STRUCTURAL PERFORMANCE OF SIMPLY SUPPORTED CROSS-LAMINATED TIMBER DIAPHRAGMS

Maximiliano Andres Wagemann Herrera

doi:10.7273/000008374

Cross-laminated timber (CLT) has emerged as a prominent mass timber product, enabling the construction of mid- and high-rise buildings with improved sustainability and efficiency. A critical component in such structures is the floor diaphragm, which is responsible for transferring lateral loads induced by wind and earthquakes to the vertical resisting elements and for defining the overall lateral behavior of the system. This response is strongly governed by its in-plane stiffness. Despite its importance, the behavior of CLT diaphragms is not yet fully understood, and current design provisions remain limited. This dissertation investigates the in-plane performance of simply supported CLT diaphragms through comprehensive numerical analyses. The research focuses on the influence of key parameters, including aspect ratio, splice connection stiffness, and the presence of boundary elements such as chords and collectors. Each parameter was examined individually through parametric studies and subsequently in combination to capture interaction effects. The numerical models were calibrated against available experimental data and implemented in a systematic framework to evaluate both stress distributions within the diaphragm and global displacement patterns. Results demonstrate that the stiffness and overall behavior of simply supported CLT diaphragms depend strongly on the stiffness of splice connections, their orientation relative to the applied lateral load, as well as both global and local aspect ratios. Furthermore, boundary elements such as chords and collectors were shown to effectively limit relative displacements between panels and, in some cases, alter the distribution of stresses within the diaphragm. This redistribution may lead to stress concentrations that are not typically considered in current design approaches. The analyses also revealed that as diaphragm stiffness increases, the structural response shifts from an I-beam type mechanism, with stress concentrations at the diaphragm ends, toward a deep-beam behavior where stresses are distributed more uniformly across the diaphragm. The analyses further demonstrated that relying on traditional simplified analytical approaches, such as those commonly applied to timber light-frame systems, does not always provide a realistic prediction of CLT diaphragm behavior. These methods do not account for the fact that, depending on connection stiffness, the diaphragm may act as a single unit or as a series of beams. Moreover, they neglect potential stress concentrations around splice regions, which can be critical for accurate design assessment. The primary contribution of this research is the development of design-oriented recommendations for simply supported CLT diaphragms, addressing gaps in current standards. These recommendations are framed within a performance-based design philosophy rather than a purely strength-based approach, explicitly accounting for factors such as splice stiffness, panel orientation relative to the applied load, global and local aspect ratios, and the presence of boundary elements. This work enhances the understanding of CLT diaphragm behavior and supports the advancement of performance-based timber engineering.

STRUCTURAL PERFORMANCE OF SIMPLY SUPPORTED CROSS-LAMINATED TIMBER DIAPHRAGMS

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