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Lagerqvist, Ove
Publications (10 of 62) Show all publications
Sabau, G., Lagerqvist, O. & Baddoo, N. (2020). Statistical Analysis of Flexural-Buckling-Resistance Models for High-Strength Steel Columns. Journal of Structural Engineering, 146(2)
Open this publication in new window or tab >>Statistical Analysis of Flexural-Buckling-Resistance Models for High-Strength Steel Columns
2020 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 146, no 2Article in journal (Refereed) Published
Abstract [en]

Flexural buckling is one of the main problems steel structures are faced with in ensuring an economic design. In Europe, the buckling resistance is calculated using an imperfection factor based on the section type, fabrication method, and steel grade. The current European design standards contain guidelines for the imperfection factor for sections made of steels with yield strength up to and including 700 MPa. However, the current design codes are based mainly on tests performed on steels with yield strength below 460 MPa. Therefore, the applicability of the methodology was reassessed. This paper reviewed the background documentation of the European flexural-buckling design methodology and discussed the current design practice described in the American National Standard. A total of 72 flexural-buckling experiments performed on cold-formed, hot-finished, and welded sections made of steel with yield strength in the range 690–960 MPa were collected and analyzed. Four models for estimating the resistance of high-strength steel struts subjected to pure compression were statistically evaluated based on the collected data. Finally, a recommendation for the estimation of flexural-buckling resistance of high-strength steel members is presented.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2020
National Category
Other Civil Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-77188 (URN)10.1061/(ASCE)ST.1943-541X.0002529 (DOI)000507309800029 ()2-s2.0-85076674659 (Scopus ID)
Note

Validerad;2020;Nivå 2;2019-12-16 (johcin)

Available from: 2019-12-16 Created: 2019-12-16 Last updated: 2020-04-16Bibliographically approved
Sabau, G., Koltsakis, E. & Lagerqvist, O. (2019). Statistical evaluation of the bearing capacity of short polygonal columns. In: František Wald, Michal Jandera (Ed.), Stability and Ductility of Steel Structures 2019: Proceedings of the International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic. Paper presented at International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic (pp. 946-953). CRC Press
Open this publication in new window or tab >>Statistical evaluation of the bearing capacity of short polygonal columns
2019 (English)In: Stability and Ductility of Steel Structures 2019: Proceedings of the International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic / [ed] František Wald, Michal Jandera, CRC Press, 2019, p. 946-953Conference paper, Published paper (Refereed)
Abstract [en]

Regular convex polygon sections (RCPS) are commonly used as towers supporting transmission lines, stadium lightning and street lamps. Their use provides advantages in the bearing capacity and can simplify erection. Over the last 50 years experimental studies have been conducted to check the applicability of the plate theory to stocky polygonal columns. The paper presents the processed data gathered from compression tests found in the literature. Results from 70 specimens tested under pure compression were statistically analysed. Specimens with yield strength varying from 235 to 700 MPa and angles varying from 144 to 175.5 (5 to 40 sides) were investigated. The local non-dimensional slenderness was calculated using buckling lengths according to EN 1993-1-3 and EN 1993-1-5 with values ranging from 0.55 to 4.52. The objective of the paper was to compare the plate buckling resistance predictions to the experimental results. The paper concludes with a buckling width recommendation for evaluating the critical stress as calculated according to EN 1993-1-3 or EN 1993-1-5.

Place, publisher, year, edition, pages
CRC Press, 2019
National Category
Other Civil Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-77605 (URN)2-s2.0-85080616553 (Scopus ID)
Conference
International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic
Note

ISBN för värdpublikation: 9780429320248

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-05-04Bibliographically approved
Sabau, G., Lagerqvist, O. & Baddoo, N. (2019). Stronger steels, higher penalties: Evaluation of flexural buckling experiments performed on welded high-strength steel struts. Paper presented at 14th Nordic Steel Construction Conference 18–20 September 2019, Copenhagen, Denmark. ce/papers, 3(3-4), 731-736
Open this publication in new window or tab >>Stronger steels, higher penalties: Evaluation of flexural buckling experiments performed on welded high-strength steel struts
2019 (English)In: ce/papers, E-ISSN 2509-7075, Vol. 3, no 3-4, p. 731-736Article in journal (Refereed) Published
Abstract [en]

Stability in a structural mechanics context has posed a continuous problem throughout history for mathematicians, engineers and architects. Flexural buckling is one of the main problems steel structures are faced with in order to ensure an economic design. Different equations have been derived to estimate critical loads that could lead to collapse of compressed members. The buckling resistance of compressed struts are calculated in Europe using the European buckling curves. The method of calculating the resistance implies the use of a reduction factor based on 5 different buckling curves. These buckling curves differ based on type of cross-section, fabrication method and steel grade. The method has been generally accepted since it proved to be reliable and versatile. The current design codes are assigning the same relevant buckling curve to the sections made of steels with yield stress of above 460 MPa. This conservative approach is one of the reasons that discourages the use of high-strength steels in common structural applications, since the designer does not see a direct benefit from the additional steel strength. The first part of the paper briefly describes the origin of the European buckling curves. The second part presents two analytical models for calculating flexural buckling limit loads. Flexural buckling experiments performed on welded box and I-sections made of high-strength steel, with the yield stress in the range of 690-960MPa. The third part analyses the existing buckling experiments and statistically evaluates the models proposed for estimating the resistance of high-strength steel struts subjected to pure compression. The final part addresses the potential future research in the context of developing adequate flexural buckling curves for high strength steel (HSS) members.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
high-strength steel, flexural buckling, state-of-art, statistical evaluation
National Category
Infrastructure Engineering Other Civil Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-77724 (URN)10.1002/cepa.1127 (DOI)
Conference
14th Nordic Steel Construction Conference 18–20 September 2019, Copenhagen, Denmark
Note

Godkänd;2020;Nivå 0;2020-02-17 (johcin)

Available from: 2020-02-15 Created: 2020-02-15 Last updated: 2020-02-17Bibliographically approved
Sabau, G. & Lagerqvist, O. (2018). INFLUENCE OF RESIDUAL STRESSES ON THE FLEXURAL BUCKLINGRESISTANCE OF HIGH-STRENGTH STEEL HOLLOW SECTIONS. In: Baniotopoulos Charalampos (Ed.), International Conference on Wind Energy Harvesting: . Paper presented at WINERCOST’18 2nd International Conference on Wind Energy Harvesting, Catanzaro, 21-23 March 2018.
Open this publication in new window or tab >>INFLUENCE OF RESIDUAL STRESSES ON THE FLEXURAL BUCKLINGRESISTANCE OF HIGH-STRENGTH STEEL HOLLOW SECTIONS
2018 (English)In: International Conference on Wind Energy Harvesting / [ed] Baniotopoulos Charalampos, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Development of the wind energy industry continues to push the need for innovative solutions in terms of structural requirements. High-performance materials are thus needed to improve the efficiency of the structures and to ease the erection costs. The materials used for the towers have not improved significantly in the past years mainly because the design guidelines do not allow the efficient use of the high-strength steels. Lattice wind turbine towers could benefit from cost reductions if cold-formed high-strength steels would be used. Currently high-strength steel members have the same reductions factors for the relevant flexural buckling curve for cold-formed members regardless of the strength of steels. The paper discusses the approach towards the current European buckling curves and draws attention to potential limitations. The residual stresses present in rectangular hollow sections are discussed based on the method of fabrication. Different patterns of residual stresses are investigated by means of finite element simulations. The results indicate that the design codes slightly underestimate the flexural buckling resistance of high-strength steel members in the medium slenderness range.

National Category
Infrastructure Engineering
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-77722 (URN)
Conference
WINERCOST’18 2nd International Conference on Wind Energy Harvesting, Catanzaro, 21-23 March 2018
Projects
Aeolus4future
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-04-28
Sabau, G., Koltsakis, E. & Lagerqvist, O. (2018). Stability analysis of newly developed polygonal cross-sections for lattice wind towers. Paper presented at WINERCOST'17 – International Conference On Wind Energy Harvesting 2017, Coimbra, Portugal, 20-21 april, 2017. Wind Engineering: The International Journal of Wind Power, 42(4), 353-363
Open this publication in new window or tab >>Stability analysis of newly developed polygonal cross-sections for lattice wind towers
2018 (English)In: Wind Engineering: The International Journal of Wind Power, ISSN 0309-524X, E-ISSN 2048-402X, Vol. 42, no 4, p. 353-363Article in journal (Refereed) Published
Abstract [en]

The pursuit for cheaper energy is leading the current wind tower design to increased heights. Common wind turbine tower designs would generate unjustified costs for transportation and erection leading to inefficient use of materials. In order to reduce these costs, several simplified erection methods have been proposed. One of such is the hybrid lattice-tubular steel tower. For economic feasibility, built-up cold-formed polygonal cross-sections have been proposed for the lattice part. This article presents a numerical investigation of the failure modes of closed polygonal cross-sections. The first part contains a presentation of structural systems which incorporate elements composed of plates and cold-formed members. The evaluation of the polygonal sections is done by means of finite element analysis considering local and global geometrical imperfections and residual stresses generated in the fabrication procedure. A comparative study is performed between several finite element models to propose a corresponding European buckling curve for calculating the flexural buckling resistance. The results show that the design of polygonal sections can be done according to European buckling curves methodology.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
Cold-formed, finite element simulation, flexural buckling, lattice wind tower, polygonal sections
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-70193 (URN)10.1177/0309524X18777366 (DOI)2-s2.0-85049948088 (Scopus ID)
Conference
WINERCOST'17 – International Conference On Wind Energy Harvesting 2017, Coimbra, Portugal, 20-21 april, 2017
Note

2018-08-02 (rokbeg);konferensartikel i tidskrift

Available from: 2018-08-01 Created: 2018-08-01 Last updated: 2020-02-15Bibliographically approved
Sabau, G., Koltsakis, E. & Lagerqvist, O. (2017). Cylindrical shell buckling under a hydraulic constraint: Numerical study. Paper presented at EUROSTEEL 2017, Copenhagen, Denmark, September 13–15, 2017. ce/papers, 1(2-3), 970-979
Open this publication in new window or tab >>Cylindrical shell buckling under a hydraulic constraint: Numerical study
2017 (English)In: ce/papers, E-ISSN 2509-7075, Vol. 1, no 2-3, p. 970-979Article in journal (Refereed) Published
Abstract [en]

Steel cylindrical shell structures are used in a large variety of civil engineering applications such as off- shore platforms, tanks, silos, wind turbine towers, etc. The local stability of such structures and their sensitivity to imperfections is a well-known problem. In current engineering practice the design method is based on the selection of an imperfection class for the shell and subsequently calculating a reduction factor,χ, to the resistance of the shell. One such methodology is supplied by the EN1993-1-6; special conditions are given to pressurized tubes subjected to meridional compression.

Past studies have focused on the stability of cylindrical shells with internal pressure. The stability problem of a long cylinder considering the internal pressure as a simple static load was addressed. Thus, the approaches considered the fluid as compressible.

The purpose of the present work is to investigate numerically the potential benefit of using an incompressible fluid fully enclosed in a circular cylindrical shell. The constraint imposed by the presence of the liquid in the interior of a shell will be referred to as “hydraulic constraint”. As liquids are nearly incompressible, the buckling of a liquid-filled shell has to satisfy the condition that the integral of all the displacements normal to the shell surface is equal to the volume variation of the contained liquid. The volume variation of the shell interior has to be equal to the dilation of the shell due to liquid pressure increments associated to the onset of geometrical instability. Additionally, the weight of the contained liquid causes additional circumferential tension in the cases of vertically placed cylinders.

The methodology followed is the numerical analysis of cylindrical shells by means of the ABAQUS Finite Element code and a comparison with the methods given in the Eurocode.

Place, publisher, year, edition, pages
Ernst & Sohn Verlag, 2017
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-65654 (URN)10.1002/cepa.137 (DOI)
Conference
EUROSTEEL 2017, Copenhagen, Denmark, September 13–15, 2017
Note

Konferensartikel i tidskrift

Available from: 2017-09-15 Created: 2017-09-15 Last updated: 2020-02-15Bibliographically approved
Andrade, P., Lagerqvist, O., Simões, R. & Veljkovic, M. (2017). Structural assessment of a column splice with opened slotted holes: Finger Connection. Paper presented at EUROSTEEL 2017, Copenhagen, Denmark, September 13–15, 2017. ce/papers, 1(2-3), 514-521
Open this publication in new window or tab >>Structural assessment of a column splice with opened slotted holes: Finger Connection
2017 (English)In: ce/papers, E-ISSN 2509-7075, Vol. 1, no 2-3, p. 514-521Article in journal (Refereed) Published
Abstract [en]

This paper introduces a novel joint based on a friction connection designed for column-splices. The jointwas developed within the scope of modular construction to improve the fast assembly of prefabricatedframes and to accommodate eventual misalignments. Gaps at the connection are considered on the jointhorizontal and vertical axis to accommodate misalignments whether they are rotations and/ordisplacements and so to allow for the easy fit of the columns. The efficiency of the joint resistance basedon different connection gaps subjected to uniform compression is assessed.

Place, publisher, year, edition, pages
Ernst & Sohn Verlag, 2017
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-65645 (URN)10.1002/cepa.88 (DOI)
Conference
EUROSTEEL 2017, Copenhagen, Denmark, September 13–15, 2017
Note

Konferensartikel i tidskrift

Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2017-11-24Bibliographically approved
Sandström, J., Wickström, U., Thelandersson, S. & Lagerqvist, O. (2017). The Life Safety Objective in Performance-Based Design for Structural Fire Safety. In: : . Paper presented at 2nd international conference on structural safety under fire & blast loading, CONFAB 2017, London, 10-12 september 2017.
Open this publication in new window or tab >>The Life Safety Objective in Performance-Based Design for Structural Fire Safety
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Structural stability is not necessarily required for buildings where life safety is the sole structural fire safety objective. However, a structural collapse is only acceptable in an area where lethal fire conditions have developed. Therefore, structural failures due to fire resulting in risks of progressing outside of the area of lethal fire conditions need to be addressed. Thus, a new type of design principles for the life safety objectives is presented here which enables an evaluation of more precise risk assessments and more cost-efficient solutions without compromising human safety.

National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-70093 (URN)
Conference
2nd international conference on structural safety under fire & blast loading, CONFAB 2017, London, 10-12 september 2017
Funder
SBUF - Sveriges Byggindustriers Utvecklingsfond, 13330
Available from: 2018-07-09 Created: 2018-07-09 Last updated: 2019-04-16Bibliographically approved
Bröchner, J. & Lagerqvist, O. (2016). From ideas to construction innovations: Firms and universities collaborating (ed.). Construction Economics and Building, 16(1), 76-89
Open this publication in new window or tab >>From ideas to construction innovations: Firms and universities collaborating
2016 (English)In: Construction Economics and Building, ISSN 2204-9029, Vol. 16, no 1, p. 76-89Article in journal (Refereed) Published
Abstract [en]

The purpose here is to study patterns of project collaboration found in one government supported programme for construction innovation. Preferred types of interaction were identified using data from two questionnaire surveys, one with experienced construction sector respondents and one aimed at construction researchers. All sixteen development projects within the Swedish Bygginnovationen programme were investigated, relying on documents and a survey of project managers. Important types of interaction, according to construction respondents, are informal contacts, joint research projects and staff mobility. For university respondents, informal contacts is also seen as the most important type of interaction, followed by MSc thesis work in firms and industrial PhD candidates. Grant applicants from manufacturing depended more on university laboratories and were less sensitive to firm/university distance. Laboratory use was also more frequent for projects relying on the field of materials engineering. In conclusion, there is a consensus about which types of collaboration are valuable. The broadness of participation in the programme, ranging over many industries, both as to origin of ideas and ultimate applications, reaches beyond narrow interpretations of the construction industry. Policy makers should recognize the innovation importance of university laboratory facilities and field testing, rather than seeing researchers as sources of ideas.

National Category
Construction Management Building Technologies
Research subject
Construction Engineering and Management; Steel Structures
Identifiers
urn:nbn:se:ltu:diva-6919 (URN)10.5130/AJCEB.v16i1.4668 (DOI)000372073600006 ()540842d5-fb7d-4e41-835e-365ca4909e88 (Local ID)540842d5-fb7d-4e41-835e-365ca4909e88 (Archive number)540842d5-fb7d-4e41-835e-365ca4909e88 (OAI)
Note

Validerad; 2016; Nivå 2; 20160321 (andbra); Bibliografisk uppgift: Construction Economics and Building (formerly known as the Australasian Journal of Construction Economics and Building [AJCEB])

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2019-08-23Bibliographically approved
Andrade, P., Lagerqvist, O., Veljkovic, M., Simoes, R. & Lundholm, J. (2016). Innovative system for the construction and management of student resisdences: Frameup system. 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 9th IABSE Congress, Stockholm 2016, September 21-23 (pp. 1364-1370). CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering
Open this publication in new window or tab >>Innovative system for the construction and management of student resisdences: Frameup system
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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. 1364-1370Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Sweden has a strong demand on the construction of student accommodations and consequently significant efforts have been taken to increase and streamline construction methods. In addition, the fluctuation on the number of students admitted at each year, in each university, lead to periods of house shortage or, in opposition to that, to eventual surplus on the housing market. For these reasons urges finding a fast execution process in construction to fulfil the market needs, together with a housing mechanism of control which balances the students’ needs with the housing availability. In this sense, the Frameup system arises as a solution to solve both problems by combining a modular construction with an innovative execution process.

The FRAMEUP buildings uses a steel frame in combination with prefabricated 3D modules - fully equipped and suitable for student accommodations – which are assembled by starting from the roof to the 1st floor. The existence of the lifting system permits the erection of the building, promoting each time the building is lifted, a clearance of one-floor-height, at ground level, for the assembly of a new floor. The procedure is repeated several times, according to the number of floors, until the 1st floor of the building, the last floor of the execution sequence, is assembled.

Alongside with its advantage on the fast execution, the Frameup system allows to efficiently increase or decrease the number of the floors and consequently its exchangeability with other buildings of same nature. Thus, assuming a net of FRAMEUP buildings at each university, its exchangeability system would create the necessary conditions so that the number of floors at each campus would follow the fluctuations of the students’ population among the different universities on different periods of time, so to suppress the needs for housing or to avoid the surplus on construction.

Place, publisher, year, edition, pages
CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016
Series
IABSE Congress Reports
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-62563 (URN)2-s2.0-85018952106 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
9th IABSE Congress, Stockholm 2016, September 21-23
Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2017-11-24Bibliographically approved
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