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Bagge, N., Plos, M. & Popescu, C. (2018). A multi-level strategy for successively improved structural analysis of existing concrete bridges: examination using a prestressed concrete bridge tested to failure. Structure and Infrastructure Engineering
Open this publication in new window or tab >>A multi-level strategy for successively improved structural analysis of existing concrete bridges: examination using a prestressed concrete bridge tested to failure
2018 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980Article in journal (Refereed) Epub ahead of print
Abstract [en]

This paper describes a multi-level strategy with increased complexity through four levels of structural analysis of concrete bridges. The concept was developed to provide a procedure that supports enhanced assessments with better understanding of the structure and more precise predictions of the load-carrying capacity. In order to demonstrate and examine the multi-level strategy, a continuous multi-span prestressed concrete girder bridge, tested until shear failure, was investigated. Calculations of the load-carrying capacity at the initial level of the multi-level strategy consistently resulted in underestimated capacities, with the predicted load ranging from 25% to 78% of the tested failure load, depending on the local resistance model applied. The initial assessment was also associated with issues of localising the shear failure accurately and, consequently, refined structural analysis at an enhanced level was recommended. Enhanced assessment using nonlinear finite element (FE) analysis precisely reproduced the behaviour observed in the experimental test, capturing the actual failure mechanism and the load-carrying capacity with less than 4% deviation to the test. Thus, the enhanced level of assessment, using the proposed multi-level strategy, can be considered to be accurate, but the study also shows the importance of using guidelines for nonlinear FE analysis and bridge-specific information. 

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-71356 (URN)10.1080/15732479.2018.1476562 (DOI)2-s2.0-85054830749 (Scopus ID)
Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2018-10-29
Sabau, C., Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2018). Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites. Journal of composites for construction, 22(6), 04018046-1-04018046-16, Article ID 04018046.
Open this publication in new window or tab >>Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites
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2018 (English)In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 22, no 6, p. 04018046-1-04018046-16, article id 04018046Article in journal (Refereed) Published
Abstract [en]

Upgrading existing buildings to new functional requirements may require new openings that can weaken the structure, promptingthe need for strengthening. In such cases traditional strengthening solutions, such as creating a reinforced concrete (RC) or steel frame aroundthe opening, imply long-term restrictions in the use of the structure compared to solutions that use externally bonded composites. Two fabricreinforcedcementitious matrix (FRCM) composites were used in this study to restore the capacity of panels with newly created doortype openings to that of a solid panel. Five half-scale RC panels acting as two-way action compression members were tested to failure.Two full-field optical deformation measurement systems were used to monitor and analyze the global structural response of each testedpanel (i.e., crack pattern, failure mechanism, and displacement/strain fields). The performance of existing design methods for RC panelshas been assessed in comparison with the experimental results. The capacity of strengthened panels with small openings (450 × 1,050 mm) was entirely restored to that of the solid panel. However, for panels with large openings (900 × 1,050 mm), only 75% of the solid panel’scapacity was restored. The capacity of the strengthened panels was about 175 and 150% higher compared to that of reference panels withsmall and large openings, respectively.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2018
Keywords
FRCM, Reinforced concrete, Walls with openings, Digital image correlation
National Category
Infrastructure Engineering Building Technologies
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-70579 (URN)10.1061/(ASCE)CC.1943-5614.0000867 (DOI)000447252600001 ()2-s2.0-85051927413 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-24 (andbra)

Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-10-29Bibliographically 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
Popescu, C., Schmidt, J. W., Goltermann, P. & Sas, G. (2017). Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach (ed.). Engineering structures, 150, 585-598
Open this publication in new window or tab >>Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach
2017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, p. 585-598Article in journal (Refereed) Published
Abstract [en]

Building refurbishment works frequently require the cutting of new openings in concrete walls. Cutting new openings weakens the overall response of such elements, so they usually require strengthening. However, current design codes offer little guidance on strengthening walls with openings, and less still on the use of non-metallic reinforcements such as FRP (Fibre Reinforced Polymers) to ensure sufficient load bearing capacity. This paper proposes a new procedure based on limit analysis theory for evaluating the ultimate load of walls with cut-out openings that have been strengthened with carbon-FRP (CFRP). First, the approach is verified against transverse (out-of-plane) and axial (in-plane) loading for unstrengthened specimens. These loading types result in different failure mechanisms: transverse loading leads to failure due to yielding/rupture of the steel reinforcement while axial loading leads to failure by concrete crushing. Second, the proposed method is further developed for CFRP-strengthened specimens under axial loading. It accounts for the contribution of CFRP indirectly, by updating the concrete model with an enhanced compressive strength as a result of confining the piers. Predictions made using the new method agree closely with experimental results.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-9022 (URN)10.1016/j.engstruct.2017.07.069 (DOI)000413125800044 ()2-s2.0-85026533028 (Scopus ID)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (Local ID)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (Archive number)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (OAI)
Note

Validerad; 2017; Nivå 2; 2017-08-15 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Popescu, C. (2017). CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests. (Doctoral dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Redesigning buildings to improve their space efficiency and allow changes in use is often essential during their service lives to comply with shifts in living standards and functional demands.This may require the introduction of new openings in elements such as beams, walls, and slabs,which inevitably reduces their structural performance and hence requires repair or strengthening.However, there are uncertainties regarding both the effects of openings and the best remedial optionsfor them. Traditionally, two methods have been used to strengthen reinforced concrete (RC) walls with openings, these being either to create a frame around the opening using RC/steel membersor to increase the cross-sectional thickness. Currently, intervention in existing buildings must be minimal in order to minimise inconvenience caused by limiting the use of the structure during repairs. One option is to use externally-bonded fibre-reinforced polymers (FRPs).

In this study, the author reports on an experimental investigation of the effectiveness of carbonFRP (CFRP)–based strengthening for restoring the axial capacity of a solid reinforced concretewall after cutting openings. Nine half-scale specimens, designed to represent typical wall panels in residential buildings with and without door-type openings, were tested to failure. The walls were tested in two-way action and subjected to axial loading with low eccentricity (defined as one sixth of the wall’s thickness) along the weak axis to represent imperfections due to thickness variation and misalignment of the panels during the construction process. An extensive instrumentation scheme was used to monitor the specimen’s behaviour during the loading cycles. In addition to classical approaches for measuring strains and displacements, optical 3D measurements were also acquired using the digital image correlation (DIC) technique. These provided better overviews of the failure mechanism by recording the crack pattern development and deformation of the walls throughout the loading history.

Reducing the cross-sectional area by cutting out openings i.e. 25% (hereafter referred to as small opening) and 50% (hereafter referred to as large opening) led to 36% and 50% reductions in peak loads, respectively. In both situations the failure was brittle due to crushing of concrete with spalling and reinforcement buckling. The CFRP strengthening increased the axial capacity of walls with small and large openings by 34 – 50% and 13 – 27%, respectively. This partially restored theircapacities to 85 – 95% and 57 – 63% of their precutting capacity (i.e. solid wall), respectively. A procedure based on a rigid-plastic approach for evaluating the ultimate load of walls with cut-out openings that have been strengthened with FRPs was also proposed in this study. Predictions made using the proposed method agree closely with experimental results.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017. p. 159
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Building Technologies
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-61515 (URN)978-91-7583-794-9 (ISBN)978-91-7583-795-6 (ISBN)
Public defence
2017-02-23, F1031, Luleå, 10:00 (English)
Opponent
Supervisors
Note

Examining Committee: Professor Karin Lundgren, Division of Structural Engineering, Department of Civil and Environmental Engineering, Chalmers University of Technology, Gothenburg, Sweden

Professor Henrik Stang, Section for Structural Engineering, Department of Civil Engineering, Technical University of Denmark, Lyngby, Denmark

Professor Mats Oldenburg, Division of Mechanics of Solid Materials, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden

Available from: 2017-01-20 Created: 2017-01-18 Last updated: 2017-11-24Bibliographically approved
Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2017). Concrete walls with cutout openings strengthened by FRP confinement (ed.). Journal of composites for construction, 21(3), Article ID 04016106.
Open this publication in new window or tab >>Concrete walls with cutout openings strengthened by FRP confinement
2017 (English)In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 21, no 3, article id 04016106Article in journal (Refereed) Published
Abstract [en]

Redesigning buildings to improve their space efficiency and allow changes in use is often essential during their service lives tocomply with shifts in living standards and functional demands. This may require the introduction of new openings in elements such as beams,walls, and slabs, which inevitably reduces their structural performance and hence requires repair or strengthening. However, there are uncertaintiesregarding both the effects of openings and the best remedial options for them. Here, the authors report on an experimental investigation ofthe effectiveness of fiber-reinforced polymer (FRP)–based strengthening for restoring the axial capacity of a solid RC wall after cutting openings.Nine half-scale specimens, designed to represent typical wall panels in residential buildings with and without door-type openings, were testedto failure. It was found that FRP-confinement and mechanical anchorages increased the axial capacity of walls with small and large openings(which had 25 and 50% reductions in cross-sectional area, respectively) by 34–50% and 13–27%, to 85–94.8% and 56.5–63.4% of their precuttingcapacity, respectively. 

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-2760 (URN)10.1061/(ASCE)CC.1943-5614.0000759 (DOI)000400524800008 ()2-s2.0-85017517559 (Scopus ID)071b8226-9b6c-41f9-9efc-499979742502 (Local ID)071b8226-9b6c-41f9-9efc-499979742502 (Archive number)071b8226-9b6c-41f9-9efc-499979742502 (OAI)
Note

Validerad; 2017; Nivå 2; 2017-04-25 (andbra)

 

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sabau, C., Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2017). Concrete Walls with Openings Strengthened Using FRCM Composites. In: Maurizio Guadagnini & Sue Keighley (Ed.), Advanced Composites in Construction: Conference Proceedings. Paper presented at 8th Biennial Conference on Advanced Composites In Construction, Sheffield, 5-7 September 2017 (pp. 188-192). Chesterfield: NetComposites Limited
Open this publication in new window or tab >>Concrete Walls with Openings Strengthened Using FRCM Composites
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2017 (English)In: Advanced Composites in Construction: Conference Proceedings / [ed] Maurizio Guadagnini & Sue Keighley, Chesterfield: NetComposites Limited , 2017, p. 188-192Conference paper, Published paper (Refereed)
Abstract [en]

In the current social and economic context, upgrading or retrofitting of existing buildings, instead of replacingwith new constructions, is becoming more and more popular due to shorter service interruptions,accessibility, and economic reasons. Upgrading building to current living standards and new functionalityneed often require new openings to be created in structural elements such as reinforced concrete walls andslabs. With the aim of improving existing strengthening solutions for such cases, this study presents someaspects of an experimental investigation of the effectiveness of fibre reinforced cementitious matrixcomposites (FRCM) strengthening for restoring the axial capacity of a solid reinforced concrete wall aftercreating new door openings. Five half-scale specimens, designed to represent typical wall panels inresidential buildings with and without door-type openings, were tested to failure. It was found that FRCMsystems were able to fully restore the axial capacity of the walls with small openings to that of the solid wall,and to restore the axial capacity of walls with large openings to approximately 75% of that of the solid wall.

Place, publisher, year, edition, pages
Chesterfield: NetComposites Limited, 2017
National Category
Building Technologies Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-66500 (URN)2-s2.0-85040222976 (Scopus ID)
Conference
8th Biennial Conference on Advanced Composites In Construction, Sheffield, 5-7 September 2017
Available from: 2017-11-08 Created: 2017-11-08 Last updated: 2018-03-28Bibliographically approved
Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2017). Performance of RC Walls with Openings Strengthened by Fiber Reinforced Polymers: An Experimental and Theoretical Investigation. In: Manu Santhanam; Ravindra Gettu; Radhakrishna G. Pillai; Sunitha K. Nayar (Ed.), Advances in Construction Materials and Systems: Proceedings of an International Conference (ICACMA), Chennai, India, September 3-8 2017. Paper presented at International Conference on Advances in Construction Materials and Systems & 71st RILEM Annual Week, Chennai, India, September 3-8 2017 (pp. 509-517). Paris-France: Rilem publications, 2
Open this publication in new window or tab >>Performance of RC Walls with Openings Strengthened by Fiber Reinforced Polymers: An Experimental and Theoretical Investigation
2017 (English)In: Advances in Construction Materials and Systems: Proceedings of an International Conference (ICACMA), Chennai, India, September 3-8 2017 / [ed] Manu Santhanam; Ravindra Gettu; Radhakrishna G. Pillai; Sunitha K. Nayar, Paris-France: Rilem publications, 2017, Vol. 2, p. 509-517Conference paper, Published paper (Refereed)
Abstract [en]

Redesigning buildings to improve their space efficiency and allow changes in use is  often essential during their service lives to comply with shifts in living standards and functional demands. This may require the introduction of new openings in elements e.g. walls, which inevitably reduces their structural performance, and hence necessitates repair or strengthening. Here the authors report an experimental investigation of the effectiveness of fibre-reinforced polymer (FRP)-based strengthening for restoring the axial capacity of a solid reinforced concrete wall after cutting openings. Nine half-scale specimens, designed to represent typical wall panels in residential buildings with and without door-type openings, were tested to failure. FRP-confinement and mechanical anchorages increased the axial capacity of walls with small and large openings (which had 25% and 50% reductions in cross-sectional area, respectively) by 34-50% and 13-27%, to 85-94.8% and 56.5-63.4% of their pre-cutting capacity, respectively. Current design models are assessed against experimentally obtained capacities.

Place, publisher, year, edition, pages
Paris-France: Rilem publications, 2017
Series
RILEM Publications ; 118
National Category
Building Technologies Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65711 (URN)978-2-35158-194-0 (ISBN)978-2-35158-191-9 (ISBN)
Conference
International Conference on Advances in Construction Materials and Systems & 71st RILEM Annual Week, Chennai, India, September 3-8 2017
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2018-05-22Bibliographically approved
Popescu, C., Sas, G., Sabau, C. & Blanksvärd, T. (2016). Effect of cut-out openings on the axial strength of concrete walls (ed.). Journal of Structural Engineering, 142(11), Article ID 4016100.
Open this publication in new window or tab >>Effect of cut-out openings on the axial strength of concrete walls
2016 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 142, no 11, article id 4016100Article in journal (Refereed) Published
Abstract [en]

Old structures are frequently modified to comply with current living standards and/or legislation. Such modifications may include the addition of new windows or doors and paths for ventilation and heating systems, all of which require openings to be cut into structural walls. However, effects of the required openings are not sufficiently understood. Thus, the objective of the work reported here was to analyze openings’ effects on the axial strength of large concrete wall panels. Three half-scaled walls with two opening configurations, corresponding to “small” and “large” door openings, were subjected to a uniformly distributed axial load with a small eccentricity. The results indicate that the 25% and 50% reductions in cross-sectional area of the solid wall caused by introducing the small and large openings reduced the load-carrying capacity by nearly 36% and 50%, respectively. The failure progression was captured using digital image correlation technique and the results indicated involvement of a plate mechanism rather than uniaxial behavior as adopted in current design codes. Using a simplified procedure, the load-carrying capacity was predicted using existing design models found in the research literature and design codes.

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-13543 (URN)10.1061/(ASCE)ST.1943-541X.0001558 (DOI)000386366600008 ()2-s2.0-84991677088 (Scopus ID)cc593011-a98a-471f-9ff8-ca86152f99d9 (Local ID)cc593011-a98a-471f-9ff8-ca86152f99d9 (Archive number)cc593011-a98a-471f-9ff8-ca86152f99d9 (OAI)
Note

Validerad; 2016; Nivå 2; 2016-11-08 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-09-18Bibliographically approved
Sabau, C., Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2016). Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation. 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 Innovative and Sustainable Built Environment. Paper presented at 19th IABSE Congress, Stockholm 2016, September 21-23 (pp. 1803-1811). CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering
Open this publication in new window or tab >>Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation
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2016 (English)In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016, p. 1803-1811Conference paper, Published paper (Refereed)
Abstract [en]

Several measuring techniques based on digital image correlation (DIC) are nowadays used in many fields. DIC measurements can facilitate documentation of crack patterns on specimens subject to loading, valuable information, which would otherwise be hard to obtain, especially in the case of reinforced concrete elements. This can not only give a better insight into the failure mechanism of the element, but also evaluate cracking as measure of serviceability.This article discusses existing serviceability limits and failure modes of reinforced concrete walls in buildings in light of results obtained using DIC on two half-scale reinforced concrete walls with openings tested to failure. Results suggest that cracks induced by a load level equivalent to 70% of ultimate load bearing capacity, do not exceed limits indicated in relevant guidelines.The failure mode of two way walls with openings was found to be similar to that of two way slabs with openings, however differences were identified in the development of the failure mechanism. Finally, two strengthening strategies of reinforced concrete walls are discussed.

Place, publisher, year, edition, pages
CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016
Series
IABSE Symposium Report
Keywords
digital image correlation, DIC, crack mapping, reinforced concrete, walls, openings, serviceability
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-62559 (URN)2-s2.0-85018991926 (Scopus ID)978-3-85748-144-4 (ISBN)
Conference
19th IABSE Congress, Stockholm 2016, September 21-23
Projects
FRP and MBC strengthening of reinforced concrete walls with openings
Funder
EU, FP7, Seventh Framework Programme, MC-ITN-2013-607851
Available from: 2017-03-18 Created: 2017-03-18 Last updated: 2018-03-28Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9423-7436

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