Characterisation of the rigid diaphragm conditions for cross laminated timber floors

This paper presents a comprehensive numerical study aimed at defining the conditions for which Cross-Laminated Timber (CLT) floor diaphragms of platform-type CLT buildings can be assumed rigid in linear seismic analyses. Numerical analyses are conducted on a regular CLT archetype within a framework of parametric analyses, in which different geometrical and mechanical parameters including the stiffness of the floor panel-to-panel connections, the stiffness of the floor-to-wall connections, the floor span, the distance between two consecutive shear-walls, the lateral stiffness of the shear-walls, and the number of storeys are varied. The conditions to ensure a rigid diaphragm behaviour are derived by calculating the discrepancies in terms of floor displacements, distribution of lateral forces in the shear-walls, and fundamental vibration period of the structure, between numerical models where the floor is modelled with its actual deformability and as rigid. The discrepancies are compared with threshold values given in Eurocode 8 and used to derive the conditions for which CLT floor diaphragms can be assumed rigid. The study reveals that the behaviour of the floor tends toward the rigid diaphragm condition by increasing the stiffness of the floor panel-to-panel connections and the number of storeys, and by decreasing the stiffness of the floor-to-wall connections, the ratio between the distance between two consecutive shear-walls and the floor span, and the stiffness of the shear-walls. Specific threshold values ensuring a rigid diaphragm behaviour are determined for the properties of the system, delivering the geometrical and mechanical conditions for rigid CLT floor diaphragms.