Workshop Report: Disproportionate Collapse Resilience of Mass Timber Buildings

Virginia Tech convened a workshop on October 24, 2025 to identify state-of-the-art challenges and research needs for mitigating disproportionate collapse in multi-story mass timber and timber-hybrid buildings. The workshop included an overview presentation by Professors Phillips and Jacques followed by a facilitated discussion structured around open-ended questions on current practice, common building configurations, connection data gaps, modeling challenges, and research priorities. Key findings: • In practice, disproportionate-collapse evaluation is most commonly pursued for tall Risk Category III/IV projects; federal facilities may also require it, but mass timber is less frequently selected for those buildings. • At-risk mass timber buildings typically use reinforced concrete core walls or steel braced frames for the lateral system, with post-and-plate (often residential) or post-and-beam (often commercial) gravity framing. Diaphragms are often cantilevers off a central core. • Connection and diaphragm detailing is dominated by nailed splines, coil straps/surface-mounted plates for ties, and proprietary concealed beam-to-column connectors. Standardized strength–rotation–stiffness properties are largely unavailable, leading to highly variable modeling practices. • Applying ASCE/SEI 76 to mass timber is limited by lack of validated connection/subassembly data; reliance on ASCE/SEI 41 does not resolve this because timber-specific parameters remain insufficient—creating a circular gap in guidance. • Dynamic/high strain-rate effects in column-loss scenarios are poorly characterized for mass timber. Recommended research priorities: • Large-scale connection tests with sustained axial load to quantify rotational capacity under combined demands. • New connection systems with high rotation capacity and reliable post-yield axial capacity (with concealed/fire-compatible detailing). • Dynamic and high strain-rate effects in progressive-collapse response (connection- and system-level). • Diaphragm panel/joint layout studies to better mobilize two-way cross-laminated timber (CLT) action and improve load redistribution. • Standardize connection performance data and expand ASCE/SEI 76 with a mass timber section comparable in specificity to steel.