# On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings
## 4 Discussion of Results
### Remarks on the Damage Tolerance  
The obtained results--concerning the structural behavior of the various structural systems listed in Table 1 with respect to the Life Safety Limit State condition--show that damage-tolerant structural solutions (either those of Group 1-A2 and Group 2) are more performant than Group 1-A1 (traditional CLT buildings) in terms of seismic behavior and structural damaging. Figure 10: Comparison between the maximum PGAs at ULS bearable by the different structural solutions. In light of this, a Damage Matrix representative of four possible damage levels (from Null to Very High) is represented in a qualitative way in Figure 11. The matrix includes different damage intensities as a function of four Limit States (i.e., Operational, Damage, Life Safety and Collapse) and of the different CLT-based structural solutions analyzed herein, giving an idea of the different damage expected among the various structural solutions. It can be noted that the damage level is gradually decreasing, passing from the solution of Group1-A1 (traditional CLT walls) to Group 1-A2 (damage-tolerant CLT walls) to Group 2 (post-tensioned walls). Nonetheless, in a general reasoning that involves damaging, LCA and costs analysis, the influence of damage tolerance of the non-structural components on the overall seismic performance of CLT buildings cannot be ignored. In fact, Performance-Based Design (PBD) of buildings requires that the influence of non-structural components--such as infill walls and partitions, ceilings, claddings, contents, etc.--cannot be neglected anymore. Thus, many codes treat the problem of safety related to non-structural components, also including criteria for determining the seismic demand at different Limit States [29, 31, 46]. Even in the presence of low-damage principal structural systems, damage to non-structural elements has a severe impact on building recovery, increasing the socioeconomic losses even for low-intensity events (i.e., Damage Limit State) [34]. This aspect is not secondary, especially when (i) the displacement capacity and/or the inter-storey drift of the structural system are significant, with the non-structural elements being forced to accommodate such displacements with a high probability of achieving a high level of damage and needing to be removed and replaced with new components and (ii) the number of non-structural elements is elevated. The latter two statements (i) and (ii) are typically recognized in post-tensioned systems because the reduced number of seismic-resistant walls due to the high seismic performance of the systems involves (necessary) the introduction of a significant number of non-structural components to realize infill and partitions (realized with light-weight timber panels or glass facades, among others). From this perspective, the system of Group 1-A2 appears optimal (also with respect to the case of Group 2) because it limits the damage of structural components and contemporarily requires a lower number of non-structural elements to realize the construction. In light of this, the damage levels indicated in the Damage Matrix of Figure 11 should probably be revised if the contribution of the damage to non-structural components wants to be included in the damage analysis. Currently, no data devoted to computing the influence of non-structural components in damage analyses for timber buildings are available in the literature, and surely future studies should be developed. Studies on the behavior of non-structural timber-based drywall equipped with low-damage connections are available in the literature [47, 48, 49]. Obviously, such systems reduce the nonstructural damage, and the serviceability of the construction is preserved, especially for low-intensity earthquakes. Moreover, the economic and environmental costs of a timber wall structure should consider the probability of a reduced or nullified efficiency of non-structural elements, especially in the presence of a severe earthquake.