Application of wood-steel hybrid systems - structural conceptual design in urban transformations.

This paper deals with the problem of load-bearing capacity and deformability of wood-steel hybrid systems, depending on the selected system constellation, and the possibility of increasing system efficiency and in real conditions by applying pre-stress, in accordance with modern principles of structural conceptual design. The subject of the research is the behaviour of pre-stressed glued laminated beams with external polygonal ropes, different researched constellations, i.e. strut type hybrid systems, in real conditions. The paper is practically divided into three methodological units: theoretical and numerical analysis, and examples of practical applications, and on the theoretical basis of urban transformations of historical units. Theoretical assumptions, as well as the current and own approach to the analysis of parameters, set the theoretical basis for the analysis of these systems and the possibility of applying numerical methods in practice. Parametric analysis of the hybrid system obtained practical expressions and diagrams for use in practice, needed to determine suitable constellations of strut type hybrid system by different geometric characteristics and pre-stressed hybrid system, and for different percentages of wooden girder moisture. In order to compare these systems, the same assumptions were used for the calculation, namely: plane behaviour of the system, and to determine the effective pre-stressing, the condition of annulment of vertical deflection in characteristic cross-sections was used, i.e. achieving the effect of vertical immobility of the struts, from which the measure of pre-stressing of the deformable system was obtained. A hybrid system with a wooden girder, which has bending stiffness, is often used in construction, and the main disadvantage of such a system is the expressed deformability in real operating conditions. The basic thesis of this paper is that by external pre-stressing of glued laminated girder achieves less deformability and increases bearing capacity, while saving base material in real conditions, and is confirmed by our own parametric analysis and laboratory testing of pre-stressed hybrid systems of different constellations. The attached parametric analysis diagrams provide a sufficiently accurate orientation for finding the correct constellations of wood-steel hybrid systems and the possibility of estimating the efficiency of hybrids in real conditions, as well as the necessary pre-stressing applications. The derived expressions of the approximate procedure and the expressions for finding the effective pre-stressing force, assuming the linear behaviour of the system, give sufficiently accurate results for the design of pre-stressed hybrid systems in practice. Also, with this or similar methodology it is possible to qualitatively investigate hybrid systems with different combinations of materials. The presented conceptual solutions for the integration of hybrid systems and modern materials in specific localities represent a contribution to the development of a methodological approach to the transformation of historical urban units. [ABSTRACT FROM AUTHOR]