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Publications (10 of 51) Show all publications
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
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
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: 2019-09-06
Persson, M., Ohlsson, U., Silfwerbrand, J. & Emborg, M. (2017). Interface stresses in concrete bridge deck overlays subjected to differentialshrinkage. In: Proceedings of the 23rd Nordic Concrete Research Symposium: . Paper presented at 23th Symposium on Nordic Concrete Research & Developement, Aalborg, Denmark, 21 - 23 August 2017. Oslo, Norway: Nordic Concrete Federation
Open this publication in new window or tab >>Interface stresses in concrete bridge deck overlays subjected to differentialshrinkage
2017 (English)In: Proceedings of the 23rd Nordic Concrete Research Symposium, Oslo, Norway: Nordic Concrete Federation , 2017Conference paper, Published paper (Refereed)
Abstract [en]

Concrete overlays on bridge decks are expected to be more durable as compared with the more common asphalt solution. Besides stresses due to traffic load and temperature variations at service, the overlays are exposed to stresses due to long term shrinkage. Of interest is to evaluate the concrete overlay due to the shrinkage induced stresses at the composite interface. Three strategies have been employed to gain knowledge on the stresses; 1) use of non-destructive test systems via field observations, 2) a numerical study on a concrete composite slab tested in laboratory, 3) recordings of realistic shrinkage and climate data on a reference bridge using vibrating strain gauges and humidity probes in the newly cast concrete overlay. The data were used as input data for a linear elastic finite element model. This article demonstrates this last phase of the work.

Place, publisher, year, edition, pages
Oslo, Norway: Nordic Concrete Federation, 2017
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65991 (URN)978-82-8208-056-9 (ISBN)
Conference
23th Symposium on Nordic Concrete Research & Developement, Aalborg, Denmark, 21 - 23 August 2017
Available from: 2017-10-06 Created: 2017-10-06 Last updated: 2018-03-27Bibliographically approved
Puurula, A., Enochsson, O., Sas, G., Blanksvärd, T., Ohlsson, U., Bernspång, L., . . . Elfgren, L. (2016). 3D non-linear FE analysis of a full scale test to failure of a RC Railway Bridge strengthened with carbon fibre bars. In: Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid (Ed.), IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment. Paper presented at 19th IABSE Congress, Strockholm, 21-23 September 2016 (pp. 2527-2535). CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering
Open this publication in new window or tab >>3D non-linear FE analysis of a full scale test to failure of a RC Railway Bridge strengthened with carbon fibre bars
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2016 (English)In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016, p. 2527-2535Conference paper, Published paper (Refereed)
Abstract [en]

At a full scale loading test to failure a 50 year old concrete railway trough bridge in Örnsköldsvik, in northern Sweden was tested to failure. The test was a part of the European Research Project “Sustainable Bridges” regarding assessment and strengthening of existing bridges. In the projectnew calculation methods were developed to capture the behaviour of the bridge during increasing load. The bridge was strengthened in bending with rods of Carbon Fiber Reinforced Polymer (CFRP) before the loading test. Failure was reached for an applied load of 11.7 MN by pulling a steel beam placed in the middle of one of the two spans downwards. The achieved failure was a combination of bond, shear, torsion and bending. The developed model, a 3D -non-linear finiteelement (FE) model with discrete reinforcement, gave accurate accounts of the response of thebridge. The FE calculations show the effect of the strengthening with CFRP and even the effect of the epoxy when using the Near Surface Mounted Reinforcement (NSMR) strengthening method.

Place, publisher, year, edition, pages
CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016
Series
IABSE Congress Reports
Keywords
Bridge, Strengthening, Full scale test, Failure Analysis, Bond, Shear, Near Surface Mounted reinforcement (NSMR), Carbon Fibre Reinforced Polymer CFRP), Ultimate load carrying capacity, 3D Non-linear finite element analysis.
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-60997 (URN)2-s2.0-85018961713 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
19th IABSE Congress, Strockholm, 21-23 September 2016
Note

EU FP6, Sjätte ramprogrammet

Available from: 2016-12-10 Created: 2016-12-10 Last updated: 2018-03-27Bibliographically approved
Ge, Y., Yu, S., Yu, Z., Tu, Y. & Ohlsson, U. (2016). A refined model of concrete carbonation by coupling of multi-factors. In: ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid (Ed.), IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment. Paper presented at 9th IABSE Congress, Stockholm 2016, September 21-23 (pp. 1198-1206). H - 8093 Zürich, Switzerland
Open this publication in new window or tab >>A refined model of concrete carbonation by coupling of multi-factors
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2016 (English)In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, H - 8093 Zürich, Switzerland, 2016, p. 1198-1206Conference paper, Published paper (Refereed)
Abstract [en]

Studies on carbonation of concrete play an important role in accurately predicting the service life. However, most research work on carbonation of concrete was carried out in qualitative ways and seldom in quantitative ways. In this paper, based on conservation of mass of C3S(s), C2S(s), CSH(s), CH(s), CH(aq), CO2(aq) and CO2(g) and one-dimensional diffusion and reaction equation, a refined mathematical model of concrete carbonation composed of a series of partial differential equations (PDEs) was built. Corresponding MATLAB codes were developed with calculus of differences to solve the mathematical model of concrete carbonation. The results of the mathematical models in this paper agree very well with measurements, which show that this model can be used to accurately predict concrete carbonation as well as remaining service life of concrete bridges and other concrete structures

Place, publisher, year, edition, pages
H - 8093 Zürich, Switzerland: , 2016
Series
IABSE Congress Reports
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-63557 (URN)2-s2.0-85018959139 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
9th IABSE Congress, Stockholm 2016, September 21-23
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2018-03-27Bibliographically approved
Qin, X.-C., Meng, S.-P., Cao, D.-F., Tu, Y.-M., Sabourova, N., Grip, N., . . . Elfgren, L. (2016). Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens. Construction and Building Materials, 125, 892-904
Open this publication in new window or tab >>Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens
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2016 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 892-904Article in journal (Refereed) Published
Abstract [en]

The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of σconσcon for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed.

Place, publisher, year, edition, pages
Elsevier, 2016
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-59653 (URN)10.1016/j.conbuildmat.2016.08.098 (DOI)000385600100088 ()2-s2.0-84984828018 (Scopus ID)
Note

Validerad; 2016; Nivå 2; 2016-10-10 (andbra)

Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2019-02-22Bibliographically approved
Wang, C., Wang, Z., Zhang, J., Tu, Y.-M., Grip, N., Ohlsson, U. & Elfgren, L. (2016). FEM based research on the dynamic response of a concrete railway arch bridge. In: Elfgren, Lennart; Jonsson, Johan; Karlsson, Mats; Rydberg-Forssbeck, Lahja; Sigfid, Britt2016 (Ed.), IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment. Paper presented at 19th IABSE Congress Stockholm, 21-23 September 2016 (pp. 2472-2479). CH - 8093 Zürich, Switzerland
Open this publication in new window or tab >>FEM based research on the dynamic response of a concrete railway arch bridge
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2016 (English)In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] Elfgren, Lennart; Jonsson, Johan; Karlsson, Mats; Rydberg-Forssbeck, Lahja; Sigfid, Britt2016, CH - 8093 Zürich, Switzerland, 2016, p. 2472-2479Conference paper, Published paper (Refereed)
Abstract [en]

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 the concrete railway arch bridge in a better way than beam element and spatial grillage models. The dynamic analysis based on this type of shell model can give an optimized suggestion for the railway operation as well as for the design of high-speed railway bridges.

Place, publisher, year, edition, pages
CH - 8093 Zürich, Switzerland: , 2016
Series
IABSE Congress Reports
Keywords
Refined shell element model, Dynamic response, Moving load, Concrete railway arch bridge
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-62172 (URN)2-s2.0-85018948830 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
19th IABSE Congress Stockholm, 21-23 September 2016
Funder
Swedish Transport Administration
Note

Financial support from the National Natural Science Foundation of China (Project No 51378104) and

"A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions, PAPD”, Southeast University (SEU).

Available from: 2017-02-25 Created: 2017-02-25 Last updated: 2019-09-11Bibliographically approved
Huang, Z., Tu, Y.-M., Grip, N., Sabourova, N., Bagge, N., Blanksvärd, T., . . . Elfgren, L. (2016). Modelling of Damage and its use in Assessment of a PrestressedConcrete Bridge. In: Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid (Ed.), IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment. Paper presented at 19th IABSE Congress, Stockholm 2016, September 21-23 (pp. 2093-2108). CH - 8093 Zürich, Switzerland
Open this publication in new window or tab >>Modelling of Damage and its use in Assessment of a PrestressedConcrete Bridge
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2016 (English)In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland, 2016, p. 2093-2108Conference paper, Published paper (Refereed)
Abstract [en]

A five-span prestressed concrete bridge has been subjected to a loading test up to failure in Kiruna, Sweden. The bridge was 55 years old and had a length of 121.5 m. The test has been used to validate and calibrate existing nonlinear finite element programs for predicting the shear behavior of reinforced and prestressed concrete structures. Two 3D finite element (FE) models of the Kiruna Bridge are built in commercial software Abaqus, one using shell-elements and one using a combination of shell and beam elements. Predictions obtained from these two models are well consistent with mode shapes and eigenfrequencies computed from acceleration measurements on the bridge before and after loading it to failure.The shear failure of the bridge is also simulated using the built-in concrete damage plasticity (CDP)model in Abaqus. The predicted load-displacement curve is in good agreement with the measurements. Verification of the CDP model is conducted at element and member level with two different damage parameter evolutions. The verification indicates that the damage parameter will affect the predicted shear behavior. It does not seem to be reliable to adopt the CDP model to simulate the shear behavior in the present research. A long term goal is to use use the measured mode shapes, eigenfrequencies and FE models for evaluating methods for damage identification. Such methods are important for maintenance of different structures, for extending their life span and for better knowledge of their load carrying capacity. The use is described of so-called sparse regularized finite element method updating (FEMU) methods. Some important properties of such methods are demonstrated using simulations on a Kirchhoff plate. For instance, the simulations suggest that both eigenfrequencies and mode shapes should be used for precise localization of the damage.

Place, publisher, year, edition, pages
CH - 8093 Zürich, Switzerland: , 2016
Series
IABSE Congress Reports
Keywords
Concrete damage plasticity model, refined shell element model, shear failure test, shear behavior, five-span prestressed concrete bridge, FEM updating, sparse regularization, Kirchhoff plate.
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-60996 (URN)2-s2.0-85018991487 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
19th IABSE Congress, Stockholm 2016, September 21-23
Available from: 2016-12-10 Created: 2016-12-10 Last updated: 2018-03-27Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5187-2552

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