Challenges on CLT structures seismic response: traditional systems vs low-damage systems

In the last two decades the use of Cross Laminated Timber (CLT) panels is strongly increased in the field of low- rise timber constructions due to their easiness and quickness of construction, transportation, sustainability and good seismic response. In Europe CLT buildings are traditionally composed by arrangement of timber panels, connected one each other, and to the foundation, by means of mechanical timber-to-steel connections. The new frontiers of earthquake engineering require, in addition to human life safety, also the damage reduction after earthquake events. This requirement usually is not completely fulfilled by the traditional systems. To this aim, low-damage post-tensioned technologies for seismic resistance was introduced. PRES-LAM walls are hybrid systems constituted by rocking dissipative timber walls, whose main advantages are: (i) re-centering of walls during the seismic motion, (ii) added hysteretic dissipation, (iii) reparability of dissipaters. In this paper a review of state of the art is reported focusing the attention on the role of connections on traditional and hybrid systems and analysing their influence on the global seismic behaviour. Results of experimental tests carried out on entire walls or on subassembly of connections founded in literature are collected, compared and carefully analysed in order to highlight differences in terms of strength, stiffness, ductility and damage level exhibited by each system.