Structural performance of concrete/cold-formed steel composite beams supporting composite floor decks

Light-gage steel (LGS) construction is widely used for commercial and industrial buildings. In such construction, the wall framing is usually an assembly of cold-formed steel (CFS) studs held between CFS tracks, and the floors are normally composite concrete/LGS decks spanning between load-bearing CFS walls. Heavy hot rolled steel angles or hollow structural sections (HSS) are attached to the top of CFS load-bearing walls to function as load distribution members (LDM) or to span wall openings. The use of hot rolled steel elements results in significant increase in construction cost and time. Such heavy steel elements would be unnecessary if the slab concrete thickening on top of the CFS wall can be made to act compositely with the CFS track. The resulting concrete/CFS composite beam would be a reinforced concrete beam where the CFS track serves as the tension reinforcement. The continuity at the interface would be provided by stand-off screws that are normally used in the construction of the composite deck.;This research involved experimental and analytical studies to assess the structural performance of concrete/CFS composite beams for use in light-gauge steel (LGS) construction. The level of composite action and the failure modes of composite concrete/CFS beams were investigated in this research. Eight full scale specimens were constructed and tested to failure. Each specimen represented a composite concrete/CFS beam on top of a CFS wall framing with a 6-foot wall opening.;Four of the test specimens were fitted with CFS L-header while the other four were. All of the composite header beams were reinforced for shear. Of the four specimens with CFS L-headers, two were reinforced with 3×3-W2.1×W2.1 wire-mesh and the other two were reinforced with a 4×4-W2.1×W2.1 wire-mesh to serve as shear reinforcement. The shear reinforcement was placed in the header only over the opening. A similar shear reinforcement regiment was adopted for the specimens without the L-headers where two of the specimens were reinforced with the 3×3-W2.1×W2.1 mesh and the other two with the 4×4-W2.1×W2.1 mesh. For each pair of identical specimens, the loading was a single-point load in one of the specimens and a two-point load in the other specimen.;All the specimens under the single-point loading failed in flexure. Three of the specimens under two-point loading failed in and one failed in flexure. The laboratory tests and the theoretical analyses showed that the failure modes and load at failure of the header beams can be predicted with reasonable accuracy. The deflection limits for live load and total load were defined as L/360 and L/240, respectively. The midspan deflection in all the specimens were less than the defined deflection limits. The theoretical and experimental flexural rigidities were determined using moment-curvature analyses. The average ratios of the experimental to the theoretical flexural rigidities in the specimens under single- and two point loading were 1.22 and 0.94, respectively.