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  • 1.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Department of Bridge & Hydraulic Design, WSP Sverige AB, Gothenburg, Sweden.
    Plos, M.
    Department of Civil and Environmental Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Norut Northern Research Institute, Narvik, Norway.
    A multi-level strategy for successively improved structural analysis of existing concrete bridges: examination using a prestressed concrete bridge tested to failure2019Inngår i: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 15, nr 1, s. 27-53Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 2.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Failure tests on concrete bridges: Have we learnt the lessons?2018Inngår i: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, nr 3, s. 292-319Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 3.
    Dăescu, Cosmin
    et al.
    Politechnica University of Timisoara.
    Nagy-György, Tamas
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Barros, Joaquim
    University of Minho.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Numerical Assessment of Dapped Beam Ends Retrofitted with FRP Composites2013Inngår i: FRPRCS-11: 11th International Symposium on Fiber Reinforced Polymer for Reinforced Concrete Structures / [ed] Joaquim Barros; José Sena-Cruz, Universidade do Minho , 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This document presents the work related to the assessment of the effectiveness of strengthening reinforced concrete (RC) dapped-end beams using carbon fiber reinforced polymers (CFRP). Several non-linear finite element analyses were performed using different strengthening configurations, from the simplest solutions to the more complex ones in which different application schemes were overlapped. The work is focused on evaluating the strengthening systems, considering the ultimate capacities they can lead to and the failure modes involved. There were modeled 17 different strengthening configurations. While some of them provided a marginal in the ultimate load that can be applied, several of them provided important load bearing capacity increase. The observed failure modes ranged from a sudden failure of the whole strengthening system up to the desired progressive failure of the individual components of each strengthening system.

  • 4.
    Floruț, Sorin-Codruț
    et al.
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Stoian, Valeriu
    Tests on reinforced concrete slabs with cut-out openings strengthened with fibre-reinforced polymers2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 66, s. 484-493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the results of experimental investigations on reinforced concrete slabs strengthened using fibre-reinforced polymers (FRP). Eight tests were carried out on four two-way slabs, with and without cut-out openings. Investigations on slabs with cut-outs revealed that the FRP can be placed only around the edges of the cut-out when retrofitting the slabs whereas, in the situation of inserting cut-outs combined with increased demands of capacity, it is necessary to apply FRP components on most of the soffit of the slab. The proposed strengthening system enabled the load and deflection capacities of the FRP-strengthened slabs, in relation to their un-strengthened reference slabs, to be enhanced by up to 121% and 57% for slabs with and without cut-outs respectively.

  • 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 tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Infrastructure, Materials and Structures, Norut, Narvik, Norway.
    Experimental study on shear deformation of reinforced concrete beams using digital image correlation2019Inngår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 181, s. 670-698Artikkel i tidsskrift (Fagfellevurdert)
    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.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests2017Doktoravhandling, med artikler (Annet vitenskapelig)
    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.

  • 7.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    FRP strengthening of concrete walls with openings2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The thesis deals with the axial strength of axially and eccentrically loaded concrete walls with cut-out openings strengthened by fiber-reinforced polymers (FRPs).Background: Functional modifications of concrete 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. These openings are a source of weakness and can size dependently reduce the structures’ stiffness and load-bearing capacity, thus, requiring the element to be repaired.Aim and objectives: The main aim of this project was to develop a toolbox containing solutions for strengthening concrete walls with existing or newly created openings using FRP materials. The two immediate objectives sought are: (1) An assessment of the research level on concrete walls with and without openings; (2) An experimental and numerical investigation of the structural behavior of the FRP strengthened walls with openings.Methods of investigation: The experimental program was defined by reviewing therelevant tests performed to date. The literature review revealed research gaps that the current study aims to fill. Moreover, preliminary nonlinear finite element analyses were performed prior to the experimental program in order to gain insight into the structural behavior of these elements. Nine specimens designed to represent typical wall panels in residential buildings, at half-scale, were constructed for testing to failure. The two types of openings examined comprised symmetric halfscaled single door-type openings, and symmetric half scaled double door-type openings. The test matrix was divided into three stages, namely: (1) Reference specimens, (2) Pre-cracked specimens strengthened by FRP and (3) Un-cracked specimens strengthened by FRP. The strengthening method used was FRP confinement with the aid of mechanical anchorages.Results: The results indicate that the 25% and 50% reductions in cross-sectional area of the solid wall caused by introducing the small opening and large opening reduced its load carrying capacity by nearly 36% and 50%, respectively. The application of the FRP confinement increases the capacity and the stiffness of the specimens with cut-out openings. The axial strengths were between 85 94.8% and 56.5-63.4% for specimens having a small and large opening, respectively, of that of a solid wall.Conclusion: The FRP-confinement together with the mechanical anchorages was able to partly restore the capacity of a solid wall. Better results might have been possible if longitudinal FRP strips or bi-directional fibers were used. The effects of steel anchorages were not investigated and it is believed that they might have had positive influences. However, the optimal distance between the anchors should be further investigated. Moreover, the influence of the prestressing force of the anchorages may also be an important parameter that has led to an increase in capacity. Keywords: Strengthening, Fiber-reinforced polymers, Concrete walls, Openings, Axial load, Eccentricity, Out-of-plane behavior, Two-Way

  • 8.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Tamás, Nagy-György
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Disturbed regions in dapped-end beams: numerical simulations of strengthening techniques2013Inngår i: Nordic Concrete Research, ISSN 0800-6377, Vol. 48, nr 2, s. 14-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the effectiveness of strengthening reinforced concrete (RC) dapped-end beams using carbon fiber reinforced polymers (CFRP). Parametric studies are performed by means of numerical simulations in which several types of composite materials as well as their orientation are combined. The primary objectives of this research were the evaluation of the strengthening systems in terms of ultimate capacities and the failure modes involved. Results show that only some of them provide significant load bearing capacity increase. The observed failure modes ranged from a sudden failure up to the desired progressive failure of the strengthening system.

  • 9.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    The Development of an Experimental Program through Design of Experiments and FEM Analysis: A Preliminary Study2014Inngår i: Nordic Concrete Research, ISSN 0800-6377, Vol. 51, s. 29-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an experimental test setup which allows investigation of the structural behaviour for axially loaded concrete walls with openings. The test matrix was developed with the help of design of experiments technique. A two level factorial experiment has been designed resulting in a total of nine wall specimens. Previous research has shown that the ultimate capacity of concrete walls is dependent on the boundary conditions. Therefore, a new test-rig was proposed and designed to work according to the imposed conditions. Nonlinear simulations calibrated on a previous experimental program were used to obtain the reaction forces.

  • 10.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Concrete walls weakened by openings as compression members: A review2015Inngår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 89, s. 172-190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this paper is to review the advances that have been made in the design of monolithic and precast reinforced concrete walls, both with and without openings, subject to eccentrically applied axial loads. Using the results of previous experimental studies, a database was assembled to enable statistical assessment of the reliability of existing design models. Several design aspects are highlighted, including the size and position of openings, and the roles of boundary conditions and geometric characteristics. In addition, the performance of fiber-reinforced polymers in strengthening wall openings is discussed. Overall it is found that design codes provide more conservative results than alternative design models that have been proposed in recent studies. Research into the strengthening of walls with openings is still in its early stages, and further studies in this area are needed. The paper therefore concludes by highlighting some areas where new investigations could provide important insights into the structural behaviour of strengthened elements.

  • 11.
    Popescu, Cosmin
    et al.
    Northern Research Institute — NORUT.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Concrete walls with cutout openings strengthened by FRP confinement2017Inngår i: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 21, nr 3, artikkel-id 04016106Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 12.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Performance of RC Walls with Openings Strengthened by Fiber Reinforced Polymers: An Experimental and Theoretical Investigation2017Inngår i: 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, s. 509-517Konferansepaper (Fagfellevurdert)
    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.

  • 13.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Effect of cut-out openings on the axial strength of concrete walls2016Inngår i: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 142, nr 11, artikkel-id 4016100Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 14.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Experimental tests on RC walls with openings strengthened by FRP2015Inngår i: 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 , 2015Konferansepaper (Fagfellevurdert)
    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.

  • 15.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    A state of the art review on walls with openings strengthened by use of fiber reinforced polymers2014Inngår i: Proceedings of The 7th International Conference on FRP Composites in Civil Engineering (CICE 2014) / [ed] Raafat El-Hacha, Vancouver, British Columbia, Canada: International Institute for FRP in Construction (IIFC) , 2014, artikkel-id 128Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The purpose of this paper is to review the advances made in designing of monolithic and precast reinforced concrete (RC) walls with openings subjected to axial and eccentric loads. Nowadays, functionality and modifications of the structures are often encountered. Therefore, openings such as new windows, doors or paths for ventilations are highly demanded for RC walls. Based on previous studies, a critical review of the experimental and theoretical aspects of walls with openings and then retrofitted by use of fiber reinforced polymers (FRPs) are also presented. The simplified method provided by design codes fails in recognizing any contribution to the wall strength of the steel reinforcement or in some cases for the effect of side restraints. The presence of a new opening will decrease the axial capacity, thus, requiring upgrading. Satisfactory results were found when FRP was placed in the vicinity of the openings, being capable to restore the initial capacity. However, despite the considerable research carried out, there are still important research gaps that need to be further investigated.

  • 16.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Experimental Program for Axially Loaded RC Walls with Openings Strengthened by FRP2014Inngår i: Nordic Concrete Research, ISSN 0800-6377, Vol. 50, s. 285-288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The presence of a new opening will decrease the axial capacity, thus, requiring upgrading. Satisfactory results were found when FRP was placed in the vicinity of the openings, being capable to restore the initial structural capacity. However, despite the considerable research carried out, there are still important research gaps that need to be further investigated. In this paper an experimental program aimed to study the influence of opening size and the strengthening pattern for RC walls will be presented. To achieve this aim, a two-level factorial experiment has been designed resulting in a total of nine wall specimens.

  • 17.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Schmidt, Jacob W.
    Department of Civil Engineering, Technical University of Denmark, Technical University of Denmark, Division of Structural Engineering.
    Goltermann, Per
    Technical University of Denmark, Division of Structural Engineering.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach2017Inngår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, s. 585-598Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 18.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Northern Research Institute - NORUT, Narvik, Norway.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    3D reconstruction of existing concrete bridges using optical methods2019Inngår i: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 15, nr 7, s. 912-924Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Routine bridge inspections usually consist of visual observations. These inspections are time-consum-ing and subjective. There is a need to identify new inspection techniques for infrastructure that reducetraffic disturbance, and improve the efficiency and reliability of the acquired data. This study comparedthe performance of three different imaging technologies for the three-dimensional (3D) geometricmodeling of existing structures: terrestrial laser scanning, close-range photogrammetry, and infraredscanning. Each technology was used to assess six existing concrete railway bridges. The technologieswere compared in terms of geometric deviations, visualization capabilities, the level of the inspector’sexperience, and degree of automation. The results suggest that all methods investigated can be usedto create 3D models, however, with different level of completeness. Measurements such as spanlength, deck widths, etc. can be extracted with good accuracy. Although promising, a full off-siteinspection is currently not feasible as some areas of the bridges were difficult to capture mainly dueto restricted access and narrow spaces. Measurements based on terrestrial laser scanning were closerto the reality compared to photogrammetry and infrared scanning. The study indicates the no specialtraining is needed for photogrammetry and infrared scanning to generate a 3D geometric model.

  • 19.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Bagge, Niklas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings2019Inngår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 187, s. 57-72Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 20.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Northern Research Institute, Narvik, Norway.
    Sas, Gabriel
    Northern Research Institute, Narvik, Norway.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites2018Inngår i: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 22, nr 6, s. 04018046-1-04018046-16, artikkel-id 04018046Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 21.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Concrete Walls with Openings Strengthened Using FRCM Composites2017Inngår i: Advanced Composites in Construction: Conference Proceedings / [ed] Maurizio Guadagnini & Sue Keighley, Chesterfield: NetComposites Limited , 2017, s. 188-192Konferansepaper (Fagfellevurdert)
    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.

  • 22.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation2016Inngår i: 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, s. 1803-1811Konferansepaper (Fagfellevurdert)
    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.

  • 23.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Review of FRCM strengthening solutions for structural wall panelsInngår i: American Concrete Institute. Publication SP, ISSN 0193-2527, E-ISSN 1094-8120Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 24.
    Sas, Gabriel
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Tamás, Nagy-György
    Politechnica University of Timisoara.
    Numerical optimization of strengthening disturbed regions of dapped-end beams using NSM and EBR CFRP2014Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 67, s. 381-390Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a parametric investigation, based on non-linear finite element modeling, to identify the most effective configuration of carbon fiber reinforced polymers (CFRP) for strengthening reinforced concrete (RC) dapped end beams. Following a field application and laboratory tests, it focuses on effects of 24 externally bonded (EBR) and near surface mounted reinforcement (NSMR) configurations on yield strain in steel and the capacity and failure mode of dapped-end beams. The investigated parameters were the mechanical properties of the CFRP, the strengthening procedure and the inclination of the fibers with respect to the longitudinal axis. Two failure scenarios were considered: rupture and debonding of the FRP. The results indicate that high-strength NSM FRPs can considerably increase the capacity of dapped-end beams and the yielding strains in reinforcement can be substantially reduced by using high modulus fibers.

  • 25.
    Täljsten, Björn
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Bagge, Niklas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. WSP.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Carolin, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser. Trafikverket.
    Häggström, Jens
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Trafikverket.
    Bridges tested to failure in Sweden2018Inngår i: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Five bridges of different types have been tested to failure and the results have been compared to analyses of the load-carrying capacity using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. There it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.The five bridges were: (1) a strengthened one span concrete road bridge - Stora Höga ; (2) a one span concrete rail trough bridge loaded in fatigue – Lautajokk; (3) a two span strengthened concrete trough railway bridge - Övik; (4) a one span railway steel truss bridge -Åby; and (5) a five span prestressed concrete road bridge - Kiruna. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy and shortcomings/potentials of different codes and models for safety assessment of existing structures

1 - 25 of 25
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