Prefabricated reinforced concrete floor slabs are prefabricated at a prefabrication site and then installed at the construction site.
Commonly used precast reinforced concrete slabs can be divided into three types according to their cross-sectional forms: flat slabs, channel slabs and hollow slabs.
(1) Types of precast reinforced concrete panels.
①Solid flat plate. The span of prefabricated solid slabs is generally small, no more than 2.4m. If made into prestressed components, the span can reach 2.7m. The plate thickness is generally 1/30 of the plate span, that is, 50 to 100mm, and the width is 600mm or 900mm. Prefabricated solid slabs are often used as walkway slabs, storage room partitions or kitchen and toilet slabs due to their small spans. It is easy to make and low in cost, but the sound insulation effect is not good.
②Trough plate. The trough-shaped plate is composed of several ribs around and in the middle and a flat plate on the top or bottom. It is a combination of ribs and plates. Because of the ribs, its allowable span can be larger. When the ribs are under the slab, it is called a positively grooved slab. The stress of the positive groove plate is reasonable, but after installation, the ceiling appears uneven due to the rib beams. When the ribs are on the board, it is called a counter-groove board. Its stress is unreasonable. After installation, there are ribs protruding from the floor, but the ceiling is flat. When using a reverse-grooved slab floor, the ribs and spaces between the ribs can be filled with loose materials, and then wooden floors can be erected on the ribs as the ground. This kind of floor has the characteristics of thermal insulation and sound insulation, and is often used in buildings with special sound insulation and thermal insulation requirements.
③Hollow plate. Hollow slabs are made by drilling holes in a flat plate along the longitudinal direction. The cross-sections of the holes include round, square, rectangular and oblong, among which round hole plates are the most common. Compared with solid flat plates, hollow core slabs can improve the bending resistance of the section and enhance structural rigidity without increasing the amount of concrete and steel bars. Hollow floor slabs have the advantages of low weight, less material, high strength, and economy, so they are widely used in a large number of buildings.
The thickness of the hollow board depends on the span of the board, which is generally 110~240mm, the width is 500~1200mm, and the span is 2.4~7.2m, among which the more economical span is 2.4~4.2m.
(2) Detailed structure of reinforced concrete precast panels.
①The shelf structure of the board. There are two ways to lay the board. One is to place the board directly on the wall to form a plate structure; the other is to place the board on the beam, and the beam is supported on the wall or column to form a beam-slab structure. The arrangement of the panels depends on the structural layout plan.
The board must have sufficient resting length on the wall, which should generally not be less than 100mm. In order to ensure a reliable connection between the board and the wall, cement mortar, commonly known as mortar, should be laid on the wall before installing the board, with a thickness of not less than 10mm. After the board is installed, the end joints of the board must be filled with fine stone concrete or cement mortar; if it is a hollow board, the holes should be plugged with bricks or concrete at both ends of the board to prevent the board ends from being crushed where they are placed. At the same time, it can also prevent fine stone concrete from flowing into the hole when grouting the slab joints. The longitudinal edge of the hollow board on the wall side should be placed against the wall, and the gap between the board edge and the wall should be filled with fine stone concrete. In order to increase the overall stiffness of the building, steel bars can be used to tie the boards to the walls and between the boards. The configuration of tie steel bars depends on the overall stiffness requirements of the building and its seismic resistance.
There are two ways to place the plate on the beam: one is to place it on the top surface of the beam, such as a rectangular beam; the other is to place it on the flange of the beam, such as a flower basket beam. In the latter way of shelving, the upper surface of the plate is flush with the top surface of the beam. In this case, the span size of the plate is the center span of the beam minus the width of the top surface of the beam.
② There are three types of side seams on the board: V-shaped seams, U-shaped seams, and groove seams.
In order to facilitate construction, when arranging panels, the fewer specifications and types are generally required, the better. Usually, there are no more than two specifications for the width and size of prefabricated panels in a room. Therefore, when laying out the floor slabs of a room, there may be a difference between the width direction of the slab and the plane size of the room, that is, there may be a gap that is not enough to clear one slab. At this time, corresponding measures should be taken to fill the gaps according to the size of the remaining gaps. When the gap is within 60mm, adjust the width of the board seam; when the gap is between 60 and 120mm, you can pick two skin bricks along the wall to solve the problem; when the gap exceeds 200mm, you need to reselect the specifications of the board.
3) Assembling monolithic reinforced concrete floor slabs
Assembling monolithic reinforced concrete floor slabs depends on the structure and construction method.
There are dense-ribbed floor slabs and superimposed floors. Types such as floor slabs,
due to the complexity of construction,
are now less commonly used.