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  • 1.
    Bagge, Niklas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. 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 University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. 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 failure2019In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 15, no 1, p. 27-53Article in journal (Refereed)
    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 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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Failure tests on concrete bridges: Have we learnt the lessons?2018In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 3, p. 292-319Article in journal (Refereed)
    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.
    Blanksvärd, Thomas
    et al.
    Skanska Sverige Teknik AB.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Norut, Northern Research Institute.
    Förstärkning av betongväggar i samband med håltagning2017In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, no 7Article in journal (Other (popular science, discussion, etc.))
  • 4.
    Dăescu, Cosmin
    et al.
    Politechnica University of Timisoara.
    Nagy-György, Tamas
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Barros, Joaquim
    University of Minho.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Numerical Assessment of Dapped Beam Ends Retrofitted with FRP Composites2013In: FRPRCS-11: 11th International Symposium on Fiber Reinforced Polymer for Reinforced Concrete Structures / [ed] Joaquim Barros; José Sena-Cruz, Universidade do Minho , 2013Conference paper (Refereed)
    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.

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  • 5.
    Floruț, Sorin-Codruț
    et al.
    Politehnica University of Timisoara, 2nd T. Lalescu, 300223 Timisoara, Romania.
    Sas, Gabriel
    NORUT, Rombaksveien E-6 47, N-8517 Narvik, Norway.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Stoian, Valeriu
    Politehnica University of Timisoara, 2nd T. Lalescu, 300223 Timisoara, Romania.
    Tests on reinforced concrete slabs with cut-out openings strengthened with fibre-reinforced polymers2014In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 66, p. 484-493Article in journal (Refereed)
    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.

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  • 6.
    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.

  • 7.
    Mirzazade, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nodeh, Maryam Pahlavan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, 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.
    Utilization of Computer Vision Technique for Automated Crack Detection Based on UAV-Taken Images2021In: International Conference of the European Association on Quality Control of Bridges and Structures: EUROSTRUCT 2021: Proceedings of the 1st Conference of the European Association on Quality Control of Bridges and Structures / [ed] Carlo Pellegrino; Flora Faleschini; Mariano Angelo Zanini; José C. Matos; Joan R. Casas; Alfred Strauss, Springer, 2021, p. 713-720Conference paper (Refereed)
    Abstract [en]

    Conventional bridge inspection is usually performed by experienced engineers, trying to detect and document damage patterns manually. By increased number of built Bridges, there is a growing interest in automated damage detection methods. Therefore, the field of autonomous bridge inspection with the application of machine learning techniques on UAV-taken images is gaining popularity. Due to recent technological advancement, a large number of datasets can be collected, with a high rate of productivity and accuracy, to train convolutional neural networks (CNNs) leading us to automated Structural health monitoring (SHM). In this paper, a case study is chosen to scan two times with almost one year as a time interval. In the first scanning, dataset was gathered to train four different CNNs. Then, the performance of CNNs was compared for the purpose of autonomous crack detection in the second round of scanning. Models evaluated on a number of performance metrics, namely- (i) accuracy, (ii) loss, (iii) computation time, (iv) model size, and (v) architectural depth. Finally, the performance of studied CNNs is discussed, which can lead researchers in the Transfer-Learning approach to generate a model for damage detection with a limited number of datasets prepared in the first turn of bridge inspection. 

  • 8.
    Mirzazade, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, 8517, Norway.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, 8517, 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.
    Application of close range photogrammetry in structural health monitoring by processing generated point cloud datasets2021In: IABSE Congress Ghent 2021: Structural Engineering for Future Societal Needs / [ed] H. H. (Bert) Snijder; Bart De Pauw; Sander van Alphen; Pierre Mengeot, International Association for Bridge and Structural Engineering (IABSE) , 2021, p. 450-458Conference paper (Refereed)
    Abstract [en]

    In bridge inspection, vertical displacement is a relevant parameter for both short and long-term health monitoring. Assessing change in deflections could also simplify the assessment work for inspectors. Recent developments in digital camera technology and photogrammetry software enables point cloud with colour information (RGB values) to be generated. Thus, close range photogrammetry offers the potential of monitoring big and small-scale damages by point clouds. The current paper aims to monitor geometrical deviations in Pahtajokk Bridge, Northern Sweden, using an optical data acquisition technique. The bridge in this study is scanned two times by almost one year a part. After point cloud generation the datasets were compared to detect geometrical deviations. First scanning was carried out by both close range photogrammetry (CRP) and terrestrial laser scanning (TLS), while second scanning was performed by CRP only. Analyzing the results has shown the potential of CRP in bridge inspection.

  • 9.
    Mirzazade, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, 8517, Norway .
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, 8517, 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.
    Predicting strains in embedded reinforcement based on surface deformation obtained by digital image correlation technique2021In: IABSE Congress Ghent 2021: Structural Engineering for Future Societal Needs / [ed] H. H. (Bert) Snijder; Bart De Pauw; Sander van Alphen; Pierre Mengeot, International Association for Bridge and Structural Engineering (IABSE) , 2021, p. 425-434Conference paper (Refereed)
    Abstract [en]

    This study is carried out to assess the applicability of using a digital image correlation (DIC) system in structural inspection, leading to deploy innovative instruments for strain/stress estimation along embedded rebars. A semi-empirical equation is proposed to predict the strain in embedded rebars as a function of surface strain in RC members. The proposed equation is validated by monitoring the surface strain in ten concrete tensile members, which are instrumented by strain gauges along the internal steel rebar. One advantage with this proposed model is the possibility to predict the local strain along the rebar, unlike previous models that only monitored average strain on the rebar. The results show the feasibility of strain prediction in embedded reinforcement using surface strain obtained by DIC.

  • 10.
    Mirzazade, Ali
    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. SINTEF Narvik AS, Narvik, 8517, 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.
    Workflow for Off-Site Bridge Inspection Using Automatic Damage Detection-Case Study of the Pahtajokk Bridge2021In: Remote Sensing, E-ISSN 2072-4292, Vol. 13, no 14, article id 2665Article in journal (Refereed)
    Abstract [en]

    For the inspection of structures, particularly bridges, it is becoming common to replace humans with autonomous systems that use unmanned aerial vehicles (UAV). In this paper, a framework for autonomous bridge inspection using a UAV is proposed with a four-step workflow: (a) data acquisition with an efficient UAV flight path, (b) computer vision comprising training, testing and validation of convolutional neural networks (ConvNets), (c) point cloud generation using intelligent hierarchical dense structure from motion (DSfM), and (d) damage quantification. This workflow starts with planning the most efficient flight path that allows for capturing of the minimum number of images required to achieve the maximum accuracy for the desired defect size, then followed by bridge and damage recognition. Three types of autonomous detection are used: masking the background of the images, detecting areas of potential damage, and pixel-wise damage segmentation. Detection of bridge components by masking extraneous parts of the image, such as vegetation, sky, roads or rivers, can improve the 3D reconstruction in the feature detection and matching stages. In addition, detecting damaged areas involves the UAV capturing close-range images of these critical regions, and damage segmentation facilitates damage quantification using 2D images. By application of DSfM, a denser and more accurate point cloud can be generated for these detected areas, and aligned to the overall point cloud to create a digital model of the bridge. Then, this generated point cloud is evaluated in terms of outlier noise, and surface deviation. Finally, damage that has been detected is quantified and verified, based on the point cloud generated using the Terrestrial Laser Scanning (TLS) method. The results indicate this workflow for autonomous bridge inspection has potential.

  • 11.
    Mirzazade, Ali
    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. SINTEF Narvik AS, 8517 Narvik, Norway.
    Gonzalez-Libreros, Jaime
    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.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Semi-autonomous inspection for concrete structures using digital models and a hybrid approach based on deep learning and photogrammetry2023In: Journal of Civil Structural Health Monitoring, ISSN 2190-5452, Vol. 13, no 8, p. 1633-1652Article in journal (Refereed)
    Abstract [en]

    Bridge inspections are relied heavily on visual inspection, and usually conducted within limited time windows, typically at night, to minimize their impact on traffic. This makes it difficult to inspect every meter of the structure, especially for large-scale bridges with hard-to-access areas, which creates a risk of missing serious defects or even safety hazards. This paper presents a new technique for the semi-automated damage detection in tunnel linings and bridges using a hybrid approach based on photogrammetry and deep learning. The first approach involves using photogrammetry to reconstruct a 3D model. It is shown that a model with sub-centimeter accuracy can be obtained after noise removal. However, noise removal also reduces the point cloud density, making the 3D point cloud unsuitable for quantification of small-scale damages such as fine cracks. Therefore, the captured images are also analyzed using deep convolutional neural network (CNN) models to enable crack detection and segmentation. For this aim, in the second approach, the 3D model is generated by the output of CNN models to enable crack localization and quantification on 3D digital model. These two approaches were evaluated in separate case studies, showing that the proposed technique could be a valuable tool to assist human inspectors in detecting, localizing, and quantifying defects on concrete structures.

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  • 12.
    Mirzazade, Ali
    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. SINTEF Narvik AS, 8517 Narvik, Norway.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Prediction of Strain in Embedded Rebars for RC Member, Application of Hybrid Learning Approach2023In: Infrastructures, E-ISSN 2412-3811, Vol. 8, no 4, article id 71Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to find strains in embedded reinforcement by monitoring surface deformations. Compared with analytical methods, application of the machine learning regression technique imparts a noteworthy reduction in modeling complexity caused by the tension stiffening effect. The present research aimed to achieve a hybrid learning approach for non-contact prediction of embedded strains based on surface deformations monitored by digital image correlation (DIC). However, due to the small training dataset collected by the installed strain gauges, the input dataset was enriched by a semi-empirical equation proposed in a previous study. Therefore, the present study discussed (i) instrumentation by strain gauge and DIC as well as data acquisition and post-processing of the data, accounting for strain gradients on the concrete surface and embedded reinforcement; (ii) input dataset generation for training machine learning regression models approaching hybrid learning; (iii) data regression to predict strains in embedded reinforcement based on monitored surface deformations; and (iv) the results, validation, and post-processing responses to make the method more robust. Finally, the developed model was evaluated through numerous statistical performance measures. The results showed that the proposed method can reasonably predict strain in embedded reinforcement, providing an innovative type of sensing application with highly improved performance.

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  • 13.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests2017Doctoral 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.

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  • 14.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    FRP strengthening of concrete walls with openings2015Licentiate thesis, comprehensive summary (Other academic)
    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

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  • 15.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dăescu, Cosmin
    Politechnica University of Timisoara.
    Tamás, Nagy-György
    Politechnica University of Timisoara.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Disturbed regions in dapped-end beams: numerical simulations of strengthening techniques2013In: Nordic Concrete Research, ISSN 0800-6377, Vol. 48, no 2, p. 14-26Article in journal (Refereed)
    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.

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  • 16.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Mirzazade, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    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.
    Häggström, Jens
    Trafikverket.
    Bridge inspections using unmanned aerial vehicles – A case study in Sweden2021Report (Other academic)
    Abstract [en]

    The aim of the current project is to digitalize inspections and monitoring of structures’ health using drones in order to identify and allow for easier inspection of damages in transport infrastructure. The objectives set are to perform aerial photogrammetry to recreate the as-is condition to enable off-site inspection of difficult to reach areas in structures and identify damages – e.g. cracks, spalling, corrosion. The drone is controlled either autonomously or with the use of a remote control by a pilot from the ground. The drone can carry a wide range of imaging technologies including still, video and infrared sensors. The high flexibility and accessibility of drones in hard-to-reach or risk exposed areas makes the airborne photogrammetry a better alternative to the ground-based method. Given the potential of UAVs to help bridge inspectors performing inspections off-site, the Swedish Transport Administration developed a demonstration project to evaluate the effectiveness and future opportunities within inspection field. Five bridges of varying sizes and types were selected as demonstrators. Data collection including the 3D model creation has been performed by three different contractors while the model-based inspection for all bridges was performed by the same team. It has been shown that the 3D models could serve as a tool for bridge inspectors from which measurements could be extracted and certain damages identified. A full off-site inspection is currently not feasible as some areas of the bridges were difficult to capture. The models are only providing near-surface information, and therefore, in-depth inspection should not be overlooked. The difficulty to capture local defects such as delaminations and narrow cracks also reduces versatility. The main conclusion from the study is that drones cannot be used independently to conduct inspections. Currently, they can only be used as a complement to traditional inspections. The added value of a 3D model derives from the possibility of using it as tool to better plan large inspections in the field and/or future maintenance work.

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  • 17.
    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.
    The Development of an Experimental Program through Design of Experiments and FEM Analysis: A Preliminary Study2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 51, p. 29-42Article in journal (Refereed)
    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.

  • 18.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    NORUT, Rombaksveien E-6 47, N-8517 Narvik, Norway.
    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.
    Concrete walls weakened by openings as compression members: A review2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 89, p. 172-190Article in journal (Refereed)
    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.

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  • 19.
    Popescu, Cosmin
    et al.
    Northern Research Institute — NORUT.
    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 cutout openings strengthened by FRP confinement2017In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 21, no 3, article id 04016106Article in journal (Refereed)
    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. 

  • 20.
    Popescu, Cosmin
    et al.
    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.
    Performance of RC Walls with Openings Strengthened by Fiber Reinforced Polymers: An Experimental and Theoretical Investigation2017In: 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 (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.

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  • 21.
    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.

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  • 22.
    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.

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  • 23.
    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.
    Täljsten, Björn
    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.
    A state of the art review on walls with openings strengthened by use of fiber reinforced polymers2014In: 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, article id 128Conference paper (Refereed)
    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.

  • 24.
    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.
    Täljsten, Björn
    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.
    Experimental Program for Axially Loaded RC Walls with Openings Strengthened by FRP2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 50, p. 285-288Article in journal (Refereed)
    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.

  • 25.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    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 University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, p. 585-598Article in journal (Refereed)
    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.

  • 26.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Northern Research Institute - NORUT, Narvik, Norway.
    Täljsten, Björn
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    3D reconstruction of existing concrete bridges using optical methods2019In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 15, no 7, p. 912-924Article in journal (Refereed)
    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.

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  • 27.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Sintef, Narvik, Norway.
    Täljsten, Björn
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    A comparison between laser scanning, photogrammetry and infrared scanning to create 3D digital models of existing concrete bridges2020In: 1st IABSE Online Symposium 2020: Synergy of Culture and Civil Engineering - History and Challenges / [ed] Jan Bien; Jan Biliszczuk; Pawel Hawryszkow; Maciej Hildebrand; Marta Knawa-Hawryszkow; Krzysztof Sadowski, International Association for Bridge and Structural Engineering (IABSE) , 2020, p. 1101-1108Conference paper (Refereed)
    Abstract [en]

    Routine bridge inspections usually consist of visual observations. These inspections are time-consuming and subjective. There is a need to identify new inspection techniques for infrastructure that reduce traffic disturbance, and improve the efficiency and reliability of the acquired data. This study compared the performance of three different imaging technologies for the three-dimensional (3D) geometric modelling of existing structures: Terrestrial laser scanning, close-range photogrammetry, and infrared scanning. Each technology was used to assess six existing concrete railway bridges. The technologies were compared in terms of geometric deviations, visualization capabilities, the level of the inspector's experience, and degree of automation. The results suggest that all methods investigated can be used to create 3D models, however, with different level of completeness.

  • 28.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik, 8504 Narvik, Norway.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Invator AB, Box 1093, 181 22 Lidingö, Sweden.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Remote bridge inspection using optical methods2022In: 24th NCR Symposium Proceedings / [ed] Johan Silfwerbrand, Nordic Concrete Federation , 2022Conference paper (Refereed)
    Abstract [en]

    Routine bridge inspections usually consist of visual observations. These inspections are timeconsuming and subjective. There is a need to identify new inspection techniques for infrastructure that reduce traffic disturbance, and improve the efficiency and reliability of the acquired data. This study compared the performance of three different imaging technologies for the threedimensional (3D) geometric modelling of existing structures: terrestrial laser scanning, closerange photogrammetry, and infrared scanning. Each technology was used to assess six existing concrete railway bridges. The results suggest that all methods investigated can be used to create 3D models, however, with different level of completeness.

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  • 29.
    Popescu, Cosmin
    et al.
    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.
    Blanksvärd, Thomas
    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.
    Jimenez, Alexander
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Crabtree Gärdin, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Carolin, Anders
    Trafikverket, Luleå, Sweden.
    Optical methods and wireless sensors for monitoring of bridges2019In: IABSE Symposium 2019: Towards a Resilient Built Environment - Risk and Asset Management, International Association for Bridge and Structural Engineering (IABSE) , 2019, p. 1191-1198Conference paper (Refereed)
    Abstract [en]

    Six railway bridges have been scanned using infrared scanning (IR), close range photogrammetry (CRP) and terrestrial laser scanning (TRS) to reconstruct point clouds and evaluate the potential ofthe technologies for building information modelling (BIM)- and assessment purposes. The resultsmay also help to improve bridge inspection routines. This is done by evaluating the accuracy and quality of the point clouds, time consumption, safety and traffic disturbance. Wireless Monitoring has been used in a demonstration project in Sweden. It consists of a base station and nodes. The base station receives signals from the node antennas and transmits thesignals to the cloud. The nodes are equipped with strain gauges, crack opening devices, temperature sensors or other suitable sensors for the investigation purpose. Results from the methods and conclusions regarding further use will be presented

  • 30.
    Saback de Freitas Bello, Vanessa
    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. SINTEF Narvik AS , 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.
    Asset Management of Existing Concrete Bridges Using Digital Twins and BIM: a State-of-the-Art Literature Review2022In: Nordic Concrete Research, ISSN 0800-6377, Vol. 66, no 1, p. 91-111Article, review/survey (Refereed)
    Abstract [en]

    The need to optimize investments in bridge maintenance has created a demand for improved bridge management systems (BMS). Outdated practices in bridge inspection and constant advances in information technology have also contributed to this demand. The use of Digital Twins (DT), although well established in other industries, is still incipient for asset management and structural analysis of bridges. There is a great deal of research on Building Information Modelling (BIM) for bridge inspection, but its post-construction potential is still under-explored. This study presents a state-of-the-art review of the literature on asset management for bridges using digital models such as BIM and digital twins. The review was conducting using a systematic approach. Despite the rapid increase in research on DT and the amount of existing research on BIM, several gaps remain to be addressed, such as the lack of consensus about the definition of digital twins, which has led to wrongful categorisation of digital models as DT. The complex data flow and software compatibility required to develop a functional DT have hindered the exploitation of their full potential so far. The integration of BIM post-construction to BMS and existing automation technologies can also significantly improve current practices of bridge management.

  • 31.
    Saback de Freitas Bello, Vanessa
    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. SINTEF Narvik AS, Narvik, 8517, 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.
    Bridge management systems: overview and framework for smart management2021In: IABSE Congress Ghent 2021: Structural Engineering for Future Societal Needs / [ed] H. H. (Bert) Snijder; Bart De Pauw; Sander van Alphen; Pierre Mengeot, International Association for Bridge and Structural Engineering (IABSE) , 2021, p. 1014-1022Conference paper (Refereed)
    Abstract [en]

    Throughout the world, many medieval and historic bridges remain in operation. Deterioration and failures have increased in the already aging bridges due to consistent growth in traffic volume and axle loads. Therefore, the importance of Bridge Management Systems (BMS) to ensure safety of operation and maximize maintenance investments has also increased. Recent improvements in technology also contribute to the demand for optimized and more resource-efficient BMS. In this study, a literature review was performed to map current bridge management practices and systems in operation in the world. The outcomes identified Bridge Information Modelling (BrIM) and Digital Twins as novel approaches that enable efficient management of the whole lifecycle of a bridge.From these outcomes, a framework of an ideal BMS is proposed to achieve automated and smart management of bridges.

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  • 32.
    Saback de Freitas Bello, Vanessa
    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.
    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.
    Framework for Bridge Management Systems (BMS) Using Digital Twins2022In: Proceedings of the 1st Conference of the European Association on Quality Control of Bridges and Structures / [ed] Carlo Pellegrino; Flora Faleschini; Mariano Angelo Zanini; José C. Matos; Joan R. Casas; Alfred Strauss, Springer, 2022, Vol. 200, p. 687-694Conference paper (Refereed)
    Abstract [en]

    Bridge structures have significantly long life spans; many medieval and historic bridges remain in operation in the world. The concept of bridge management contains the activities related to managing bridge inspections and condition assessment, which can be gathered into a Bridge Management System (BMS). Deterioration and failures have increased over the years in the already aging bridges; therefore, the importance of BMS to ensure safety of bridge operation and maximize investments in bridge maintenance has also increased. Digital Twin (DT) technology can be applied in the construction industry to achieve smart management through the entire life cycle of structures. Unlike the aerospace and manufacturing industries, the maturity of development of DT models in the construction industry still lags behind. In this study, a literature review was initially performed to gather knowledge on the origins of the digital twin concept and current best practice focused on bridge structures. A systematic approach for the literature review is presented in the methodology. Lastly, a framework for facility management of bridge structures using digital twins is proposed.

  • 33.
    Saback de Freitas Bello, Vanessa
    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. SINTEF Narvik AS, Narvik, 8517, 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.
    Framework for facility management of bridge structures using digital twins2021In: IABSE Congress Ghent 2021: Structural Engineering for Future Societal Needs / [ed] H. H. (Bert) Snijder; Bart De Pauw; Sander van Alphen; Pierre Mengeot, International Association for Bridge and Structural Engineering (IABSE) , 2021, p. 629-637Conference paper (Refereed)
    Abstract [en]

    The maturity of Digital Twin (DT) models has evolved in the aerospace and manufacturing industries; however, the construction industry still lags behind. DT technology can be applied to achieve smart management through the entire life cycle of structures. Particularly for bridge structures, which play an essential role in any transportation system and can have high maintenance demands throughout their long life spans. In this study, a literature review on DTs was performed, from the origins of the concept until current best practice focused on bridges. Especially concerning structural analysis and facility management, few studies that employ DT for bridges were encountered. The main challenges identified are related to treatment of the large amount of data involved in the process, mostly gathered from different platforms. Finally, a framework for smart facility management of bridges using DTs was proposed to tackle potential solutions

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  • 34.
    Saback, Vanessa
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Gonzalez-Libreros, Jaime
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Daescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Department of Civil Engineering and Installations (CCI), Politehnica University of Timisoara, Timisoara, Romania.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, Norway.
    Garmabaki, Amir Soleimani
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Adapting to climate change: snow load assessment of snow galleries on the Iron Ore Line in Northern Sweden2024In: Frontiers in Built Environment, E-ISSN 2297-3362, Vol. 9Article in journal (Refereed)
    Abstract [en]

    The snow galleries along the Iron Ore railway line in northern Sweden have facedproblems in recent years due to increasingly large snow loads, and several gallerieshave been damaged. These incidents motivated an evaluation of the maximumload supported by the galleries before collapse, which is presented in this study. In2021, a monitoring system was installed in one of the main frames of two snowgalleries built in the 1950s to follow up with temperature and displacements,including a trigger that sends out a warning message when a critical load isreached. A literature review on snow loads was performed, followed bycalculations on snow distribution on the galleries based on the Eurocodes andNational Swedish Standards. Finite element 2D and 3D models were created usingAxisVM to accurately assess the efforts in the structural elements. Analysis anddiscussion are complemented by observations from site visits. It was concludedthat the critical loads supported by the galleries are lower than the requirements oftoday’s standards, but since secondary construction elements were damagedbefore the main frames reached their full capacity, no major collapse has yet takenplace. The cobweb effect (load re-distribution between the neighboring elementsin a 3D structure) influenced the behavior of the galleries in the 3D analysis and thecapacity of the main frames proved to be significantly increased compared to the2D assessment.

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  • 35.
    Saback, Vanessa
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Mirzazade, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Gonzalez, Jaime
    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.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik AS, Narvik, 8517, Norway.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Daescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Politehnica University of Timisoara, Romania.
    Petersson, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Crack monitoring by fibre optics and image correlation: a pilot study2022In: IABSE Symposium Prague, 2022: Challenges for Existing and Oncoming Structures, Report, International Association for Bridge and Structural Engineering, 2022, p. 437-444, article id O-048Conference paper (Refereed)
    Abstract [en]

    As reinforced concrete structures reach the end of their design lives, technology for improving accuracy and efficiency of inspections and structural health monitoring rapidly progresses. Concrete cracking and reinforcement strains are two relevant parameters in assessing damage and safety ofthese structures. The use of Digital Image Correlation (DIC) systems and distributed Fibre Optic Sensors (FOS) to evaluate these parameters are two of the technologies that have been gaining momentum due to their advantages over other approaches. This study presents an experimental investigation of crack propagation of a reinforced concrete beam specimen through FOS and DIC.The FOS were positioned inside a groove carved in the rebar and in the concrete immediately outside the bar for comparison. The results showed a significant difference between both positions, with more reliable data coming from inside the bar. The addition of the DIC crack propagation images to the FOS analysis complemented the results, and good visual correlation was identified between both methods. This study is part of a broader research program, which aims at applying DIC and FOS for structural health monitoring of a real scale bridge structure.

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  • 36.
    Saback, Vanessa
    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. SINTEF Narvik AS, 8517 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.
    Analysis of Digital Twins in the Construction Industry: Practical Applications, Purpose, and Parallel with other Industries2024In: Buildings, E-ISSN 2075-5309, Vol. 14, no 5, article id 1361Article, review/survey (Refereed)
    Abstract [en]

    Digital Twins (DT) have become a widely discussed subject, believed to have the potential to solve various problems across different industries, including Engineering & Construction (E&C). However, there is still significant misconception concerning the definition of DT and their purpose within E&C. This study dives deep into identifying DT applications within E&C and the other prominent industries, i.e., Aerospace & Aviation, Manufacturing, Energy & Utilities, Automotive, Healthcare, Smart Cities, Oil & Gas, and Retail. The main challenges to the evolution of DT practical applications are also analyzed. A combination of literature review, multi-case study analysis, and comparative analysis compose the deployed methodology. Standardization and a maturity level classification are proposed to drive progress of the adoption of DT. The distinct aspects of the different industries and their assets are evaluated to the conclusion that DT are better employed to maintenance of structures within E&C. DT have become a well-worn topic, but the abundance of complex theoretical frameworks is met with simple or inexistent practical applications. Therefore, the novelty of this study lays in its comprehensive analysis of DT applications and real-world implementations – a departure from the often-theoretical discussions surrounding DTs.

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  • 37.
    Saback, Vanessa
    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. SINTEF Narvik AS, 8517, Narvik, Norway.
    Täljsten, Björn
    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.
    Analysis of Digital Twins in the Construction Industry: Current Trends and Applications2023In: Building for the Future: Durable, Sustainable, Resilient - Proceedings of the fib Symposium 2023 - Volume 2 / [ed] Alper Ilki, Derya Çavunt, Yavuz Selim Çavunt, Springer, 2023, Vol. 2, p. 1080-1088Conference paper (Refereed)
    Abstract [en]

    The construction industry has a significant impact in terms of financialand environmental resources but is vastly behind other sectors in terms of digitalization.The potential of this industry to be improved by new technology has beenreflected in huge trends in research for terms such as “digital twins”. However, thepurpose of such technologies and how they can be applied to specific needs andassets in the construction sector is not always clear. This paper proposes an analysisof the purpose, current and future states of digital twins in the constructionindustry, based on a reviewof the evolution of research in the topic and recentmarketapplications. Even though there is a discrepancy between research and levelof development of tangible applications, it is undeniable that the digital transformationwill reach the construction industry. The efforts should then be focusedon technology that can be translated to its assets, such as smart management, andwill generate tangible results that can survive outside the theoretical realm.

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  • 38.
    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.

  • 39.
    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, 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.

  • 40.
    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.

  • 41.
    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.

  • 42.
    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. Northern Research Institute, Norway.
    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 at the Northern Research Institute (NORUT), Narvik, Norway .
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Skanska Sweden.
    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 panels2018In: SP-327: The 13th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures / [ed] Raafat El-Hacha; Lijuan (Dawn) Cheng; Maria Lopez de Murphy; William J. Gold, American Concrete Institute, 2018, p. 38.1-38.18Conference paper (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.

  • 43.
    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.

  • 44.
    Sabourova, Natalia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Duvnjak, I.
    University of Zagreb, Zagreb, Croatia..
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Damjanovic, D.
    University of Zagreb, Zagreb, Croatia..
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. School of Civil Engineering, Southeast University, Nanjing, China.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Detection of sparse damages in plates2020In: IABSE Symposium, Wroclaw 2020: Synergy of Culture and Civil Engineering – History and Challenges / [ed] Jan Bień, Jan Biliszczuk, Paweł Hawryszków, Maciej Hildebrand, Marta Knawa-Hawryszków, Krzysztof Sadowski, Zürich: International Association For Bridge And Structural Engineering (IABSE) , 2020, p. 1141-1148Conference paper (Refereed)
    Abstract [en]

    Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of the structure. This property of damage has not been utilized in the field of structural damage identification until quite recently, when the sparsity-based regularization developed in compressed sensing problems found its application in this field. In this paper we consider classical sensitivity-based finite element model updating combined with a regularization technique appropriate for the expected type of sparse damage. The validity of the proposed methods is demonstrated using simulations on a bridge. The pros and cons of these methods are discussed.

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    Sabourova
  • 45.
    Sas, Gabriel
    et al.
    NORUT, Rombaksveien E-6 47, N-8517 Narvik, Norway.
    Dăescu, Cosmin
    Politehnica University of Timisoara, 2nd T. Lalescu, 300223 Timisoara, Romania.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nagy-György, Támas
    Politehnica University of Timisoara, 2nd T. Lalescu, 300223 Timisoara, Romania.
    Numerical optimization of strengthening disturbed regions of dapped-end beams using NSM and EBR CFRP2014In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 67, p. 381-390Article in journal (Refereed)
    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.

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  • 46.
    Sas, Gabriel
    et al.
    SINTEF Narvik AS, Narvik 8517, Norway.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bista, Dipen
    SINTEF Narvik AS, Narvik 8517, Norway; Norwegian University of Science and Technology (NTNU), Trondheim 7491, Norway.
    Seger, Andreas
    SINTEF Narvik AS, Narvik 8517, Norway.
    Arntsen, Bård
    SINTEF Narvik AS, Narvik 8517, Norway.
    Johansson, Fredrik
    Royal Institute of Technology (KTH), Stockholm 10044, Sweden.
    Lia, Leif
    Norwegian University of Science and Technology (NTNU), Trondheim 7491, Norway.
    Influence of large-scale asperities on the shear strength of concrete-rock interface of small buttress dams2021In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 245, article id 112952Article in journal (Refereed)
    Abstract [en]

    This paper presents an investigation of the influence of large-scale asperities on the shear strength of four physical models of a pillar (also known as buttress web) from Kalhovd dam in Norway. The objective was to observe the structural behaviour of the pillar under design and ultimate loading scenarios and to compare results of the tests with those of nonlinear finite element analysis (FEA) and standard guideline methods. Four models at 1:5 scale were prepared with different interface profiles and tested. The results from model test and the results of a benchmarking process carried out with nonlinear FEA are presented. Furthermore, the FEA was expanded to other hypothetical scenarios to extend understanding of effects of the locations and inclinations of large-scale asperities on the sliding stability of concrete dams. The results are compared with those obtained using standard design methods and estimated safety factors are presented.

  • 47.
    Täljsten, Björn
    et al.
    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.
    Sas, Gabriel
    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.
    Nilimaa, Jonny
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Carolin, Anders
    Trafikverket, Luleå, Sweden.
    Häggström, Jens
    Trafikverket, Luleå, Sweden.
    Bridges tested to failure in Sweden2018In: IABSE Conference Copenhagen 2018: Engineering the Past, to Meet the Needs of the Future, International Association for Bridge and Structural Engineering (IABSE) , 2018, p. 64-70Conference paper (Refereed)
    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

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  • 48.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Paulsson, Björn
    Luleå University of Technology. Charmec, Chalmers tekniska högskola, Göteborg, Sweden.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    WSP Group, Göteborg, Sweden.
    Nilforoush, Rasoul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Emborg, Mats
    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.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment of prestressed concrete bridges - challenges2020In: IABSE Symposium, Wroclaw 2020: Synergy of Culture and Civil Engineering – History and Challenges / [ed] Jan Bień, Jan Biliszczuk, Paweł Hawryszków, Maciej Hildebrand, Marta Knawa-Hawryszków, Krzysztof Sadowski, Zürich: International Association For Bridge And Structural Engineering (IABSE) , 2020, p. 487-494Conference paper (Refereed)
    Abstract [en]

    Prestressed concrete bridges are important parts of our infrastructure. They are susceptible to different kinds of deterioration processes. Examples of damages and deficiencies are cracking, corrosion, voids, bond loss, reduction of cover layer, delamination, fatigue and loss of stiffness and strength. This necessitates methods to continuously assess their condition in order to avoid problems that might lead to shorter service life or reduction of structural integrity. Many of the existing prestressed bridges in Europe are now approaching their design life length. However, with proper and continuous inspection, monitoring and assessment, we may plan proactive maintenance and the structural safety can be assured or – if necessary - increased. This will save both money and decrease the environmental impact of the structure.

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    Täljsten e a
  • 49.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Invator AB, Box 1093, 181 22 Lidingö, Sweden.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik, 8504 Narvik, Norway.
    Corrosion-free concrete structures by the use of FRP (Fibre Reinforced Polymers)2022In: 24th NCR Symposium Proceedings / [ed] Johan Silfwerbrand, Nordic Concrete Federation , 2022Conference paper (Refereed)
    Abstract [en]

    Fibre reinforced polymers may be suggested as a solution to one of the major durability problems with reinforced concrete; the corrosion of the internal steel reinforcement. The durability of fibre reinforced polymers, FRP, e.g. towards chlorides, has the potential of saving extensive maintenance costs and avoiding resulting inconveniences for the public. This paper presents a pilot study with the use of glass fibre reinforced polymers, GFRP, as internal reinforcement for concrete structures. In the comparison between major international design guidelines, similar design procedures for ultimate limit state, ULS, but different design procedures for serviceability limit state, SLS, are used. Four T-beams, of which two were reinforced with GFRP rebars and the other two with steel rebars, were tested to failure in 4-point bending. Optical strain measuring equipment was used for the measurement of crack propagation. A comparison between predictions of failure loads, deflections and crack widths based on the design guidelines and the experimental results has been performed. For both GFRP reinforced beams different from predicted failure modes occurred, but at loads almost at the predicted level or higher. Extensive deflections and crack propagation gave clear warnings before failure. The behavior of the GFRP reinforced beams in SLS was reliable predicted by the design guidelines for FRP with the same accuracy as for the reinforced concrete beams. The SLS predictions of crack widths and deflections showed increasing overestimation for increasing reinforcement ratios. SLS criteria have shown to be governing in the design for the GFRP reinforced members.

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  • 50.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Invator AB, Box 1093, 181 22 Lidingö, Sweden.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SINTEF Narvik, 8504 Narvik, Norway.
    Nilforoush, Rasoul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Wireless monitoring for assessment of concrete railway bridges – Experiences from field tests2022In: 24th NCR Symposium Proceedings / [ed] Johan Silfwerbrand, Nordic Concrete Federation , 2022Conference paper (Refereed)
    Abstract [en]

    This paper focus on assessment on a prestressed three span concrete box bridge by the use of a wireless monitoring system in combination with visual inspection. The bridge is located in the very north of Sweden, in Abisko. A visual inspection of the bridge carried out the 18th of August in 2016 several crack patterns were mapped on the inside of the box girder bridge located near supports in the spans on both sides of the bridge. The cause of the cracks are not completely clear. To reveal the reason for cracking a long term project has been initiated by Trafikverket. Here a new developed wireless system has been used. Investigating change in crack widths by the use of LVDTs and strain gauges. Also accelerations are monitored together with the temperatures. In addition also fibre optic systems and non-destructive tests were carried out (not reported here). The results/conclusions presented in the paper are preliminary and final results will be presented 2021.

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