Experimental Studies on Large-Scale Timber Trussed Systems

Abstract

Trusses have been widely used for roof and bridge construction, to provide mankind with a means to meet the most indispensable of needs. Despite the extensive use of trusses, it is still believed that the significant simplifications and assumptions made to facilitate design e.g. frictionless pin-joints, are far from reality, resulting in over designed, uneconomical members. This study is a sequel to previous work, and evaluates the realistic structural behaviour of prototype timber trussed systems viz-a-viz the empirical or semi-empirical design assumptions, with the goal of seeking to optimize the very scarce timber resource in Kenya. A prototype timber fink truss was subjected to nodal point loads gradually to failure. Results obtained suggest that internal web members of the truss may be regarded as axially loaded, while continuous top and bottom chord members are mainly loaded in bending in contrast to design assumptions. Extensive deflections were recorded, and according to limit state design requirements the truss is considered to have failed in serviceability limit state of deflections, much below the recorded ultimate capacity of the truss. Generally, the results are quite similar to previous work on parallel chord bridge truss, and confirm the much held opinion that conventional analysis of timber trusses is an oversimplification that is far unrealistic, too conservative and hence against the current global trend towards sustainability and resource efficiency. Journal of Civil Engineering Research and Practice Vol.1(2) 2004: 77-90