# On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings
## 4 Discussion of Results  
### Structural Behavior  
Figure 9a,b reports the pushover curves of the four analyzed numerical models described in Table 1 for the X and Y directions separately. Moreover, the curves obtained with the two different values of the axial strain of the tensile-resistant elements (\(\varepsilon=1\%\) and \(\varepsilon=2\%\)) are reported for the sake of comparison. Figure 8: Position of the walls and view of the numerical model—Group 2 along Y direction. Figure 7: Position of the walls and view of the numerical model—Group 2 along X direction. The pushover curves point out some differences in terms of the structural response of the systems depending on the layout and performance of the connections. As a comparison between the two SH criteria herein adopted, it is evident that (i) Approach A1 involves higher post-elastic displacements than Approach A2 (either for \(\varepsilon=1\%\) and \(\varepsilon=2\%\) assuming an ultimate axial strain for the tensile-resistant elements) and that (ii) the maximum base shear obtained in the case of Approach A1 is higher than those of Approach A2. Both statements (i) and (ii) are due to the higher overstrength of the tensile-resistant elements designed with Approach A1 than Approach A2. The higher overstrength of Approach A1 is due to the adoption of the commercial cross-section for the HDs, while in the case of Approach A2 the cross-section area of the tensile-resistant elements is calibrated to be equal to that strictly required by the moment demand. In particular, in the case of (i), the overstrength of the tensile-resistant elements designed according to Approach A1 addresses the failure mechanisms towards the crisis of compressed timber before that of the tensile-resistant elements. The overstrength resulting from Approach A1 with respect to A2 is accentuated in the cases of coupled walls, probably because of additional strength given by vertical joints in combination with the overstrength of the base connections, whereas this additional strength is not completely exploited in the case of Approach A2, being the ultimate displacement of the walls achieved with a plasticization in both tensile and compressed zone. If the influence of the ultimate axial strain (\(\varepsilon\)) of the cases belonging to Group G1 is analyzed, it is observed that, despite double values of e, the displacement capacity of the walls does not increase proportionally. This occurs as the failure mechanisms of the walls are ruled by the achievement of the maximum axial strain of timber in compression zones which limits the overall displacement capacity of the walls. Figure 9: Comparison between the pushover curves: (**a**) walls in direction X, (**b**) walls in direction Y. As far as Group G2 is concerned, the pushover curves are the same in comparison with directions X and Y. This is because the same number of walls (four)--and with the same cross-section area and pre-stressed forces--was used in the two orthogonal X and Y directions (Figure 6). Comparisons between the pushover curves of Group G1 and G2 show that, in the second case, additional overstrength is avoided because the walls are designed to achieve exactly the base shear demand at ULS. Contrariwise, the displacement capacity of the post-tensioned system is significantly higher than that of Group 1 because of dissipating seismic energy through the rooking behavior of the walls, without plastic dissipation concentrated in a few tensile-resistant elements. The overstrength generated from the design approaches A1 and A2 of Group 1 are more evident by looking at Figure 10, where the maximum seismic capacity bearable by the structure at the LS limit state expressed in terms of PGA/g is evaluated according to the N2 method for the cases of Group G1 [36] and according to the Capacity Response Spectrum in the case of G2 [45]. From the structural point of view, post-tensioned systems are optimal because they are designed to satisfy the seismic demand without additional overstrength and have optimal displacement capacity.