Prefabricated slabs are generally divided into strip slabs, ribbed slabs, hollow slabs, etc., and most of the force forms are simply supported slabs. The commonly used reinforcement methods include the enlarged section reinforcement method and the carbon fiber fabric reinforcement method, as well as the structural force transmission method reinforcement method.

The enlarged section reinforcement method is to add a post-cast layer of reinforced concrete not less than 40mm thick to the slab surface or bottom. In order to facilitate construction, slab pouring is often used to form rigid floors and roofs. If it is necessary to use the bottom of the slab to cast the superimposed layer, it is necessary to chisel the bottom of the slab and use the spray method for construction.

The prefabricated slab reinforced with carbon fiber fabric is to adhere the carbon fiber cloth to the tensile part of the bottom of the plate along the direction of the slab through structural adhesive, and it must be reliably anchored at its end. The advantage is that the carbon fiber cloth has light weight and high strength, and can be pasted or bent. After reinforcement, it basically does not increase the weight of the original component, and does not affect the structural shape. It can not only improve the structural bearing capacity but also enhance the structural rigidity.

Changing the structure force transmission method reinforcement is to add beams and columns at the bottom of the prefabricated slab, greatly reduce the bending moment of the slab and improve the bearing capacity of the structure, so as to achieve the purpose of reinforcement. The additional beams and columns can be divided into reinforced concrete members and steel members according to different materials. Generally, in order to reduce the wet operation, additional steel beams are used for reinforcement.

So how to deal with the opening and reinforcement of prefabricated plates?

Generally speaking, after opening the prefabricated plate, the original force transmission path and reinforcement are partially cut off. On the one hand, the internal force of the surrounding plate of the opening is increased, which will cause stress concentration. On the other hand, the reduction of the plate reinforcement is the reduction of the bearing capacity. Therefore, a reasonable reinforcement method should be selected for the reinforcement of the opening by internal force analysis and bearing capacity calculation after the opening.

Generally speaking, when the width of the hole perpendicular to the direction of the plate is less than 300mm or the diameter of the hole is less than 300mm, and the number of cut steel bars is less than 5%, no reinforcement treatment is required.

When the width or diameter of the opening is not more than 1000mm, and the impact on the plate is small after opening the hole, only by structural reinforcement, it is possible to use the reinforced steel method or the carbon fiber cloth to reinforce the hole.

When the opening is large or the number of cut steel bars is 20% and there is a large concentrated load around the opening, and when the prefabricated plate cuts the main rib, a side beam should be provided to support the force transmission. Generally, the side beams are rigid beams or cast-in-place concrete beams, and the new components need to be reliably anchored with the original components.