Comparative Design of Some Nigerian Timber Roof Trusses Using BS5268.

This work was done to determine and compare the performance of ten different roof trusses. The truss design was done in accordance with BS5268 part 3 (1998). The design load was resolved to act on the joints of the trusses. The trusses were then analysed using method of joints, to determine the compressive and tensile axial forces acting on the truss members. The truss members wereanalysed as simply supported beams. Clapyron's theorem of three moment was used to determine the support moments, while the span moments and shear forces on the members were determined using method of section. The values of applied and permissible stresses of the trusses members are compared between the trusses. The ratio of the values of the applied to permissible stresses are determined for each truss, and compared against values of from other trusses. It was found that the lower the ratio value, the higher the adequacy of the truss member against the stresses. The average stress ratio for the different trusses were also calculated. The ratio of the applied to permissible stresses were used to evaluate the performances of the various trusses in different conditions. The comparisons were done with respect to the values of applied to permissible stress ratios. From the results obtained, the flat truss had a better performance against the others on a general basis, but this type of truss usually has drainage problems. The attic truss performed better against bending and shear stress. The mono pitch roof truss performed better against tensile stress, while the gambrel truss performed better against compressive stress.