Flexural behavior of composite ribbed slabs employing cold-formed steel lipped channels: Fid-Bau Portal

Flexural behavior of composite ribbed slabs employing cold-formed steel lipped channels

de M. Candido, Daniel C. / Gomes, André V.S. / Favarato, Lucas F. / Ferrareto, Johann A. / Vianna, Juliana da C. / Calenzani, Adenílcia F.G.

Abstract

Highlights • Experimental investigation of CFS profiles coupled to trusses (construction phase). • Experimental investigation of full-scale composite ribbed slabs. • Trusses provided a maximum increase of flexural stiffness and strength of 708% and 357%, respectively during construction phase. • Proposal of a design approach to analytically determine the flexural strength of the slabs during serviceability. • Proposed formulation presented 95% accuracy in determining the flexural behavior of the prototypes. • Experimental results and semi-empirical equations indicate that the area of the steel formwork can be fully considered as steel reinforcement for sagging bending moment.

Abstract By means of a series of full-scale laboratory tests, this research studied the flexural behavior of a composite ribbed slab employing cold-formed steel profiles as formwork before and after concrete casting. An experimental program was devised and separated in two sets of tests. The first set consisted of the execution of four-point bending tests on eight specimens to represent the system during construction, featuring three specimen types; isolated profile, profile with plastic spacers along the channel and a full assembly including the profile, the plastic spacers and a rebar truss. Displacement and strain as a function of load were measured and the data was used to analyze the influence of the different components on the flexural strength and stiffness of the system. On the second set of tests, three ribbed composite slab specimens featuring steel profiles were subjected to four-point bending. Displacement was registered along with strain on the concrete layer. A formulation to determine the flexural strength of the slabs based on Eurocode is presented and compared to experimental observations. The first phase indicates significant increases of flexural strength and stiffness by coupling a truss to the profile and varying the height of the former, namely a maximum increase of 708% in stiffness and 357% in strength. Isolated profiles and profiles with plastic spacers all failed by distortional buckling, while the full assembly specimens failed by instability of the top chord on the trusses. Second phase results show that the analytical prediction is adequate to determine the flexural strength of the prototype slabs, with approximately 95% accuracy for this sample size. All slab specimens failed by plastic hinge formation within the pure moment span. Furthermore, strain measurements on the concrete indicate that the formulae chosen to determine the effective width of the concrete “tee” section is also adequate.