# On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings
## 3 Methodology
### Design and Modelling of the Wall System  
The cross-section dimensions of the vertical CLT walls (both for those of Group 1 and Group 2) were determined as a function of the vertical loads. The vertical walls were 5-ply panels 140 mm thick, while the horizontal panels (i.e., floors) were 7-ply panels 240 mm thick. The strength class corresponds to solid wood class C24, in compliance with the Standard ETA-14/0349 [35]. The modeling of CLT structures involved three different levels: (a) CLT'material', (b) connecting zones and (c) global structural scheme (floors, spandrels, etc.) [29; 40; 41; 42]. Being out of the scope of this paper, a detailed description of the modeling strategies and their effectiveness and the modeling criteria herein adopted are summarized in the following. The structural models have been developed with SAP 2000 v. 18 software [43]. With regards to CLT'material', simplified methodologies suitable for macro-scale modeling of the CLT material are available in the literature. Basically, such approaches calculate the elastic moduli of the CLT by reducing the multi-layer material in a single-layer one: for the two in-plane orthogonal directions of the panels, the contribution of the layers having the grain direction parallel with respect to the considered one is accounted for. It has been proved that this approach provides reliable modeling of the CLT material and does not affect the global behavior of the CLT walls. This is because the contribution of the in-plane deformability of the panels, with respect to the global deformability of the multi-story CLT walls, is negligible compared to that provided by the mechanical connections. [2; 41]. In this paper, the in-plane behavior of the CLT panel was modeled through homogenized orthotropic 2D shell elements: the panel thickness is equal to the actual one, while the elastic moduli of the base material are reduced as a function of the effective number of layers present in the vertical and horizontal directions. More sophisticated is the schematization of wall-to-wall and wall-to-foundation connection zones. Generally, they are modeled on an analogy with the reinforced concrete cross-sections, assuming the tensile-resistant elements are equivalent to steel rebars, the shear-resistant elements are equivalent to stirrups and timber-to-timber-to-concrete contact as the part devoted to resist compression forces [2; 44]. In this study, the tensile-resistant elements were schematized as provided with tensile resistance only and unable to resist compression, moment and shear (i.e., pendulums). Instead, the timber-to-timber (or timber-to-foundation) contact was schematized with pendulums provided with compression resistance only, whereas the angle brackets have been schematized with flexural and shear-resistant frame elements. Tensile-resistant and contact elements were schematized with an elastic-perfectly plastic (axial) behavior, whose threshold strength is defined according to the selected SH criterion (\(R_{d}\) or \(N_{pl}\) in the case of approaches A1 and A2, respectively). Instead, the maximum axial displacement capacity of the tensile-resistant elements was assumed variable and equal to the values \(\varepsilon=1\%\) and \(\varepsilon=2\%\). This strain range was used to account for the uncertainties associated with the calibration of the threshold, especially in the case of HDs nailed to CLT panels where the length on which the axial strain is evaluated is still difficult to evaluate [29]. The limit value of the axial strain in the orthogonal-to-grain direction of the compressed elements was set equal to 5% [28; 42]. Vertical joints fasteners of the coupled walls were modeled with elastic springs, linked to the nodes of the adjacent panels and provided with shearing stiffness (\(\mathrm{k_{ser}}\)) calculated according to Eurocode 5 [9].