3D lattice model for post-yield and fracture behaviour of timber.

The paper describes the development of a bespoke Finite Element program to model timber with a three dimensional lattice of single spring elements. These springs mimic meso-scale timber behaviour, namely the crushing and separation of fibre bunches by following a tri-linear loaddisplacement curve. Strength and stiffness parameters for longitudinal, lateral and diagonal elements are randomised for heterogeneity. To save computing time, two specialised algorithms have been implemented to perform a nonlinear analysis faster than an iterative Newton-Raphson algorithm. The algorithms have been adopted and extended to suit a 3D lattice model for timber. Furthermore lattice elements have only been used in areas where plasticity and fracture is expected, with transverse isotropic continuum elements elsewhere. The general calibration procedure of this hybrid model to tested timber specimens of Sitka spruce (Picea sitchensis) is described