# On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings
## 5 Concluding Remarks  
Among the various timber building typologies, massive CLT buildings have grown rapidly in the last decades both for residential and non-residential buildings. This rapid development has not been supported by up-to-date and codified design rules, leading to design approaches that limit the overall performances of the CLT buildings because they are based on structural considerations only.  
In this context, insight into the influence of design approaches of the connections on the overall performance of CLT buildings has been presented in this paper, highlighting the need for comprehensive and integrated design methodologies including the aspects related to damage control, costs and environmental impact. The results of the conducted research can be summarized as follows:  
Figure 14: Impact of the different structural solutions on LCA.  
The adoption of damage-tolerant structural systems is a fundamental requisite to achieve high performances of CLT buildings in terms of structural behavior, damage control, costs and environmental impact.
* Traditional CLT buildings (Group 1-A1) are low-performant because damage is expected in the connecting zones depending on the level of seismic demand. After an earthquake, the structural components must be demolished/repaired and then reconstructed, involving additional costs and environmental impact.
* Low-damage solutions (Group G2) are efficient from structural, architectural and environmental points of view, but the high damage to non-structural components--related to high displacement capacity of the structure--can compromise their serviceability. In fact, if damage control systems for nonstructural components are not installed, costs related to their damage can become very significant. On the other hand, low-damage solutions are expensive for non-structural elements and increase construction costs.
* CLT buildings equipped with low-damage connecting systems at the base of the panels (Group 1-A2) represent a balance between traditional constructions (Group 1-A1) and those post-tensioned (Group 2), as no damage in structural components is expected and the use of the non-structural element is limited.  
The comparative analyses described herein are certainly not comprehensive and need further investigations and validations to overcome their limitations. Firstly, attention must be primarily focused on the technology and on the expected dissipative capabilities of the connections, whose optimization requires a rigorous scientific approach and an efficient code implementation. Next, studies focusing on the quantification of costs related to the damage to non-structural components and their effect on LCA are lacking a clear identification of the role of the response of components in view of the optimized design approach herein proposed.  
Finally, digital BIM-based tools should be developed to implement an automated design procedure including a rational design approach accounting for all the aspects related to damage control, costs and the Life Cycle process.  
Conceptualization, A.S. and G.F.; methodology, A.S. and G.F.; software, A.S.; validation, I.T., G.F. and F.S.; formal analysis, A.S.; investigation, S.I. and A.S.; data curation, A.S. and S.I.; writing--original draft preparation, A.S., S.I. and F.S.; writing--review and editing, A.S., S.I., I.T. and G.F.; visualization, I.T., F.S. and G.F.; supervision, A.S. and G.F. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
Data Availability Statement: Raw data are not publicly available.  
The authors declare no conflict of interest.