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.

A numerical method for design of beams and frames with complex topology is proposed. The method is based on extended multi-scale finite element method where beam finite elements are used on coarse scale and continuum elements on fine scale. A procedure for calculation of multi-scale base functions, up-scaling and downscaling techniques is proposed by using a modified version of window method that is used in computational homogenization. Coarse scale finite element is embedded into a frame of a material that is representing surrounding structure in a sense of mechanical properties. Results show that this method can capture displacements, shear deformations and local stress-strain gradients with significantly reduced computational time and memory comparing to full scale continuum model. Moreover, this method includes a special hybrid finite elements for precise modelling of structural joints. Hence, the proposed method has a potential application in large scale 2D and 3D structural analysis of non-standard beams and frames where spatial interaction between structural elements is important. (C) 2018 Elsevier Inc. All rights reserved.

In this study, a new strength and stiffness numerical analysis approach of fiber reinforced concrete with oriented fibers and re-bars is proposed. The model is based on discrete lattice simulation that is obtained from standard tetrahedron mesh. Area of cross section of lattice members is obtained by homogenization of each tetrahedron finite element. A non-linear material constitutive model that takes into account fiber orientation, concrete damage and plasticity of re-bars is proposed. Re-bars are embedded in fiber concrete lattice by using a special joint elements that are consistent with re-bar's surface pattern. The numerical model is validated by using four-point bending test results of high performance fiber concrete with oriented fibers. Moreover, the model showed a good agreement with re-bar pull-out test results for ultra-high performance concrete with oriented fibers. The proposed model is used to analyze a ribbed concrete panel with oriented fibers and best optimal fiber orientation for three-point bending is proposed.

A numerical analysis and experimental validation of T-stub steel joint with pre-loaded bolts is done. Design codes have a very imprecise analysis methodology that might not take into account the actual behavior of this joint. The calculations are done with state-of-the-art open source software Code_Aster by taking into account large strains, nonlinear plasticity and contact mechanics. Experimental validation of truss T-stub joint's ultimate load and displacements shows good agreement with numerical simulation results. Parametric studies show, that the ultimate load and stiffness is highly affected by the pre-loading level of bolts and thickness of flange. By increasing the thickness of flanges up to 40mm, nearly equal stress distribution in all bolts is obtained. The joint with 70% pre-loaded bolts has around 30% higher ultimate load than the joint with 0% pre-loaded bolts. The design of T-stub flanges can be significantly improved by using state-of-the-art open-source finite element simulation tools.

The problem related to nonlinear analysis of steel frames is analyzed by taking into account local and global imperfections. A new method for estimation of optimal (in the worst case scenario causes smallest buckling load) pattern for geometrical and material imperfections is developed. The method is based on the optimization of structural topology. The topology is optimized in a way where maximal compliance (minimal stiffness) and strain energy is reached. According to the gradient of compliance function the pattern of geometrical and material imperfections is iteratively obtained. Global geometrical imperfections are applied by using buckling modes (Eigenmodes) with a pre calculated weight coefficient according to the compliance function for each buckling mode. The proposed methods showed to be robust and practically applicable for designing complex steel structures.DOI: http://dx.doi.org/10.5755/j01.sace.17.4.16644

A virtual design method for medium density fiberboards (MDF) is proposed with the aim to optimize the fiber orientation and lay-up of MDF. The new method estimates the stiffness and strength by using microstructure models of the MDF fiber network. The virtual design is used to improve the manufacturing technology of MDF plates with multilayer oriented fiber structure. Experimental investigations of the mechanical behavior of MDF microstructure for various fiber geometries, glue content and distribution are complicated, time consuming and expensive. On the other side, virtual microstructure design allows to develop a new wood fiber based material with less experimental work. Microstructure models help to better understand the non-linear damage mechanical behavior of a wood fiber network depending on fiber geometrical parameters. Such parameters as crack distribution and fiber deformation on micro-scale level are complicated to experimentally measure, but possible to model using computer simulations. The virtual design tool requires less empirical data. The model takes into account information on average wood fiber orientation, fiber diameter, fiber length and mechanical properties of wood fiber cell wall and glue. The numerical method for strength and stiffness analysis of MDF microstructure was calibrated using standard MDF with non-oriented fibers. It turned out that this method gives precise results for MDF with oriented fibers and even with multilayer structure. The proposed virtual microstructure design tool can significantly improve and speed-up the optimization manufacturing technology of MDF and other wood fiber based composites.

The ever increasing tendency of more complex architecture and increasing use of basalt fibers in concrete, mainly due to corrosion resistance, requires a suitable, accurate and computationally efficient numerical method for modelling of mechanical behavior. A novel numerical modelling methodology for basalt fiber reinforced concrete structures is proposed. In this paper, the main focus is on modelling concrete beams with basalt longitudinal rebars and steel shear rebars. The proposed method is based on two step simulation method. On the first step a database of flexural stiffness depending on stress-strain state is created using non-linear simulations with continuum finite elements. The database of flexural stiffness is used in second step by performing nonlinear beam finite element simulation of frame structures. The numerical method showed good agreement with experimental results. The use of pre-computed database of flexural stiffness significantly accelerate non-linear simulations and whole building can analyzed by taking into account material non-linearity.

In this research, the shear and tensile strength of birch plywood edge-to-surface were investigated with specially made specimens for determination of these properties for narrow glued joint. Various thicknesses (4,0; 6,5; 9,0) of plywood and the fiber orientation of surface layer (0̊ and 90) were investigated. The average results showed that shear strength is 7.11MPa and the tensile strength is 3.39MPa. It was found that the orientation of plywood surface layer has minor influence on the shear and tensile strength of edge-to-surface joint.

This paper presents numerical methods for the characterization of fiber orientation and fiber bundles of medium density wood fiberboards (MDF). The strength and stiffness of MDF is significantly affected by the fiber orientation and fiber bundles. Proposed methods and results are necessary to virtually generate realistic fiber networks and optimize MDF by using computer simulations. Based on 3D \(\mu\)CT images for laboratory manufactured MDF with oriented fibers, the fiber orientation is calculated in two ways. Firstly, we use an image processing method based on Hessian matrix directly on \(\mu\)CT image. Secondly, we computed the effective heat conductivity by solving PDEs on a segmentation of the \(\mu\)CT image to estimate the fiber orientation. A fiber bundle segmentation method based on local fiber orientations is introduced. Fiber bundles, which are segmented by this method show good agreement with manually segmented ones. It was observed that fiber bundles are oriented in MDF plane with log-normal distribution of bundle length. The proposed methods are general and can be used also to calculate fiber orientation and segment fiber bundles in fiber concrete, paper, glass and carbon fiber 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.

This article shows numerical investigations of composite sandwich plywood plates with birch plywood faces and a core of straight and curved plywood honeycomb-type ribs in comparison to standard plywood plates and other core type plates. This shape of core ribs provides several improvements for these plates in manufacturing process as well as mechanical properties. The influence of core element shapes on stiffness in longitudinal direction of a plate is insignificant although it is possible to vary with stiffness in transverse direction of these plates by changing form of plate’s ribs. The results are describable as specific strength or stiffness (stiffness to mass or strength to mass ratio etc.) in both directions. The various results depending on chosen variables (according to strength-stiffness criteria) plywood composite macrostructure is obtained for one span plate with uniformly distributed loading. The results show that it is possible to reduce material consumption causing reduction in stiffness but in general increasing stiffness to weight ratio for about 30% or even more if it is possible to increase height of a plate more than maximum standard plywood plate. All thicknesses of elements are chosen according to plywood supplier assortment. A various thicknesses of plywood sheets (0/90/0+90/0·n) are taken for straight ribs as well as various plates coverings for waved part of ribs the 3 layer plywood was taken (90/0/90) or (0/90/0) due to simplification of manufacturing process. For all parts of plate were Birch plywood plates used, as well as reference plywood were Standard Birch plywood plates chosen.

A numerical two scale method for the prediction of tensile and bending stiffness and strength of medium density fiberboards (MDF) is proposed with the aim to study the fiber orientation influence on mechanical properties of MDF. The method requires less experimental data to optimize MDF and to improve industrial manufacturing technology of MDF. A new method for computing orientation tensors of the compressed fiber network is proposed. First, the virtual microstructure is generated by simulations of a fiber laydown and a subsequent compression to obtain the necessary density. The density profile, fiber length, thickness, and orientation are used for the microstructure generation, which are obtained from mu CT images and image analysis tools. Then a new damage model for the wood fiber cell walls and joints is introduced. The microstructural problem is formulated as a Lippmann-Schwinger type equation in elasticity and solved by using Fast Fourier Transformation (FFT). The macroscopic three point bending test is simulated with hexahedral finite elements and analytical methods based on Euler Bernoulli theory. The difference between bending strength and stiffness numerically obtained and corresponding experimentally measured values is less than 10%. This study lays a foundation for the optimal design of MDF fiber structures and the optimization of industrial manufacturing processes. The first results show an increase of up to 60% for bending stiffness in the case of strongly oriented fibers. (C) 2014 Elsevier Ltd. All rights reserved.

This article shows numerical investigations of ribbed plywood panels with top and bottom plywood flanges and a core of curved plywood ribs. It is possible to vary with stiffness in transverse direction of a plate by changing form of panel ribs. This property can be described as structure’s or material’s level of anisotropy or the other results are describable as specific strength or stiffness (to mass of whole construction). The numerical simulation of plywood structure is done by using classical linear Kirchoff Love theory of thin plates and Finite Element Method. The various results depending on chosen variables (according to strength-stiffness criteria) plywood composite macrostructure is obtained for one span panel. Results show that by increasing number of waves it is possible to decrease level of anisotropy and by changing parameters of waves stiffness in transverse directions could be increased and these results can be used for creating ribbed panel design guidelines. It is proven that these parameters remain constant at different panel height. All FEM calculations were done by 3D ANSYS software.

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. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

The new optimization method for fiber orientation angle optimization of symmetrical multilayer plates like plywood is proposed. Optimization method consists of seeking for minimal compliance by choosing appropriate fiber orientation angle in outer layers of flexural plate. The discrete values of fiber orientation angles are used in method. Optimization results of simply supported plate and multispan plate with uniformly distributed load are provided. Results show that stiffness could be increased up to 20% by changing wood fiber orientation angle in one or two outer layers. Keywords—Minimal compliance, flexural plate, plywood, discrete fiber angle optimization.

The new optimization methods of outer layer fibre directions and concentrations of plywood plate with glass fibre-epoxy outer layers are proposed. The first method minimizes structural compliance. It consists of two phases. The fibre directions are optimized in the first phase and concentrations in the second phase. The second method maximizes buckling load for the first buckling mode. The increase of stiffness is about 31% of plate with optimized fibre direction and concentration comparing to similar non-optimized plate. The buckling load of single span rectangular plate could be increased about 34% when optimized GFRP-plywood plate by proposed method.

A new optimization technique of composite plates with discrete varying stiffness is proposed. It consists of three main steps. Analysis of optimal continuous varying bending and shear stiffness of plate is done in the first step by minimizing structural compliance and stress field differences. Size optimization of discrete domains is done in the second step by solving minimization problem with a Genetic Algorithm. Dimension optimization of plates internal structure is done by previously trained feed-forward artificial neural network in the third step. A simply supported rectangular plate with uniformly distributed load and multispan plate with concentrated loads are optimized by the using of proposed method. The deflection of optimized plate could be reduced up to 50%, and average increase of strength to mass ratio is about 20%. (c) 2012 Elsevier Ltd. All rights reserved.