Experimental Research On Rectangular Truss Multi-ribbed Hollow Composite Floor

This paper proposes a new type of rectangular steel truss which is used as the stress skeleton of prefabricated floor,and then the rectangular truss multi-ribbed hollow composite floor system is put forward.Rectangular truss multi-ribbed hollow composite slab is a new type of prefabricated floor system belonging to two-way plate stress system,which is suitable for the houses with a large open space and flexible division of free space.As one of the floors of the new large space PCSI system,rectangular reinforced truss prefabricated slabs have the same advantages as the other prefabricated floors such as high degree of prefabrication,fast construction,short construction period,cost effectivity and environmental conservation.Moreover,the span length and out-of-plane stiffness of this type of slabs are obviously better than those of the traditional triangular reinforced truss prefabricated slabs.The concrete near neutralization axis were replaced with the built-in lightweight foamed concrete block so that the slabs could gain more advantages than other prefabricated floors such as thermal insulation,light weight and long span.The experimental study on mechanical behavior of the rectangular truss multi-ribbed hollow composite slab is of great significance to the application of this floor in civil engineering.A 1:1 full-scale element plate model was made to study the composite process in this paper.Due to the reinforcement of steel truss,the deformation of the floor slabs in the process of compositing is very small,which can meet the requirements of large-span,none-formwork,assembly and so on.The full-scale experimental study of double simply supported rectangular truss multi-ribbed hollow composite slab was carried out.The cracking bending moment,bending bearing capacity and failure characteristics of this kind of composite slabs were obtained.The development rules of concrete crack and the stress-strain relationships of steel bar and concrete were acknowledged.The test results reveal that the failure of the composite floor slab is characterized by the fact that the crack width reaches the limit value in the code,and the ultimate bearing capacity is actually much larger than the cracking moment.Before the mid-span bending moment reaches the cracking moment,the overall stiffness of the slab is large,the strain of steel bar and concrete increases simultaneously,and the magnitude of the stiffness is approximately 0.8 times of the overall bending stiffness of the section.After concrete cracks,the stiffness decreases gradually with the development of cracks,and the strain growth rate of steel bar at the bottom of the slab increases significantly,while the strain of the steel bar at the top of the slab is similar to that of concrete.Considering the damage of concrete,the finite element model of the test specimen is established.The comparisons of the test results and the finite element analysis results show good agreement.The composite floor slabs(in tests)have similar mechanical properties to the whole casted floor(in finite element models).Based on the results of test and finite element analysis,the calculation expressions of bearing capacity and stiffness of composite slabs are given in this paperand the constructional requirements for the connection of this kind of slabs are put forward.Compared with the equal thickness ordinary concrete slab,the weight of rectangular truss multi-ribbed hollow composite slab is reduced by 1/3,the bearing capacity is basically the same,and the stiffness is reduced by 18%.Due to the decrease of self-weight,the bearing capacity of the new-type floor is obviously better than that of the ordinary floor,and the economic advantage is obvious.The research results of this paper provide a reference for the compilation and engineering application of rectangular truss multi-ribbed hollow composite slabs.