A form finding method for post formed timber grid shell structures.

Timber grid shells provide efficient ways of covering large openings with relatively small amount of materials. With three-dimensional CAD software, it is now possible to model a free-form surface and discretize it in smaller straight elements, thus postponing the design of the node-connections geometry to the manufacturing process (i.e. by Computer-Aided-Manufacturing). A "low-tech" method for building free-form timber grid shell structures with standardized connections is that of assembling an initially flat grid of continuous rods and then, post-forming (bending) it in a double curved shape. Accordingly, the latter method doesn't require high-tech manufacturing processes. However, being the final shape influenced by equilibrium of the internal forces, a form-finding procedure is required. A novel "facilitating" numerical framework is introduced in this paper: For a given continuous reference shape, a geometrically similar discrete model is found by implementation of the Dynamic Relaxation method. Numerical methods to the finding of grid cutting pattern, as well as, a Newton-Raphson method to assess the allowable timber cross-section, are illustrated.