The paper presents an innovative approach in the modelling of multi-storey timber-framed buildings, where double-skin façade elements (DSF) are additionally considered as load-bearing wall elements against a horizontal load impact. The mathematical model with a fictive diagonal element developed for timber-framed wall elements with classical oriented strand boards (OSB) or fibre–plaster sheathing boards (FPB) is upgraded for DSF elements. The diameter of the fictive diagonal is determined with either experimental results or numerically obtained results using the time-consuming FEM model with elastic spring elements, which simulates the bonding line between the timber frame and both glazing panes. In the second part of the study, the numerical analysis of a specially selected three-storey timber-framed building was performed using the developed mathematical model with fictive diagonal elements. Two alternative calculations were performed with the DSF elements as non-resisting and racking-resisting wall elements. It was demonstrated on the selected case that the racking resistance (R) of a building can essentially increase up to 35% if DSF elements are considered as resisting wall elements. As a secondary goal of the study, it is also important to point out that by using DSF elements as racking-resisting elements, the distortion in the first floor essentially decreased. It is demonstrated on the selected numerical example that this torsional influence decreased notably (by almost 18%) when the load-bearing DSF elements were used for seismic excitation in the X direction. Therefore, such an approach can open new perspectives in designing multi-storey timber-framed buildings with a more attractive and dynamic floor plan and structure.

This study analyses the many different parameters of the in-plane flexibility problem regarding the lateral behaviour of light timber-framed (LTF) wall elements with different types of sheathing material (FPB, OSB, or even reinforced concrete), as well as the thickness of the timber frame elements (internal or external wall elements). The analysis simultaneously considers bending, shear, and timber-to-framing connection flexibility, while assuming stiff-supported wall elements as prescribed by Eurocode 5. Particular emphasis is placed on the sliding deformation between sheathing boards and the timber frame, which can significantly reduce the overall stiffness of LTF wall elements. The influence of fastener spacing (s) on sliding deformation and overall stiffness is comprehensively analysed, as well as the different bending and shear behaviours of the various sheathing materials. The results show that reducing the fastener spacing can significantly improve the stiffness of OSB wall elements, while it is less critical for FPB elements used in mid-rise timber buildings. A comparison of external and internal wall elements revealed a minimal difference in racking stiffness (3.3%) for OSB and FPB specimens, highlighting their comparable performance. The inclusion of RC sheathing on one side of the LTF elements showed significant potential to improve torsional behaviour and in-plane racking stiffness, making it a viable solution for strengthening prefabricated multi-storey timber buildings. These findings provide valuable guidance for optimizing the design of LTF walls, ensuring improved structural performance and extended application possibilities in modern timber construction.

The use of a double-skin façade (DSF) is a quite new approach in the building renovation process, complementing conventional renovation strategies. A double-skin façade is an envelope wall construction that consists of two transparent surfaces separated by a cavity and can essentially improve the thermal and acoustic resistance of the building envelope. The main double-skin wall components are usually composed of a hardened external single glazing pane and a double or triple thermal insulating internal glass pane, which are connected to the frame structure. Recently, many studies have analysed the thermal and acoustic performance of DSF elements, but almost none in terms of structural behaviour, especially in terms of determining the racking resistance of such wall elements. Moreover, with a view to reduce the global warming potential, an eco-friendly timber frame instead of a commonly used steel, aluminium or plastic frame is studied in this analysis. However, structurally combining timber and glass to develop an appropriate load-bearing structural element is a very complex process involving a combination of two materials with different material properties, where the type of bonding can be selected as a crucial parameter affecting the racking resistance range. Since the costs of experiments performed on such full-scale DSF elements are very high and such experiments are time-consuming, it is crucial to develop special mathematical models for analysing the influence of the most important parameters. Therefore, the main goal of this paper is to develop the finite element mathematical model of the studied DSF structural elements with a highly ecological solution by using a timber frame. In the second step, the developed model is further implemented in the numerical analysis of racking stiffness and followed by a comprehensive parametric numerical study on different parameters influencing the horizontal load-bearing capacity of such DSF timber elements. The obtained results indicate that the new approach of the developed load-bearing prefabricated timber DSF elements can essentially improve racking resistance and stiffness compared with the widely studied timber-glass single-skin wall elements and can thus be fully recommended especially in the structural renovation process of old buildings.