English：

The stress mechanism of composite slab at different stages is analyzed, and the calculationformulas of vertical compressive stress and horizontal shear stress of unidirectional composite slabcomposite surface under vertical load are derived. It is found that the shear stress of the composite surfaceincreases linearly with the increase of the plate span. The vertical stress of the composite surface isrelated to the shear slope, and the smaller the plate load is, the smaller the compressive stress of thecomposite surface is, or even decreases to the tensile stress, but the tensile stress value is much smallerthan the bonding force of the new and old concrete composite surface. The numerical simulation of thecomposite slab with or without steel bar truss is carried out. It is found that the steel bar truss improvesthe stiffness of the floor to varying degrees in the construction stage. However, at present, the slab spanis limited in the construction stage, and the prefabricated floor has enough bearing capacity, so the steelbar truss can be completely cancelled. The stiffness of the composite slab and the relative slip of thecomposite surface are obviously improved by the steel bar truss in the use stage. However, due to theinherent bonding force and friction force of the new and old concrete, the composite slab without steel bartruss can also meet the needs of bearing capacity, and the steel bar truss can also be cancelled. Finally,it is suggested that on the basis of ensuring the bonding quality of the new and old concrete compositesurface, the steel bar truss can be cancelled to reduce the amount of steel used and facilitate the on⁃siteconstruction.