# On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings
## 1 Introduction  
The introduction of high-performing engineered wood products (i.e., Glue-Lam, Cross-Laminated Timber, Laminated Veneer Lumber, etc.) encouraged the construction of timber buildings worldwide [1]. Today, low- and mid-rise Cross-Laminated Timber (CLT) buildings represent a valid alternative to traditional masonry or reinforced concrete buildings, both for residential and non-residential uses [2]. The beneficial properties of the base material related to reduced weight, thermal insulation and its natural origin place CLT buildings at very high levels of structural, seismic, energetic and sustainability performance [3; 4; 5]. Traditional CLT buildings are erected with platform construction technology: they are made of horizontal CLT floors installed between two vertical CLT walls (as a \"sandwich\"), interrupting the vertical continuity of the walls [6]. Wall-to-wall and wall-to-foundation contact consist of mechanical connections made with (a) hold-downs (HDs) bearing tensile forces due to moment demand, and (b) angle brackets (ABs) aimed at covering the shear demand. These connections play a crucial role in the seismic response of CLT buildings [7; 8]. They are designed according to the strength criteria provided by Eurocode 5 [9], i.e., fail according to [PERSON]'s plastic failure mechanisms under seismic-like actions characterized by localized timber embedding combined with the yielding of metal fasteners [10; 11; 12; 13; 14; 15; 16]. Basically, such mechanisms are ductile, but sometimes they are anticipated by brittle failure modes if end edge distances or spacing between the metal fasteners are not respected, nullifying the dissipative behavior of the CLT building. As a main drawback, traditional HDs and ABs point out the activation of permanent damage mechanisms allocated in the vertical timber panels due to the embedding of wood, as documented in Figure 1, where typicalfailure mechanisms of HDs and ABs observed during experimental testing are shown. Due to timber damage, vertical timber panels result in being heavily damaged, making their reparation impractical after an earthquake, so the demolition of the building (or some of its portions) results in being the most rational option, entailing additional costs due to both demolition and reconstruction, recycling of materials and environmental impact. The issue of damage prevention in CLT timber panels represents a (relatively) recent research topic. To overcome this problem, alternative construction technologies, connection systems and their design criteria are available in the literature. Connecting systems, in substitution of HDs and ABs have been proposed with the aim of concentrating the damage in the metallic parts only (steel bars or plates with particular shapes), as documented in [17; 18; 19; 20]. As a shortcoming, these connections, which yield tension and/or shear after a seismic event, must be removed from the vertical timber panels, substituted or changed in position along the base of the wall to repair the connections: these operations produce damage of the CLT panel, additional repairing or demolition costs and environmental impact related to the phases of 'use' and 'end of life' within the Life Cycle Assessment (LCA) framework. Indeed, low-damage timber systems were first claimed in New Zealand in 2005 [21]. They are made with post-tensioned rocking timber walls connected by means of 'plug and play' connecting systems (placed at the base of the vertical walls only) to the foundation [22]. These connections, which consist of fuse-type metal bars in which the plastic damage is concentrated, can protect the vertical timber panels against damage due to the embedding of wood. The metal bars can be easily substituted after a seismic event, restoring the original structural behavior of the seismic-resistant walls. Taking inspiration from this idea, studies on damage-tolerant and replaceable connecting systems in substitution of traditional HS and ABs have been introduced in the literature. For instance, [PERSON] et al.