Experimental and numerical analysis of cold-formed steel floor trusses with concrete filled compression chord

Abstract

Floor trusses fabricated from cold-formed steel (CFS) sections offer several advantages over more conventional floor systems. The current paper reports the findings of an integrated experimental and numerical study focusing on the behavior of CFS floor trusses made of lipped channel sections with the compression chord member filled with concrete. This type of configuration occurs when CFS trusses are used together with a cast-in-place concrete slab. The experimental part of the study included load testing of seven full-scale CFS floor trusses, while numerical investigation included three-dimensional finite element modeling of these trusses. An analytical procedure based on a simple linear-elastic mechanics approach was also developed in an attempt to predict the response of steel-concrete composite CFS trusses without the need of detailed FE analysis or physical testing. Test results indicate that presence of concrete infill inside the compression chord member prevented the initiation of chord local/distortional buckling. In these specimens the failure mode was tension yielding of the bottom chord member. With the introduction of concrete infill within compression chord, significant improvement in truss response in terms of increase in stiffness and load capacity was obtained. The increase in load capacity was 41% and 46% depending on the orientation of the compression chord member. Presence of a concrete slab resulted in an additional 27% increase in load capacity. Truss response predicted by nonlinear FE analyses agrees well with the measured response, both in terms of global load-deflection behavior and chord strains.