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Sunday, March 7, 2021

What is the difference between pre-tensioning and post-tensioning?



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In the method of prestressed the tensile are generally stressed with the help of steel in which the compressive stresses are taken by concrete. The method of prestressed is included with two methods - internal prestressing and external prestressing. There are two types of internal prestressing and they are pre-tensioning and post-tensioning. Pre-tensioning is a process in which the steel tendon is usually tensioned before casting the concrete whereas, in Post-tensioning, the steel tendon is usually tensioned after casting the concrete.


What is tensioning concrete?

Tensioning concrete is a process of concrete in which the internal stress is introduced for putting the element into compression. In this process, the tensile bending gets stressed because of self and applied loading which is offset with the help of inbuilt compression. It is introduced by tensioning steel and is done either before casting the concrete which is called pre-tensioning and also after casting the concrete which is referred to as post-tensioning. In the process of tensioning concrete reinforcement of steel bars and fabric are placed in the areas in which the tensile stresses can occur under the load. Hence the reinforcement of the steel is very strong in tension since it is able to absorb the stress that is developed in the concrete. Apart from that, this type of tensioning concrete has high tensile strength but does not exceed pre-compression stresses and cracking. 


How pre-tensioning is done?

Pre-tensioning is the process in which the steel tendons are tensioned before casting the concrete. In this process, the tendon is tied down against a particular projection. Once the concrete is set and solidified the tendon are cut or discharged. For pre-tensioning concrete, it is highly required to tensioned the steel in between the anchorages that remain external to the member. After that, the concrete is cast around it and it has developed a sufficient amount of strength the tension. Once the concrete is casted force can be transmitted to the concrete over a particular distance from each end of the member.        


How post-tensioning is done?

Post-tensioning is the process that is made by casting concrete and it contains the ducts through which the tendon is threaded. Another way to do post-tensioning is to cast the concrete which is greased as well as encased in a plastic sleeve. The tendons are tensioned at the time when the concrete gets enough strength with the help of a portable jack. Then the load will be transmitted and the steel is stressed. That means in this process of post-tensioning concrete is poured before the tension is applied and is stressed before the load is applied.  


What are the advantages of prestressed concrete?

Prestressed concrete comes up with several benefits as compared to conventional concrete. Some of the common advantages of prestressed concrete are given as follows:

The whole concrete cross-section of prestressed concrete has the capacity to resist the applied force. That is the reason why in this process the whole concrete does not suffer in case of cracking. 
The duration and longevity of prestressed concrete are comparatively longer than that of the reinforced concrete.
The length of the longer span enhances the untroubled floor space as well as parking facilities.
A longer span will require fewer joints and this needs less maintenance.
Since the concrete is crack free the probability of steel corrosion as well as the subsequent concrete deterioration is declined.
Prestressed concrete has longer durability.
Prestressed concrete can bear a reversal of stress, impact, vibration as well as a shock since in this process there is no risk of cracking.
In prestressed concrete the dead loads are neutral and the weight of the dead load of the structure is decreased because of which the consumptions of materials is reduced.
Large liquid such as the Hollow hydraulic cylinder that is constructed from the prestressed concrete is less costly. Apart from that, such types of cylinders are also safe against cracking and there is no risk of having leakage. 
Prestressed concrete also comes up with low deflection. 
What is the difference between pre-tensioning and post-tensioning?
There are many differences between pre-tensioning and post-tensioning and some of the major differences are listed as follows:
Pre-tensioning is usually done in factories whereas post-tensioning is done in both factories and sites.
In the case of pre-tensioning, the strands are tensioned prior to the casting of the concrete but in the process of post-tensioning, the strands are mainly carried out once the concrete attains enough strength.
With pre-tensioning, you can create small sections whereas there is no restriction of size and you can create long sections as per your requirement.  
In Pre-tensioning the loss of prestressing

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