Capacity design of typical earthquake-resistant connections for CLT structures

Earthquake-resistant CLT structures can be designed in accordance with the concept of non-dissipative or dissipative structural behaviour. In the second case, modern Italian and European seismic codes require the compliance with the capacity design, to assure the development of plastic deformations in the dissipative components before failure of the non-dissipative ones. For timber structures, this requirement is crucial, because no regions outside the defined nonlinear zones, i.e., steel connections, exhibit dissipative capacity. The load-bearing capacity of connections with dowel-type fasteners is currently estimated according to conservative design methods for static actions, which do not take advantage of their entire strength in the seismic design. Such underestimation of their actual capacity, the high scattering of their mechanical parameters demonstrated by experimental tests and the use of different partial factors for material properties for each component of the same connection, introduce indecisions in the capacity design and in the overstrength factors to be used. Additionally, the recent diffusion of multi-storey CLT buildings in earthquakeprone areas like Italy, makes these issues particularly relevant. In this work, the concept of capacity design and its application in the seismic deign of CLT buildings are discussed, also in terms of suitable values of overstrength factors for this structural system. Moreover, an overview of capacity-design rules for timber structures introduced by the latest reviews of Italian and European Codes and Standards is given. Finally, an applicative example of capacity design of a typical connection for CLT buildings and main outcomes are analysed.