Seismic Performance and Vibration-Based Damage Identification of Two-Storey Balloon-Framed CLT Shear Walls

Abstract

While cross-laminated timber (CLT) is increasingly utilized in lateral force-resisting systems in mass timber construction, research has predominantly focused on platform-type construction. Balloon-type CLT shear wall systems offer distinct structural advantages, notably the elimination of cumulative perpendicular-to-grain compression and a reduced number of panel-to-panel connections. Despite their potential, limited research has addressed the dynamic properties and damage evolution of balloon-type CLT shear walls. In this study, four full-scale, two-storey balloon-framed structures were subjected to quasi-static reversed cyclic loading, according to the ISO-16670 protocol, up to 5.7% lateral drift. Experimental modal testing using a shaker was performed at multiple damage stages to identify shifts in natural frequencies, mode shapes, and damping ratios. Additionally, impact hammer vibration tests on individual panels provided elastic constants for finite element (FE) modal analysis and subsequent damage assessment via connection stiffness updating. The results showed up to a 32% frequency reduction associated with 85% stiffness degradation after completion of the cyclic tests. Throughout the testing, damping ratios remained within the range of 1%–3% for all configurations. FE model updating confirmed that accurately reproducing the dynamic response of damaged structures requires accounting for specific boundary condition changes and the degradation of wall-to-wall connections.