18/02/2023
SEISMIC DESIGN OF CROSS-LAMINATED TIMBER BUILDINGS (CLT)
The provisions for capacity design at the connection level are intended to provide a ductile failure mode characterized by the yielding of fasteners (nails or screws) in steel-to-timber or timber-to-timber connections and avoid any brittle failure mechanisms such as tensile and pull-through failure of anchor bolts or screws and steel plate tensile and shear failure in the weaker section of hold-down and angle brackets connections.
However, the revision of the chapter for the seismic design of timber buildings within EC8 is in progress and will include CLT (Follesa et al 2015; Follesa et al 2018), as is the revision of the EC5 where CLT will be included as a wood based product.
According to the new specifications in EC8, CLT buildings will be classified as dissipative structures with two different values of the behavior factor q for the ductility class medium (DCM) and ductility class high (DCH), respectively classes 2 and 3.
General rules and capacity design rules will be provided both at the building level and at the connection level to avoid any possible global instability or soft-story mechanism at a global level and to prevent any possible brittle failure in the ductile structural elements at a local level.
The general rules will include a general description of the structural system, of the main structural components (walls, floors, and roof), type of connections generally used for the CLT system, and some regularity provisions, also common to other structural systems.
No limitations on the maximum number of stories will be given.
Seismic Design of CLT Buildings in Canada
The CSA-O86 (CSA O86 2016) provisions are based on the assumption that each CLT panel acts as rigid body and that the lateral resistance of CLT shear walls (and diaphragms) is governed by the connection resistance between the shear walls and the foundations or floors, and the connections between the individual panels. Energy dissipative connections of CLT structures need to be designed such that 1) a yielding mode governs the connection resistance, 2) the connection needs to be at least moderately ductile in the directions of the CLT panel’s assumed rigid body motions, and 3) the connection needs to have sufficient deformation capacity to allow for the CLT panels to develop their assumed deformation behavior.
According to the underlying capacity-based design principle, all non-dissipative connections are expected to remain elastic under the force and displacement demands that are induced in them when the energy-dissipative connections reach the 95th percentile of their ultimate resistance or target displacement.
The expectation is that manufacturers of connection systems will make such data available to designers.
Looking at the data provided by the SHARE project regarding the seismic hazard in Europe (Woessner et al 2015), the highest hazard is concentrated along the North Anatolian Fault Zone with values of peak ground acceleration (PGA) up to 0.75 g, considering the results for a 10% exceedance probability in 50 yr. This fault area runs from the southwestern coast of Turkey to the northern coasts of Albania crossing the western coast of Greece and the Cephalonia fault zone, see Fig 1.
