# Seismic Design of Timber Buildings: Highlighted Challenges and Future Trends
## 4 Conclusions  
Due to rapid development of high-performance engineered wood products and new timber technologies, resulting in taller and larger timber buildings with applications spanning through all building types, current building codes and standards reflect a deficiency of provisions for contemporary seismic design. State-of-the-art research in various fields of timber seismic design are presented in this paper and crucial challenges, research needs and opportunities are discussed. The new generation of Eurocode 8--timber part--will address many topics which are not present in the current version. An updated list of timber-based structural systems with definitions of dissipative and non-dissipative zones in structures, which are needed for newly-introduced capacity design rules and overstrength factors for each type of structural system, will be included. Further, adapted q-behavior factors values for different ductility classes will be defined and a new procedure for application of non-linear static (pushover) analysis will be included. Tall timber buildings with more than ten stories are already present in moderate- and high-seismic zones around the world. Further, due to climate and economic reasons, more and more conceptual architectural designs for taller timber buildings, including timber skyscrapers, are being proposed, which poses several additional engineering challenges to overcome. A holistic design approach including architectural, structural, durability, fire and acoustic designs as an integrated process is crucial, as all these topics are interrelated. Challenges in terms of numerical modeling of timber and hybrid structural systems, ensuring lateral stability due to wind and seismic actions, high-performingenergy dissipating connections, acoustic insulation vs. seismic design philosophy, execution and building monitoring need to be addressed more in depth. In addition to traditional timber composites with steel and concrete, recent research and developments have shown potential for timber-glass and timber-polymers composites as well. A timber-glass seismic-resistant structural system consists of a timber frame and a structural glass infill bonded together with adhesive, or based on friction contact forming a lateral-resisting wall system. The main advantage of this structural system is increasing lateral stability of buildings with high proportion of facades with glass surfaces by avoiding diagonal bracings or moment connections. Experimental and numerical studies have shown encouraging results in terms of load-bearing and stiffness, whereas the durability aspect needs further examination. Cross-laminated timber (CLT) has proved to be a great solution for new mid- and high-rise timber buildings. Recently, CLT has also been studied for seismic and energy retrofitting of existing older masonry and concrete buildings, which do not meet current seismic design and energy efficiency criteria. In terms of seismic performance, increased strength and stiffness were observed, yet the research is still ongoing and needs additional investigation of connections between the CLT strengthening panels and the existing structure, with its application to a wider range of existing buildings. New technologies and knowledge in timber engineering opened many new possibilities in timber application, not only for new timber buildings, but also in combination with other conventional building materials forming hybrid and composite assemblies and structural systems, and also for retrofitting of existing buildings. In this paper, in addition to an overview of some of the current challenges and emerging trends of seismic behavior of timber structures, the focus was set on three topics of advanced engineered wood products applications (tall timber buildings, composites with timber and seismic retrofitting with timber), which are representing new trends of timber engineering and push the boundaries of timber for the use in sustainable construction.