PSI - Issue 78

Beatrice Travasoni et al. / Procedia Structural Integrity 78 (2026) 1111–1118

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Fig. 4. Wall-to-diaphragm connection systems and corresponding axial force–displacement curves: (a) structural detail of Connection Type 1, with steel angle bracket fixed to the underside of the timber beam, and analytical response law derived from Mirra (2021); (b) structural detail of Connection Type 2, with chemical anchors and perimeter CFS angle bracket aligned with the diaphragm level and tensile response plywood-side screws according to Karki et al. (2022); (c) structural detail of Connection Type 3, with chemical anchors and perimeter angle bracket aligned with the diaphragm level and tensile response with cyclic envelopes from experimental tests (black), averaged response (dashed red), and bilinear approximation (solid red) based on four cyclic tests according to Tselios et al. (2023). 2.3. Calibration of timber diaphragm Four diaphragm configurations were considered in the study: simple boards, diaphragms strengthened with additional timber boards, plywood panels, and concrete topping slabs. These configurations reflect those tested in the experimental campaign by Baldessari (2010), which investigated the in-plane behaviour of full-scale timber floors with various retrofitting techniques. The materials and strengthening layouts adopted in the present numerical models were defined on the basis of those experimental results. Nonlinear analyses showed that the relative in-plane deformation of the diaphragms remained within the elastic range in all configurations. Accordingly, the diaphragms were modelled as orthotropic elastic plates, neglecting material nonlinearity. The in-plane stiffness parameters were defined using the formulations proposed by Guerrini et al. (2021), which provide effective estimates of the orthotropic elastic properties of existing timber diaphragms, both unreinforced and retrofitted. 3. Numerical analysis and modelling strategy A nonlinear static analysis was performed applying a lateral load proportional to the seismic mass in the Y direction (perpendicular to the façade wall), to investigate the influence of diaphragm stiffness and wall-to diaphragm connections on the global seismic response. As shown in Fig. 5, the in-plane stiffness of the diaphragm, the stiffness of the connections, and their ultimate displacement capacity play a key role in governing the seismic response. This is clearly reflected in the load– displacement curves of Fig. 5a, where the control displacement is measured at the centroid of the second-floor diaphragm. The influence of diaphragm stiffness is further highlighted in Fig. 5b, where more deformable configurations limit the activation of walls parallel to the seismic direction, while stiffer diaphragms promote a more integrated structural response.