TIMBER-CONCRETE COMPOSITE RIBBED SLABS WITH HIGH-PERFORMANCE FIBRE-CONCRETE

Composite of such renewable material as timber and the most popular man-made material as concrete offers many benefits. Such of them are high load-bearing capacity with low dead load and increased structural bending stiffness. Higher specific strength of high-performance concrete in comparison with ordinary concrete ensures more efficient use of the material. Addition of fibres can reduce the fragility and autogenous shrinkage cracks of high-performance concrete and makes it possible to design thinner layers of concrete for timber-concrete composite structures. Ribbed slabs as solution for the floor slabs, allows to reduce material consumption and to integrate engineering communications into the structures. The current study focuses on determining the effect of the use of high-performance fibre reinforced concrete for timber-concrete composite ribbed slabs with adhesive connection between layers, as the most effective connection type for composite action. The effect of the use of high-performance fibre reinforced concrete is determined by comparison of mid-span displacements of the ribbed slabs numerical models. Three-dimensional finite element models of timber and ordinary concrete composite ribbed slab and high-performance fibre reinforced concrete with additional longitudinal reinforcement ribbed slab are validated by experiment data. Developed numerical models makes it possible to predict the dependence of applied load on mid-span displacement in three-point bending with sufficient precision. Obtained results showed, that replacement of ordinary concrete layer by high-performance fibre reinforced concrete in timber-concrete composite ribbed slab with adhesive connection up to 1.68 times decrease vertical mid-span displacements.

Optimal design of rational fiber orientation for variable stiffness plywood-plastic plate – numerical and experimental investigations

The new optimization method of outer layer fiber directions and concentrations of plywood plate with glass fiber-vinyl ester resin outer layers are proposed. The method minimizes structural compliance. It consists of two phases. The fiber directions are optimized in the first phase and concentrations in the second phase. The increase of stiffness is about 30% of plate with optimized fiber direction and concentration comparing to similar non-optimized plate

Mikrostruktursimulation der mechanischen Deformation von Fasermaterialien

Die Deformation von porösen Natur- und Kunstfasermaterialien unter Zug-, Druck- oder Biegebelastung hängt sehr stark von den geometrischen und mechanischen Eigenschaften der verwendeten Fasern und den Eigenschaften der Faser-Faser-Kontaktstellen ab. In den betrachteten Materialien besitzen die Fasern häufig eine Orientierung, die zu elastisch anisotropen Eigenschaften führt. Um das Materialverhalten beim Herstellungsprozess und im Einsatz vorherzusagen werden in dieser Arbeit Fasernetzwerkmodelle zur Beschreibung der Mikrostruktur verwendet. Im Vergleich zu ähnlichen Verfahren werden sehr komplizierte dreidimensionale Fasernetzwerke mit einem effizienten numerischen Verfahren gelöst. Das Lösungsverfahren basiert auf einer Formulierung der Elastizitätsgleichungen als Integralgleichung vom Lippmann-Schwinger-Typ. Diese Integralgleichungen werden iterativ mit Hilfe der schnellen Fourier-Transformation (FFT) gelöst. Die Anwendung dieser Lösungstechnik auf poröse Medien ist neu. Im Vortrag werden Simulationsergebnisse für verschiedene Fasermaterialien erläutert und diese mit entsprechenden Messungen verglichen. Dabei werden geometrisch und physikalisch nichtlineare Verformungen betrachtet. Mit Hilfe der entwickelten Mikrostruktursimulationstechnik (Softwarepaket FeelMath) lässt sich die Abhängigkeit der makroskopischen Deformationseigenschaften von den Eigenschaften der Einzelfasern und der Faserorientierung analysieren. Damit kann die Anzahl der notwendigen Messungen reduziert werden und die Eigenschaften der Materialien lassen sich für den speziellen Einsatzzweck optimieren. Das vorgestellte Lösungsverfahren ist ebenfalls für nichtporöse Verbundwerkstoffe und zur Lösung von Wärmeleitproblemen in Fasernetzwerken geeignet

Numerical modelling of flax short fibre reinforced and flax fibre fabric reinforced polymer composites

The ever-increasing demand of flax short fibre-reinforced and flax fibre fabric-reinforced polymer composites in various engineering applications calls for accurate predictions of their mechanical behaviors. In this study, numerical methods to generate and simulate mechanical properties of flax short fibre-reinforced and flax fibre fabric-reinforced polymer composites are proposed. The microstructures of short flax fibres with different fibre length-to-diameter ratios are generated by algorithm taking fiber defects (e.g. kink band) and fiber bundles into account. Bidirectional flax fabric is generated and discretized by tetrahedron 4-node finite elements. A brittle material law for fibre defects and interfacial zones of fibre bundles is proposed. Flax short fibre/polypropylene and flax fabric/epoxy composites are modeled by a non-linear plasticity model considering an isotropic hardening law and non-local continuum damage mechanics. The numerical modelling results are compared with the experimental results of these composites. This study shows that the simulation can capture the main damage mechanisms of the composites such as fibre breakage initiated at the fiber defects, damage of polymer matrix and the fibre debonding at fibre/matrix interface accurately. In addition, the simulation results exhibit good agreements with the experimental results in the aspects of elastic properties and nonlinear tensile stress-strain behavior of the short fibre and fibre fabric reinforced polymer composites