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  • 1.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley H.
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, Norut Narvik AS.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Effect of Confinement with FRCM Composites on Damaged Concrete Cylinders2017In: Strain-Hardening Cement-Based Composites: Shcc4 / [ed] Mechtcherine, Viktor; Slowik, Volker; Kabele, Petr, Dordrecht: Springer, 2017, p. 770-777Conference paper (Refereed)
    Abstract [en]

    Confinement of axially loaded concrete members in existing structures is required when a change in use is expected or when there is a need to upgrade the structure to meet current design standards. In addition, after unusual overloading events (e.g., earthquakes), axially loaded members can suffer damage that increases the need of their retrofitting by means of confinement. The study of fiber reinforced cementitious matrix (FRCM) composites for confinement of compression members has gained attention in recent years due to the capability to overcome some of the disadvantages associated with more traditional strengthening techniques. However, the available experimental evidence is still scarce, and research on the topic is necessary. In this paper, the results of an experimental campaign performed on concrete cylinders confined with FRCM jackets are presented. Before strengthening, some specimens were preloaded in order to achieve specified damage levels. The specimens were then subjected to uniaxial concentric compressive loading. The axial load and axial strain response was recorded for each specimen. In addition, the elastic modulus of confined and unconfined specimens was determined. Results show that confinement with FRCM composites is able to provide an increase in the axial capacity of undamaged and damaged concrete cylinders.

  • 2.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Experimental investigation on RC beams strenghened in shear with  externally bonded composites2016In: Eighth International Conference onFibre-Reinforced Polymer (FRP) Composites in Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, p. 384-389Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of an experimental campaign carried out to investigate the behavior of reinforcedconcrete (RC) beams strengthened in shear using externally bonded advanced composite materials. In order tocompare their performance, two different types of composite materials were used to strengthen the beams: fiberreinforced polymer (FRP) and fiber reinforced cementitious matrix (FRCM) composites. The beams were thentested in four-point bending scheme, and measurements regarding applied load and mid-span displacements wereacquired. Observations regarding the gain in shear strength, influence on mid-span deflection and ductility, andcomparison of the performance of the two strengthening systems are provided. For specimens strengthened withFRCM composite, the contribution to the shear strength provided by the FRCM strengthening system is comparedwith the value predicted by an analytical model found in the available literature.

  • 3.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Shear strengthening of RC beams with FRCM: what do we know so far?2016In: Eighth International Conference onFibre-Reinforced Polymer (FRP) Compositesin Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, p. 462-467Conference paper (Refereed)
    Abstract [en]

    Shear failure of reinforced concrete (RC) beams is an undesirable mode of failure due to its sudden and brittlenature and thus needs to be carefully evaluated when planning a strengthening intervention. The use of fiberreinforced polymer (FRP) composites has shown to be capable of providing an adequate increase in shear strength.However, in recent years, there is interest in developing new techniques in which the positive attributes of FRPare utilized but some of its drawbacks are overcome. Among these techniques, fiber reinforced cementitious matrix(FRCM) composites, in which the organic resins are replaced by inorganic mortars, have shown promising results.In this paper, a bibliographical review of the available literature on FRCM shear strengthening of RC beams iscarried out. Two available design models are evaluated using a database compiled by the authors. The reviewshows that FRCM is able to provide an increase in strength and performance comparable to RC beams strengthenedwith FRP. However, the models are not able to accurately predict the behavior of FRCM strengthened beams.

  • 4.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    State of research on shear strengthening of RC beams with FRCM composites2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 149, p. 444-458Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the properties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment.

  • 5.
    Huang, Zheng
    et al.
    School of Civil Engineering, Southeast University, Nanjing, China.
    Tu, Yongming
    School of Civil Engineering, Southeast University, Nanjing, China.
    Meng, Shaoping
    School of Civil Engineering, Southeast University, Nanjing, China.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Infrastructure, Materials and Structures, Norut, Narvik, Norway.
    Experimental study on shear deformation of reinforced concrete beams using digital image correlation2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 181, p. 670-698Article in journal (Refereed)
    Abstract [en]

    This paper presents an experimental program aimed at providing reliable and comprehensive experimental data for assessing the available models of predicting the shear deformation of diagonally-cracked reinforced concrete (RC) beams. The non-contact measuring technique, Digital Image Correlation (DIC), was used to monitor the full-field displacement and strain in the shear span of five RC beams with thin webs. Virtual measuring grids were created to measure the mean shear strain and other critical deformation results which reflects the mechanism of shear deformation after shear cracking (i.e. the principal compressive strain angle, the principal compressive strain, the mid-depth longitudinal strain and the mean vertical strain). The experimental mean shear strain and other critical deformation results were compared with the predictions with several available models. The comparison indicates the available models fail to reproduce the principal compressive strain angle, the mid-depth longitudinal strain and the mean vertical strain which constitute the key parameters in estimating the shear deformation after shear cracking. As a result, significant discrepancies in the shear deformation of the beams tested in this paper are observed between the experimental and calculated results. It is also found that the predicted shear deformation of a number of beam specimens tested by other researchers with the available models deviates considerably from the experimental results. In general, the existing models are not capable of providing accurate predictions of the shear deformation of RC beams and further investigation into this topic is needed.

  • 6.
    Nilimaa, Jonny
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. WSP.
    Puurula, Arto
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Savonia University.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Skanska.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Carolin, Anders
    Trafikverket.
    Paulsson, Björn
    Charmec Railway Center.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment and Loading to Failure of Three Swedish RC Bridges2018In: 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.

  • 7.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Effect of cut-out openings on the axial strength of concrete walls2016In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 142, no 11, article id 4016100Article in journal (Refereed)
    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.

  • 8.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Experimental tests on RC walls with openings strengthened by FRP2015In: The 12th International Symposium on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asia-Pacific Conference on Fiber Reinforced Polymers in Structures (APFIS-2015) / [ed] Zhishen Wu; Gang Wu; Xin Wang, Nanjing, China: Southeast University , 2015Conference paper (Refereed)
    Abstract [en]

    Functional modifications of the old structures are common because existing structures must often be adapted to comply with current living standards. 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. The purpose of this experimental program is to investigate the behaviour of two-way RC walls with openings and strengthened by FRP. Nine half scale RC walls with two opening configurations, i.e. small and large door opening, were subjected to a uniformly distributed axial load with a small eccentricity. The paper presents the results of the experimental programme such as the ultimate capacity and deflection profiles. Moreover, the influence of the opening and the strengthening contribution to the overall capacity was also assessed and presented in this paper.

  • 9.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    FRCM-Composites for Strengthening Concrete Walls with Openings: Experimental and Numerical Analysis2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Upgrading existing buildings to new functional requirements may require new openings that can weaken the structure, prompting the need for strengthening. In such cases, traditional strengthening solutions, such as creating a reinforced concrete or steel frame around the opening, imply long-term restrictions in the use of the structure.

    In this study, the author carries experimental and numerical investigations on fiber reinforced cementitious matrix (FRCM) composites and their effectiveness for strengthening reinforced concrete walls with openings.

    To assess the performance of FRCM composite having different fiber types and their suitability for strengthening reinforce concrete walls with openings, single-lap direct shear tests were carried out using carbon, glass, and basalt FRCM-concrete joints. A novel non-contact measurement approach, based on digital image photogrammetry, applied to the experimental study of the bond behavior of FRCM composites was proposed and investigated. The proposed measurement approach showed higher spatial measurement resolution and increased accuracy compared to traditional contact approaches.

    The effect of cutout openings on the structural behavior of concrete walls was investigated experimentally, by loading to failure, half-scale, precast reinforced concrete panels with and without openings. The tested specimens were two-way action panels to which axial load with a small eccentricity was applied, thus the tested panels were representative of wall panels in buildings. The effect of cutout openings on the global behavior of a building structure was investigated through finite element analysis of an existing building where cutout openings were introduced in wall panels. Depending on their size, cutout openings can significantly decrease the capacity of the wall. The effectiveness of FRCM strengthening to restore the capacity walls with cutout openings was investigated experimentally. FRCM strengthening increased the capacity of walls having small door type openings (opening width was 25% of the wall’s width) to that of the solid wall. The capacity of the walls with large cutout openings was (opening width was 50% of the wall’s width) was increased to 75% of the solid wall’s capacity. The numerical and experimental analysis indicated that the decrease in axial load caused by cutout openings was proportional to the width opening. However, the numerical analysis of buildings structure indicated that the effects of openings on the buildings load carrying capacity are less severe.

  • 10.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Gonzalez-Libreros, Jaime
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT,.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Influence of the fiber type and matrix age of the bonding of FRCM composite strips applied to concrete substrates2016In: Eighth International Conference on Fibre-Reinforced Polymer (FRP) Composites in Civil Engineering / [ed] J.G. Teng and J.G. Dai, 2016, p. 456-461Conference paper (Refereed)
    Abstract [en]

    Fiber reinforced cementitious matrix (FRCM) composites represent an alternative to fiber reinforced polymer(FRP) composites for strengthening existing civil structures. FRCM is comprised of fibers, usually in the form ofa textile with an open-mesh configuration, embedded in an inorganic mortar matrix. It shares the advantages ofFRP systems and overcomes some of its drawbacks, which makes it suitable for a wide range of applications.Although research on this topic is still scarce, it has been shown that debonding represents a key factor in itsperformance. In order to gain more insight in this issue, a series of classical push-pull single-lap direct shear testswere carried out on basalt, carbon, and glass FRCM-concrete joints. The results allow for comparing theperformance of the joints with carbon, basalt, and glass fibers in terms of applied load – global slip response andfailure mode. The influence of matrix age was also investigated. The curing time of the mortar matrix was foundto influence the load carrying capacity of carbon FRCM – concrete joints.

  • 11.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Gonzalez-Libreros, Jaime
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT, .
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Use of image correlation system to study the bond behavior of FRCM-concrete joints2017In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 50, no 3, article id 172Article in journal (Refereed)
    Abstract [en]

    This paper presents a non-contact measurement approach, based on digital photogrammetry,applied to the experimental study of the bond behavior of fiber reinforced cementitious matrixcomposite (FRCM) - concrete joints tested in single-lap direct shear tests. The use of digitalphotogrammetry techniques and traditional contact measurement approaches for determiningdisplacement and strain are investigated and compared. The results show that measurements ofstrain in the fiber bundles determined using the image correlation system (ICS) correlate well withthose obtained from electrical strain gauges. However, differences of 38% to 52% were observedbetween the maximum strain measured with either ICS or electrical strain gages attached to thefiber bundles and the maximum strain in the fiber bundles computed from the maximum appliedload. ICS is also used to measure slip and strain of bare fiber bundles, and results show that theload distribution among fiber bundles is non-uniform. The proposed measurement approach showshigher spatial measurement resolution and increased accuracy compared to traditional contactapproaches by enabling measurements in each fiber bundle and overcoming the need to attachadditional elements to the tested specimen.

  • 12.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 187, p. 57-72Article in journal (Refereed)
    Abstract [en]

    This paper presents the finite element analysis (FEA) results of a multi-story reinforced concrete (RC) building having precast and cast-in-place load bearing walls. Door-type cut-out openings (height: 2.1 m, width: 0.9–4.4 m) were created at the first and second story of the building. Results from experimental tests on axially loaded RC panels were used to verify the modeling approach. The influence of cut-out openings on the response of individual RC panels, failure modes, and load redistribution to adjacent members was analyzed. Moreover, the wall bearing capacities obtained from FEA were compared with the values calculated from design equations. The results revealed that the robustness of multi-story buildings having RC load bearing wall systems decrease considerably with the creation of cut-out openings. However, owing to the initial robustness of the buildings, large cut-outopenings could be created under normal service conditions without strengthening of the building structure. Furthermore, design equations provided very conservative predictions of the ultimate capacity characterizing the solid walls and walls with small openings, whereas similar FEA and analytically predicted capacities were obtained for walls with large openings.

  • 13.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Northern Research Institute, Narvik, Norway.
    Sas, Gabriel
    Northern Research Institute, Narvik, Norway.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites2018In: 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)
    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.

  • 14.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Concrete Walls with Openings Strengthened Using FRCM Composites2017In: Advanced Composites in Construction: Conference Proceedings / [ed] Maurizio Guadagnini & Sue Keighley, Chesterfield: NetComposites Limited , 2017, p. 188-192Conference 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.

  • 15.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation2016In: 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 (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.

  • 16.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Review of FRCM strengthening solutions for structural wall panelsIn: American Concrete Institute. Publication SP, ISSN 0193-2527, E-ISSN 1094-8120Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the state-of-the-art on the topic of structural wall panels strengthened using fabric reinforced cementitious matrix composites (FRCM) composites. A systematic review of the literature is carried out to identify gaps in the available literature. A database of experimental tests, relevant for structural panels, was created and used to assess the influence of parameters such as test method, fiber type and material compressive strength, on the performance of FRCM strengthening. Since experimental investigations on walls strengthened with FRCM composites is still limited and mostly focused on shear, further investigations on walls as compression members can be considered timely, especially walls with openings, which have been overlooked. Experimental tests performed by the authors on reinforced concrete walls with openings are presented and assessed relative to the complete database. It was shown that FRCM composites are suitable repair solutions when new openings need to be created in existing walls.

  • 17.
    Sabau, Cristian
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Popescu, Cosmin
    Northern Research Institute – NORUT.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Schmidt, Jacob W.
    echnical University of Denmark, Department of Civil Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Strengthening of RC beams using bottom and side NSM reinforcement2018In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 149, p. 82-91Article in journal (Refereed)
    Abstract [en]

    The allowable strain in fibre reinforced polymers reinforcement is limited by design codes to avoid debonding. The near-surface mounted (NSM) reinforcement technique has been proven to produce better anchorage behaviour compared to externally bonded reinforcement solutions. However, NSM solutions do not always eliminate debonding issues, with concrete cover detachment (CCD) typically occurring in RC beams strengthened for flexure. This experimental study investigated the efficiency of side mounted (S) compared to bottom mounted (B) NSM bars to prevent CCD. The experimental results were compared to models available in the literature that predict the observed failure modes and the crack spacing in the NSM anchorage zone. Compared to B-NSM, the S-NSM solution was successful in avoiding brittle CCD failure and showed increased rotational capacity and energy dissipation at failure. Existing CCD debonding models were found to be conservative.

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