Author(s)

TÕNIS TEPPAND, PEEP NURME, SIIM TEPPAND

Abstract

CAD/FEM/CAM software is used to design the 3D model of grid shell. The longitudinal length of the laths is measured along the curved side. The position of the crossing nodes (x, y, z; different on each lath) is used to produce the half lap joints at exact places by CNC-workstations on straight laths. The laths will be connected by half lap joints with half-dovetailed joints (without metallic fasteners) to bear internal forces from the top of the shell to the edges. There is no more need for excessively long laths. The length is limited only by the cross-sectional measure of the lath capable to carry the dead weight of the cantilever laths themselves while supported only from the first and second crossing node. The laths will be connected longitudinally with a gradual tenon on one end and mortise at the other end. The laths are produced as glue-laminated wood, but in this case of lamellae, they are installed together as multiple hollow square-tubes, one in another. Different species of timber with various physical properties can be used. By gradually displacing the square-tubes of lamellae upwards, starting from the inside layer, the tenon and mortise will be generated during the gluing process. After fixing the first row of laths (inclined with respect to the foundation plane) to the external beam or foundation, the shell structure starts “rising” upwards by connecting the laths longitudinally. Every subsequent layer of laths has mirrored inclination, adding thickness and strength to the grid shell. Laths will be bent and twisted during the assembly process, until the half-dovetailed and half lap joints of two crossing laths lock. The internal forces generated by the bending and torsion of the laths keep the designed shape of the grid shell without any need for additional supports.

Keywords

grid shell, GL, carpentry joints, FEM software, CNC-workstation