What are the working characteristics of assembled concrete building steel bars?

Some people think that there is no difference in the content and method of steel bar operation between prefabricated concrete buildings and traditional cast-in-place concrete buildings, and insufficient attention is paid to the unique steel bar operation procedures and technical training of prefabricated concrete buildings. In fact, there is a big difference between the two. For example, the processing method of steel bars in prefabricated concrete buildings is usually to bind or weld the processed single steel bar into a steel bar skeleton first, and then hang the steel bar skeleton into the formwork. When hoisting into the formwork, it is necessary to ensure that the steel skeleton is not deformed. If it is deformed, the thickness of the protective layer of steel bars will be too large or too small, which leads to the connection mode of steel bars in assembled concrete buildings is very different from that in traditional cast-in-place concrete buildings. In traditional cast-in-place concrete buildings, the connection modes of steel bars are mainly welding, lapping and binding, while in assembled concrete buildings, the connection modes of steel bars are grouting sleeve connection, mortar anchor lap connection and mechanical connection. Ensuring the quality of steel bar connection is the most important task of steel bar operation in assembled concrete buildings.

As a practitioner of assembled concrete buildings, in order to produce qualified and high-quality steel products, produce high-quality prefabricated components and ensure the quality of assembled concrete construction projects, we must fully understand the characteristics and key points of steel bar operation in assembled concrete buildings.

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From the fabrication and installation of prefabricated components in precast concrete buildings, there are many differences between steel bar operation and traditional cast-in-place concrete buildings. The operation of steel bars in precast concrete buildings has its own characteristics, which can be summarized as follows:

(1) The focus of steel bar operation has shifted from site construction to factory construction. Assembled concrete building is to disassemble the building structure, prefabricate most prefabricated components in the factory, and then transport them to the construction site for installation and joint connection, so as to make it a whole building. In this way, most of the reinforcement work is transferred to the factory.

(2) The reinforcement work on the construction site is changed from on-site production to on-site connection.

Because the construction method has changed from on-site construction to on-site installation, most of the reinforcement work on the construction site has been reduced. The main work of on-site reinforcement is the reinforcement connection between components (Figure 1), the reinforcement connection of nodes and a small amount of floor reinforcement construction (Figure 2).

(3) The quality of steel bar connection becomes the focus of quality control.

Precast members are all produced in the factory, and the quality can be guaranteed. Therefore, the quality of on-site installation becomes the key to the quality of precast concrete buildings, and the connection quality of the most important and critical steel bars in on-site installation quality becomes the focus of quality control (Figures 3 and 4).

Fig. 3 Mechanical connection of steel bars

Fig. 4 Reinforcement binding connection

(4) The degree of automatic processing of steel bars is high.

The steel bars of prefabricated components are processed in the factory, and batch and automatic processing can be realized by using automatic equipment, which can greatly improve the efficiency of steel bar processing compared with on-site processing (Figure 5).

Fig. 5 Automatic processing equipment for truss reinforcement.

(5) The degree of refinement of steel bar processing is greatly improved.

Most prefabricated steel bars are processed by automatic or semi-automatic equipment in the factory, and the processing accuracy of steel bars reaches millimeter level (Figure 6), which is greatly improved compared with on-site processing.

Fig. 6 Steel mesh automatically processed by the factory.

(6) The rebar operation is highly correlated with the formwork.

In order to ensure the integrity of the whole building, most prefabricated members will extend steel bars on the side, which requires opening holes (Figure 7) or grooving in the corresponding parts of the formwork, which does not exist in cast-in-place concrete buildings.

Fig. 7 The hole on the formwork where the steel bar protrudes.

(7) The accuracy requirement is high, and the allowable error of the length and position of steel bars is very small.

Precast members are installed on site, and the protruding reinforcement of the lower member is connected with the sleeve or reserved blind hole of the upper prefabricated member, which requires high accuracy of the length and position of the protruding reinforcement (Figure 8) to ensure effective and reliable connection.

Fig. 8 The length and position of the lower member protruding from the steel bar shall ensure the accuracy.

(8) Tolerance for omissions and errors is reduced.

All kinds of embedded parts or protruding steel bars in prefabricated components have specific functions. Once it is omitted or deviated, it will bring inconvenience to the installation of prefabricated components or affect the connection of components, and even lead to the scrapping of prefabricated components.

(9) Take measures to avoid the interference of embedded parts and inserts.

All kinds of embedded parts and objects in prefabricated components will affect the installation of steel bars to a certain extent, so it is necessary to avoid steel bars reasonably according to the design and specification requirements.

(10) The requirements for concrete protective layer are more stringent.

In order to ensure the durability of prefabricated components to meet the design requirements, the factory has extremely strict requirements on the protective layer of steel bars in the production process (Figure 9).

Fig. 9 Steel protective layer gasket

(1 1) During installation, attention should be paid to the collision and interference of steel bars.

When precast members are installed on site, the deviation of the position of protruding steel bars or the conflict with the position of reserved steel bars on site are likely to cause collision and interference, which will affect the construction.

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The characteristics of steel bar operation in prefabricated concrete buildings determine the key points of steel bar processing operation. In the process of assembling concrete building steel bars, we must firmly grasp the following points.

Key points of reinforcement processing operation

1. It is necessary to open a hole or slot on the formwork to extend the reinforcement, and the position and length of the extended reinforcement must be accurate. A setting device can be added to ensure that there is no deviation between the position of the protruding steel bar and the protruding length (Figure 10).

Figure 10 Positioning of protruding reinforcement

2. Grouting casing is the key component of structural connection, with large diameter and volume and smooth appearance. Usually, stirrups should be reinforced around the grouting sleeve, and the thickness of the protective layer of steel bars must meet the requirements.

3. In order to ensure the firm and reliable connection between embedded parts and prefabricated parts, steel bars or other connectors are often used to connect with steel bars to disperse the stress and avoid being pulled out or pulled off when stressed. At the same time, because the embedded parts and embedded parts may force the steel bar to shift, bend or cut off, it is necessary to analyze the steel bar diagram and component diagram in advance before the steel bar processing, and adjust the steel bar in the impacted part reasonably to ensure the accuracy of steel bar processing.

The above are collected and sorted by Zhong Da Consulting Company.

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