The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform

Hamid Valipour - One of the best experts on this subject based on the ideXlab platform.

  • efficient finite Element modelling of timber beams strengthened with bonded Fibre reinforced polymers
    Construction and Building Materials, 2011
    Co-Authors: Hamid Valipour, Keith Crews
    Abstract:

    Abstract This paper presents development and application of a simple and efficient frame finite Element (FE) able to estimate the load-carrying capacity of timber beams flexurally strengthened with externally bonded Fibre reinforced polymer (FRP) strips and near-surface mounted FRP bars. The developed Element is able to model collapse due to timber crushing under compression, timber fracture under tension and FRP rupture and it is developed in the framework of a flexibility-based Fibre Element formulation. Furthermore, a novel method based on central difference method in conjunction with composite Simpson’s integration scheme along the Element axis is developed to take account of shear-slip. The developed model is employed to predict the loading capacity and the applied load-mid span deflection response of timber beams strengthened with FRP and the numerically simulated responses agree well with the corresponding experimental results. The major features of this frame FE are its simplicity and efficiency compared with more complex and computationally expensive FEs which makes it a suitable tool for practical use in design-oriented parametric studies.

  • Nonlinear reinforced concrete frame Element with torsion
    Engineering Structures, 2010
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    Abstract In this paper an Element for nonlinear analysis of reinforced concrete framed structures subjected to torsion is developed using a force-based formulation. The interaction between the axial force and bending moment is taken into account by adopting the Navier–Bernoulli assumption and using the Fibre Element approach. The torsional DOFs are formulated independently and the effect of normal and tangential forces on the torsional stiffness of section is accounted for by modifying the torque–twist curve of a section under pure torsion. Furthermore, the torsional warping effects on the section stiffness are considered by adding an extra strain field to the section axial strain caused by normal generalised forces. The formulation accuracy and efficiency are verified by some numerical examples.

  • Nonlinear static and cyclic analysis of concrete-filled steel columns
    Journal of Constructional Steel Research, 2010
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    Abstract This paper presents the formulation of a one-dimensional (1D) composite frame Element for the nonlinear static and cyclic analysis of concrete-filled steel (CFS) beam–columns. A two-node frame Element is formulated using the force interpolation concept, and the material nonlinearity at section level is taken into account by employing a total secant stiffness and modified Fibre Element approach. The size effect and steel tube confinement on the concrete strength and ductility are taken into account. Further, the effect of steel tube local buckling on the member strength is addressed. Concerning geometrical nonlinearities at the Element level, the equilibrium equations are satisfied for the deformed Element to take account of P – Δ effects. The formulation accuracy and efficiency of the model are verified by some numerical examples of the static and cyclic analysis of CFS members.

  • An Improved Flexibility Formulation for Nonlinear Analysis of Reinforced Concrete Frames
    2007
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    In this paper the finite Element flexibility-based formulation for a reinforced concrete frame Element is discussed. The formulation takes account of material non-linearity on the basis of the one-dimensional stress-strain relationships akin to the traditional Fibre Element. However, the Fibres in this method are replaced by transverse integration points to improve the efficiency of the method. The compatibility of strain in each section is satisfied by adopting the Navier-Bernoulli hypothesis and effect of shear tractions on the nonlinear response of the material is neglected. Two different iterative solution strategies based on secant and tangent stiffness, consistent with the flexibility formulation are employed for solving the governing equation. The accuracy of assumptions and performance of the solution schemes are studied by a numerical example.

  • Long-term coupled analysis of steel-timber composite (STC) beams
    Construction and Building Materials, 1
    Co-Authors: A.a. Chiniforush, Hamid Valipour, Ali Akbarnezhad
    Abstract:

    Abstract In this paper, the long-term behaviour of steel-timber composite (STC) beams under sustained load is numerically investigated. The long-term constitutive law of timber that accounts for the effect of elastic modulus change due to the moisture content (MC) variation, creep, mechano-sorption, inelastic shrinkage/swelling, and thermal strain is adopted from the literature to develop a 1D Fibre Element model for long-term analysis of the timber components. The time-dependent behaviour of shear connectors is considered in the formulation by a time-dependent shear-slip model calibrated against the results of long-term pushout tests. A 3D diffusion analysis based on finite difference (FD) scheme is coupled with the 1D Fibre Element model to simulate the variation of MC and temperature within the timber section due to variations in the ambient relative humidity and temperature. The coupled hygro-thermo-mechanical model is verified against experimental and numerical models available in the literature and incorporated into the 1D composite Fibre Element formulation to simulate long-term behaviour of the STC beams under variable environmental condition. The accuracy of the analytical tool is verified against available experimental data and the model is used to estimate the creep coefficient of the STC floors for a service life of 50-year. Furthermore, the evolution of nonlinear time-dependent stress–strain in timber and shear forces in shear connectors are comprehensively investigated and discussed, and the influence of service load level, panel width, and shear connectors’ spacing on the long-term performance of the STC floors are highlighted. The results of parametric studies suggest a creep coefficient of 0.35 for 50-years’ design life of STC beams (applicable to a wide range of shear connectors).

Toshihiro Ishikawa - One of the best experts on this subject based on the ideXlab platform.

  • SA-Tyrannohex-Based Composite for High Temperature Applications
    Advances in Science and Technology, 2010
    Co-Authors: Toshihiro Ishikawa
    Abstract:

    To modify the relatively low fracture toughness of monolithic ceramics, the incorporation of long ceramic Fibre within a matrix material has been extensively performed. In this case, as cracks form in the matrix material and approach the Fibres, they will be deflected at the interface between the Fibre and the matrix. We developed another approach toward improving the toughness of ceramics involving the creation of a textured internal structure within the ceramic itself, similar in some respects to the fibrous structure of wood. Actually, we developed a tough ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar Fibres with a thin interfacial carbon layer between Fibres. The interior of the Fibre Element was composed of sintered beta-silicon carbide crystal. This concept is fundamentally different from that described previously, in that it is extremely difficult to distinguish separate “Fibre” and “matrix” phases in the traditional composite sense. The toughness of the material in this case derives from the tremendous amount of interface area created within the internal structure through the close packing of the hexagonal columnar Fibres. Furthermore, this ceramic also achieved the excellent high temperature properties, high thermal conductivity and low density. These properties will make it very attractive for replacement of heavy metal super alloy components.

  • Cryogenic properties of Si-Ti-C-O Fibre-bonded ceramic using satin weave
    Journal of Materials Science, 2001
    Co-Authors: Kenji Matsunaga, Toshihiro Ishikawa, Shinji Kajii, Toshihiko Hogami
    Abstract:

    Mechanical and thermophysical characteristics of Si-Ti-C-O Fibre-bonded ceramic produced by hot-pressing the laminated material of oxidized satin-woven Si-Ti-C-O Fibre have been investigated at room and cryogenic temperatures. The Fibre Element (diameter: 8 μm, Fibre volume fraction: 85 ± 1%) constructing the Si-Ti-C-O Fibre-bonded ceramic showed a close-packed structure of the oxidized Si-Ti-C-O Fibre mainly composed of fine SiC crystals, amorphous SiO2-based phase and turbostratic carbon. The Si-Ti-C-O Fibre-bonded ceramic with lightweight (density: 2.45 × 103kg/m3) and low porosity (

  • 24th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 21, Issue 4 - High heat-resistant SiC-polycrystalline Fibre and its Fibre-bonded ceramic
    24th Annual Conference on Composites Advanced Ceramics Materials and Structures: B: Ceramic Engineering and Science Proceedings Volume 21 Issue 4, 1
    Co-Authors: Toshihiro Ishikawa
    Abstract:

    Here we describe a type of SiC polycrystalline Fibre (SA Fibre) obtained by sintering an amorphous Si-Al-C-O Fibre precursor at 1900°C in Ar atmosphere. Furthermore, we also explain a sintered SiC Fibre-bonded ceramic (SA-Tyrannohex), which was synthesized by hot-pressing piled sheets of the amorphous Si-Al-C-O Fibre precursor prepared from an organosilicon polymer. The former SA Fibre with high strength showed no reduction in strength on heating to 2000°C in inert atmosphere. This Fibre also showed excellent creep resistance in air, high thermal conductivity and good weave-ability. The latter SA-Tyrannohex consisted of highly ordered, close-packed structures of very fine hexagonal columnar Fibres with a thin interfacial carbon layer. The interior of the Fibre Element was composed of sintered SiC crystal. This material with high strength showed fibrous fracture behaviour, high thermal conductivity and excellent high-temperature strength up to 1700°C.

Toshihiko Hogami - One of the best experts on this subject based on the ideXlab platform.

  • Cryogenic properties of Si-Ti-C-O Fibre-bonded ceramic using satin weave
    Journal of Materials Science, 2001
    Co-Authors: Kenji Matsunaga, Toshihiro Ishikawa, Shinji Kajii, Toshihiko Hogami
    Abstract:

    Mechanical and thermophysical characteristics of Si-Ti-C-O Fibre-bonded ceramic produced by hot-pressing the laminated material of oxidized satin-woven Si-Ti-C-O Fibre have been investigated at room and cryogenic temperatures. The Fibre Element (diameter: 8 μm, Fibre volume fraction: 85 ± 1%) constructing the Si-Ti-C-O Fibre-bonded ceramic showed a close-packed structure of the oxidized Si-Ti-C-O Fibre mainly composed of fine SiC crystals, amorphous SiO2-based phase and turbostratic carbon. The Si-Ti-C-O Fibre-bonded ceramic with lightweight (density: 2.45 × 103kg/m3) and low porosity (

Luca Martinelli - One of the best experts on this subject based on the ideXlab platform.

  • Multi‐scale modelling approach for the pushover analysis of existing RC shear walls—Part I: Model formulation
    Earthquake Engineering & Structural Dynamics, 2007
    Co-Authors: Maria Gabriella Mulas, Dario Coronelli, Luca Martinelli
    Abstract:

    This work focuses on the modelling issues related to the adoption of the pushover analysis for the seismic assessment of existing reinforced concrete (RC) structures. To this purpose a prototype reference structure, one of the RC shear walls designed according to the multi-fuse concept and tested on shaking table for the CAMUS project, is modelled at different levels of refinement. The meso-scale of a stiffness-based Fibre Element and the micro-scale of the finite Element (FE) method are herein adopted; in the latter separate Elements are adopted for the concrete, the steel and the steel-concrete interface. This first of the two companion papers presents in detail the wall under study, illustrating the design philosophy, the geometry of the wall, the instrumentation set-up and the test programme. The two modelling approaches are then described; the most important points in terms of Element formulation and constitutive relations for materials are presented and discussed for each approach, in the light of the particular design of the wall and of its experimental behaviour.

Stephen J. Foster - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear reinforced concrete frame Element with torsion
    Engineering Structures, 2010
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    Abstract In this paper an Element for nonlinear analysis of reinforced concrete framed structures subjected to torsion is developed using a force-based formulation. The interaction between the axial force and bending moment is taken into account by adopting the Navier–Bernoulli assumption and using the Fibre Element approach. The torsional DOFs are formulated independently and the effect of normal and tangential forces on the torsional stiffness of section is accounted for by modifying the torque–twist curve of a section under pure torsion. Furthermore, the torsional warping effects on the section stiffness are considered by adding an extra strain field to the section axial strain caused by normal generalised forces. The formulation accuracy and efficiency are verified by some numerical examples.

  • Nonlinear static and cyclic analysis of concrete-filled steel columns
    Journal of Constructional Steel Research, 2010
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    Abstract This paper presents the formulation of a one-dimensional (1D) composite frame Element for the nonlinear static and cyclic analysis of concrete-filled steel (CFS) beam–columns. A two-node frame Element is formulated using the force interpolation concept, and the material nonlinearity at section level is taken into account by employing a total secant stiffness and modified Fibre Element approach. The size effect and steel tube confinement on the concrete strength and ductility are taken into account. Further, the effect of steel tube local buckling on the member strength is addressed. Concerning geometrical nonlinearities at the Element level, the equilibrium equations are satisfied for the deformed Element to take account of P – Δ effects. The formulation accuracy and efficiency of the model are verified by some numerical examples of the static and cyclic analysis of CFS members.

  • An Improved Flexibility Formulation for Nonlinear Analysis of Reinforced Concrete Frames
    2007
    Co-Authors: Hamid Valipour, Stephen J. Foster
    Abstract:

    In this paper the finite Element flexibility-based formulation for a reinforced concrete frame Element is discussed. The formulation takes account of material non-linearity on the basis of the one-dimensional stress-strain relationships akin to the traditional Fibre Element. However, the Fibres in this method are replaced by transverse integration points to improve the efficiency of the method. The compatibility of strain in each section is satisfied by adopting the Navier-Bernoulli hypothesis and effect of shear tractions on the nonlinear response of the material is neglected. Two different iterative solution strategies based on secant and tangent stiffness, consistent with the flexibility formulation are employed for solving the governing equation. The accuracy of assumptions and performance of the solution schemes are studied by a numerical example.