PSI - Issue 73

Marek Johanides et al. / Procedia Structural Integrity 73 (2025) 38–44 Marek Johanides and Antonín Lokaj/ Structural Integrity Procedia 00 (2025) 000–000

39

2

Keywords: ductility; load capacity; timber; frame connection; screws; bolts and dowels; glued-laminated timber;

1. Introduction Timber is an important building material for the sustainable development of the construction industry. The diagnostics of existing structures involves testing their mechanical properties [1]. Modern timber processing technologies also enable the design of multistory buildings [2] and long-span structures [3], where it is essential to apply lessons learned from past accidents and structural failures [4]. For timber and timber structures, experimental testing of structural details [5, 6] or structural components—such as entire frames [7]—is crucial. Numerical modeling based on the finite element method is also an important tool [8, 9]. Recent significant experimental studies have been presented in [10]. Ductility of connections is a key requirement in structural design. Eurocode 5 [11] mandates ductile redistribution of internal forces within joints. However, it does not clearly specify the level of ductility required to prevent premature splitting or collapse. Ductility refers to the ability of a material or connection to undergo large deformations without a significant loss in load-bearing capacity or the occurrence of severe damage. Achieving this property is challenging without reinforcement, especially when timber elements are subjected to bending, tension, or shear. Large deformations are typically only possible in timber under compressive loading. In addition to deformation in the timber elements themselves, significant deformations can also occur in the joints. A typical example is a connection using a single slender fastener, provided it is properly designed to prevent brittle failure. It is important to note that the redistribution of internal forces due to ductility is linked to the compressed zone of the timber. Timber tends to fail in a brittle manner under tension; thus, achieving plastic behavior under bending requires significantly greater tensile strength than compressive strength. While this may be true for homogeneous timber, real structural timber includes imperfections such as knots, making plastic behavior harder to achieve. Plasticity is only possible if such defects are limited to the compression zone. Reinforcement can facilitate the desired plastic behavior. In cases where it is not possible to achieve the required level of ductility in a connection, various reinforcement methods have been developed to prevent brittle failure due to shear or tension perpendicular to the grain. These methods include the use of construction screws, steel sleeves, glued rods, and similar solutions. In the case of frame connections, specifically designed reinforcement using full-threaded screws—positioned as shown in Fig. 1—can be applied.

Fig. 1. Reinforcement of the frame connection from the point of view of increasing the ductility of the connection.