The potential of nailed all timber box beams

Abstract

The potential of combining small dimension timber with timber webs of suitable thickness has been demonstrated by of this experimental investigation on nailed built up timber box beams of different cross sectional profiles in which the flanges and webs are entirely of timber. No literature was available on such timber box beam construction. The effect of web thickness, overall depth, and shape of flange on the load carrying capacity and flexural rigidity of timber box beams were investigated. Timber beams consisting of webs of 25 mm thickness and overall depth of 225 mm were shown to be the most cost effective. The profile of the flange does not appear to have a significant effect on either the load carrying capacity or flexural rigidity. No attempt wa<i made to model the nail deformation on either the load capacity or the flexural rigidity. Rather, analytical studies showed that the load capacity of the 225 mm deep built-up all timber box beams are approximately 30% and their flexural rigidity is in the range of 25% to 40% that of an integral hollow timber section of identical dimensions. Thus at first glance, the advantage of built up beams of these dimensions may seem questionable. However, considering the fact that integral hollow sections of these dimensions are not available and that there is value addition to the small dimension timber sections whose capacity in bending as solid timber sections acting alone is very small, the all timber built up box beams have immense potential.