Structural analysis and design of Timber Light-Frame shear walls

The thesis aims at investigating the seismic performances of timber light-frame shear walls with focus on the contribution offered by the sheathing-to-framing connections in terms of energy dissipation and ductility. Numerical non-linear analyses under displacement-controlled loading conditions are carried out using an original parametric finite element (FE) model developed within the open-source software OpenSees (McKenna and Fenves, 2007) in order to allow the easy variation of some basic design variables affecting the overall racking capacity of the wall, namely: i) aspect ratio, ii) nails spacing, iii) number of vertical studs and iv) cross-section size of the framing elements. In fact, although many researches dealt with the in-plane behavior of a fully-anchored timber shear wall, few efforts have been spent so far to analyze the mechanical behavior and the energy dissipation attributable to the sheathing-to-framing connections that, with hold-down connections, represent the highest contribution in terms of a wall deformation. There are few parametric analyses that consider different wall configurations (Salenikovich, 2000; Salenikovich and Dolan, 2003; Dhonju et al., 2017) of a fully-anchored timber shear wall. Several experimental tests have demonstrated that the dissipative behavior of a shear wall is mainly influenced by its connections. Timber has, in general, a poor dissipative capacity and is a brittle material in bending and in tension, unless it is properly reinforced (Jorissen and Fragiacomo, 2011). Conversely, the steel connections ensure a good amount of energy dissipation and cyclic ductility notwithstanding their significant pinching, strength degradation and softening. This evidence is well reflected into many numerical models proposed in literature, where the non-linear wall response is related to the load-deformation relationships of the connections (Tuomi and McCutcheon, 1978; Gupta and Kuo, 1985; Gupta and Kuo, 1987). Observing the results of the sensitivity analyses and starting from the study by Casagrande et al. (2016) - who model the timber shear wall considering rigid framing elements - an analytical procedure is here proposed to predict the capacity curve of a timber light-frame shear wall. Considering the characteristic non-linear softening-type behavior of timber structures, an analytical expression of the equivalent viscous damping is provided, which allows to assess the ductility of a common timber shear wall configuration. Finally, optimal configurations of a timber light-frame shear wall, considering two values of aspect ratio (2 and 1), are provided to show how the design variables affect the variation of racking capacity and costs.