Post tension foundations are not that common in construction. However, presently, the construction of the post-tension and pre-tension structures is increasing rapidly with their advantages compared to reinforced concrete structures. Though the post-tension systems cannot be used for every type of construction, they could apply to certain areas of construction.
What is Post Tensioning
Post-tensioning is a kind of strengthening method used in construction. This is mostly used in the construction of post tension slabs and beams.
Firstly, we cast the slab or the beam. Then we the stretching of the cable to develop stresses in the opposite direction to stresses applied from the external loading.
With the post-tensioning, we can increase the spans and reduce the beam heights, etc. and as a result of that, we could economize the structure.
Types of Post Tension Foundations
The post tension foundation can be categorized into different types based on their applications and the nature of the construction. The following can be considered more common.
- Post tension slab foundations
- Post tension raft foundations
Let’s discuss each type of foundation type in detail.
Post Tension Slab Foundations
Slab foundations are used in the construction of small buildings. The slab will be constructed as the foundation and wall will be started from the slab.
In post tension slab foundation, both precast options and cast in-situ slab options can be used.
Precast slab panels post-tensioned to bear the applied loads from the walls and could be placed closely. When the groundwater table is close to the ground surface, this option is not feasible.
Cast in-situ post tension slab foundation are comparatively useful compared to the precast slab option. Post tension cables will be laid on the ground in a manner it can bearer the loads applied by the superstructure elements.
Post Tension Raft Foundations
Raft foundations are more common in construction as an economical type of shallow foundation when compared to deep foundation systems such as cast in-situ bored piles.
Raft or mat foundations are more frequently constructed in medium-rise buildings when they cannot be constructed on shallow foundations like isolated pad footing, combined footing, or strip footings.
Plat raft foundations, beam raft foundations, etc., we used the post-tension systems to enhance their load-carrying capacity. The same as the other design procedures, tendons will be provided where the sagging and hogging moment is developed to bear the induced stress by applied loads.
With the introduction of the post-tension systems to the raft foundations, the amount of reinforcement provided to carry the tensile stresses could be reduced. Further, section dimensions could also be able to reduce.
The conventional post tension systems can be used for the construction of the raft foundation and the correct estimation of the design loads and following the standard construction practices is a must in these types of construction. Since the whole structure depends on the post-tension system, it is the responsibility of the designer to carry out the design without errors.
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