Research: Seismic Design for Braced Timber Frames
Last updated May 17, 2023
By Ian Story
https://www.intechopen.com/chapters/52795
Eurocode 8 (chapter 8) (link: https://www.phd.eng.br/wp-content/uploads/2015/02/en.1998.1.2004.pdf) introduces the concept of a Dissipative Zone in timber structures. The timber members themselves are considered to have minimal ductility, but the connections between timber members can have significant ductility.
Systems with rigid connections or that depend on bending of timber members for their resistance are considered non-ductile, and need to be designed for nearly full seismic loads (R = 1.5, this matches ASCE’s very limited treatment of timber systems).
However, systems where connections between beams and columns are designed to resist rotation in a ductile manner get an additional credit for dissipating energy in the Eurocode system. Canadian building codes contain a similar provision.
Research note: “hyperstatic” is synonymous with “structurally indeterminate”
Another source: https://www.mdpi.com/2075-5309/12/2/240. Defines several equations for ductility. Generally the measure of ductility seems to be represented by the character μ. Eurocode 8 defines μ as μ=ΔFu/ΔFy.
While the research on this topic is complicated, the short answer is that it is hard to create a consistent ductile timber frame without substantially engineered detailing (i.e. beyond what would be practical for a residential project).
Connections such as traditional Chinese timber frame details, which involved numerous layers of interlocking timber ties with a significant moment arm, were probably reasonably successful at creating ductile moment frames, due to the significant amount of friction and crushing between components, which could dissipate energy and allow significant rotation before fully stressing the attached beams and columns.