This report presents the seismic design of a 10-storey Cross Laminated Timber (CLT) building in Vancouver, BC, conducted according to the National Building Code of Canada. The multi-storey condominium consists of 20 apartments for a total floor area of about 2000 m2. First, a preliminary simplified model is formulated assuming the same stiffness per meter for each wall of the building. The Equivalent Seismic Force Procedure is applied and the results serve for a preliminary design of all the major connections that play a significant role on the lateral stiffness of the building, assuming rigid in plane floor diaphragms and well-anchored CLT walls. Based on the results of the preliminary design, a 3 dimensional finite element model is created, describing analytically the modelling approach adopted, and both the Equivalent Seismic Force Procedure (referred as static analysis) and the Modal Response Spectrum Method (referred as dynamic analysis) are applied to obtain the design forces for each wall of the building. Based on the results from the dynamic analysis, the final seismic design of the building is performed and the results are presented for connections dedicated to transfer (i) shear forces from floor diaphragms to walls below and from walls to diaphragms below, (ii) uplift forces for each wall, (iii) boundary forces between CLT panels within the same walls, (iv) boundary forces between perpendicular walls, and (v) boundary forces between CLT floor panels. All connections prescribed to provide ductility and energy dissipation are designed to fail in ductile failure mode according to the CSA 086-09 while connections that should remain within the elastic range to allow the ductile connections to yield are designed with overstrength factor.
Cross Laminated Timber (CLT) structures are nowadays increasingly used worldwide and mostly in Europe where the system originated. However, in spite of this diffusion which led to the construction of a great number of multi-storey buildings all over Europe, still Eurocodes are almost completely missing provisions for CLT designers, especially regarding the seismic design. Nevertheless, Eurocode 8 requires in most cases, due to the regularity criteria being not fulfilled for most of the buildings, the use of the modal response spectrum analysis method, i.e. the linear dynamic analysis. This method requires the correct estimation of the lateral stiffness of the building in order to accurately calculate the design seismic forces in the building, which may be significantly underestimated or overestimated depending on the size of the building and the shape of the design spectrum. This can be done by modelling each connection with different methods that are often based on available test results, which are not easily accessible by a practicing engineer. This paper provides a design approach for dynamic linear modelling of CLT structures using SAP 2000. Equations are proposed based on available design codes and literature references, and used to design a 3-storey case study building. Further provisions for the seismic design of CLT buildings which are not included in Eurocode 8 are also given. Finally, the proposed design model is also compared with the results of the shaking table tests conducted in 2006 in Japan by CNR-IVALSA on a three-storey CLT building.