Design Analysis for a Pyramidal Steel Roof Truss Fabricated from Equal-Angle Sections

Abstract

Steel angle-iron trusses remain one of the most widely used roofing solutions for institutional and residential buildings in Nigeria, valued for their light weight, ease of fabrication, and economy of material relative to reinforced-concrete alternatives. This study presents the structural design analysis and governing equations for a hip/pyramidal steel roof truss fabricated entirely from 50 mm × 50 mm × 5 mm mild-steel equal-angle sections, as set out in the accompanying isometric working drawing. The truss is idealized as a set of pin-jointed plane trusses decomposed from the pyramidal form, and the governing dead, live and wind loading equations are formulated in accordance with BS 6399 Parts 1 and 2. Member axial forces are obtained by the method of joints and verified by the method of sections, with free-body diagrams extracted from the working drawing to illustrate the equilibrium equations at each stage. Tension, compression, slenderness, connection, and deflection checks are then developed to BS 5950-1:2000, including the modified single-angle slenderness provisions relevant to angle members connected through one leg only. The resulting framework of 32 governing equations provides a complete, code-consistent basis for verifying the adequacy of the 50 × 50 × 5 mm angle for every member class shown in the drawing, and for re-sizing members where a check is not satisfied.