An Experimental and Analytical Study on Cold Formed Steel Floor Trusses with Bare and Concrete Filled Compression Chords

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Cold-Formed Steel Research Consortium (CFSRC) Colloquium
Floor trusses fabricated from cold-formed steel (CFS) sections are commonly preferred for floor system construction in CFS buildings in certain parts of the world. An integrated experimental and numerical study has been conducted to investigate the behavior of such trusses. The investigation included both bare CFS trusses, as well as trusses with the top chord members filled with concrete in an attempt to eliminate compression buckling. Bare steel truss tests included seventeen full-scale trusses with the major test variables of CFS section thickness, type of diagonal-to-chord connection, and number of connection fasteners. Test results have shown that the analytically calculated and measured responses differ in terms of truss stiffness. Measured stiffness of the trusses within the service load level came out to be lower than the stiffness obtained using two dimensional analytical models. Hence, additional experiments on screw connections were conducted and by these results analytical expressions were developed to simulate connection flexibility. An additional five truss specimens were tested as part of the investigation on steel-concrete composite trusses. Test results indicate that the presence of concrete infill inside the compression chord member prevents the initiation of chord local/distortional buckling and provides significant improvement in truss response in terms of increase in stiffness and load capacity.