The effect of the relative slip between plies of multiple-ply timber girder trusses subjected to single face loading

Abstract

Certain three-dimensional effects are sometimes ignored in the analysis of multiple-ply timber girder trusses that are loaded on one face of the combined truss, namely relative slip between the trusses and torsion. The effect of torsion on timber girders has been discussed in a previous paper and this paper now looks at the effect of the relative slip only. An analytical model is used and the results are compared with experimental values obtained by Enjily and Whale (1994). Their results are included in BS 5268-3:1998 for the design of nail plates and web members in multiple-ply timber girder trusses. This paper shows how their values may be obtailled through using relatively simple analyses. The author goes further and warns that the distribution of the bending moment in the bottom chords of the individual plies may be greater than anticipated.