Structural performance of strong timber diaphragms: High-capacity light-timber frames and cross-laminated timber

Abstract

The construction of tall timber buildings is not only challenging because it requires stronger vertical lateral systems but also because it demands much Stronger Timber (ST) diaphragms in comparison to the ones required by low-rise timber construction. Two main ST alternatives exist: High-capacity Light-Timber Frame (HLTF) and Cross-Laminated Timber (CLT) diaphragms. Both approaches provide more strength, stiffness, and still have the potential to provide ductile failure than traditional timber diaphragms. However, it is unclear the structural performance differences between these two ST alternatives, which is the aim of this research. In this study, an experimental program comprising the monotonic and cyclic testing of several representative sheathing-to-framing connections, plus the full-scale monotonic bending testing of six HLTF and CLT diaphragms was accomplished to characterize and compare the performance of both ST diaphragm configurations. Failure modes and mechanical properties such as stiffness, load-bearing capacity, and ductility were evaluated for all specimens. Results show that HLTF diaphragms have larger load-bearing capacity than CLT ones. Conversely, CLT diaphragms perform more ductile than HLTF ones, with a mean of μ= 1.87 and μ= 3.5, respectively, where the first was due mainly to high plastification of fasteners and the second to premature brittle failure of some components. Furthermore, the experimental findings were utilized to evaluate the precision of prevailing analytical and numerical models, thereby illustrating their capability to adequately represent the elastic and nonlinear responses of both ST alternatives. Finally, a sensitivity analysis of a two–story wall building with varying diaphragm (LTF, HLTF and CLT) and different light-frame shear walls (rigid and flexible) was studied. Both the diaphragms and shear walls were modeled under two different equivalent diagonal link models. The sensitivity analysis concluded that both flexible diaphragm assumption and envelope approach might not be an efficient solution, while semi-rigid approach with flexibility index η ranging 0–0.5 may be expected when using ST with LTF shear walls. Finally, the diaphragm model employed enabled the validation of its elastic behavior under lateral loads, with use factors under 30% for typical setups.