Study On The Bearing Behavior Of Cold-Formed Steel Joists-Fine Aggregate Concrete Composite Beam

As a new type of composite beam, the the behavior of cold-formed steel joist-fine aggregate concrete composite beam has not been well studied. This paper summarizes some findings in a recent experimental study, in which three large-scale specimens were tested to study the ultimate flexural bearing capacity and deformation capacity. Based on both theoretical analysis and finite element simulation, the author deeply studied the performance of this new type of composite beam, and puts forward the design method.First of all, the mechanical properties and deformation process of composite beams were studied in this paper. The destruction mechanism and the effect of steel mesh and Z shear connectors were analyzed. The research indicate that: the destruction mechanism of composite beams is due to: the composite beams loss it’s combination effect and causing the web of Cshape joists plastic yield, and the C-shape joists distortional buckling in the end of composite beam where concentrated load acted. And the top flange of steel beam appear plastic yield, partial shear screw failure, final, the composite beam in overall yield; some measures such as set shear connectors can slightly improve the ultimate bearing capacity but effectively reduce the middle-span deflection of the composite beams.Secondly, some finite models are established in ANSYS to simulate the models in this paper, which has been proved to be accurate by the author. Different factors, such as the span of beam, space between screws, thickness of concrete slab, width-height ratio and heightthickness ratio of floor joists, and strength of steel are analyzed in though finite element method. The conclusions are: The span of composite beam has a great influence on the ultimate bearing bending capacity and failure mode, suggesting that the economic mid span of this beam should be 2400 mm to 5400mm; With the improving of the concrete slab thickness and strength of steel and reducing of the screw spacing, the flexural bearing capacity of composite beams increases effectively. Thus, the thickness of concrete slab is recommend to be 30 ~70 mm, and 100 ~ 300 mm for the screw spacing. For the composite beam, the higher width-height ratio and height-thickness ratio lead to an increase in ultimate flexural capacity but a decrease in shear bearing capacity.Finally, the design method for partial shear connection of composite beam is established in this paper. Considering the effects of width-height ratio and height-thickness ratio and screws for shear resistance, coefficient of flexural capacity of partial shear η is put forward, which can be used in ultimate flexural bearing capacity calculation.