In-Plane Elastic Flexibility of Cross Laminated Timber Floor Diaphragms

No appropriate method exists to calculate the in-plane flexibility of Cross Laminated Timber as a floor diaphragm. This flexibility affects the load distribution between shear walls, bracing or cores, as well as adding to local deflections and inter-storey drift. This paper presents a sensitivity analysis based on experimentally measured connection behaviour from the literature and the present study. An important new contributing factor is described: the connection of the floor panels to the supporting wall panels below allows the walls to act as top and bottom chords in the bending and shear of the panel. A new equivalent frame model is described to capture the significant mechanisms of deformation of the diaphragm, validated against a planar finite element model of the elastic behaviour of the panels and the connections between them. The low computational cost of the simplified model allows a wide sensitivity analysis to be carried out, and also makes it suitable for practical design calculations. The flexibility of the floors studied here was seen to be dominated by the slip between panels, rather than panel rotation or bending of the panels themselves. The supporting walls have a strong influence on the moment distribution, but do not strongly influence the slip between panels