Struktura e çatisë se drunjtë te Banesës së Skendulajve, Gjirokastër - Procesi i njohjes per konservimin e saj

Banesa e Skendulate is part of the historical centre of the museum - city of Gjirokastra (Albanian UNESCO World Heritage), a unique and well-preserved example of Albanian urban traditional architecture influenced by the Ottoman architectural style, situated in a strategic position in the valley of the Drinos. Banesa e Skendulate represents not only the typical compositional characteristics of this architecture but also a culture and a lifestyle deeply rooted in its own traditions. As it’s known, historic roofings are load-bearing structures made of timber according to an empirical and intuitive design, without structural engineering theory support, and Banesa e Skendulate’s roof shows the ability of the local craftsmen to deal with the support of heavy stone roofing. The knowledge process requires to gain information on the geometrical and mechanical properties of timber members, as well as on the loads that the structure was and will be subjected to. Moreover, in old timber structures, the mechanical properties of timber are affected not only by the duration of load and moisture content, but also by the biological decay. So that, due to the influence of vary issues not considered in the original design, like ageing, load history, biological decay, etc., the usual procedure of design for new timber structures cannot be directly applied in the safety evaluation of the existing timber structures. Banesa e Skendulate's roof structure consists of a single main warping covering the building's C-plan composite shape, timber planks and stone slabs of different sizes and thickness, placed without mortar or metal hook connections. The main warping is composed by horizontal beams, struts/rafters, posts and horizontal longitudinal elements placed about at 1/3 of the span covered by struts. Furthermore, there are seven king posts resting on the horizontal bedding beam arranged transversely to the central set of horizontal beams and supporting the ridge beam every 1.25 m. Elements are connected each other with nails in a very simple heel joint considering the connection between horizontal beams and rafters, and an half-lap joint concerning the connection between rafters and posts located in the central area of the C - shape plan and forming the radial system of posts. In the end, the horizontal beams are nailed to the timber ties system of the stone masonry which reinforces horizontally the walls ensuring the overall behaviour. The overabundance of posts is able to contribute to the stability of the system and compensate to the poorness and simplicity of the connections. The importance of the preservation of traditional timber roofs on their historic buildings is quite evident. In fact, timber roofs are usually more compatible in terms of stiffness and mass with the traditional bearing masonry wall and preserve them through interventions that respect the original conceptual structural design, when it is statically probed, means preserve the uniqueness of the overall constructional concept of the entire building and its historical values. Consequently, the importance to preserve these timber structures is clearly understandable since otherwise, exceptional structural systems belonging usually to traditional building techniques risk to be lost forever