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  • 251.
    Gille, Marika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Design of Modularized Data Center with a Wooden Construction2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this thesis is to investigate the possibility to build a modular data center in wood. The goals is to investigate how to build data centers using building system modules, making it easier to build more flexible data centers and expand the business later on. Investigations have been conducted to find out advantages and disadvantages for using wood in a modularized data center structure. The investigation also includes analysing the moistures effect on the material and if there are any other advantages than environmental benefits in using wood as a building material.

    A literature study were conducted to examine where research already have been conducted and how those studies can be applicable to this thesis. Although the ICT sector is a rapidly growing industry little research has been published in regards to how to build a data center. Most published information involves electric and cooling, not measurements of the building and how materials is affected by the special climate in a data center. As a complement to the little research interviews were conducted and site visits were made. Interviews were conducted with Hydro66, RISE SICS North, Sunet and Swedish modules, whilst site visits were made at Hydro66, RISE SICS North, Sunet and Facebook.

    As a result of these studies, limitations were identified with regards to maximum and minimum measurements for the building system and service spaces in a data center. These limitations were used as an input when designing a construction proposal using stated building systems and a design proposal for a data center.

    During the study, access have been granted to measurements of temperature and humidity for the in- and outgoing air of the Hydro66 data center. These measurements have been analyzed with the facts about HVAC systems and the climates effect on wood, for example in regards to strength and stability. This analysis has shown that more data needs to be collected during the winter and that further analysis needs to be conducted, to beable to draw conclusions if the indoor climate of a data center has an effect on the wooden structure.

    A design proposal for a data center have been produced with regards to the information gathered by the litterature and empirical studies. The proposal were designed to show how the information could be implemented. The result have increased the understanding on how to build data center buildings in wood and how this type of buildings could be made more flexible towards future changes through modularization.

  • 252.
    Girardin, Bertrand
    et al.
    R2Fire/UMET − UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev - Bât. C7a, CS 90108, 59652, Villeneuve d'Ascq, France.
    Fontaine, Gaëlle
    R2Fire/UMET − UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev - Bât. C7a, CS 90108, 59652, Villeneuve d'Ascq, France.
    Duquesne, Sophie
    R2Fire/UMET − UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev - Bât. C7a, CS 90108, 59652, Villeneuve d'Ascq, France.
    Försth, Michael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. SP Fire Research, SP Technical Resesarch Institute of Sweden.
    Bourbigot, Serge
    R2Fire/UMET − UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev - Bât. C7a, CS 90108, 59652, Villeneuve d'Ascq, France.
    Measurement of kinetics and thermodynamics of the thermal degradation for flame retarded materials: application to EVA/ATH/NC2017In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 124, p. 130-148Article in journal (Refereed)
    Abstract [en]

    The modelling of the behavior of a material exposed to fire is very complex and needs the coupling of fluid dynamics, combustion, heat and mass transfer, kinetics and so forth. A growing amount of studies and numerical models are reported in this field since the last decade. The aim of these models is to predict the fire behavior of wood, charring or non-charring polymers and even intumescent materials. However, these studies are seldom applied to formulated materials and especially flame retarded materials. In this study, an ethylene-vinyl acetate copolymer was formulated with a flame retardant (aluminum tri-hydroxide) and a synergist (nanoclays). A systematic approach for the characterization of the thermo-physical properties of the material as well as of its optical properties and the heat capacity of the decomposition gases is proposed and applied in this study. It is shown that it is possible to evaluate the input data required for pyrolysis modelling, even for multi decomposition steps materials. It is also shown that the diffusion of the gases inside the material had to be considered on the opposite of the classical assumption found in other studies. Indeed, using low mass diffusivity was the sole way to predict in the same time the temperature distribution and the mass loss rate of the material in a gasification experiments.

  • 253.
    Girardin, Bertrand
    et al.
    R2Fire Group/UMET-UMR CNRS 8207, Ecole Nationale Supérieure de Chimie de Lille, Unité Matériaux et Transformations (UMET), École Nationale Supérieure de Chimie de Lille, University of Lille.
    Fontaine, Geêlle
    R2Fire / UMET – UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev – Bât. C7a, CS 90108, 59652 Villeneuve d’Ascq, Unité Matériaux et Transformations (UMET), École Nationale Supérieure de Chimie de Lille, University of Lille.
    Duquesne, Sophie
    R2Fire / UMET – UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev – Bât. C7a, CS 90108, 59652 Villeneuve d’Ascq, Unité Matériaux et Transformations (UMET), École Nationale Supérieure de Chimie de Lille, University of Lille.
    Bourbignot, Serge
    R2Fire / UMET – UMR CNRS 8207, ENSCL, Avenue Dimitri Mendeleïev – Bât. C7a, CS 90108, 59652 Villeneuve d’Ascq, Unité Matériaux et Transformations (UMET), École Nationale Supérieure de Chimie de Lille, University of Lille.
    Försth, Michael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Characterization of thermo-physical properties of EVA/ATH: Application to gasification experiments and pyrolysis modeling2015In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, no 11, p. 7837-7863Article in journal (Refereed)
    Abstract [en]

    The pyrolysis of solid polymeric materials is a complex process that involves both chemical and physical phenomena such as phase transitions, chemical reactions, heat transfer, and mass transport of gaseous components. For modeling purposes, it is important to characterize and to quantify the properties driving those phenomena, especially in the case of flame-retarded materials. In this study, protocols have been developed to characterize the thermal conductivity and the heat capacity of an ethylene-vinyl acetate copolymer (EVA) flame retarded with aluminum tri-hydroxide (ATH). These properties were measured for the various species identified across the decomposition of the material. Namely, the thermal conductivity was found to decrease as a function of temperature before decomposition whereas the ceramic residue obtained after the decomposition at the steady state exhibits a thermal conductivity as low as 0.2 W/m/K. The heat capacity of the material was also investigated using both isothermal modulated Differential Scanning Calorimetry (DSC) and the standard method (ASTM E1269). It was shown that the final residue exhibits a similar behavior to alumina, which is consistent with the decomposition pathway of EVA/ATH. Besides, the two experimental approaches give similar results over the whole range of temperatures. Moreover, the optical properties before decomposition and the heat capacity of the decomposition gases were also analyzed. Those properties were then used as input data for a pyrolysis model in order to predict gasification experiments. Mass losses of gasification experiments were well predicted, thus validating the characterization of the thermo-physical properties of the material

  • 254.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Deformationskapacitet hos balk-pelarinfästningar vid linbärverkan och skadetålighet hos dynamiskt överpåverkande konstruktioner1979Report (Other academic)
  • 255.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dynamic deformations of elasto-plastic two-span beams subjected to loss of interior support: a comparative study of different calculation methods1978Report (Other academic)
  • 256.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dynamic fail-safe behaviour of steel structures1980Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The fundamental behaviour and the capacity of steel structures subjected to loss of interior load-bearing elements are studied. The ultimate load-bearing and deformation capacity of certain beam-to-column connections and the dynamic fail-safe behaviour of some ordinary steel structures are investigated in detail. A number of different geometrical models of steel structures in the area of primary damage are analysed. Both bending and catenary action of the models are treated and the strength properties of both members and connections are considered. Two types of connections are investigated, viz. the "bolted heel connection" and the bolted end-plate connection (with a degree of moment rigidity of 25%). No stability problems are treated. A rigid-body method of analysis is applied. Design methods for the bolted heel and bolted end-plate connections under catenary action are proposed, which safely predict the over-all behaviour and the ultimate load-bearing and deformation capacity of each connection. For structures having these two types of connections, the static damage endurance capacity under catenary action is approximately equal. The applicability and accuracy of the riqid-body method is evaluated. The accuracy is determined by comparison with an elasto-plastic vibration theory and an equivalent mass-spring method. The rigid-body model proves to be a suitable model in order to determine the failsafe behaviour of most steel structures. The ultimate dynamic load-bearing capacity under bending action regarding member characteristics and under catenary action regarding partly member characteristics and partly joint characteristics is evaluated in great detail. It is found that the dynamic capacity under bending action approximately equals the static one provided that the greater deformations obtained under dynamic conditions can be absorbed. No regard to the time of removal of the load-bearing element is thus necessary if only the deformation capacity of the structure is verified. Also, strain-hardening effects and geometrical non-linearity need not be considered. The dynamic capacity under catenary action regarding member characteristics is only half of the static one, and regarding joint characteristics only one third of the static one for structures with bolted heel connections, and half of the static one for structures with bolted end-plate connections. The high efficiency of catenary action compared to bending action found under static conditions, is reduced considerably under dynamic conditions. For many practical cases only full end constraints, momentary loss of load-bearing elements and geometrical linearity need to be considered. The maximum column reactions at ultimate dynamic load always fall below the maximum reactions at ultimate static load. Deflections and reactions determined theoretically from the rigid-body models employed agree well with those measured.

  • 257.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dynamisk överpåverkan på stålkonstruktioner: en problemöversikt1976Report (Other academic)
  • 258.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    General dynamic analysis of elasto-plastic structures with stationary plastic hinges1978Report (Other academic)
  • 259.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    On the boundary and matching conditions for dynamic beam element systems1978Report (Other academic)
  • 260.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rabo - väggelement1980Report (Other academic)
  • 261.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Samverkanskonstruktioner i trä1983Report (Other academic)
  • 262.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ultimate capacity of beam-column connections in damaged steel structures1987In: Proceedings of the International Conference on Steel and Aluminium Structures: Composite steel structures : advances, design and construction ; [proceedings of the International Conference on Steel and Aluminium Structures, Cardiff, UK, 8 - 10 July 1987] / [ed] R. Narayanan, London: Elsevier, 1987, p. 835-844Conference paper (Refereed)
    Abstract [en]

    An experimental study is presented of the ultimate force-deformation capacity of two types of beam-column connections commonly used in Sweden. The behaviour of the structural joints was investigated for damaged steel structures (due to a column collapse), which are capable of developing catenary action. For each type of connection, the idealized overall behaviour and ultimate capacity of the joint are discussed.

  • 263.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Atashipour, Seyed Rasoul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    A study on shear deformations of deep composite box-Type beams used in timber building structures2013In: Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, 3-6 September 2013, Cagliari, Sardinia, Italy / [ed] Barry H.V. Topping; Peter Ivaniy, Stirlingshire: Civil-Comp Press , 2013Conference paper (Refereed)
    Abstract [en]

    The higher-order shear deformation beam theory of Reddy-Bickford predicts accurately the shear deflection without the need of a shear correction factor. However, for more complicated cross-sections, e.g. including holes, it is shown that this theory is not adequate. To be able to predict accurately the shear deflections of deep composite box-type cross-sectional beams, a simple engineering approach is used to derive a closed-form expression for the shear correction factor for those types of beams. The high accuracy and reliability of the developed procedure is demonstrated by comparing those results with accurate three-dimensional finite element results and with Timoshenko and Reddy-Bickford theories. A comprehensive parametric study is presented to investigate the effects of various mechanical properties and geometric dimensions of the box-type of beams for the various models. There is very good agreement between the proposed engineering method and the three-dimensional finite element model

  • 264.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Atashipour, Seyed Rasoul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Analysis of shear deflections of deep composite box-type of beams using different shear deformation models2015In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 155, p. 42-53Article in journal (Refereed)
    Abstract [en]

    The deflection of deep box-type elements due to shear deformations is treated. A closed-form expression for the shear correction factor is derived by using an energy approach. The high accuracy and reliability of the developed procedure is demonstrated by comparing its results with accurate 3-D finite element results and also with the results of the conventional theories of Timoshenko with constant shear coefficient and of Reddy–Bickford applied to this kind of cross-section. A comprehensive and comparative parametric study is presented to investigate the effects of various mechanical properties and geometric dimensions for the different models. Unlike the higher-order shear deformation theories, which are accurate only for beams with rectangular cross-sections, there is a very good agreement between the results of the proposed method and the 3-D FE model. Clearly, the proposed energy method is applicable to more complicated cross-sections, including those with abrupt changes in the geometry, e.g. due to holes.

  • 265.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Daerga, Per-Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Källsner, B.
    Linnéuniversitetet.
    Recommendations for design of anchoring devices for bottom rails in partially anchored timber frame shear walls2011In: 11th World Conference on Timber Engineering 2010, WCTE 2010, Red Hook: Curran Associates, Inc., 2011, Vol. 2, p. 1218-1227Conference paper (Refereed)
    Abstract [en]

    The authors have developed a new plastic design method for light-frame timber shear walls. The method is capable of analyzing the load-bearing capacity of partially anchored shear walls. For proper application of the plastic method it is necessary to ensure ductile behaviour of the sheathing-to-framing joints and to avoid brittle failure of the bottom rail in particular. In a partially anchored shear wall the leading stud is not fully anchored against uplift and corresponding tying down forces are developed in the sheathing-to-framing joints along the bottom rail in the sheathing segments close to the leading stud. These tying down forces in the joints may introduce a number of possible brittle failure modes or serviceability problems for the bottom rail that need to be eliminated or restricted in order for the plastic method to be applicable. This paper describes experimental results for proper design of washers or bearing plates for the anchor bolts in order to avoid splitting failure of and excessive washer indentation into the bottom rail. Specimens with both double and single sided sheathing and different locations of anchor bolts are studied. With respect to splitting of the bottom rail, the tests indicate that the failure load depends on the distance from the edge of the washer to the loaded edge of the bottom rail. With respect to large deformations due to bearing stresses of the washers of the anchoring bolts, the size of the washer is the most important parameter. The test results indicate that the bearing strength for large washers is lower than that proposed by Eurocode 5. In this paper, it is therefore proposed to make the bearing strength inverse proportional to the diameter or side length of the washer. Then, good agreement with the test results was found. The results show that failure due to splitting is the determining design mode.

  • 266.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Gopu, Viljayak A.
    Luleå tekniska universitet.
    Analysis of the P-d effect in composite beam-columns of timber and concrete1986Report (Other academic)
  • 267.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Gustafsson, P.J.
    Department of Building Sciences, Lund Institute of Technology.
    Källlsner, Bo
    School of Engineering, Linnæus University, Växjö.
    Finite element modelling of shear walls using connector shear elements based on continuum plasticity2010In: Proceedings of the Tenth International Conference on Computational Structures Technology: Valencia, Spain, 14 - 17 September 2010, Klippen: Civil-Comp Press , 2010Conference paper (Refereed)
    Abstract [en]

    Light-frame timber buildings are often stabilised against lateral loads by using diaphragm action of roofs, floors and walls. The mechanical behaviour of the sheathing-to-timber joints has a significant impact on the structural performance of shear walls. Most sheathing-to-framing joints show non-linear load-displacement characteristics with plastic behaviour. This paper is focused on the finite element modelling of shear walls. The purpose is to present a new connector shear element based on the theory of continuum plasticity. The incremental load-displacement relationship is derived based on the elastic-plastic stiffness tensor including the elastic stiffness tensor, the plastic modulus, a function representing the yield criterion and a hardening rule, and another function representing the plastic potential. The plastic properties are determined from experimental results obtained from testing actual connections. Load-displacement curves for shear walls are calculated using the connector shear model and they are compared with experimental and other computational results. Also, the ultimate horizontal loadcarrying capacity is compared to results obtained by an analytical plastic design method. Good agreements are found

  • 268.
    Girhammar, Ulf Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Juto, Henrik
    Provning av tvärböjning och spjälkning av syllen i partiellt förankrade skiv-regelväggar2014Report (Other academic)
  • 269. Girhammar, Ulf Arne
    et al.
    Källsner, Bo
    Linnéuniversitetet.
    Andreasson, Sverker
    Plasisk dimensionering av horisontalbelastade skiv-regelstommar i trä2010In: Samhällsbyggaren, ISSN 2000-2408, no 5, p. 45-48Article in journal (Other (popular science, discussion, etc.))
  • 270.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Experimental investigation on RC beams strenghened in shear with  externally bonded composites2016In: Eighth International Conference onFibre-Reinforced Polymer (FRP) Composites in Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, p. 384-389Conference paper (Refereed)
    Abstract [en]

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

  • 271.
    Gonzalez-Libreros, Jaime
    et al.
    Department of Civil, Environmental and Architectural Engineering, University of Padua.
    Sabau, Cristian
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sneed, Lesley
    Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology.
    Pellegrino, Carlo
    Department of Civil, Environmental and Architectural Engineering, University of Padua,.
    Sas, Gabriel
    Department of Infrastructure, Materials and Structural Engineering, NORUT.
    Shear strengthening of RC beams with FRCM: what do we know so far?2016In: Eighth International Conference onFibre-Reinforced Polymer (FRP) Compositesin Civil Engineering / [ed] J.G. Teng and J.G. Dai, Hong Kong, China: The Hong Kong Polytechnic University , 2016, p. 462-467Conference paper (Refereed)
    Abstract [en]

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

  • 272. Gozzi, Jonas
    Patch loading resistance of plated girders: ultimate and serviceability limit state2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Patch loading or partial edge loading of steel girder webs is a load case where a concentrated force is introduced perpendicular to the flange of a girder. This usually induces a local failure of the girder web in the vicinity of the loaded flange. In structural applications concentrated forces are a common load case for girders introduced for example; at supports, by purlins, from crane wheels and during launching of bridges. For fixed loads, the problem of concentrated forces are usually solved by transverse stiffeners but for moving loads this is nor practically possible neither an economical solution. Further, it would be possible to use longitudinal stiffeners when the load is moving but stiffeners are expensive to fit and for girders with web depth below 3 m longitudinally stiffeners are not economically justified. Instead, the girder web itself has to resist the applied load in such cases. From the fifties and later a large amount of studies on this subject have been performed, starting with investigations on the elastic buckling of plates where only a part of the edge was loaded and followed by many test series and resistance functions. The earlier proposed resistance models were usually divided into two separate checks, one for yielding and one for instability. However, the test results do not show of any clear distinction between those two cases. This thesis deals with patch loading of plated girders without longitudinal stiffeners in both the ultimate and the serviceability limit state. A resistance model in the ultimate limit state is proposed, that have a continuous transition from yielding to buckling and hence, that is harmonized with the procedure for other buckling problems. The model contains three significant parts; the yield resistance, the elastic buckling load used to establish the slenderness and a reduction factor that relates the slenderness to the actual resistance. The advantage with the design model presented herein, which is a modification of the work presented by Lagerqvist and later introduced in EN 1993-1-5, is that the same equations are used irrespective of failure mode. The in this thesis proposed design procedure for patch loading gives a better accuracy of the predicted resistance compared to the design rule in EN 1993-1-5. Most of the experimental studies performed by others contain tests with very short loaded lengths, i.e. very concentrated loads. In order to gain more knowledge of the influence of the loaded length, three patch load tests were conducted where only the loaded length was varied. By means of the test results and a parametric study with the finite element method it was concluded that the variation in loaded length could be well described by the design procedure proposed in this thesis. For a bridge girder, the problem concerning resistance to patch loading usually occurs during launching. Bridge launching is a common method to erect steel and composite bridges and means that the bridge girders are assembled on ground behind the abutment and then pushed out over launching shoes into the final position. The launching shoe on which the girder travels will introduce a concentrated force to the girder, which can be of a magnitude that governs the web thickness and even a small increase of the web thickness can add a substantial amount of steel. Therefore, it is important to find a suitable criterion for the serviceability limit state for patch loading, i.e. for bridge launching. Compared to the ultimate resistance the amount of available research considering the serviceability limit state is very small. In fact, only one serviceability limit criterion proposed by Granath, which was developed for stationary loadings, was found. A number of FE-analyses of the launching process were carried out to investigate at what loads different girder cross sections will have a repeatable behaviour. A girder section of a bridge girder was subjected to several repeated travelling loads corresponding to a long bridge girder launched over several supports together with a co-existing bending moment. By means of these FE-analyses a serviceability criterion is established with a limit criterion not allowing any effective plastic membrane strains. The bridge designer can beneficially use the proposed serviceability criterion for bridge launching.

  • 273. Gozzi, Jonas
    Plastic behaviour of steel: experimental investigation and modelling2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the plastic behaviour of steel. It comprises an investigation with focus on biaxial tests and constitutive modelling. Tests were performed on one stainless steel grade in two different strength classes, C700 and C850, as well as one extra high strength structural steel grade. An earlier developed concept for biaxial testing of cross-shaped specimens was utilised. However, there was a demand for new specimen designs to enable testing of the extra high strength steel. A comprehensive test programme including an initial and one subsequent loading was carried out. This provides data for stress-strain curves in two steps as well as stress points describing initial and subsequent yield criteria. The Bauschinger effect was evident for all grades. Furthermore, the behaviour in subsequent loadings was found to be direction dependent and the transition from elastic to plastic state was observed as gradual. A constitutive model with the possibility of depicting the phenomenological observations from the tests was earlier developed at Steel Structures, LTU, and proposed for annealed stainless steels. Further, it is a two surface model utilising the concept of distortional hardening and it was applied to the steel grades tested in this work. The model was found to be applicable to the steels tested in this study as well and compared to simpler models the applied model clearly improves the agreement with experimental tests.

  • 274. Gozzi, Jonas
    et al.
    Olsson, A.
    Extra high strength steel plasticity: experimental work and constitutive modelling2005In: Advances in steel structures: proceedings of the fourth International Conference on Advances in Steel Structures / [ed] Z. Y. Shen, Amsterdam: Elsevier, 2005, p. 1571-1576Conference paper (Refereed)
  • 275. Gozzi, Jonas
    et al.
    Olsson, A.
    Swedish Institute of Steel Construction.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Experimental investigation of the behavior of extra high strength steel2005In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 45, no 6, p. 533-540Article in journal (Refereed)
    Abstract [en]

    This paper comprises a study concerning the mechanical behavior of extra high strength steel. This is investigated by means of biaxial testing of flat cross-shaped specimens in the full σ1-σ2 plane, a concept developed earlier at Steel Structures, Luleå University of Technology. Furthermore, new specimen designs had to be developed to enable testing of a material with high yield strength and low ultimate over yield strength ratio, such as the extra high strength steel Weldox 1100. The tests are performed in two steps: one initial loading followed by unloading and a subsequent loading in a new direction. The test results, containing data from 15 biaxial tests, are characterized by a slightly anisotropic initial yield criterion where the proof stress in compression is consequently somewhat higher compared to the results in tension. In the subsequent loading the observed phenomena are a Bauschinger effect in the direction opposite the initial loading direction and that the transition from elastic to plastic state in subsequent loadings is gradual and direction-dependent.

  • 276. Gozzi, Jonas
    et al.
    Olsson, Anders
    Stainless steel: plasticity and constitutive modelling2003In: Stainless Steel in Structures: International Experts Seminar 20th May 2003, Ascot, UK. Proceedings, 2003, p. 115-122Conference paper (Refereed)
    Abstract [en]

    This paper presents a constitutive model proposed for stainless steel. The model is a two surface model utilizing the concept of fuzzy sets. An experimental investigation has been performed on two differentstainless steel grades as a reference to the model. The tests were performed with a procedure containing load reversal. Each specimen was initially loaded in one direction of the principal stress plane followed by unloading and subsequent loading in a new direction. The model is relatively simple but still depicts the effects of observed phenomena such as the Bauschinger effect. Hence the qualitative response to subsequent loadings can be described with the model. The proposed model has been implemented into the finite element package ABAQUS. Comparisons between test results and the response predicted utilizing the model are presented in this paper.

  • 277.
    Graciano, Carlos
    Luleå tekniska universitet.
    Patch loading: resistance of longitudinally stiffened steel girder webs2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In most cases, longitudinal stiffeners increase the resistance of steel girder webs subjected to concentrated forces, commonly referred to as patch loading. During the last three decades, a number of experimental investigations have been undertaken in all over the world in this regard. The test results shows that the patch loading resistance increases when a longitudinal stiffener is placed rather close to the loaded flange, however very little has been done to quantify this increase which in most design codes has been disregarded. At first the effect of a longitudinal stiffener on the structural behaviour of plate girder webs subjected to patch loading is investigated by means of nonlinear finite element analysis. Two plate girders with extreme values for the flange-to-web thickness ratio were modelled taken into account material and geometrical nonlinearities. The numerical results were validated with test results from others. Thereafter, a parametric study was conducted in order to investigate the relevance of some parameters such as the relative position and flexural rigidity of the stiffener and the size of the loaded flange in increasing the ultimate resistance of the steel girder webs to patch loading. In the past, it has been customary to calculate the patch loading resistance of the girder web with a longitudinal stiffener by multiplying the corresponding resistance of the unstiffened girder web (web only with transversal stiffeners) with a correction factor, obtained by a regression analysis, depending mainly on the relative location of the stiffener. Herein, a sensitivity analysis was conducted showing also the relevance of the flange-to-web thickness ratio and the ratio of the yield strength of the flange to the yield resistance of the web. Accordingly, a new correction factor was proposed taken into account the aforementioned parameters. The failure mechanism of longitudinally stiffened girder webs subjected to patch loading observed in the experiments is similar to that of unstiffened girder webs. This is characterised by the presence of elastoplastic deformation in the patch loaded flange (plastic hinges) and in the web (yield lines). From this deformed configuration, a mechanism resembling the distortions in the web plate and loaded flange was developed in order to obtain the patch loading resistance of longitudinally stiffened girder webs. This failure mechanism model fails in that the actual material and geometrical properties of the stiffener are not taken into account and certain assumptions are accordingly made to overcome this situation. In the latest edition of the Eurocode 3 Part 1.5 the patch loading resistance of unstiffened girder webs is obtained using a resistance reduction factor applied to the yield resistance to patch loading. This factor depends on a slenderness parameter, which is the square root of the ratio of the yield resistance to the critical buckling load (according to classical theory of elasticity) for patch loading. However, the interaction with longitudinal stiffening is not considered. In some respect the use of a longitudinal stiffener is comparable with a reduction in the slenderness ratio of a girder web. An expression is found for the buckling coefficient used for calculating the critical buckling load for patch loading based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener (open and closed section) was considered in the numerical analysis. Consequently, the critical buckling load increases due the presence of the stiffener and then the slenderness parameter is reduced. This leads to an increase in the patch loading resistance. Finally, the results obtained using the methodologies described above and those found in the literature are compared with available tests results. The goodness and flaws of each methodology are further discussed.

  • 278.
    Graciano, Carlos
    et al.
    Luleå tekniska universitet.
    Johansson, Bernt
    Resistance of longitudinally stiffened I-girders subjected to concentrated loads2003In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 59, no 5, p. 561-586Article in journal (Refereed)
    Abstract [en]

    This paper presents a design procedure for the determination of the ultimate resistance of longitudinally stiffened girder webs to concentrated loads. The influence from the longitudinal stiffener is considered in the slenderness parameter λ, through the buckling coefficient kf. This procedure is harmonized with other design procedures currently used for describing buckling problems in steel structures. An expression is developed for the buckling coefficient based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener was considered in the analysis. The ultimate strength according to the design procedure presented herein and the results are compared with available experimental results. The interaction with bending is also investigated

  • 279.
    Granath, Per
    et al.
    Chalmers University of Technology.
    Lagerqvist, Ove
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Behaviour of girder webs subjected to patch loading1999In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 50, no 1, p. 49-69Article in journal (Refereed)
    Abstract [en]

    This paper concerns the behaviour of bridge girder webs subjected to concentrated forces that are introduced in the web during launching, a load case usually referred to as patch loading. So far, this type of loading has, in engineering practice, been dealt with using formulas originating from investigations concerning the ultimate load carrying capacity. Numerous bridge launchings have, however, led to unwanted damages of the girder web, i.e. plastic deformations of such magnitudes that the webs had to be repaired. To avoid these damages it is necessary to have a design method, for launching situations, which focuses more on avoiding some irreversible behaviour than on the ultimate load carrying capacity. Such a design method has to be based on a deeper understanding of the behaviour of the girder. In Ref. [1] the first author discusses the fact that yielding of the flange occurs only after the web plate has been severely damaged. This paper describes the deformation behaviour of the web plate due to patch loading. For small loads the deformations will be similar to the first linear buckling mode. As the load increases a smaller buckle, in the opposite direction, will start to develop in the web plate close to the load. This behaviour, which may be named post-critical buckling, occurs also for girders of a perfectly elastic material. The investigations are based on laboratory tests and non-linear finite element analyses of three typical girders representing different slenderness categories.

  • 280.
    Granlund, Jan
    Luleå tekniska universitet.
    Structural steel plasticity: experimental study and theoretical modelling1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [sv]

    Föreliggande avhandling behandlar konstitutiv modellering av konstruktionsstål i elastoplastiskt område. Ett koncept för tvåaxlig provning i huvudspänningsplanet har utvecklats vilket sedan har använts för att generera försöksdata för att formulera en konstitutiv modell för sambandet mellan spänningar och plastiska töjningar. Utgångspunkten har varit att söka en modell som på ett bättre sätt beskriver stålets beteende än de modeller man normalt använder i finita elementmetoder idag. De modeller som normalt används idag klarar egentligen inte av att beskriva materialets beteende vid annat än monoton pålastning. Vid påföljande avlastning och förnyad pålastning i annan riktning, såsom exempelvis kallformning, har en betydande anisotropi introducerats vilket gör att man sannolikt erhåller ett dåligt resultat. Skälen till att man i många sammanhang använder dessa modeller, t.ex. isotropt eller kinematiskt hårdnande, är bl.a. att försöksdata som underlag saknas för mer avancerade modeller. Det koncept för tvåaxlig provning av plan plåt i leveranstillstånd med korsformade provkroppar som har utvecklats, kan med anbringande av stödplåtar för att förhindra buckling ut ur planet genomföra provning i hela huvudspänningsplanet. Denna utrustning har använts för att utföra omfattande provning av två olika stålsorter, en höghållfast och en av normal hållfasthet. Konceptet klarar i det aktuella utförandet töjningar upp till drygt 3%. Initiellt flytvillkor samt påföljande flytvillkor för två olika förbelastningsnivåer samt förändringen av den plastiska modulen har studerats. Vidare har även kvalitativa studier av den plastiska flytlagen gjorts. Resultaten visar att det initiella flytvillkoret faller mellan det som förutspås av von Mises och Trescas villkor. Vad påföljande flytvillkor beträffar visar resultaten att man har en påtaglig Bauschingereffekt, dvs. en reduktion av flytgränsen i riktning rakt motsatt pålastningen. Vinkelrätt pålastningsriktningen hårdnar materialen i nästan samma omfattning som i pålastnings~ riktningen. Man tydligt se att vid återpålastning så fås en gradvis övergång från elastiskt till plastiskt tillstånd även om materialet initiellt har en skarp övergång däremellan. Ett förslag till en konstitutiv modell presenteras. Modellen använder en elastisk gränsyta samt en minnesyta. Den gradvisa övergången mellan elastiskt och plastiskt tillstånd vid återpålastning beskrivs med en teori grundad på sk "fuzzy sets". Den elastiska gränsytan beskrivs med teori för distortionshårdnande vilket ger goda möjligheter att beskriva Bauschingereffekten vid generella spänningstillstånd. Modellen kräver bara två ytterligare parameter jämfört med en enkelytemodell med blandat hårdnande varför den är enkel att använda. Jämförelser mellan experimentella data och simuleringar med den föreslagna modellen visar på god överensstämmelse generellt. Jämförelser med existerande modeller visar också att betydande förbättringar av beskrivningen erhålls. Speciellt tydligt är detta för det höghållfasta stålet där det dominerande bidraget till hårdnandet kommer från Bauschingereffekten.

  • 281.
    Granlund, Jan
    Luleå tekniska universitet.
    The yield point phenomenon of structural steel: experimental and phenomenological aspects1993Licentiate thesis, monograph (Other academic)
  • 282.
    Granlund, Jan
    et al.
    Luleå tekniska universitet.
    Olsson, Anders
    Luleå tekniska universitet.
    A method for determining parameters for a steel plasticity model using biaxial testing1998In: Proceedings / Nordic Steel Construction Conference 98: Bergen, Norway, September 14th - 16th, 1998 ; new materials, new codes, new applications, Oslo: Norwegian Steel Association , 1998, p. 763-773Conference paper (Refereed)
    Abstract [en]

    This paper proposes three different test programs, with varying degrees of experimental effort, for the determination of model parameters for a steel plasticity model proposed by Granlund(1997). The proposed programs are based on the experiences from the extensive biaxial testing that has been performed by the authors. The biaxial testing comprised five steel grades. Two structural, Granlund(1997), and three stainless steel grades, Olsson(1998). The biaxial testing has been performed utilizing a unique testing equipment, developed at the Division of Steel Structures, Lulea University of Technology, that allows for testing in the full principal stress plane sigma sub 1 - sigma sub 2 , i.e. also in compression. The use of the plasticity model is most advantageous in cases where stress reversals can occur, such as for instance in buckling problems, but it can also be beneficial in simpler cases including e.g. residual stresses caused by welding. The model does compared to a simple plasticity model utilizing isotropic hardening only require three additional parameters and thus it has the potential of being practically used. Materials: S275, Domex 690, 304 and 2205 steel

  • 283.
    Granlund, Jan
    et al.
    Luleå tekniska universitet.
    Olsson, Anders
    Modelling of the plastic behaviour of structural steel based on biaxial testing1998In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 46, no 1-3, p. 404-405Article in journal (Refereed)
    Abstract [en]

    The biaxial testing of structural steel in the principal plane σ1-σ2 is presented. The initial yield criterion of the steel falls between the von Mises and Tresca criteria. The subsequent yield criteria are characterized by a pronounced Bauschinger effect and more gradual transition into plastic state in subsequent loading opposite to preloading.

  • 284.
    Granlund, L.J.
    Luleå tekniska universitet.
    Biaxial testing of structural steel with cross shaped specimen1995In: Nordic Steel Construction Conference '95: proceedings : [new materials, new codes, new applications] : Malmö, Sweden, June 19-21, 1995, Stockholm: Stålbyggnadsinstitutet , 1995, p. 49-56Conference paper (Refereed)
    Abstract [en]

    The rapid development of computer capacity makes it possible to perform more and more complicated design calculations. The accuracy obtained in such calculations depends on the correctness of the material model that is used. The number of theoretical models and concepts available are more than sufficient, but no model that can describe the characteristic behaviour of structural steel in a proper way can be found. This paper presents a concept for biaxial testing of flat products in structural steel that can provide the necessary parameters for a model. The frame is a two cylinder self aligning concept designed at the Division of Steel Structures at the University of Technology in Lulea, Sweden. The results of a preliminary series of tests are presented in which the initial yield criterion and the flow rule are studied. The material chosen is Domex240YP which is a mild hot rolled sheet steel similar to S235 but also suitable for cold forming.

  • 285.
    Grip, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Southeast University, Nanjing.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Vibrationsanalys för tillståndsbedömning av byggkonstruktioner: Tillämpningsexempel : (Main results and summary in Swedish. Detailed results in English Appendices.)2017Report (Other academic)
    Abstract [en]

    In the project,methods are presented and appliedfor assessment ofdifferent types ofbuilding structures with and without damages.The assessmentis done withhelp ofvibration analysis.Detection of defects of different types and sizes are discussed. The influence of boundary conditions isstudied in order to get agreement between predicted and measured Eigen modes and Eigen frequencies.With the program that has been developed,is it now possible to detect cracks in simple concrete structures with help of measurements of vibrations. For more advanced structures there is a potentialto further develop the program. Measurements and analyses have been made for fivestructures:(1) A concrete slab–Cracks have been detected based on vibrationmeasurementsand a successivelyupdated Finite Element Model (FEM).(2) Aconcrete archbridge at Långforsen in Kalix River-Unknown boundary conditions havebeen possible todetermine with help of vibration measurementsregarding for example foundation properties. Detection of specific damages hasnot yet been possible.(3) A steel truss bridge over Åby River–Some detection of damages hasbeen possible to carry outwith Finite Element Model updatingregarding corrosion and mechanical damages.. (4) A prestressed concrete bridge to the mine in Kiruna-Several models of theundamaged and damagedbridgehave been established and they have been calibrated to measured vibration propertieswith good results.(5) A nine storey concrete building in Luleå–A FEM model has been developedfor the serviceability limit stateand results from it has been compared to measured vibrationswith good results.A general presentation is given ofthe developedmethods and resultsin the main text. Detailed descriptions are provided in Appendices.A program is presented with ready-to-use models for the studied structures. The program may be downloaded and is presented in detail in an Appendix.

  • 286.
    Grundberg, Staffan
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    A comparison of exact and approximate analyses of partially interacting composite Beam-Columns2015In: Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing / [ed] J. Kruis; Y. Tsompanakis; B.H.V. Topping, Stirlingshire: Civil-Comp Press , 2015, article id 261Conference paper (Refereed)
    Abstract [en]

    This paper deals with deflection analysis of a deep composite box beam due to inplane shear deformations, especially the modelling of the shear deformations in the webs is considered. The beam is composed of three framing members with sheathings on both sides. The sheathings or webs between the framing members are modelled as shear media with equivalent slip moduli corresponding to the partially composite beam model with three separated layers and two interlayer slip areas. The minimum total potential energy principle is employed to obtain the governing equilibrium equations and corresponding boundary conditions. The coupled set of governing equations is recast into an uncoupled form and solved explicitly together with the corresponding boundary conditions. The closed-form solutions obtained are compared to those based on the conventional beam theories. It is shown that the model is capable of predicting accurately the deflections for a wide range of geometry and property parameters, especially for small shear stiffness (slip modulus) values for the webs. The formula for the deflection is reduced to the Timoshenko formula for full composite interaction when the shear slip modulus of the web approaches infinity. Comparative numerical results are presented to show the influence of bending deformations, shear deformations in the framing layers and the in-plane shear deformations in the sheathings

  • 287.
    Grundberg, Staffan
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hassan, Osama A B
    Umeå University. Department of Applied Physics and Electronics.
    Vibration of axially loaded and partially interacting composite beams2014In: International Journal of Structural Stability and Dynamics, ISSN 0219-4554, Vol. 14, no 1, article id 1350047Article in journal (Refereed)
    Abstract [en]

    The vibrations of axially loaded composite beams with partial interaction are considered. The equations of motion and the pertaining boundary conditions are derived from Hamilton's principle. Mainly free - but also forced - vibrations are considered. The natural frequencies are calculated as a function of the axial force and the stiffness of the interaction between the layers. The analytical result obtained for the eigenfrequencies of the simply supported beam is taken as a starting point for an approximation of the eigenfrequencies of beams subject to other boundary conditions. The proposed approximation - which has no numerical fitting parameters - is shown to be in good agreement with the exact solutions, especially for the case of a beam clamped at both ends

  • 288.
    Grundberg, Staffan
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Hassan, Osama A.B.
    Umeå University. Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Dynamics of axially loaded and partially interacting composite beams2012In: Proceedings of the 15th European Conference on Composite Materials, Venice, 24-28 June 2012 / [ed] Marino Quaresimin; Liszlo Kollar; Leif Asp, Venice, 2012Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to study the dynamics of partially interacting composite beams subjected to axial loads. The eigenfrequencies are derived for the simply supported composite beam subjected to an axial force. Measurements of the fundamental frequencies of a simply supported composite beam consisting of three layers connected by shear connectors are carried out considering different values of the applied axial force. The agreement between the theoretical and experimental results is discussed. It is also shown that the application of the axial force introduces frictional moments at the boundaries, which make the experimental boundary conditions deviate somewhat from those of an ideal simply supported beam.

  • 289.
    Gustafsson, Andreas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    On the Simulation of Progressive Deformation in Nuclear Piping2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis the performance of different constitutive models in ratchet simulation is investigated. Ratcheting is accumulated plastic strains which may occur when a structure is subjected to a constant load in combination with cyclic loading. In the assessment of nuclear class 1 pressure retaining component ratcheting is one of the three failure modes that are addressed and may limit the design life of nuclear pressurized components and piping systems.A steel structure subjected to a constant load in combination with cyclic loading into the plastic region undergoes a change of the material characteristics in several aspects. These cyclic material characteristics are complex and may vary for different load situations, load levels, temperatures and materials. In addition to this, the presence of a mean stress may also affect the material cyclic characteristics.In previous numerical investigations on ratcheting there has not been a sufficiently robust case of simulation. However, in most of these investigations, the simulation response is compared with ratcheting experiments which either are conducted under load levels which are not common for a nuclear pressurized component, the experimental specimen is not comparable with a pressurized component or only a few experimental tests have been conducted. Hence, it has not been settled which material characteristics need to be considered to accurately simulate ratcheting in a pressurized piping component under load levels common in a nuclear power plants. As a result of this, it is not obvious which types of constitutive material models is needed and how the model parameters should be calibrated in order to simulate ratcheting in a nuclear component accurately.As part of this thesis an extensive experimental program has been conducted on pressurized tube specimens. In total 30 test specimens made of two different materials, 316L and P235, have been manufactured and tested. In order to determine material properties, monotonic tensile load and internal pressure experiments have been performed. The remaining test specimens have been used for ratcheting experiments.The experimental results show ratcheting in the hoop direction when the tube is subjected to certain combinations of internal pressure and cyclic axial strains. The higher the pressure is and the larger the strain ranges are, the higher the ratcheting response becomes. In addition to this, also the cyclic hardening and softening behavior in the tubes axial direction and the direction of the incremental plastic strain tensor is investigated. The results show that the material cyclic hardening or softening behavior and direction of the plastic strain vector varies strongly depending on the level of primary and secondary loads.Measured ratcheting strains are compared to numerical simulations using different constitutive models. In this thesis the interrelated models of Prager, Armstrong-Frederick and Chaboche are investigated. In addition to these, the Besseling model is investigated. Among the constitutive models investigated, the Besseling multi-linear model shows by far the best agreement with the ratcheting experiments. The more advanced models are able to capture the material ratchetingbehavior, but overestimate the hoop strain in the tube tests.Investigation results also indicate that significant cyclic hardening material behavior influence the direction of the plastic stain vector and, hence, affect the accuracy of predicted results when disregarded. This effect is most apparent for the experiments subjected to high pressure and high deformation controlled loads. In the tests which experience significant cyclic hardening, the direction of the plastic strain vector starts to deviate after roughly 20 loading cycles.Simulation of ratcheting should be done with an as simple constitutive model as possible, while still capturing the essential response. Important reasons are that simple models are easier to understand and work with, and that fewer tests are needed for determining model parameters. Based on this the Besseling constitutive model is recommended for simulation of pressure equipment subjected to cyclic plastic deformation. However, if shake-down does not occur at relative early stage, effects related to cyclic softening or hardening may need to be taken into consideration.

  • 290.
    Gustafsson, Andreas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Möller, Mikael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Experimental and Numerical Investigation of Ratcheting in Pressurized Equipment2015In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 130, p. 1233-1245Article in journal (Refereed)
    Abstract [en]

    part of a project within the Swedish nuclear industry with the objective to investigate the performance of different constitutive models in ratchet simulation, an extensive experimental program has been conducted on pressurized tube specimens. In total 30 test specimens made of two different materials, 316L and P235, have been manufactured and tested. In order to determine material properties, monotonic tensile load and internal pressure experiments have been performed. The remaining test specimens have been used for ratcheting experiments. The experimental results show ratcheting in the hoop direction when the tube is subjected to certain combinations of internal pressure and cyclic axial strains. The higher the pressure is and the larger the strain ranges are, the higher the ratcheting response becomes. Measured ratcheting strains are compared to numerical simulations using different constitutive models. In this paper the interrelated models of Prager, Armstrong-Frederick and Chaboche are investigated. In addition to these, the Besseling model is investigated. Based on the result from this investigation, recommendations on how to conduct ratcheting simulation of pressurized equipment subjected to cyclic secondary loading are presented

  • 291.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Katainen, Jukka
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    An experimental study on adsorption of benzene on Co(0001)2002In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 507, p. 57-61Article in journal (Refereed)
    Abstract [en]

    The adsorption of benzene on Co(0 0 0 1) was studied by X-ray photoelectron spectroscopy, temperature programmed desorption, low energy electron diffraction (LEED) and work function measurements. The adsorption was found to be molecular at room temperature and to saturate at a fractional coverage of 0.125 ML. With LEED a c(2root3 x 4) overlayer structure was seen. Below 220 K at high exposures a p(root7 x root7)R19degrees LEED pattern was observed corresponding to a coverage of 0.143 ML. Temperature programmed desorption measurements stated that benzene starts to decompose around 340 K to hydrogen and a hydrocarbon fragment, most likely C6H5. While the hydrogen desorbed, the hydrocarbon stayed at the surface. The desorption of molecular benzene was negligible. The activation energy for the dehydrogenation was calculated to be about 102 kJ/mol. The work function of Co(0 0 0 1) decreased by 1.3 eV upon saturation with benzene. The induced dipole moment was calculated to be 1.9 Debye/molecule.

  • 292.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Kauraala, K.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology.
    Hydrogen on cobalt: effects of carbon monoxide and sulphur additives on the D-2/Co(0001) system2004In: Physica scripta. T, ISSN 0281-1847, Vol. T108, p. 28-32Article in journal (Refereed)
    Abstract [en]

    Hydrogen reaction on catalytic surfaces is an important field of research in fuel cell science. The adsorption of hydrogen (deuterium) on Co(0001) and the influence of carbon monoxide and sulphur on the adsorption were studied by XPS, TDS, WF measurements and LEED. The WF increased due to D2 adsorption, revealing the electronegative character of deuterium. It was found that the deuterium saturation coverage is similar to 0.17 ML at 320K and similar to 0.27ML at 180 K. The activation energy for desorption was estimated to be 33 kJ/mol. The coadsorption measurements with CO indicated a decrease in the deuterium yield by 50%. A downward shift of 50K in the deuterium desorption temperature was observed as a consequence of coadsorbed CO, but changes in the CO desorption were minimal. At small CO exposures the (2 X 2) LEED structure of deuterium was seen, while at exposures of above 5 L the (2 root 3 x 2 root 3)R30... structure was detected by LEED as with pure CO adsorption. Coadsorption with sulphur led also to a decrease in the D2 yield leading to a complete inhibition of hydrogen adsorption at sulphur saturation. The sulphur (2 X 2) LEED structure did not underwent changes due to deuterium adsorption. As assumed, sulphur worked as a strong poison to the adsorption on Co(0001).

  • 293.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology.
    Sulfur poisoning of the CO adsorption on Co(0001)2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 573, no 2, p. 183-190Article in journal (Refereed)
    Abstract [en]

    CO adsorption on a sulfur covered cobalt surface at 185 K has been studied using XPS, TDS, LEED, and WF measurements. As in the case of CO adsorption on the clean Co(0001) surface, CO adsorbs and desorbs molecularly and no dissociation was observed. The saturation coverage of CO decreases linearly from 0.54 ML to 0.27 ML when the S pre-coverage increases to 0.25 ML. The WF increased during CO adsorption, but did not reach the value obtained for CO adsorption on the clean surface. The smaller work function change is explained by the reduced adsorption of CO on the sulfur-precovered surface. A reduction in the activation energy of desorption for CO from 113 kJ/mol to 88 kJ/mol was observed indicating weaker bonding of the CO molecules to the surface. The behavior of the CO/S/Co(0001) system was explained by a combination of steric and electronic effects.

  • 294.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Coadsorption of CO and C6H6 on Co(0 0 0 1)2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 584, no 1, p. 70-76Article in journal (Refereed)
    Abstract [en]

    We have studied the influence of CO on the adsorption of benzene on the Co(0 0 0 1) surface using LEED, XPS, TDS and work function measurements. CO was found to reduce the benzene adsorption, but even at saturation CO exposure no complete blocking was observed. Thermal desorption of the coadsorbed layer featured CO and H2 peaks indicating partial dehydrogenation of benzene and retaining of the CO bond. Ordered LEED structures were found with all coverages: Pre-adsorption of CO led to patterns already seen for pure carbon monoxide adsorption. Pre-adsorption of benzene showed the known (7×7)R19°structure of pure benzene also with small CO exposures, but higher CO exposures yielded a mixture of (7×7)R19°and (3×3)R30°patterns

  • 295.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Laboratory of Physics, Helsinki University of Technology.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Methanol on Co(0 0 0 1): XPS, TDS, WF and LEED results2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 598, no 1-3, p. 128-135Article in journal (Refereed)
    Abstract [en]

    The adsorption and decomposition of methanol on clean Co(0 0 0 1) was studied as a function of temperature and exposure by means of TDS (thermal desorption spectroscopy), XPS (X-ray photoelectron spectroscopy), WF (work function measurements) and LEED (low energy electron diffraction). Methanol was adsorbed by OH-bond scission as methoxide on the cobalt surface. TD and XP spectra revealed that beside a small amount of molecularly desorbing methanol, it decomposed during heating to the final products: CO and H2. Desorption of H2 took place around 356 K and desorption of CO around 390 K. These temperatures are characteristic for desorption of these species on clean cobalt. Work function measurements showed that the adsorption of methanol resulted in a lowering of the WF by 1.1 eV. Heating - and therewith decomposition - led to an increase in the WF of +0.4 eV. After all decomposition products had desorbed, the WF returned to the value for the clean Co(0 0 0 1) surface. LEED exhibited a combination of two ordered structures: p(2 × 2) and (7×7)19.1°. The (7×7)19.1° pattern was formed by methoxide or hydrogen and vanished below 340 K. The p(2 × 2) structure was still found above 380 K and was therefore assigned to CO

  • 296.
    Hallberg, Johannes
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Utvärdering av passivhus i Kiruna: Analys av mätningar från Sjunde huset2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    I januari 2021 träder EU-direktivet om nära-noll-energibyggnader i kraft. Det kommer att innebära att de svenska byggnormerna blir betydligt strängare med avseende på energieffektivitet än dagens krav. Det finns redan idag flera framarbetade normsamlingar som kommer att klara de kommande kraven även om de inte är nationella krav enligt lag idag. En av de normsamlingar som kommer att uppfylla de nya kraven är passivhus. Passivhus som initiativ kommer från Centraleuropa och det är även där tekniken och kraven är som mest tillämpade och utbredda. Passivhuskraven kan tillämpas på många sätt runt om i världen beroende på den geografiska platsens förutsättningar men gemensamt är att de är mycket energieffektiva. I Sverige har det byggts passivhus enligt en nationell kravspecifikation sedan 2000-talet.

    I denna rapport undersöks Sjunde huset i Kiruna. Projektet är ett samarbete mellan Luleå Tekniska Universitet, Kiruna Kommun och NCC. Målet har varit att bygga ett bostadshus i subarktiskt klimat som klarar kraven enligt den svenska passivhusspecifikationen, FEBY12. Utmaningarna att bygga ett passivhus i Kiruna är att kunna behålla inomhusvärmen utan att effektbehovet blir allt för stort under den kalla vintern. Det är särskilt utmanande under den mörka tiden över midvintern där solen under en period inte bidrar med något direktljus. Det är också en utmaning att klara årskravet på förbrukad energi för uppvärmning eftersom endast två månader per år räknas som uppvärmningsfria.

    Sjunde huset har under tid utvärderats med omfattande mätning. I denna rapport har data från mätningen analyserats. Mätdata visar att värmeförlusttalet i Sjunde huset uppfyller krav som ställs i de svenska passivhusbyggnormerna, FEBY12. Det är även troligt att huset när det är bebott kommer att klara passivhuskravet för specifik energianvändning. I denna rapport har förbrukningen beräknats med härledning av Sveby – brukarindata för bostäder i Sverige. Beräkningen visar att Sjunde huset klarar kravet som ställs i FEBY12. 

  • 297.
    Haller, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Critical design activities in house-building projects: an industrial process perspective2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dealing with planning accuracy respectively design errors is a big issue within construction. It has been argued that design errors are a major cause for waste in housing projects, despite all technical development. Reasons for design errors are well investigated and often relate to human acting. Because of the complex structure of the design process, i.e., the strong interrelation of the activities in the design phase, several activities have to be iterated if a design error at a certain activity occurs and is not detected immediately. Deviations from a planned sequence of activities, i.e., flow interruptions in Lean terminology, do not only imply rework but means also a higher risk for loosing control over the project. It can result in, e.g. poor coordination of project participants, necessary changes in schedules, possible time pressure to hold the schedule and about all a higher risk for making errors again.The long term goal of this research is to reduce cost variability of building projects by enhancing flow control in the design phase. A good flow control means to be able to carry out an activity sequence as planned. Existing literature mainly gives general, rather strategically advises what to do or not to do in order to enhance flow. But only few studies can be found dealing with the complex structure of the design process, enabling the development of concrete countermeasures at certain activities, e.g. placing checkpoints. The idea of this research is that not every faulty activity output will have the same effect on the flow in the design phase. The research question is how activities with a high impact on the flow in the design phase can be identified.A housing project was mapped in detail with focus on the activities carried out and theirs relations amongst each other in order to get a better understanding about the complexity of a building design process. The building is a two storey residential home with about 1100 m2. It is carried out in a new building system, a prefab system that is based on timber frame elements. The project was organised in an open building system and the project team consisted of around 10 contractors, small and medium sized enterprises from all over Sweden. An important postulate for this work is that, even there is a high variation of performance across projects, there is an underlying process structure, i.e. relations between the activities, which do not vary much for a certain building system. By applying design structure matrix algorithms a standard sequence of activities (reference process) has been derived. The execution of projects has been simulated via arbitrary deviations from the sequence, where a deviation had a certain consequence for the further proceeding because of the existing relations. The output variable of the simulation model is a measure for the occurrence of sequence deviations.The simulation result indicates that activities with a high number of subsequent activities with long working hours have a bigger influence on the flow in the design phase than activities that dominate only few activities with low working hours.

  • 298.
    Haller, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Design Iteration Control Framework for Offsite Building Projects2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the course of the studies this thesis is based upon a designiteration control framework for offsite building projects wasconceptualized. The ultimate goal was to develop a robust tool to assistproject managers to find the optimal balance between maintainingsufficient project-by-project iteration to solve complex designproblems, and avoiding excessive iteration, which unnecessarilycomplicates design and scheduling. In total three frameworkcomponents were developed. The thesis describes the problemaddressed, presents background information, describes the developmentof the framework components, and discusses their potential utility inconstruction contexts.Offsite building has been advocated as an effective means toincrease product quality while reducing project duration and cost,provided the design process is efficient. A main challenge in managingthe design process is iteration. It must be possible to alter details inorder to react to changes in conditions and meet project-specificrequirements, but unplanned design iteration should be avoidedbecause it can lead to departures from planned activity sequences,thereby increasing both scheduling and design complexity. In projectmanagement literature, two groups of approaches (system dynamic andmodel-based) for managing design have been established. The firstgroup is used to identify factors that affect design iteration and thusactions that could improve the process, while model-based approachesare used to investigate and predict possible effects of specific designiterations on project outcome. A problem is that current methods donot support attempts to quantify effects of specific improvementactions on project outcome, which could greatly facilitate effectivemanagement of resource-constrained projects.Due to the notion that all building projects are unique (which isprevalent in construction management literature) and the complexstructure of design processes, it is generally difficult to identify and mapiteration phases, cycles or loops in terms of specific actions.However, in offsite building projects it is reasonable to assume thatthe same design activities have to be carried out in all projects(regardless of the variation in their conditions), albeit to varying extentsand, furthermore, that the precedence relations between activities isinvariant. Thus, in this thesis (and the underlying studies) offsitebuilding design projects are considered as realizations of a process thatis characterized by varying activity extent but invariant precedencerelations.The suggested framework is a model-based continuousimprovement approach (plan-do-check-act cycle). Essentially it consistsof cycles of observing effects of applied actions over the course ofseveral projects, drawing inferences about the effectiveness of theactions from the observations, identifying improvements, applyingimproved actions and observing their effects. The frameworkincorporates techniques such as design structure matrix (DSM)-basedsimulation and Monte-Carlo inverse analysis. It comprises a method tocalibrate DSM-based simulation models, a relative measure of designiteration, and a method to identify the most critical process phases (interms of design iteration). The framework is mainly based on datarelated to the design process of a two-storey offsite timber framebuilding, supported by probability density functions for 35 other offsitetimber frame multi-storey building projects. The practical applicabilityof the framework components has been tested in simulationexperiments where they were applied to assess design processes relatedto this type of project, with variations in key conditions. To a lesserdegree the framework was also applied to a planning and buildingapproval process. The results of the simulations indicate that thecomponents have high potential practical applicability, providedaccurate records of activity execution sequences and correspondingwork amounts are available.

  • 299.
    Haller, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Lu, Weizhuo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Stehn, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Jansson, Gustav
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    An indicator for superfluous iteration in offsite building design processes2015In: Architectural Engineering and Design Management, ISSN 1745-2007, E-ISSN 1752-7589, Vol. 11, no 5, p. 360-375Article in journal (Refereed)
    Abstract [en]

    Enhancement of iteration management in the design phase is important for successful offsite building projects. Design iteration has two aspects. Although iteration is necessary to deal with design requirements when solving complex problems (i.e. increasing quality through iteration), it has also been identified in numerous studies to be one of the main causes of design errors and time and cost overruns (i.e. superfluous iteration), as it increases scheduling and design complexity. Current building project management tools do not provide a means to control the reduction of superfluous iteration. One problem is that existing research has difficulty precisely relating the effects of specific management actions to superfluous iteration. The idea of this study is to develop an indicator, the sequence deviation quotient (SDQ), which reflects the amount of superfluous design iteration in a project. It can be thought of as a tool supporting project managers to make systematic and continuous (from project to project) design process improvement. A premise is that the impact of varying project conditions on the process structure of design processes, i.e. the precedence relationships between the design activities, is only small. In this paper, we provide a definition of superfluous iteration. We tested the feasibility of the SDQ by subjecting it to project variation and input perturbation by means of a Monte Carlo simulation. The simulations are based on the data from a real offsite design building process, the designing of a 1100 m2 residential building in Sweden.

  • 300.
    Haller, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Stehn, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Evaluation of efficiency in housing construction design2012In: ARCOM, twenty-seventh annual conference 2011, September 5-7, Bristol / [ed] Charles Egbu ; Eric Choen Weng Lou, Reading: Association of Researchers in Construction Management , 2012, Vol. 2, p. 797-806Conference paper (Refereed)
    Abstract [en]

    In housing projects a lot of time is spent for rework, entailing the risk of additional costs, time and deficient quality. As much as 50% or more of rework is originated in faulty output from the design phase. Activities within this phase are strongly interrelated and are carried out by several design consultants. Once the sequence of work in an ongoing project is interrupted the risk for loosing control is high. This results in, e.g., poor coordination of project participants, necessary changes in schedules, possible time pressure and about all a higher risk for making errors. The goal with this study is to reduce the risk of work sequence interruptions in the design phase of housing projects, or in terms of Lean, to make activities in the design phase flow. A timber housing multi dwelling building project in Sweden has been mapped in detail. In total 212 activities have been observed and recorded, spanning from the sales to the erection phase. Iterations (rework) have been identified by using process mining techniques in combination with supplemental interviews. A map of the complete design process consisting of 112 activities (exclusive of iteration) has been derived. A measurement model to detect process regions with a high share of iteration has been proposed that, together with the process map, serves as a starting point for further process optimisation. The efficiency of an activity is assessed by comparing the working hours, ignoring the time used for negative iteration (waste), with the working hours actually used to execute this activity. A Pareto-analysis of the occurring iteration with negative impact on quality then provides an indication of a suitable order for process optimisation.

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