355

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