# Seismic Design of Timber Buildings: Highlighted Challenges and Future Trends
## 2 European Seismic Design Norms, Standards and Guidelines  
Recent developments in timber engineering and exponential intense of timber in construction required the evolution of currently existing standards. Materials like cross-laminated timber (CLT) proved that timber can be an excellent material for mid- and high-rise buildings even in seismic areas [19; 20]. Cross-laminated timber (CLT) is used for floors and walls and can be considered as floor diaphragms and shear walls in seismic design [21; 22; 23]. Significant development has also been achieved at the connection level. Self-tapping screws [24; 25], glued-in rods [26; 27; 28] and a lot of different innovative systems [29; 30; 31; 32] show improved behavior in seismic applications than traditional  
Figure 1: Future need for a research in timber engineering. -dowel-type connections. At the system level, hybrid systems with concrete [33], EWPs [34; 35], steel [36; 37], polymers [38] and glass [39; 40; 41] are in development and are intensely researched. Current seismic design approaches in building codes around the world (e.g., Eurocode (EC8) [42], NBCC [43], ASCE-7 [44]) follow force-based design methods. At the moment there are only a few norms on seismic assessment of existing structures [45; 46; 47; 48] and future development in research shall be focused in this direction as well. Nevertheless, timber as a structural material is poorly represented in the current norms (i.e., ECS has only four pages related to seismic design of timber structures). In the current Eurocode 8--Section 8: \"Specific rules for timber buildings\", no information is provided for seismic design of widely used structural systems such as cross-laminated timber structures. In addition, no provisions are given regarding capacity design methods for different types of timber structural systems, which proved to be crucial in seismic design of timber buildings [49; 50; 51], as well as provisions and rules for transfer zones for continuity of shear walls along the building's height in multi-story timber buildings. The revision process of the Eurocodes began in 2015 and the final updated version is expected to be released sometime after 2020. The new proposal of timber part, prepared by Work Group 3 of CEN Technical Committee 250 (CEN/TC 250/SC 8/WG 3), is explained by [PERSON] et al. [18] and is based on following modifications and recommendations:  
* Changes in the general definitions and design concepts,
* Update of the list of wood-based materials,
* Definition of dissipative and non-dissipative zones,
* Update of the list of timber based structural types with addition of new structural systems (modification of the description of the existing structural types including graphic presentations of structural systems)
* Modification of behavior factors values for different ductility classes,
* Introduction of capacity design rules for each structural type and of overstrength factors to be used in the design of the brittle components,
* Modification of the current equations for safety verifications
* A new provision for application of non-linear static (pushover) analysis. Above-mentioned new provisions and concepts of timber structures seismic design will demand additional information on mechanical properties of timber connection systems such as connection ductility under cyclic loading, overstrength factors, elastic and plastic stiffness, strength degradation properties under cyclic loading, energy dissipation properties, etc. Therefore, in the near future European technical assessment documents (ETA) for timber connections shall include more information on mechanical properties of connections under cycling loading, defined in EN 12512 standard [52]. Current trend of exponential growth of new timber buildings, larger, taller and more complex projects not only requires higher volume of engineered wood products production, but also higher demand for skilled carpenters and tradespeople with proper education and training on timber construction.