Study On The Behavior Of Cold-Formed Steel Concrete Composite Floor

As a new type of floor structure, the mechanical performance of cold-formed steel concrete composite floor has not been well studied. Through the experimental study, finite element analysis and theoretical analysis, the mechanical performance of composite floor was studied, and the corresponding design method is put forward.Firstly, through the full-scale test of cold-formed steel concrete composite floors, which are different in structure installations, such as, space between screws connecting the profiled steel sheet and floor joists, rigid blockings, quantity of floor joists and the boundary constraints, the mechanical performance at construction stage and serviceability limit stage was studied. The influence to strength and rigidity at construction stage, bending rigidity and fundamental frequency at serviceability limit stage, ultimate flexural capacity and the failure mechanism of composite floor are systematically analyzed for the first time. The research shows, reducing the space between screws connecting the profiled steel sheet and floor joists, reinforcing the end constraint and setting rigid blockings can increase the strength, rigidity and fundamental frequency of the composite floor. The ultimate flexural capacity of composite floor increases with the increase of floor joists and the decrease of space between screws connecting profiled steel sheet and cold-formed steel joists. And the characteristic of failure is the compression flange, curing, and web plates are relatively bucking while the floor beams appear bending and torsion deformation, the wave length of bucking is the distance between adjacent screws. The concrete slab near the support separates from the profiled steel sheet, and distortion damage of floor joists where concentrated load acted.Then mechanical properties of experimental models at different stages were simulated with finite element method based on ANS YS program, the feasibility of linear analysis with finite element method, modal analysis, and nonlinear analysis considering geometrical, material and contact, were approved. Using finite element method based on ANSYS program, different influencing factors were analyzed, such as the change of space between screws, thickness of floor joists, thickness of concrete slab, plate shape of profiled steel sheet, space between floor joists, width of floor, selling, rigid blocking and flat strap, width-height ratio of floor joists, height-thickness ratio, strength of steel, strength of concrete, etc. The analysis shows, at construction stage and serviceability limit stage, the change of space between screws, thickness of floor joists and concrete slab, space between floor joists, width-height ratio of floor joists and height-thickness ratio have great influence to the strength, rigidity and fundamental frequency of composite floor, but the shape and width of profiled steel sheet nearly have no influence. The ultimate flexural capacity of composite floor can be increased remarkably by reducing the space between screws, the space between floor joists, width-height ratio of floor joists, height-thickness ratio, increasing the strength of steel, the thickness of floor joists and concrete slab, width of floor, but the ductile performances of composite floor have nothing to do with the strength of concrete, space between floor joists, width of floor. Based on these performances, for the first time, this paper suggested when the space between screws connecting the profiled steel sheet and floor joists is one wavelength of corresponding shape of profiled steel sheet, permissible value of deflection corresponding to the width-height ratio of floor joists and height-thickness ratio of web with different sections should not bigger than//300 at construction stage. Under the nominal combinations of loads at the serviceability limit stage, the fundamental frequency of composite floor should not smaller than 10Hz, and the corresponding deflection at mid-span had better smaller than 3.Omm.And T shape composite joists is suggested as the simple model of composite floor.At last, adopting elastic theory and plastic theory, theoretical analysis method of simply supported composite beam is established. Considering the effects of width-height ratio and height-thickness ratio of floor joists, correction coefficient of flexibility y (at construction stage) andψ(at serviceability stage), coefficient of flexural capacity shearing completelyηare put forward. At last a formula for calculating fundamental frequency of simply supported composite beam is deduced, and correction coefficient of fundamental frequencyζi and correction coefficient of boundary constrainsλare put forward.The test results and finite element analysis results of this text can be referenced in design and research, basing on certification of further test the formula can be used in engineering design.