Mechanical properties of composite beams with web openings under negative bending moments

Experimental research and nonlinear finite element parameter analysis were performed to study the mechanical properties and ultimate bearing capacity of composite beams with web holes under a negative bending moment, and the mechanical properties of composite beams reinforced around the holes. The results indicate that, after the holes were opened, the stiffness and bearing capacity of the composite beams in the negative moment zone were significantly reduced. The stress–strain distribution in the section of the cave entrance no longer accords with the hypothesis of the plain section and shows an S-shaped distribution. The thicknesses of the concrete slab and steel beam web significantly affected the ultimate bearing capacity. The concrete wing slab significantly contributed to the shear capacity of the composite beams with web holes in the negative-moment zone. The interface slip value of the hole area increased significantly, indicating that the stud exhibited plastic deformation. Based on the serious problem that the load-bearing capacity and deformation capacity of composite beams after web holes are weakened, and combined with current mainstream reinforcement measures, a new reinforcement measure is proposed to change the shear distribution around the holes and improve the ductility and bearing capacity of composite beams with holes in the negative bending moment area.