Model studies of timber shell roofs.

• Main Author: Walford, G. B.
• Language: en
• Published: University of Canterbury. Civil Engineering 2011
• Online Access: http://hdl.handle.net/10092/5878

The effects of four types of fastening and of scaling on the properties of a timber shell membrane were studied. The membrane was a three layer type made of ex 4 x 1 in. T & G radiata pine boards, the centre layer running at right angles to the outer layers. The fastenings were three densities of nailing and one of nail-gluing. Timber properties were characterised by grading modulus (g.m.) which was the stiffness of prototype boards on the flat under centre point loading over a 3 ft span while the fastenings were characterised by the load-slip behaviour of representative joints. The joint behaviour showed little correlation with g.m. Prototype and 1/5 scale model elements were tested in compression shear, bending and torsion and elastic constants were computed. The various constants were affected to different degrees by the four types of fastening according to the level of stress carried by the fastening under the various element loadings. The model similitude obtained in the elements was good when this was based on g.m., the load-slip behaviour of representative joints and the weight of glue spread per unit area of glueline. Two 1/5 scale model cylindrical timber shells were built and tested, one nailed and the other nail-glued. Their deflections were about twice those calculated by a simplified analysis for orthotropic shells. Their relative behaviour was similar to the relative behaviour of the model elements in shear which suggests that the discrepancy between calculated and observed deflections arose from shear deformation which the analysis ignored.