There are many things to consider for which the use of concrete makes our life a lot easier. The different materials that are used to form concrete are much easily available which makes the mixture a lot accessible too. Apart from that the strength of the material is also one of the important factors to take into consideration. There can be different parts in which the material can be divided depending on its use.
The various types of losses that can be seen in the different pre-stressed and post-tensioning concrete are given below:
Elastic deformation: The particular type of loss is mainly due to the elastic deformation taking place in the concrete which largely depends on the modular ratio between the modulus elasticity of the steel and that of the concrete. The modular ratio is generally calculated at the level of the steel.
Relaxation of stress: Everyone is aware of the fact about the different characteristics of the steel and that they also possesses some of the similarities to that of the properties of concrete. Creep is one of such characteristics in steel whose values stay somewhere 3% to 5%, mostly 3% in steel. The losses related to the relaxation of stress on the steel generally vary with the different types of steel along with its initial pre-stress, age and temperature. So it is better to conduct different experiments to know the right value of the creep in steel.
Shrinkage: Shrinkage that takes place in the different sections of the pre-stressed members, generally making the tensioned wire to shorten in length, contributing to the different loss of stresses. The nature of shrinkage is much influenced by the different characteristics of the type of cement used along with the aggregates and the method of curing followed.
Creep: Generally the pre-stressed members in the concrete are the major reason for the creep. This effectively creates an amount of stress in the different parts of the high tensile steel. The factors that influences the various characteristics of the creep are humidity, level of stress, the strength of the cement used, the age of loading of the mixture, the duration of the stress, the ratio of water and cement in the particular mixture. In order to know the actual amount of creep characteristics that is being affected in the concrete one can conduct two different calculation methods: the Ultimate creep stain method and the creep co-efficient method.
Friction: It can be considered as one of the important factors to influence the different losses that take place in the different parts of the post tensioned concrete. The tendons are generally in the form of ducts in this type of members and are either straight or in the form of a curved profile. Loss of stress generally takes place when the curves of the tendons are generally influenced by the introduction of the tension.
Anchorage slip: In the particular system that involves post-tensioning, the cable is tensioned in order to release the jacks for the sole function of transferring the pre-stress to the different wedges along with the grip to the wires. The slip which is generally present at a mere smaller distance from the wires is forced between the wedges. The different types of wedges and the stresses present in the different parts of the wires much influence the stresses of the post-tensioned part.
Conclusion
The varied use of concrete is not only limited to the part that we are generally aware of. If it can be seen from the perspective of a civil engineer than there are lot of ways that the material is useful that is much unaware to us and there can be problems that can affect that particular related parts too.
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