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  • 1.
    Bonath, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Petrich, Chris
    Northern Research Institute Narvik.
    Sand, Bjørnar
    Northern Research Institute Narvik.
    Fransson, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Morphology, internal structure and formation of ice ridges in the sea around Svalbard2018Ingår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 155, s. 263-279Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The results from 3 years of comprehensive field investigations on first-year ice ridges in the Arctic are presented in this paper. The scopes of these investigations were to fill existing knowledge gaps on ice ridges, gain understanding on ridge characteristics and study internal properties of ice. The ability of developing reliable simulations and load predictions for ridge-structure interactions is the final principal purpose, but beyond the scope of this paper. The presented data comprise ridge geometry, ice block dimensions from ridge sails, ice structure in the ridge and values on the ridge porosity and the degree of consolidation. The total ridge thickness conformed to other ridges studied in the same regions. The consolidated layer thickness was on average 2–3 times the level ice thickness. Minimum 33% and in average 90% of the ridge keel area was consolidated. The distribution of ice block sizes and block shapes within a ridge appears to be predictable. A new approach for deriving a possible ridging scenario and ridge age is presented. Different steps of the ridge building process were identified, which are in good agreement with earlier simulated ridging events. After formation of very thin lead ice between two floes deformation occurs through rafting and ridging until closure of the lead. Subsequently the adjacent level ice floe fractures proceeding ridge formation until ridging forces exceed driving forces. A time span of 10 days could be assessed for a possible ridge formation date, estimating the ridge age of the studied ridge located east of Edgeøya at 78° N to be 7 to 8 weeks.

  • 2.
    Häggström, Jens
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Bridge over Åby River: Evaluation of full scale testing2017Rapport (Övrigt vetenskapligt)
  • 3.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Concrete Walls with Openings Strengthened Using FRCM Composites2017Ingår i: Advanced Composites in Construction: Conference Proceedings / [ed] Maurizio Guadagnini & Sue Keighley, Chesterfield: NetComposites Limited , 2017, s. 188-192Konferensbidrag (Refereegranskat)
    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.

  • 4.
    Orosz, Katalin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Early age autogenous deformation and cracking of cementitious materials – Implications on strengthening of concrete2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 5.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sneed, Lesley H.
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, Norut Narvik AS.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Effect of Confinement with FRCM Composites on Damaged Concrete Cylinders2017Ingår i: Strain-Hardening Cement-Based Composites: Shcc4 / [ed] Mechtcherine, Viktor; Slowik, Volker; Kabele, Petr, Dordrecht: Springer, 2017, s. 770-777Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 6.
    Blandine, Feneuil
    et al.
    Aalto University, Concrete Technology Laboratory, Department of Civil and Structural Engineering, School of Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Cwircen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Erratum to: Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste2017Ingår i: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 11, nr 2, s. 255-255Artikel i tidskrift (Refereegranskat)
  • 7.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Dury, Robin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Laue, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Progressive Landslide Analysis in Canadian Glacial Silty Clay in Churchill River2017Ingår i: / [ed] Vikas Thakur, Jean-Sébastien L’Heureux, Ariane Locat, 2017, s. 1-Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The poster presents the risks for a progressive landslide in a natural dam. The stability will be critical when the water level is raised after the building of a hydro power plant, Bernander (2016), Dury (2017). The analysis is based on a finite difference method developed by Stig Bernander (2011), Bernander et al.(2016)

     

    The following issues will be discussed:  

    - Material properties

    - Risk for liquefaction

    - Three possible failure surfaces: one horizontal, one inclined and one curved

    - Failure riska for different material propeties

    - The need to check the real properties of the soil

  • 8.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Riverbank stability in loose layered silty clays: Comments on the North Spur Dam at Muskrat Falls in Churchill River, Labrador, Newfoundland2017Rapport (Refereegranskat)
    Abstract [en]

    The differences are outlined in landslide analysis between the classic limit equilibrium method with assumed plastic properties of the soil and a progressive analysis applying softening material properties.

    The risk for failure is studied in the dam at the North Spur riverbank ridge at Muskrat Falls in Churchill River in Labrador, Newfoundland, Canada. A sloping failure surface is much more critical than the horizontal surfaces which have hitherto been studied. Results from new analyses have now been obtained applying softening material properties probable for the ridge. The results indicate safety factors lower than 0.5, i.e. there is a high risk that the ridge will fail if the water level is raised to the proposed level.

    Three reports are appended where Stig Bernander argues in detail for the need for a proper progressive failure analysis based on measured material properties. He also proposes how such properties may be obtained and gives an example of a way to stabilize the ridge if the soil properties show a softening behaviour. Finally examples of progressive failure analyses are included using probable material properties.

  • 9.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla .
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua, .
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    State of research on shear strengthening of RC beams with FRCM composites2017Ingår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 149, s. 444-458Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 10.
    Hösthagen, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. anders.hosthagen@ltu.se.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilsson, Martin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Thermal Crack Risk Estimations of Concrete Walls: Temperature and Strain Measurements Correlated to the Equivalent Restraint Method2017Ingår i: Proceedings of the 23rd Nordic Concrete Research Symposium, Oslo, Norway: Nordic Concrete Federation , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

     Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. The method has previously been analyzed but needs to be further examined and validated. Recordings of tunnel sections were performed and compared to calculated values by ERM. Satisfying correlation between theoretically estimated and observed temperatures, strains and time of through cracking was achieve which is promising for future implementation and testing of the method.

  • 11.
    Mahal, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    A two-scale damage model for high-cycle fatigue at the fiber-reinforced polymer-concrete interface2016Ingår i: Computers and Concrete, ISSN 1598-8198, Vol. 116, s. 12-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a new two-scale damage model of the fiber-reinforced polymer (FRP)-concrete bond under high-cycle fatigue. The material behavior is modeled as elastic-plastic coupled with damage for the microscale analysis and as elastic for the mesoscale analysis. A new damage law for the interface joint is described. The two-scale damage model has been implemented as a material model for a three dimensional an eight-node interface element of zero thickness and used to simulate a double shear joint specimen under high cycle fatigue. The numerical calculations were performed with a full incremental cycle solution and a new cycle jump approach. Comparing the results from the finite element method (FEM) model with experimental data shows that the model is capable of accurately predicting the cyclic fatigue loading slip response of the joint interface.

  • 12.
    Feneuil, Blandine
    et al.
    Aalto University, Concrete Technology Laboratory, Department of Civil and Structural Engineering, School of Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Cwirzen, Andrzej
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste2016Ingår i: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 10, nr 2, s. 224-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this experimental study, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were dispersed by intensive sonication in water in the presence of superplasticizer and subsequently mixed with Portland cement with water/ cement ratios varying between 0.3 and 0.4. The autogenous shrinkage in the fresh stage was investigated. The CNTs and CNFs were characterized by high resolution scanning electron microscopy (SEM) and the hydrated pastes were studied by X-ray diffraction and SEM. The results showed a reduction of the autogenous shrinkage by 50% for pastes containing small amounts (0.01 wt%) of nanomaterials. Higher additions appeared to be less effective. The highest reduction of shrinkage was observed for carbon nanofibers which were long, rather straight and had diameters of around 200 nm. The result showed that the addition of nanomaterials accelerated the hydration processes especially in the early stages of hydration. The effect was the most pronounced in the case of functionalized nanotubes. The proposed mechanism resulting in the reduction of the autogenous shrinkage was a combination of nano-reinforcing effects, alterations of hydration and microstructure of the hydrated matrix.

  • 13.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kullingsjö, Anders
    Skanska Teknik, Göteborg, Chalmers University of Technology.
    Gylland, Anders K
    Multiconsult, Norwegian University of Science and Technology (NTNU), Trondheim.
    Bengtsson, Per-Evert
    Statens Geotekniska Institut, Linköping, PEB Geoteknik.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Olofsson, Jan
    Skanska Sverige AB, Skanska Teknik, Göteborg.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Downhill Progressive Landslides in Long Natural Slopes: Triggering Agents and Landslide Phases modeled with a Finite Difference Method2016Ingår i: Canadian geotechnical journal (Print), ISSN 0008-3674, E-ISSN 1208-6010, Vol. 53, nr 10, s. 1565-1582Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A large landslide in Tuve (Gothenburg, Sweden 1977) initiated the development of a model for slope stability analysis taking the deformation-softening of soft sensitive clays into consideration. The model studies triggering agents and five phases in progressive slope failure are identified: (1) in-situ, (2) disturbance, (3) unstable ‘dynamic’, (4) transitory (or permanent) equilibrium, and (5) ‘global’ failure. The clay resistance in these phases may differ widely; mostly due to different rates of loading. Two time dependent failure criteria are defined: (i) the triggering load condition in the disturbance Phase (2), and (ii) the transitory equilibrium in Phase (4), indicating whether minor downhill displacements or a veritable landslide catastrophe will occur. The analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further down-slope. The model has been applied to landslides in Scandinavia and Canada. Three case studies are briefly discussed. The model is a finite difference approach, where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above the potential (or the established) failure surface. Software and an easy-to-use spreadsheet are introduced as well as recent developments. See also Video Abstract.

  • 14.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Effect of cut-out openings on the axial strength of concrete walls2016Ingår i: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 142, nr 11, artikel-id 4016100Artikel i tidskrift (Refereegranskat)
    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.

  • 15.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand. Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Experimental investigation on RC beams strenghened in shear with  externally bonded composites2016Ingår i: Eighth International Conference onFibre-Reinforced Polymer (FRP) Composites in Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, s. 384-389Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 16.
    Mahal, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Experimental performance of RC beams strengthened with FRP materials under monotonic and fatigue loads2016Ingår i: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 122, s. 126-139Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon fiber-reinforced polymers (CFRPs) are increasingly being used to repair and strengthen reinforced concrete (RC) bridge members. CFRP strengthening may be applied by bonding polymeric plates to the exterior of the member’s tension surface or by placing CFRP bars inside the concrete member cover to provide near-surface mounted reinforcement. It is not clear which of these approaches is most effective at resisting fatigue loads. To compare their efficacy, four-point bending tests with reinforced concrete beams were conducted under monotonic and fatigue loading using both strengthened and unstrengthened RC beams having steel reinforcements with identical stress levels. The influence of the strengthening material’s properties and prior cracking of the member are investigated and discussed by analyzing failure mechanisms, load-deflection curves, and strain measurements for steel bars and CFRP materials observed during loading experiments. The results obtained indicate that the efficiency of strengthening is primarily determined by the relief of local stress in the member’s reinforcing steel bars before they rupture, and the fatigue life of the reinforcing steel after its initial fracturing. The latter of these quantities is related to the strengthened member’s ability to absorb the energy released at the moment the reinforcing bar fractures.

  • 17.
    Mahal, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Fatigue analysis of RC beams strengthened in flexure using CFRP2016Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The increasing use of Fiber Reinforced Polymers (FRP) to repair, strengthen or upgrade reinforced concrete (RC) structural elements means that there is a need to develop analytical methods for analyzing the behavior of strengthened members under fatigue loading. This paper describes an analytical model for simulating the fatigue behavior of RC beams strengthened with Carbon Fiber Reinforced Polymer (CFRP). Fatigue calculations are performed using a lamellar model that considers the fatigue behavior of the RC and CFRP strengthening materials during loading. The model’s output is compared to experimental data for four CFRP-strengthened beams, showing that the new model accurately predicted the deflection and strain of each one. In addition, various models for predicting the fatigue life of CFRP-strengthened RC beams were tested and a model capable of providing conservative fatigue life estimates was identified.

  • 18.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Gonzalez-Libreros, Jaime
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT,.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Influence of the fiber type and matrix age of the bonding of FRCM composite strips applied to concrete substrates2016Ingår i: Eighth International Conference on Fibre-Reinforced Polymer (FRP) Composites in Civil Engineering / [ed] J.G. Teng and J.G. Dai, 2016, s. 456-461Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 19.
    Täljsten, Björn
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kompositförstärkning av betong2016Bok (Övrigt vetenskapligt)
  • 20.
    Nilforoush, Rasoul
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilsson, Martin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Söderlind, Gunnar
    SP Technical Research Institute of Sweden, Borås.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Long-Term Performance of Adhesive Bonded Anchors2016Ingår i: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 113, nr 2, s. 251-261, artikel-id MS No. S-2014-302.R2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Post-installed adhesive anchors used for fastening nonstructural and/or structural elements to concrete structures are prone to creep under sustained loads over their service life, which may considerably affect their long-term performance. In this study, the influence of various in-service conditions and sustained loading levels on the long-term performance of adhesive anchors was experimentally examined. The tested adhesive was an unsaturated polyester resin and the bonded anchors were subjected to sustained loads of 23, 47 and 70% of their mean ultimate short-term capacities for up to 10376 days (28.4 years). The tested in-service conditions were indoor temperature, outdoor temperature and humidity variations, wetness and presence in the concrete of salt additives.Results indicate that the tested bonded anchors did not fail indoors when subjected to sustained loads up to 47% of their mean ultimate short-time capacity. However, the long-term performance was substantially impaired outdoors, presumably due to temperature and humidity variations, leading to failure for sustained loads higher than 23% of the anchors’ mean ultimate short-time capacity.

  • 21.
    Sabau, Cristian
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Monitoring structural behavior of reinforced concrete walls with openings using digital image correlation2016Ingår i: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016, s. 1803-1811Konferensbidrag (Refereegranskat)
    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.

  • 22.
    Nilimaa, Jonny
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bagge, Niklas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    NSM CFRP Strengthening and Failure Loading of a Posttensioned Concrete Bridge2016Ingår i: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 20, nr 3, artikel-id 04015076.Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two carbon-fiber-reinforced polymer (CFRP) systems developed as possible means to strengthen existing concrete structures have been applied to a bridge at Kiruna (Sweden). The bridge was no longer in service and was thus used in extensive tests to failure. It was a posttensioned five-span bridge consisting of three longitudinal main girders topped with a concrete slab. The program reported here consisted of a series of three tests of the girders in the second span: loading each girder up to 2.0 MN before strengthening, loading each girder up to 2.0 MN after strengthening, and loading to failure after strengthening. One of the girders was strengthened by installing three 10×10  mm 2 near-surface mounted (NSM) CFRP bars on the soffits, and another by installing three prestressed 1.4×80  mm 2 CFRP laminates. This paper focuses on the NSM-strengthened girder, which failed at a maximum load of 6.1 MN, with a corresponding midspan deflection of 159 mm. The failure was a combination of flexure and shear, and the strain in the NSM bars at the ULS was 1.2%.

  • 23.
    Edrees, Tarek
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Posicast Control of Structures Using MR Dampers2016Ingår i: Structural Control and Health Monitoring: The Bulletin of ACS, ISSN 1545-2255, E-ISSN 1545-2263, Vol. 23, nr 8, s. 1121-1134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a novel application of a semi active Posicast control scheme for structures with Magneto- Rheological (MR) dampers is presented. MR dampers are considered to be highly promising of semi-active control systems, which are becoming increasingly popular for alleviating the effects of dynamic loads on civil engineering structures because they combine the merits of both passive and active control systems. The main contribution of this article relates to the design, application, tuning and performance evaluation of the novel Posicast control scheme for structural control. The efficiency of the suggested control strategy was evaluated by performing numerical simulations of a benchmark three-story building with an MR damper, rigidly attached between the first floor and the ground. The damper’s behaviour was simulated using the Bouc-Wen model. Seven evaluation criteria were used to assess the performance of the proposed posicast control scheme in reducing the excited structure’s responses to dynamic loading. The simulation’s results indicated that the Posicast control scheme had significant advantages over conventional alternatives in terms of performance and efficiency.

  • 24.
    Al-Gburi, Majid
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilsson, Martin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Reduction of Early Age Crack Risks in Concrete Walls by Using a New Casting Technique2016Ingår i: Structural Engineering International, ISSN 1016-8664, E-ISSN 1683-0350, Vol. 26, nr 3, s. 216-224Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Volumetric changes in early age concrete that are restrained might lead to cracks. The degree of restraint is influenced by the casting sequence and the dimensions of the castings. In the current study a new casting technique is proposed to reduce restraint in the newly cast concrete with a new arrangement of the structural joint to the existing old concrete. The proposed technique is valid for the typical structure wall-on-slab using one structural joint. This casting method means that lower part of the wall is cast together with the slab, and that part is called a kicker. Hereby, the behavior of the structure changes from a typical case wall-on-slab to a typical case wall-on-wall. It has been proven by the beam theory and demonstrated by numerical calculations that there is a clear reduction in the restraint from the slab to the wall using kickers. In the paper different kicker heights are studied with the aim of determining the minimum restraint in the upper part of the wall cast in contact with the kicker. The technique using kickers is compared with common measures used in the field to avoid cracking, such as cooling pipes in the new casting and/or heating cables in the adjoining old concrete. The presented method is both cost and time effective, as it opens the possibility to use larger structural length of each casting sequence.

  • 25.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Shear strengthening of RC beams with FRCM: what do we know so far?2016Ingår i: Eighth International Conference onFibre-Reinforced Polymer (FRP) Compositesin Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, s. 462-467Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 26.
    Edrees, Tarek
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Hedlund, Hans
    Skanska Sverige AB Technology, Bridge and Civil Engineering.
    A state-of-the-art review of Structural Control Systems2015Ingår i: Journal of Vibration and Control, ISSN 1077-5463, E-ISSN 1741-2986, Vol. 21, nr 5, s. 919-937Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nowadays the utilization of structural control systems for alleviating the responses of civil engineering structures, under the effects of different kinds of dynamics loadings, has become a standard technology, while still there are numerous of current research approaches for advancing the effectiveness of these methodologies. The aim of this article is to review the state of the art technologies in structural control systems by introducing a general literature review for all the types of vibrations control systems that have been appeared till now. These systems can be classified into four main groups: a) passive, b) semi active, c) active, and d) hybrid based on their operational mechanism. A brief description of each of these main groups and their subgroups, with their corresponding advantages and disadvantages will be also extendedly reported in this review. This article will conclude by providing an overview of some innovative practical implementations of devices, which are able to demonstrate their potentials and future directions of structural control systems in civil engineering.

  • 27.
    Häggström, Jens
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Assessment and full scale failure test of a steel truss bridge2015Ingår i: IABSE Workshop Helsinki 2015: Safety, Robustness and Condition Assessments of Structures, Zürich: International Association for Bridge and Structural Engineering, 2015, s. 288-295Konferensbidrag (Refereegranskat)
    Abstract [en]

    Large amount of resources has been invested in maintaining existing infrastructure. Several of thesestructures are now becoming old and do not meet the requirements of today or are reaching the endof their lifecycle. It is not possible to replace all of these structures that are deemed or are about tobe deemed obsolete, due to high cost and environmental impacts.One way to keep these structures in use for a longer time is innovative and intelligent assessment ofthe actual state of stress and behaviour. In such cases, using structural health monitoring to assessthe structure might be an efficient way to extend the life of the structure.This paper will describe a unique monitoring program over two similar 33 m long steel trussbridges situated in Sweden. One of these bridges, Aby River, had a regulated axle load of 25 tonsand was tested to failure in 2013. The other bridge, Rautasjokk, has a regulated axle load of 30 tonswhich will be upgraded to 32.5 tons and will be in use for the coming years.The monitoring program was performed as; monitoring of the bridge over Aby river when it wasstill in service. After replacement the old bridge was moved and tested under static loads to assessboundary conditions and state of stress. Parts of this bridge were then disassembled to be tested formaterial properties and fatigue capacity. A theoretical assessment of the Rautasjokk bridge was thenperformed based on the conclusions from the measurements on the Aby bridge. Finally the plan isto verify findings by performing measurements on live loading for the Rautasjokk bridge in servicelimit state.The aim for this project is to verify the continuous safety for the Rautasjokk bridge by using inputfrom tests performed at both bridges.

  • 28.
    Häggström, Jens
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Skanska Teknik, Göteborg.
    Collin, Peter
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Ramböll Sverige AB, Luleå.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Assessment and full scale failure test of a steel truss bridge2015Ingår i: IABSE symposium Madrid 2014: Engineering for progress, nature and people, Zürich: International Association for Bridge and Structural Engineering, 2015, s. 2757-2764Konferensbidrag (Refereegranskat)
    Abstract [en]

    Large amount of resources has been invested in maintaining existing infrastructure. Several of these structures are now becoming old and do not meet the requirements of today or are reaching the end of their lifecycle. It is not possible to replace all of these structures that are deemed or are about to be deemed obsolete, due to high cost and environmental impacts.One way to keep these structures in use for a longer time is innovative and intelligent assessment of the actual state of stress and behaviour. In such cases, using structural health monitoring to assess the structure might be an efficient way to extend the life of the structure.This paper will describe a unique monitoring program over two similar 33 m long steel truss bridges situated in Sweden. One of these bridges, Aby River, has a regulated axle load of 25 tons and is deemed to have reached is end of life due to fatigue. The other bridge, Rautasjokk, has a regulated axle load of 30 tons but will be in use for the coming years.The monitoring program has the following outline; monitoring of the bridge over Aby river when it is in service, after replacement this bridge will be moved and tested under static loads to assess boundary conditions and state of stress, then parts of this bridge will be disassembled and these parts will be tested in laboratory environment for fatigue life assessment, all of these results will then be controlled by monitoring of the bridge over Rautasjokk in service limit state.The outline of this project will give input for the fatigue life models that are used today and probably upgrade the fatigue life of the bridge over Rautasjokk.

  • 29.
    Puurula, Arto
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Savonia University of Applied Scinces, Kuopia, Finland.
    Enochsson, Ola
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Bodens kommun.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Ohlsson, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bernspång, Lars
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Carolin, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Trafikverket.
    Paulsson, Björn
    Trafikverket.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Assessment of the Strengthening of an RC Railway Bridge with CFRP utilizing a Full-Scale Failure Test and Finite-Element Analysis2015Ingår i: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 141, nr 1 (Special Issue), s. D4014008-1-D4014008-11, artikel-id D4014008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the loadcarrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the Railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States.

  • 30.
    Elfgren, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bagge, Niklas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Shu, Jiangpeng
    Chalmers University of Technology.
    Plos, Mario
    Chalmers University of Technology, Department of Civil and Environmental Engineering , Chalmers University of Technology.
    Larsson, Oskar
    Faculty of Engineering, LTH, Department of Constructional Sciences, Lund University.
    Sundquist, Håkan
    Kungliga tekniska högskolan, KTH, KTH, Structural Engineering & Bridges.
    Brottbelastning av en 55 år gammal spännbetongbro i Kiruna - Kalibrering av modeller för tillståndsbedömning: Slutrapport till BBT2015Rapport (Refereegranskat)
    Abstract [sv]

    En 55 år gammal spännbetongbro med fem spann med längden 121,5 m har provats till brott för att studera och kalibrera metoder för tillståndsbedömning av befintliga broar. Projektet harbidragit till att ge svar på flera av de frågor som ställs beträffande hållbart byggande och uppföljning av befintliga konstruktioner inom BBT - Branschprogram för forskning och innovation avseende byggnadsverk inom transportsektorn. Framför allt adresseras följande områden:A.2.1 Säkerhet, robusthet och sårbarhet – En betydande robusthet finns i den studerade typen av broar och säkerheten mot brott är större än den som erhålls med modellerna i de europeiska betongnormerna.A.2.4 Metodik för individuell bärighetsklassning av broar – En kombination av FE-modellering och analytiska studier baserade på verklig geometri och aktuella materialdata har goda förutsättningar att kunna ge betydligt mer kvalificerade bedömningar av kvarvarande bärförmåga än nu tillämpade metoder.A.2.5 Beständighet och livslängd hos nya byggnadsverk – Projektet ger underlag för förbättrade metoder att bestämma beständighet och livslängd hos spännbetongbroar.A.3.1 Mätmetoder – I projektet har en ny metod för fotografisk töjningsmätning provats. Resultaten har ännu inte hunnit helt utvärderas men de ser lovande ut.A.3.2 Bedömning av tillstånd och livslängd – Projektet ger underlag för förbättrade metoder för bedömning av tillstånd och livslängd.Projektet har hittills redovisats i en doktors- och en licentiatavhandling och i tio tidskrifts- och konferensartiklar.

  • 31.
    Edrees, Tarek
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Comfort Level Identification for Irregular Multi-storey Building Subjected to Vibrations2015Ingår i: Automation in Construction, ISSN 0926-5805, E-ISSN 1872-7891, Vol. 50, s. 40-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, the System Identification approach is being used to identify the vertical frequencies of the top storey in a multi-storey building prefabricated from reinforced concrete in Stockholm. Before building construction, detailed investigation indicated that the building will not be affected by train vibrations from the nearby railway yard. After building completion, disturbing vibrations were observed in the building. Three measurement types namely: ambient vibration test, forced vibration test on the rails, and forced vibration test have been performed in order to specify the probable reasons for these vibrations. Five methods of structural identification approach, specifically: ARX, ARMAX, BJ, OEand State Space Models have been implemented for the identification process in this study usingthe tests' results. All the test types and model structures utilized have identified a concentration inthe floor only, which is close to the frequencies of human body parts. Furthermore, the article concludes that the ARMAX model and the Output Error model have indicated an excellent performance to predict the mathematical models of vibration's propagation in the building, when compared with other models used from the three types of tests. In addition, the results of the aforementioned system identification methods, implemented for this study, have indicated that there are no other reasons for the disturbing vibrations still observed in the building. Furthermore, the results confirmed the correctness of the previous theoretical and experimental results obtained by different specialists, who stated that the values of floor acceleration are within the acceptable limits, and the probable reason for any disturbance is the resonance between the generated low frequencies and the human body parts’ frequencies.

  • 32.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Concrete Bridges: Improved Load Capacity2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    There are many beautiful old structures around the world, some of which were designed for completely different purposes than their current applications. For example, Swedish railway bridges were only designed to carry axle loads up to 200 kN in the beginning of the 20th century, while modern loads can be twice as high. The traffic intensities have also increased dramatically and the velocities are now higher than ever before. In order to maintain old structures while the loads increase, upgrading of their load carryingcapacity may be needed. Administrative upgrading refers to increasing their nominal capacity to withstand stresses beyond original limits by refined calculations, using real material data, geometry and loads. This sometimes allows bridges to be upgraded with little or no physical modification. Upgrading by strengthening refers to physical alteration of the structure.The objective of the studies this thesis is based upon (reported in detail in five appended papers, designated Papers I-V) was to evaluate several strengthening systems by assessing their in-situ effects on existing bridges.First, a novel strengthening method involving internal post-tensioning of bridge slabs was developed and examined in a laboratory test (Paper I). The material used in the test consisted of two 1:3 scale trough bridge specimens, and the purpose was to study effects of the method in a controlled (laboratory) environment. The results were encouragingand the method was subsequently applied to a real railway bridge in Haparanda, Sweden. To assess the method’s ability to increase load capacities, the bridge’s response to a train load were monitored before and after strengthening (Paper II). The results showed how the bridge’s tensile strains from the train load were completely counteracted by the posttensioning.Next, an assessment procedure, consisting of curvature monitoring wasproposed for double-trough bridges. The proposal was based on results of the field test in Haparanda (Paper III).In addition, the effects of two systems for strengthening post-tensioned concrete bridges were investigated in tests using a highway bridge in Kiruna, Sweden, which was taken out of service due to increasing ground movements. Near-surface mounted carbon fiber reinforced polymer (CFRP) bars (Paper IV) and prestressed CFRP laminates (Paper V)were installed on different girders of the bridge, then loaded to failure while the structure was monitored by a battery of sensors. The results showed that both systems can reduce tensile strains in the steel reinforcement and improve post-tensioned bridge’s load capacity.In summary, the research has provided insights into the effects of several strategies for upgrading bridges that may prolong their service life, simplify their health monitoring and enhance the cost-effectiveness of maintaining a bridge stock.

  • 33.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. NORUT, Department of Infrastructure Structures and Materials.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Concrete walls weakened by openings as compression members: A review2015Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 89, s. 172-190Artikel i tidskrift (Refereegranskat)
    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.

  • 34.
    Popescu, Cosmin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sabau, Cristian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Experimental tests on RC walls with openings strengthened by FRP2015Ingår i: The 12th International Symposium on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asia-Pacific Conference on Fiber Reinforced Polymers in Structures (APFIS-2015) / [ed] Zhishen Wu; Gang Wu; Xin Wang, Nanjing, China: Southeast University , 2015Konferensbidrag (Refereegranskat)
    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.

  • 35.
    Nilimaa, Jonny
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Häggström, Jens
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Tu, Yongming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Carolin, Anders
    Trafikverket, Trafikverket, Luleå.
    Paulsson, Björn
    Trafikverket, UIC, Banverket.
    Extend the life of existing railway bridges: Results from EU FP7 project MAINLINE2015Ingår i: IABSE Conference Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges, Geneva: International Association for Bridge and Structural Engineering, 2015, s. 1219-1226Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    There is a need to extend the life and capacity of many existing bridges. One of the objects of the EU FP7 Project MAINLINE, 2011-2014, was to facilitate this. Guidelines for assessment and strengthening methods are presented as well as case studies in which existing bridges are studied in order to extend their life length. One example is the prestressing of the slab in a one-span concrete trough bridge in order to increase its load-carrying capacity. Horizontal holes were drilled trough the slab and in them steel bars were placed and post-tensioned. In this way a compressive stress was introduced into the concrete section so that it’s bending and shear capacity was increased.In another study a metal truss bridge was monitored in order to check strain and stress ranges in critical connections to enable an enhanced evaluation of the remaining fatigue resistance. The studied bridge was then replaced and loaded to failure to study its robustness and the reliability of applied assessment methods. The results could then be applied to prolong the life of an identical twin bridge located in the northern part of Sweden. A Life Cycle Assessment Tool (LCAT) has been developed to enable Infrastructure Managers to choose optimal maintenance strategies.

  • 36.
    Mahal, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Fatigue Behaviour of RC beams Strengthened with CFRP: Analytical and Experimental investigations2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Repeated cyclic loading of reinforced concrete (RC) structures such as bridges can cause reduced service life and structure failure due to fatigue even when the stress ranges applied to the structural components are very low. These problems can be mitigated by using fiber-reinforced polymer (FRP) composites to increase the structures’ load carrying capacity and fatigue life or service life. Strengthening of this sort may be a suitable way to prolong the service life of concrete structures. FRP strengthening involves externally bonding a plate, sheet or rod of the strengthening material to the surface of the concrete member or placing the strengthening element in grooves cut into the member’s surface. The bonding of plates or sheets to the surface is often referred to as EBR (externally bonded reinforcement) whereas the placement of strengthening bars in grooves carved into the member’s surface is referred to as NSM (Near Surface Mounted) reinforcement. When this research project was initiated, it was not clear whether EBR or NSM strengthening was more effective at alleviating the effects of fatigue loading, and there were many aspects of their use that warranted further investigation. The main objectives of the work presented in this thesis were to study the behaviour of materials and structures under fatigue loading, to assess the structural challenges presented by fatigue loading of members strengthened with EBR plates or NSM bars, and to identify analytical models suitable for the design and analysis of FRP-strengthening elements and strengthened concrete members. The scientific approach adopted in this work is based on experimental fatigue loading tests of RC beams strengthened with EBR plates and NSM bars together with the development and assessment of analytical methods for describing the fatigue behaviour of tested strengthened beams and numerical models for predicting the behaviour of bond joints under fatigue loading. The analytical models were then verified against experimental results. The theoretical and experimental studies were supported by a state-of-the-art literature review that was conducted to gather existing knowledge concerning FRP strengthening of RC members and their fatigue behaviour at the material and structural levels

  • 37.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Fatigue Capacity of Concrete Structures: Assessment of Railway Bridges2015Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Present codes are mostly written for the design of new structures. When assessing existing structures it is possible to ascertain actual properties and to use them instead of using very conservative estimates. Possible reinforcement fatigue damage can e.g. be assessed with partial damage methods in the same way as is done for steel structures and with similar failure stresses.- The definition of a load cycle depends on the structure and what part of it that is studied. For ballasted bridges often two bogies for adjacent wagons can be identified as one load cycle. For the highest stress ranges often a whole train can be looked upon as one load cycle. The influence of earlier traffic can be checked with a damage hypothesis.- Material properties. The concrete capacity is often underestimated, especially its capacity to carry shear forces in slabs without stirrups. For stirrups usually no reduction normally needs to be considered of the stress range capacity due to bending of the bars. This is true as long as the cracks in concrete crossing the bars are not situated in the corners of the cross sections- Dynamic factors can often be reduced from the ones obtained from standard code values after an evaluations and/or measurement on the structure in question.- The need for closed stirrups and reductions of capacity due to splicing of reinforcement bars can be reduced if the reinforcement is fully bonded as e.g. when it is situated in compressed concrete.- More research is needed to calibrate design and assessment methods to real full scale tests on bridges. Here new measurement technology makes it possible to check real strain and stress ranges, which may be considerably smaller than the ones obtained from conservative design models.- Recommendations for assessment procedures are given in Appendix A. Examples of assessments of two concrete trough bridges are presented in Appendix B (Övre Bredån) and Appendix C (Kallkällan).

  • 38.
    Patil, Aniket
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sand, Björnar
    Fransson, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Finite element simulation of punch through test using a continuous surface cap model2015Ingår i: Proceedings of the 23nd International Conference on Port and Ocean Engineering under Arctic Conditions: POAC 2015, Trondheim, Norway; 14-18 June 2015, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    An attempt has been made to calibrate the material model parameters of the continuous surface cap model with data from punch through tests performed in the Northern Gulf of Bothnia. An axisymmetric finite element model has been used to simulate the field tests. The continuous surface cap model based on a combination of elastic-plastic and continuum damage mechanics formulation is used as constitutive model for ice rubble. Material properties such as internal friction angle, cohesion and Young’s modulus are evaluated in a parametric study and the response is compared to the experimental data for the chosen test. An optimization algorithm is used for determining the parameters used for describing the continuous surface cap model. The material model parameters are chosen to get best fit to test load displacement curve. Conclusion has been drawn based on the application of continuous surface cap model on ice rubble.

  • 39.
    Popescu, Cosmin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    FRP strengthening of concrete walls with openings2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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

  • 40.
    Elfgren, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Skanska Sverige AB Technology, Bridge and Civil Engineering.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. STO Scandinavia AB.
    Casas, Joan R
    Universitat Politècnica de Catalunya.
    Bell, Brian
    UIC, International Federation of Railways, Paris, Network Rail, London.
    Lundgren, Karin
    Chalmers University of Technology, Department of Civil and Environmental Engineering.
    Guideline for application of new technologies to extend life of elderly rail infrastructure: Deliverable 1.4 in MAINLINE - a project within EC 7tf Framework Programme2015Rapport (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    There are many traditional technologies available to extend the life of elderly rail infrastructure, some of which are being improved or developed, whilst new technologiescontinue to emerge. In this guideline some of the most promising new or updated technologies are presented forbridges, track and earthwork regarding: - Assessment methods- Repair and Strengthening methodsIn an Appendix strengthening methods are presented in more detail with examples of designcalculations and work carried out.The guideline is based on work presented in earlier reports in MAINLINE: ML-D1.1 (2013):Benchmark of new technologies to extend the life of elderly rail infrastructure, ML-D1.2(2013): Assessment methods for elderly rail infrastructure and ML-D1.3 (2014): Newtechnologies to extend the life of elderly infrastructure; In these reports, backgroundinformation and more references can also be found.

  • 41.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Warr, Laurence
    Institute of Geography and Geology, Ernst-Moritz-Arndt-University of Greifswald.
    Kasbohm, Jörn
    Institute of Geography and Geology, Ernst-Moritz-Arndt-University of Greifswald.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Interaction of clay and concrete relevant to the deep disposal of high-level radioactive waste2015Ingår i: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 118, s. 178-187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A concept for the disposal of highly radioactive waste at depth in the Earth’s crust using very deep bore-holes requires that the upper 2 km’s of the 800 mm diameter, steeply drilled holes, be effectively sealed. This can be achieved by using dense smectitic clay where the rock is weakly fractured and strengthening with concrete when fracture zones are encountered. Earlier investigations have shown that chemical reactions between the clay and concrete can be expected both in the upper part where the temperature is lower than 90oC and in the deeper section where the temperature reaches up to 150oC. To study further this interaction, hydrothermal experiments were conducted using mixed-layer (illite/smectite) Holmehus clay and a low pH slag-based concrete placed in contact under isothermal conditions at 21°C, 100oC and 150oC for a period of 8 weeks. The sample sets, which consisted of two clay discs separated by concrete cast on the lower clay disc, were extracted in undisturbed form and exposed to uniaxial pressure for measuring the compressive strength at successively increasing pressures. Compression tests underenhanced thermal conditions led to strengthening of both the clay and concrete. X-ray diffraction and electron microscopy analysis of the material revealed an increasing degree of cation exchange at higher temperatures with the cement, whereby Ca replaced Na in the interlayer sites of smectite layers. Dissolution of illite/smectite was also evident occurring at enhanced temperatures, with a decrease in K, Mg and Fe content with advanced alteration. The enhanced strength of clay can be partly attributed to the precipitation of cement phases from circulating fluids, including precipitation of gypsum.

  • 42.
    Collin, Peter
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Häggström, Jens
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Hällmark, Robert
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    International workshop on strengthening of steel/composite bridges2015Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The European infrastructure is rapidly aging, and steel/composite bridges are noexception to the rule. With thousands of older steel/composite bridges, there is ademand of rational methods to strengthen the older bridges to compensate not onlyfor their age, but also for higher loads and new codes, of which perhaps the newfatigue rules for highway bridges in EC3-2 will be the hardest to meet.Within the frames of the European R&D project Prolife (RFCS-CT-2015-00025) aworkshop was arranged in Stockholm September 28th 2015. Bridge owners,designers and researchers from 12 countries participated, and the similaritiesbetween the countries as well as the variety of technical solutions were highlighted.The contributions are presented in this report and the organizers want to thank allparticipants for making this seminar successful.

  • 43.
    Edrees, Tarek
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Investigation of changes in modal characteristics before and after damage of a railway bridge: A case study2015Ingår i: The IES Journal Part A: Civil & Structural Engineering, ISSN 1937-3260, E-ISSN 1937-3279, Vol. 8, nr 2, s. 131-144Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The linear, time-invariant transfer function Txy has been utilized for the construction of FRF, based on the ambient vibration measurements. The results presented here indicated the possibility to identify and localize damages in steel railway bridges from the variations in the modal characteristics of the structure. The comparison between the modal characteristics for the healthy and collapsed bridge confirmed that damage had been existed. The abnormal percentage of change in modal damping, between the healthy and any other condition for a structure, can be regarded as a serious indicator for early stages of damage, while the high percentage of change in modal damping can clearly indicate the existence of damage in that structure. The average ratio of change in the damping ratio from the healthy to the collapsed bridge was about 206 % and this ration could be regarded as an index for the existence of a serious damage in steel bridges, which needs further evaluation in other test cases.

  • 44.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Tu, Yongming
    College of Civil Engineering, Southeast University, Nanjing.
    Carolin, Anders
    Trafikverket.
    Loading to failure of a 55 year old prestressed concrete bridge2015Ingår i: IABSE Workshop Helsinki 2015: Safety, Robustness and Condition Assessments of Structures, Zurich: International Association for Bridge and Structural Engineering, 2015, s. 130-137Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to provide relevant data for calibration and development of methods for assessment ofexisting bridges, a 55 year old posttensioned concrete bridge has been subjected to non-destructiveand destructive tests. The bridge, located in Kiruna, Sweden, was a 121 m long girder bridgecontinuous in five spans. The test programme included failure loading of the girders and slab,respectively, condition assessment of the post-tensioned cables and material tests. Moreover, twostrengthening systems, using carbon fibre reinforcing polymer (CFRP), were evaluated. In this paperthe experimental programme and some preliminary results are presented to give an insight to researchproject.

  • 45.
    Elfgren, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bell, Brian
    UIC, Network Rail, London.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Häggström, Jens
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Tu, Yongming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. College of Civil Engineering, Southeast University, Nanjing.
    Lundgren, Karin
    Chalmers University of Technology, Department of Civil and Environmental Engineering.
    Plos, Mario
    Chalmers University of Technology, Department of Civil and Environmental Engineering.
    Larsson, Oskar
    Faculty of Engineering, LTH, Department of Constructional Sciences, Lund University.
    Casas, Joan Ramon
    Universitat Politècnica de Catalunya.
    New technologies to extend the life of elderly rail infrastructure: Deliverable 1.3 in MAINLINE - a project within the EC 7th Framework Programme2015Rapport (Refereegranskat)
    Abstract [en]

    There are many traditional technologies available to extend the life of elderly rail infrastructure, some of which are being improved or developed, whilst new technologies continue to emerge.In two earlier reports a benchmark of new technologies was given and assessment methods were presented, ML-D1.1 (2013) and ML-D1.2 (2013). In this report, ML-D1.3, an overview is given of some of the most promising new or updated technologies. Based on the findings, work in the Mainline project has focused on the following two areas for bridges, tunnels and track:- Assessment methods- Repair and Strengthening methodsSome of the methods are still under development and may not yet be available commercially. Hence these are presented on a “for information” basis and as something that may be introduced on a broader scale in a near future.In the report assessment and strengthening of bridges are treated in Chapter 4 and Chapter 5.Tunnels are treated in Chapter 6 and track and earthwork in Chapter 7.The report also includes with five appendices with details of important work that has been donein the MAINLINE project. Appendix A presents results from the assessment and full scale testing to failure of a 50 year old metallic truss bridge. Appendix B presents results from the strengthening by post-tensioning of a concrete trough bridge. Appendix C presents methods to extend life for tunnels. Appendix D proposes methods for the assessment of fatigue andAppendix E, finally, gives a fairly comprehensive list of references on how to extend the life of structures.A Guideline for application of the new technologies is given in ML-D1.4 (2014).

  • 46.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Blanksvärd, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bernspång, Lars
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sas, Gabriel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. Norut Northern Research Institute, Narvik.
    Tu, Yongming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion. College of Civil Engineering, Southeast University, Nanjing.
    Carolin, Anders
    Trafikverket, Trafikverket, Luleå.
    Performance of a prestressed concrete bridge loaded to failure2015Ingår i: IABSE Conference Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges, Geneva: International Association for Bridge and Structural Engineering, 2015, s. 1088-1095Konferensbidrag (Övrigt vetenskapligt)
  • 47.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Enochsson, Ola
    Sabourova, Natalia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Lundmark, Tore
    Ramböll Sverige AB, Luleå.
    Tu, Yongming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Protecting a five span prestressed bridge against ground deformations2015Ingår i: IABSE Conference Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges, Geneva: International Association for Bridge and Structural Engineering, 2015, s. 255-262Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A 55 year-old, 121.5 m long, five span prestressed bridge was situated in the deformation zone close to a mine in Kiruna in northern Sweden. There was a risk for uneven ground deformations so the bridge was analyzed and monitored. Results and measures taken to ascertain the robustness of the bridge are presented.The analysis resulted in an estimate that the bridge could sustain 24 mm in uneven horizontal and 83 mm in uneven vertical displacement of the two supports of a span. To be able to sustain larger deformations, the columns of the bridge were provided with joints, where shims could be inserted to counteract the settlements. To accomplish this, each one of the 18 columns of the bridge was unloaded by help of provisional steel supports. The column was then cut and a new foot was mounted to it. This made it possible to lift each individual column with two jacks, when needed, and to adjust its height by inserting or taking away shim plates.The deformations of the bridge and the surrounding ground were monitored. The eigenmodes of the bridge were studied with accelerometers and by analysis with finite elements (FE) models. Comparison indicated good agreement between the model and the actual bridge, with calculated eigenfrequencies of 2.17, 4.15 and 4.67 Hz, for the first transversal, vertical and torsional modes, respectively. Measurements during winter resulted in higher values due to increased stiffness caused by frozen materials.

  • 48.
    Bagge, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Shu, Jiangpeng
    Chalmers University of Technology.
    Plos, Mario
    Chalmers University of Technology.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Punching Capacity of a Reinforced Concrete Bridge Deck Slab Loaded to Failure2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Full-scale failure tests of a 55 year old prestressed concrete girder bridge have been carried out to calibrate models for assessment of existing bridges. This paper summarises the outcome from the punching test and analytical analysis according to the model stated in the Eurocode. The experimental load was approximately 2.4 times the code value using measured material properties.

  • 49.
    Al-Gburi, Majid
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Restraint Effects in Early Age Concrete Structures2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks.Volumetric deformations in early age concrete are caused by changes in temperature and/or the moisture state. If such movements are restrained, stresses will occur. If the tensile stresses are high enough, there will be a damage failure in tension and visible cracks arise. These stresses are always resulting from a self-balancing of forces, either within the young concrete bodyalone, i.e. without structural joints to other structures, or from the young concrete in combination with adjacent structures through structural joints.The decisive situation within a young concrete body alone is typically high stresses at the surface when the temperature is near the peak temperature within the body. This situation occur rather early for ordinary structures, say within a few days after casting for structures up to about some meters thickness, but for very massive structures like large concrete dams, it might take months and even years to reach the maximum tensile stresses at the surface. Usually this type of cracks is denoted "surface cracks", and in some cases only a temperature calculation may give a good perception to make decisions of the risk of surface cracking.On the other hand, the decisive situation within a young concrete body connected to adjacent structures, might include both risk of surface cracking at some distance away from the structural joint and risk of through cracking starting in the neighborhood of the structural joint. If the young concrete body is small in accordance to the adjacent structure, or, in other words, if thereis an overall high restraint situation in the young concrete, the risk of early surface cracking might be out of question. So, restraint from adjacent structures represents one of the main sources of thermal and shrinkage stresses in a young concrete body.This study is mainly concentrated on establishing the restraint inside the young concrete body counteracted by adjacent structures, and how to estimate the risk of through cracking based on such restraint distributions. The restraint values in the young concrete are calculated with use of the finite element method, FEM. Any spatial structure may be analyzed with respect to the level of restraint. Calculations of risk of cracking are demonstrated with use of existing compensation plane methods, and a novel method denoted equivalent restraint method, ERM, is developed for the use of restraint curves. ERM enables the use of both heating ofthe adjacent structure and/or cooling of the young concrete, which are the most common measures used on site to reduce the risk of early cracking.In a design situation many parameters are to be considered, like type of cement, different concrete mixes, temperature in the fresh concrete, surrounding temperatures, temperature in the adjacent structure, measures on site (heating/cooling/insulation), sequence order of casting.Therefore, in general a lot of estimations concerning risks of cracking are to be performed. The main objective with the present study is to develop methods speeding up and shorten the design process.Furthermore, established restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the slab, wall, and roof for the typical structure Tunnel. It has been shown that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, results from the neural network can be represented by a series of basic weight and response functions, which enables that the restraint curves easily can be made available to any engineer without use of complicated software.A new casting technique is proposed to reduce restraint in the newly cast concrete with a new arrangement of the structural joint to the existing old concrete. The proposed technique is valid for the typical structure wall-on-slab using one structural joint. This casting method means that the lower part of the wall is cast together with the slab, and that part is called a kicker. It hasbeen proven by the beam theory and demonstrated by numerical calculations that there is a clear reduction in the restraint from the slab to the wall using kickers.Restraint is affected by casting sequence as well as boundary conditions and joint position between old and new concrete elements. This study discusses the influence of different possible casting sequences for the typical structure wall-on-slab and slab-on-ground. The aim is to identify the sequence with the lowest restraint to reduce the risk of cracking.

  • 50.
    Patil, Aniket
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sand, Björnar
    Norut Northern Research Institute, Narvik.
    Fransson, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Smoothed particle hydrodynamics and continuous surface cap model to simulate ice rubble in punch through test2015Ingår i: Proceedings of the 23nd International Conference on Port and Ocean Engineering under Arctic Conditions: POAC 2015, Trondheim, Norway; 14-18 June 2015, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Recent trend in computational mechanics shows considerable development of numerical methods to simulate discrete materials such as ice rubble. Ice rubble has highly nonlinear behavior and to simulate shear properties requires a new numerical method. An attempt has been made to simulate a punch through test using the Lagrangian mesh-free partial based method formulation known as smoothed particle hydrodynamics. A newly implemented material model in LS-Dyna called the continuous surface cap model has been used in this simulation. A continuous surface cap model based on a combination of elastic-plastic and continuum damage mechanics formulation is used as constitutive model for ice rubble. The material model parameters are chosen to get best fit to test load displacement curve. A brief overview of the smoothed particle hydrodynamics is given. Finally, the results from simulations have compared with experimental results.

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