Experimental and Design Parametric Study of a Novel Grouted Square Steel Tube Upper Chord–Concrete Composite Floor

A novel composite floor consisting of an upper chord of a grouted square steel tube truss and a lower chord of a reinforced concrete slab is proposed to address existing problems with precast composite floors, such as a complex construction process, high cost, significant resource consumption, and severe environmental pollution. Sixteen-point loading tests were carried out on five simply supported one-way slabs to simulate the stress state of the floor under a uniform load and to investigate the stiffness, cracking moment, load-carrying capacity, and failure mode of the composite floor system. The results showed that the composite floor system exhibited ductile failure, with cracks uniformly distributed at the bottom of the slab; additionally, the grouted steel tube did not experience uplift or out-of-plane buckling, and the truss welds did not fracture, indicating that the composite floor system still had further deformation capacity and load-carrying capacity with satisfactory stress conditions. After unloading, the residual deformation of the composite floor accounted for 28% to 36% of the maximum deflection, demonstrating good deformation recovery ability. The bottom slab thickness and truss height are key parameters that influence the new composite floor, and increasing the two parameters enhances the cracking load, deformation resistance, and flexural capacity of the composite floor, with a significant improvement achieved by increasing the truss height. The floor slab should have a minimum thickness of 60 mm, as required by China’s Code for Design of Concrete Structures, and the truss height-to-span ratio should be 1:30, which meets the deformation and load-carrying requirements of the floor and conforms to the design concept of green buildings.

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