# Sustainable Cross-Laminated Timber Structures in a Seismic Area: Overview and Future Trends
## 4 Modeling Strategies of the Components
### Connection Modeling  
As mentioned, in design practice the in-plane flexural behavior of CLT shear-walls is ruled by rocking and translation due to connections. Thus, to evaluate the flexural load-bearing capacity of the panel, an adequate modeling of the connections is of paramount importance. The majority of methods presented in literature assume that the panel to panel and the panel to foundation are modelled in analogy with reinforced concrete cross-sections. The HDs represent the tensile-resistant elements (e.g., steel bars), ABs are the shear-resistant elements (e.g., stirrups), while timber to timber contact represents the concrete in the compressed zone (this latter is defined by a neutral axis depth). Two different groups of methods can be defined: (a) simplified and (b) detailed. In the first case the contribution of timber in the compressed zone is disregarded, while in the second case it is considered. A simplified mechanical model to evaluate the in-plane flexural load-carrying capacity of CLT panels has been proposed in [60]. It is based on the equilibrium between the internal forces developed by HD and the overturning moment, assuming that the panel rotates around its edge and that the tensile stress distribution at the base cross-section of the panel is linear (Figure 9a). [PERSON] and [PERSON] [61], instead, refined the methodology proposed in [60] considering also the possibility of the shear to tension interaction in the connectors, and in particular in the ABs as tests showed that HDs do not provide significant shear resistance. Figure 9: Assumption on normal stress distributions at a pane to panel and panel to foundation contact. [PERSON] et al. [62], introduced another simplified method based on a linear tensile stress distribution again, but the connector's elongation and its stiffness and strength are considered. The tensile strength of each connector is proportional to the distance of the connector from the panel edge. A triangular distribution of the connector displacement is considered based on the fact that the furthest connector reaches its total elastic tensile strength. The timber to timber or timber to foundation compression strength in evaluating the load-carrying capacity of CLT panels has been considered in [63]. Herein, the compressed zone is modelled by means of a stress-block diagram with maximum design strength equal to that of timber in parallel to grain direction (f\({}_{\text{c},0,\text{d}}\)) (Figure 9b). An advancement of this method is presented in [64], where both elongation capacity of connection elements and the compressed timber contribution are considered. In particular, the maximum compression strength in parallel to grain direction and the Young's (E\({}_{90}\)) modulus in orthogonal to grain direction have been adopted for the compressed timber in the case of timber to timber contact; while for timber to (reinforced concrete) foundation contact the Young's modulus (E\({}_{0}\)) in parallel to grain direction has been assumed. A further study recently developed in [50] proposes a theoretical model which includes both orthogonal to grain compression strength (f\({}_{\text{c},90}\)) and orthogonal to grain Young' modulus for timber to timber contact (while E\({}_{90}\) and f\({}_{\text{c},90}\) are changed with E\({}_{0}\) and f\({}_{\text{c},0}\) in the case of timber to concrete contact at the foundation) (Figure 9c). A parabola-rectangular stress (\(\sigma_{\text{c},90}\))-strain (\(\epsilon_{\text{c},90}\)) model has been proposed (using the relationships proposed by Eurocode 2 for the concrete) to model the compressed timber in orthogonal to grain direction. Such methods remain also valid in the case of coupled walls, provided that the contribution of the vertical joints is included in the evaluation of the flexural strength of the panels. Simplified model which do not consider the compressed timber contribution can be found in [47], while in [49] the panel to panel orthogonal to grain compression stresses have been also included in the model.