- What is the primary purpose of inducing internal stresses in prestressed concrete structures?
- What role does the anchorage block play in the stability of prestressed concrete structures?
- Why is it necessary to carefully select the cable profile in prestressed concrete construction?
Introduction
Prestressed concrete is a procedure wherein the internal tensions or stresses intensionally induced in order to improve its performance without imposing external loads upon it. The agenda of inducing these internal tensions in the structure acts as a counter force against the external loads induced on the structure of concrete (Fabbrocinon and et. al., 2017). There are different terms defined with respect to prestressed concrete. These are elaborated effectively in the assignment below:
Differential Shrinkage
This is the term applied for determining the difference between precast concrete's overall tension characteristics and on-site concrete's shrinkage characteristics. If applied effectively, differential shrinkage could affect strength of the prestressed concrete in terms of cracking and warping. In prestressed concrete beams, presence of this factor has a serious impact on its time dependent behavior. In addition to this, it also affects steel relaxation, compression steel, untensioned steel presence, etc.
Anchorage Block
The anchorage in the prestressed concrete consists the length of tendons, and is directly contacted with the concrete. In the post-stressed concrete, an anchorage plate is applied. There are various methods used to connect the tendons with the plates like button-heads, wedges and so forth. Plates smaller in size than the concrete required to be compressed are used for the purpose. However, this aspect in prestressed concrete is very crucial and stress is extremely complex. It has various components like curved trajectories and it is essential that it does not crack in order to ensure sustainability of the structure.
Bursting Pressure
Burst pressure is the type of pressure that could be handled by a tube or a pipe before bursting. There is a significant role of environment in determining this pressure. Inside prestressed concrete beams, there are pre-tensed cables that are pulled by each ends surrounding the anchorage. These are pulled till the necessary tensile force (Hurst, 2014). Due to its elastic contraction, this prestressed pressure is them transferred as compression over the beam. As a result, there is a pressure on the beam ends near anchors. After that the pressure is transferred effectively to the overall cross section. It is imperative that the end blocks sustain such high compression. This pressure induced by end block forces is called bursting pressure,
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Concordant Cable Profile
Concordant cable profile refers to a profile which produces a force coincident with the profile. While prestressed, it does not produce any deflection of the beam over the support. Thus, no reaction is induced. It is very essential that the most suitable type of cable profile is used for the prestressed concrete structure. The most appropriate design for the cable profile must be chosen in order to ensure the stability and strength in the structure.
Conclusion
Thus, it is important that to effectively establish a prestressed design, the engineer must be well affiliated with these aspects of the prestressed concrete. It is necessary to determine the design as well as their working to effectively support the structure made by the prestressed concrete.
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References
- Fabbrocino, F., and et. al., 2017. Optimal prestress design of composite cable-stayed bridges. Composite Structures. 169. pp.167-172.
- Hurst, M.K., 2014. Prestressed concrete design. CRC Press.
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