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

Mechanical properties of geopolymer concretes reinforced with waste steel fibers

The article presents the research that try to determinate the possibilities of utilization the waste came from used tires to create the composites based on geopolymer matrix. The tire is multicomponent construction. It mainly consists of elastomer (rubber), metal and textile fibres such called textile cord. A lot of components causes difficulties in the tire recycling process. The main aim of the research was determinate the possibilities of recycling the waste steel from used tires in geopolymer composites and develop the eco-friendly material for construction industry. The matrix based on fly ash from power station located in city named Skawina (Poland) and fine sand at a ratio of 1:1. The process of activation was made by 10M sodium hydroxide solution combined with the sodium silicate solution. In order to manufacture these composites the addition of 2% and 3.5% of waste steel fibres by mass was applied. Also specimen without steel fiber reinforcement were made to get reference specimens. The waste steel fibres came from recycling company from Argentina - 'Regomax'. The specimens were prepared according to the methodology described in the standard EN 12390-1. The research methods used were: microstructure research, tensile strength and compressive strength tests as well as analysis of breakthroughs.Fil: Gailitis, R. Riga Technical University; LetoniaFil: Korniejenko, K. Cracow University Of Technology; PoloniaFil: Lach, M. Riga Technical University; LetoniaFil: Sliseris, J. Riga Technical University; LetoniaFil: Moran, Juan Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Rodriguez, Exequiel Santos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Mikula, J. Cracow University Of Technology; Poloni

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

RESPONSE OF SANDWICHES UNDERGOING STATIC AND BLAST PULSE LOADING WITH TAILORING OPTIMIZATION AND STITCHING

A numerical study is presented where tailoring optimization and stitching are applied to improve the structural performances of sandwich plates undergoing static and blast pulse pressure loading. The purpose is to recover the critical interlaminar stresses at the interface with the core and contemporaneously keep maximal the flexural stiffness. Optimized distributions of the stiffness properties for the faces are obtained solving an extremal problem whose target is the minimization of the energy due to transverse shear and bending stresses under spatial variation of the stiffness properties, along with the maximization of the energy due to in-plane stresses. The contribution of stitching is computed through 3-D finite element analysis and it is incorporated as modified elastic moduli into the refined, hierarchic zig-zag model employed as structural model to carry out the analysis accurately accounting for the layerwise effects of the out-of-plane transverse shear and transverse normal stresses and deformations. Approximate solutions giving the ply fibre orientation at any point (compatible with the current manufacturing technologies) are considered in the numerical applications. The numerical results show that stitched sandwiches incorporating optimized low-cost glass-fibre plies can achieve the same bending stiffness as sandwiches with uniform stiffness carbon fibre faces, with a consistent reduction of critical out-of-plane stresses. The amplitude of vibrations under blast pulse loading can be consistently reduced with a proper choice of the curvilinear paths of fibres incorporated in the faces

Free vibration analysis and design optimization of SMA/Graphite/Epoxy composite shells in thermal environments

Composite shells, which are being widely used in engineering applications, are often under thermal loads. Thermal loads usually bring thermal stresses in the structure which can significantly affect its static and dynamic behaviors. One of the possible solutions for this matter is embedding Shape Memory Alloy (SMA) wires into the structure. In the present study, thermal buckling and free vibration of laminated composite cylindrical shells reinforced by SMA wires are analyzed. Brinson model is implemented to predict the thermo-mechanical behavior of SMA wires. The natural frequencies and buckling temperatures of the structure are obtained by employing Generalized Differential Quadrature (GDQ) method. GDQ is a powerful numerical approach which can solve partial differential equations. A comparative study is carried out to show the accuracy and efficiency of the applied numerical method for both free vibration and buckling analysis of composite shells in thermal environment. A parametric study is also provided to indicate the effects of like SMA volume fraction, dependency of material properties on temperature, lay-up orientation, and pre-strain of SMA wires on the natural frequency and buckling of Shape Memory Alloy Hybrid Composite (SMAHC) cylindrical shells. Results represent the fact that SMAs can play a significant role in thermal vibration of composite shells. The second goal of present work is optimization of SMAHC cylindrical shells in order to maximize the fundamental frequency parameter at a certain temperature. To this end, an eight-layer composite shell with four SMA-reinforced layers is considered for optimization. The primary optimization variables are the values of SMA angles in the four layers. Since the optimization process is complicated and time consuming, Genetic Algorithm (GA) is performed to obtain the orientations of SMA layers to maximize the first natural frequency of structure. The optimization results show that using an optimum stacking sequence for SMAHC shells can increase the fundamental frequency of the structure by a considerable amount

An accelerated simulation method of medium density wood fiber boards

An accelerated micro-scale simulation method for the prediction of the stiffness of medium density fiber boards is proposed with the aim to increase the speed of the coupled micro-macro simulation and to study the influence of fiber orientation on material properties. The stiffness is interpolated between loads in a n-dimensional simplex figure, which is constructed in a macroscopic strain, temperature, moisture, time and other load