Prestressed Anchor Flexible Member

A friend or friend once asked me a question like "Can you describe what prestress is in simple language? The editor with this question about prestressing equipment will lead you to talk about what is prestressing. The simplification of complex knowledge is conducive to our understanding. Prestress is actually to actively generate stress in the component through methods such as tension, compression and bending before the structure works normally (stress is the concept of material mechanics, which can be understood as the unit force inside the material). What is the main purpose of this?

1. Give full play to the strength of materials. Some materials have low tensile strength and are only suitable for compression, otherwise they will easily crack and damage, such as concrete and stone; some materials have high tensile strength, but cannot be compressed and cannot bear under pressure. Such as steel cables. When two materials work together as a whole, due to the different characteristics of the materials, the strength of the materials is often not fully utilized. For example, reinforced concrete, that is, high-strength steel and concrete are used. Because of material strain, the strength of steel is always far from being destroyed, and the concrete has been crushed first. This requires the use of prestressing methods, which can reduce the strain of concrete in the compression zone during normal operation, so as to make full use of the strength of high-strength steel and concrete.

2. Reduce material deformation during normal work. For most objects that can be seen in daily life, force and deformation are inseparable brothers. There must be deformation when it is strong, although it may not be visible to the naked eye. Therefore, the pre-stress will cause a certain deformation of the component, and usually make this deformation opposite to the deformation under the normal working state, thereby offsetting and reducing the deformation of the component under normal working. The normal use of buildings requires deformation. Excessive deformation may cause cracking of paint, glass crushing, corrosion of steel bars, leakage of gas and radioactive materials, etc. The editor of the prestressing machine reminds everyone that you can imagine why a wine barrel composed of pieces of wooden boards through iron hoops can be filled with wine without leaking?

3. Changing the stress distribution during normal work. Before normal work, stress is generated inside the component in advance, and this stress can be superimposed with the stress under normal working conditions. Thereby improving the stress distribution in the cross section. For example, the stress distribution in a curved beam section is partly tensioned and partly compressed. If a reverse bending moment is added before normal work, the expected tension part is compressed and the compressed part is tensioned. The stresses can cancel each other out during work, thereby reducing the ultimate stress in the component.

4. The cables and membranes that make the flexible members rigid and flexible are slack when they are not stretched and cannot bear any external force. Only pre-tensioning can provide rigid performance (stress stiffness) to carry external loads. And the greater the tension, the higher the stiffness. There is a type of structure where the components under tension are completely flexible, and the components under compression or bending are completely rigid. This type of structure is a tensioned overall structure. The chair shown at the beginning of the article is a typical tensioned overall structure. The existence of prestress makes the thin cable and the central iron chain both under tension. The system may fail in the following two forms:

1. System instability (including insufficient prestress, too small tension of the thin cable, and structural collapse).

2. The heavy object is too heavy, exceeds the strength limit of the iron chain, and breaks.

In daily life, pre-stressed structures are extremely efficient, light and handy, and have good construction effects. They are also extremely economical in terms of material consumption. They are deeply loved by structural engineers in the field of construction.