Razvoj novega postopka za ojačitev starih lesenih stropov : doktorska disertacija

slovenian

doktorska dela

2020

Univerza v Mariboru, Fakulteta za gradbeništvo, prometno inženirstvo in arhitekturo

Timber floors are often strengthened in such a way that metal or polymer strips are attached to the underside of its timber joists. This process blocks the surface view that determines the appearance of the timber floor and consequently the original architecture of the timber floor is compromised. With the development in the field of glass and partial glass structures (composite materials) and with the development of the quality of the production of glass, a transparent material, there is also the unconventional possibility of using glass for reinforcements, e.g. in timber structures. In the case of glass elements used to strengthen timber floors, the original appearance would largely be retained. The idea of using glass elements to strengthen timber floors raises many questions which are the subject of this dissertation. In the context of timber-glass composites, the dissertation deals with the development of a method for the strengthening of old timber floors with glass elements in the form of strips in the tensile zone of the cross section. As a first step of the reinforcement method, cross laminated timber panels (CLT) are already provided in the compression zone of the cross section. Self-tapping screws were considered for the connection of the CLT panel with the timber floor joist, while for the contact of the glass strip with the timber floor joist, adhesive bonding and point (mechanical) fastening were considered. The point (mechanical) fastening for the glass-timber connection was developed within the scope of this dissertation. The dissertation includes shear tests of timber-glass adhesive joints at different timber moisture contents and different temperatures. It was confirmed that the bonded timber-glass contact has the potential to be used for old timber structures which may be exposed to different environmental conditions. The shear tests of the new timber-glass point connection have shown that under certain conditions glass elements can also be connected to timber elements using self-tapping screws. The timber-glass point connection with self-tapping screws represents a non-invasive, reversible and optically inconspicuous connection of the two materials. Analytical expressions were also developed to evaluate the load-bearing capacity and stiffness of the new point connection, and a numerical analysis of the stiffness of the point connection was also carried out. The numerical analysis was also used to estimate the stress factors in the glass element around the point connection under various loads, which provides the possibility to estimate the glass stresses around the point connection by analytical calculation. The most important part of the dissertation are the four-point bending tests with the new procedure for strengthening old timber floors. Old timber floor joists from the Manor Zgornja Polskava were used, which were removed from the building due to severe damage. The mechanical properties of the timber floor joists were determined on the basis of tensile tests on timber samples taken from the old timber floor joists. In parallel, analytical and numerical calculations of the load-bearing capacity and stiffness of the strengthened timber floor joists were carried out, whereby the loading conditions were equal to the load in the four-point bending test. In addition, a parametric analysis of the new procedure for strengthening of old timber floors is presented, which was used to determine the most important parameters influencing the load-bearing capacity of the strengthened timber floor joists. Finally, the contribution of glass strips to the bending stiffness of the timber floor joists was demonstrated. Under certain conditions, glass strips can also increase the load-bearing capacity. The adhesively bonded glass strip was shown to be more effective, but the mechanically connected glass strip can also contribute to the load-bearing capacity of a timber floor joist under certain conditions.

07.08.2023