Experimental determination of the elastic constants of orthotropic composite materials and their bearing capacity (strength) for furniture intended for sitting, and numerical verifi cation of the experiment results by analysing with the fi nal elements, was performed on the basis of the theory of elasticity of orthotropic and anisotropic composite materials. The requisite and suffi cient material constants were determined in the experiments: moduli of elasticity and Poisson's coeffi cients (longitudinal and tangential) and skate modulus for plain stress. These constants, calculated by 3D measurements of deformation, are suffi cient for determining the constitutive matrix of the lamina, and for reducing stiffness of the composite irrespective of the thickness of the layers, fi bre orientation and choice of material. Experiments were conducted for the stiffness, shear and fl exing of uniformly and complexly layered beech veneer sheets, while for new materials experiments for stiffness and shear in a uniform orientation were suffi cient. Analysis of stiffness and deformations were conducted layer by layer, as well as by reduced volume stiffness for multi-layered orthotropic shells of chair systems by a method of fi nal elements by application of a composite fi nal element, where combined reduced membrane matrices and fl exing matrices are used. Numerical verifi cation of the experiments, including systems of furniture intended for sitting-chairs-was conducted using the KOMIPS software system, which contains in its library a composite fi nal element of the sheet. Experiments with chairs were performed with the aim of determining the stiffness of such systems, and they were confi rmed by analytical results and measurement of the real movements on selected models. The results of research provide the design, redesign , construction and determination of the dimensions of not just chairs, but also of any other girder or surface system based on laminates.

Both the scientific experience and the engineering practice indicate that the decision making processes in the course of solving complex designing problems require an analysis of a great number of different construction variants. These types of decision-making processes are time consuming and do not always result in the selection of an optimal solution. That is why the methods of numerical optimization are applied in a wide range of technical sciences to assist in the selection of the best solution. The first step in solving the problem by using the Finite element method is to determine the type of chair earmarked for modeling, and to determine the dimensions of the chair elements

Strength and durability of different types of chairs is mostly function of rigidity and type of joints. Classification of chairs was completed upon their critical points. Based on this divide, chairs were classified into six categories. Based on previous research, strength of joints have been influenced by gluing surface, machining quality, type of fit, species and humidity of wood material, glue quality and gluing parameters. Research have been carried out on two groups of chairs, and two groups of joints. Machining quality, type of fit and gluing surface, have been varied during experiment

The quality of products represents one of the key aims of any modern organized production. In the production practice, it is essential to establish the optimal relationship between quality, production economy and delivery deadlines. Furniture quality is evaluated by three levels and they are: basic quality, high quality and especially high quality. The results presented in this paper are based on the sample measurements of chairs and tables during 2007 and 2008 at the Institute for Furniture Quality Control

The result of parallel investigation of chair durability, which has been made in two different wood species (beach and Paulwonia tomentosa) has been presented in this paper. Static and dynamic loads has highest values in seating furniture, and that is the reason why chair has been chosen to bee representative for testing new species, which could be used in furniture production in Serbia. A shown results indicates on possibility that this species can be used only for production furniture which wont bee imposed with heavy loads during exploitation