Flexural tests of two full-scale composite trusses

Abstract

Steel trusses acting compositely with concrete slabs on wide rib profile steel deck have proven to be an economical system for long span floors. The flexural behaviour of two composite trusses with a span of 11.5 m was studied. The truss configuration consisted of hollow structural section chords with double angle web members welded on either side. The flexural tests showed that ductile behaviour up to failure can be obtained without failure of the web members, provided that the design is based on the ultimate tensile strength of the bottom chord, and the web members and shear connection are designed for the concomitant forces. The maximum moments attained were about 1.2 times the unfactored ultimate moment predicted by CSA Standard S16.1. The maximum strain in the bottom chord of both trusses was significantly higher than the yield strain, but did not reach the ultimate strain due to premature shear connection failure. The failure mode of the first composite truss demonstrated the need for additional rules for establishing the length of stud shear connectors for use in slabs on ribbed deck, as has been incorporated in S16.1-M89. A design procedure for double angle web members was developed, based on the test results. Key words: behaviour, composite steel–concrete trusses, flexure, long span, ultimate moment resistance.