Mechanics of laterally loaded nail joints in timber

Abstract

The mechanics of both laterally loaded single nail joints and moment resisting multi-nail Iap joints are examined in this thesis. In the first section an experimental programme was conducted in order to investigate the influence of timber properties, nail characteristics, and joint configurations on the mechanical behaviour of single nail joints. The test data obtained was used as input for a finite element analysis, this being a modification of that originally developed by Foschi (1974). The behaviour of single nail joints was shown to be dependent on many interrelated parameters, and as a consequence the influence of any one parameter was considered difficult to assess. The analytical method gave predictions of single nail joint behaviour that were in good agreement with experimental tests. The analysis also yielded accurate predictions of behaviour for a wide range of single nail joint configurations. In the second section the testing of a multi-nail, moment resisting, portal frame, knee joint is described. A finite element method of analysing the joint was developed. The timber was modelled as an orthotropic linear elastic material. Realistic properties of the joint plate were adopted, and the nails modelled as non-linear elements between the timber and plates. Experimental strains, nail slips, and displacements were shown to be in good agreement with predictions from the theoretical analysis. Significant shear and tension stresses perpendicular to the grain, as well as longitudinal direct stresses, were found to exist in the joint region. The peak stresses were greater than predicted by simple beam theory and rivet group joint analysis. The methods described in both investigating many aspects of sections of this thesis provide a means of joint design without requiring rigorous experimental tests to be conducted on whole joints.