Istraživanje temperature i vlage pri sjedenju na uredskim radnim stolicama Received -prispjelo: 22. 12. 2011. Accepted -prihvaćeno: 16. 5. 2012 674.23 doi:10.5552/drind.2012 Original scientifi c paper • Izvorni znanstveni rad

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.

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• The studies of offi ce chair constructions have identifi ed differences in perception of

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