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  • 1.
    Grundberg, Staffan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Luleå tekniska universitet.
    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 and B.H.V. Topping, Stirlingshire, UK: Civil-Comp Press , 2015, 261Conference paper (Refereed)
    Abstract [en]

    Solutions of the static Euler-Bernoulli equations of composite beam-columns with interlayer slip have been compared with an approximate theory. The inter-layer force was taken to be proportional to the inter-layer slip. The general solutions were obtained for four different sets of boundary conditions corresponding to the four Euler cases: clamped-free, pinned-pinned, clamped-pinned and clamped-clamped. A transverse static point load was considered. The beam was axially loaded. The contribution of the axial force to the bending moment, or equivalently the work done by the axial force on the beam due to its deflection, was taken into account in the second order theory and neglected in the first order theory. In the approximate theory the second order effects were described by an approximate magnification factor obtained from critical loads calculated by approximating the buckling length coefficients of the composite beam with interlayer slip by the buckling length coefficients of a solid beam. The contribution of second order effects to deflections and internal actions were calculated in terms of exact magnification factors at different stiffness of the composite action and the results were compared with the approximate theory. Two composite beams were considered. The first was a combination of concrete and timber and the second was a combination of concrete and steel. The positions of the maximum internal shear forces were shown to occur at different positions in the two layers of the beam of concrete and steel when the exact first and second order calculations were compared. The approximate theory was fairly accurate for the deflection but showed higher deviations for other quantities. The approximate theory needs further evaluation. The exact results have been obtained by analytical calculations in combination with numerical evaluation.

  • 2.
    Grundberg, Staffan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Luleå tekniska universitet.
    Hassan, Osama A. B.
    Umeå University, Faculty of Science and Technology, 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, 1350047- p.Article 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.

  • 3.
    Grundberg, Staffan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Hassan, Osama
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Dynamics of axially loaded and partially Interacting  composite beams2012In: Proceedings of the 15th european conference on composite materials, 2012Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to study the dynamics of partially interacting composite beams subjectedto axial loads, a situation occurring in e.g. beam-columns. The eigenfrequencies arederived for the simply supported composite beam subjected to an axial force. Measurements ofthe fundamental frequencies of a simply supported composite beam consisting of three layersare carried out considering different values of the applied axial force. The agreement betweenthe theoretical and experimental results is discussed. It is also shown that the application ofthe axial force introduces frictional moments at the boundaries, which make the experimentalboundary conditions deviate somewhat from those of an ideal simply supported beam.

  • 4.
    Hassan, Osama
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Grundberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Girhammar, Ulf Arne
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Dynamics of partially interacting composite beams2012In: Proceedings of the 15th European Conference on Composite Materials, 2012Conference paper (Refereed)
    Abstract [en]

    In this work, a combined variational calculus and experimental approach are used to characterize the structural vibration behaviour of layered composite beams. Experimental dynamic tests are carried out on a composite simply supported beam with varied interaction strength between the layers. From the results, the influence of connections on the flexural natural frequencies, flexural deformation and damping is investigated. A good agreement between the derived theoretical equations and experimental results is obtained.

  • 5.
    Ohlsson, K.E. Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Östin, Ronny
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Staffan, Grundberg
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Olofsson, Thomas
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Dynamic model for measurement of convective heat transfer coefficient at external building surfaces2016In: Journal of Building Engineering, ISSN 2352-7102, Vol. 7, 239-245 p.Article in journal (Refereed)
    Abstract [en]

    Uncertainties in current empirical models for the convective heat transfer coefficient (CHTC) have large impact on the accuracy of building energy simulations (BES). These models are often based on measurements of the CHTC, using a heated gradient sensor, where steady-state convective air flow is assumed. If this requirement is not fulfilled there will be a dynamic measurement error. The objectives were to construct a validated dynamic model for the heated gradient sensor, and to use this model to improve accuracy by suggesting changes in sensor design and operating procedure. The linear thermal network model included three state-space variables, selected as the temperatures of the three layers of the heated gradient sensor. Predictions of the major time constant and temperature time evolution were in acceptable agreement with experimental results obtained from step-response experiments. Model simulations and experiments showed that the sensor time constant increases with decreasing CHTC value, which means that the sensor response time is at maximum under free convection conditions. Under free convection, the surface heat transfer resistance is at maximum, which cause enhanced heat loss through the sensor insulation layer. Guidelines are given for selection of sampling frequency, and for evaluation of dynamic measurement errors.

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