One is a flat plate and the other is a beam. For beams and plates, according to the position relationship between beams and plates, they are divided into low plate position, middle plate position and high plate position.
So how do you distinguish between board positions?
The bottom of the beam is flush with the bottom of the plate, which is called low plate position;
The plate is in the middle of the beam, which is called the middle plate position;
The top of the beam is flush with the top of the plate, which is called the high plate position.
For the flat type, it doesn't matter who is tall or low. Large reinforced concrete slab belongs to slab type.
Figure 1 Flat Beam Raft Foundation
Next, let's look at the shapes of beams and plates. As shown in Figure 2, it is a typical form commonly used in modern residential buildings. The form of pipe-in-pipe may be the elevator room, and the others are the rooms of the house. Then the whole bottom foundation is a flat plate without height difference, which belongs to a kind of flat raft foundation.
Figure 2 Flat Raft Foundation
In Figure 2, the stress on the flat raft foundation is relatively dispersed. For each part with relatively concentrated stress in Figure 2, reinforcement design needs to be carried out separately because it is relatively dispersed and unsystematic.
As shown in fig. 3, beam-slab raft foundation has columns above the slab, and the columns below are a form of frame beams and columns. However, the bottom plate is a whole flat plate regardless of its height, but in this flat plate, the force on the flat plate is clear, the force on the flat plate under the column is definitely greater, and the force between columns will be smaller.
Fig. 3 Raft foundation with beam and slab
If you want to use the beam-slab raft foundation as shown in Figure 3, because the concentrated force under the column is relatively large, you need the beam to transfer the force load, from the column to the beam, then from the beam to the plate, and then from the plate to the foundation below. However, this method will lead to irregularity under the whole floor, higher height, more steel bars and higher cost.
Therefore, if you don't want to use the beam under the column, you can use the method shown in Figure 4. In this way, from the external section of concrete, the height is the same, but it is reinforced with steel bars, such as the position under the column, which is represented by strips. In two directions (X or Y direction), the reinforcement under the column is matched with the lower plate of the column, and the middle of the lower plate of the column is a mid-span plate, which is also in two directions. The mid-span plate is less stressed, so the reinforcement will be less. These two kinds of plates and belts are staggered to form reinforcement and distinguish the overall stress. Although it is only distinguished by the steel bars of the plate, the whole concrete looks like a whole flat plate in appearance. Therefore, the raft foundation with flat plate is also a flat raft foundation.
Fig. 4 Plate-shaped flat raft foundation
Next, let's look at the beam-slab raft foundation. There is a foundation beam under the column, which connects the main beams of the column, and there is a secondary beam between the main beams. Beam-slab raft foundation is composed of beam and slab.
So what kinds of components are there in the beam-slab raft foundation?
Foundation main beam (under column), foundation secondary beam and beam slab raft foundation slab. There is no foundation secondary beam in Figure 3, and the knowledge of main beam and secondary beam is the same as that of beam. We will explain it in detail in the knowledge of 16G beam and reinforcement atlas. Let's pay attention to how tablets read pictures.
Fig. 5 Number of Raft Foundation Members of Beam-slab
As shown in Figure 6, the flat raft foundation is shown on the plan view. Generally speaking, the raft foundation has the thickness of the raft, which can be indicated on the drawing or explained in the description. When the thickness of some different joint parts is different, there will be detailed drawings to explain.
Therefore, when you look at the picture, you should look at it completely. Then, according to the methods and steps of recognizing the structural drawing mentioned above, you should read all the structural design descriptions and floor plans, as well as the drawing descriptions and detailed drawings of each floor plan together.
Then use the above method to understand the thickness of the raft first, and then look at the reinforcement of the board. The reinforcement of the plate has upper and lower reinforcement, so the upper and lower reinforcement should be marked when marking. The upper reinforcement and lower reinforcement in X and Y directions, together with * * *, form a large steel mesh. After concrete pouring, it is the whole concrete foundation.
Fig. 6 Plan of Flat Raft Foundation
Then we will take the actual engineering drawing (Figure 7) as an example to illustrate. First of all, the whole raft foundation has a large overall reinforcement, and then when the superstructure is loaded, it means that there is a concentrated force. In these places, there is a concentrated punching force acting on the plate, which means that the force on the plate will increase in these places. So there will be some additional steel bars (additional upper and lower parts) in these places, and the additional steel bars in some special parts will work together with the original steel bars on the whole board. That is to say, the whole plate is reinforced, and the local reinforcement is carried out in the weak links with large stress, which can not only meet the needs of flexible layout of the raft foundation superstructure, but also meet the role of efficient cost saving. This is also a widely used way of raft foundation. So when looking at the picture, in addition to the general reinforcement arrangement, we should also pay attention to the arrangement of each additional reinforcement.
Figure 7 Flat Raft Foundation 1 Figure
Finally, let's look at another kind of flat raft foundation. Except for the reinforcement arrangement mentioned above, as mentioned above, the overall height of the raft foundation looks the same, but it is not.
For the board, sometimes there are some independent columns, or some foundation pits, or other equipment foundations and so on. All these may lead to depression or local reinforcement of the raft. So there are some corresponding local details on our drawings. Therefore, the flat raft foundation looks like a flat plate on a large scale, but it may protrude, sag and break in some places. It is necessary to correspond the position of the detailed drawing with the position of the cross section on the drawing and figure out what each part is in order to understand the drawing. In other words, only in the first step can you understand the drawings and steel bars; In order to calculate the drawings and reinforcement in the second step.
Figure 8 Figure 2 Flat Raft Foundation
In the flat raft foundation, there is a special form called plate raft foundation. Steel belts are divided into under-column steel belts (ZXB) and mid-span steel belts (KZB). Each bar is indicated by its width, and the steel bars are staggered when arranged. As shown in fig. 8, the arrangement in the red dotted frame is called the slab under the column, and the part between the red dotted frames is the mid-span slab.
Fig. 9 Schematic diagram of plate belt under column
Plate raft foundation has centralized labeling and in-situ labeling. The contents marked centrally include: 1, serial number, and the section size of b=xxxx indicates the width of the strip (the thickness of the foundation slab is illustrated in the diagram). 2, the bottom and top through longitudinal reinforcement. The rules and arrangement of non-penetrating longitudinal reinforcement at the bottom and top are the same as the foundation slab of beam-slab raft foundation.
Figure 10 Through reinforcement and non-through reinforcement
The specific use scenario is designed with reference to the specific drawings, as shown in figure 1 1. The strip in one direction (X or Y direction) only has the reinforcement in the corresponding direction, and the reinforcement in the two directions is merged to form a mesh reinforcement. This is strip reinforcement. As for the reinforcement of beam-slab raft foundation, it is equivalent to the reinforcement of plate+beam, and the marking form is similar to that of beam, which will be explained later.