Theoretical Analysis and Experimental Study on Bending Behavior of Steel-Concrete Composite Flat Beams

The steel-concrete composite slim floor has the advantages of small height of the floor structure, good fire resistance, good appearance of the lower surface, easy pipeline laying, and smaller beam height in the economic span, and has been widely used in foreign countries (especially the United Kingdom and Northern Europe). The steel-concrete composite slim floor commonly used in the actual project is SP prestressed hollow slab and deep deck steel plate composite floor. When used in residential buildings, there are the following deficiencies:1) The lower flange of the steel beam is exposed, requiring anti-corrosion and fire protection. 2) The uneven bottom flange of composite slim beam with deep deck needs to be suspended, which increases cost and structural height. 3) SP prestressed hollow slab and deep rib profiled steel plate both are one-way slabs, which results in a large floor thickness, and it is difficult to further reduce the height of the floor, which restricts the application of the steel-concrete composite slim floor in practical projects. To this end, this paper presents the concept of prefabricated concrete hollow slab and composite slim beam with concrete hollow slab. The prefabricated concrete hollow floor is composed of prefabricated concrete hollow slab and cast-in-place concrete, which can achieve two-way force transmission. Because this new type of composite slim beam with concrete hollow slab is different from the traditional SP prestressed hollow slab and deep rib profiled steel plate. In order to study the cooperative working performance and design method of the new composite slim beam with concrete hollow slab, theoretical analysis and experimental study of the bending performance of the new steel-concrete composite slim beam with concrete hollow slab were carried out.
In this paper, two specimens of composite slim beam with concrete hollow slabs were designed and manufactured. The main changing parameters were the opening pattern of steel beam webs and the settings of shear keys. The steel beams are welded unequal flange steel beams, and the floor slabs are prefabricated concrete hollow slab. The steel grade is Q345B, the floor concrete is C35, and the steel bar is HRB400. The calculated length of the test piece is 3 800 mm, and the geometric length is 4 000 mm. Through experiments, the bearing capacity, ductility, deformation performance, crack development, stress and strain development of the new steel-concrete composite flat beam were studied. On the basis of experimental research, a simplified assumption for the calculation of the ultimate bending capacity of prefabricated concrete hollow slab is proposed, and the calculation formula of the ultimate bending capacity of the prefabricated concrete hollow slab is derived based on the failure strength theory.
The following conclusions were obtained through theoretical analysis and experimental research:1) The composite slim beam with concrete hollow slab has excellent bearing capacity and ductility. When the deflection span ratio of the specimen reaches 1/32, the bearing capacity of the specimen has not decreased significantly, and the specimen exhibits the characteristics of ductile failure. 2) When the bottom flange of the steel beam and the tensile steel bar yield, the test piece reaches the yield bearing capacity; when the steel beam full-section yields, the tensile and compression steel bar yields, and the concrete in the compression zone collapses, the test piece reaches the ultimate bearing capacity. Before the peak load, the strain distribution of the concrete and steel beam sections is approximately linear, and the flat section assumption can be used. 3) The calculation formula of the bending capacity of the composite slim beam with concrete hollow slab based on the failure strength theory is in good agreement with the test results and is safe.