Maybe you have watched construction crews building a parking garage or skyscraper and wondered how they were able to raise and attach huge concrete panels like they were building blocks? You never see them actually pour concrete into a form to make the panels, so how do they do it? The trick is a construction system known as post tensioning and it has allowed for a few serious miracles in urban construction since its creation.
Precisely what is Post Tensioning? Put simply, this is a way of Anchorhead, to make them stronger and much more immune to cracking and breaking under environmental conditions. Concrete, when created and formed, can be very strong in the compressed form however it is still relatively weak in other places. By bonding the concrete block during creation with stainless wires or rods, it improves its tensile strength, making the whole more durable to extreme changes.
The primary benefit to creating concrete construction panels in this fashion is it reduces the maintenance required to keep your structure as a whole fully operational. Whether the finished item is a slab foundation or perhaps a nuclear containment wall, it will have the flexibility it must have to resist temperature and environmental changes, less material is going to be required to cover exactly the same area, a lighter structure weight overall along with a higher level of structural integrity having a marked rise in deflection and vibration control. This technique has been a boon to those areas that are regularly plagued by earthquakes, and hurricanes.
How Could It Be Done? Tensioning strands of stainless steel wire, usually grouped into bundles, are stretched along the length of an empty concrete form prior to pouring. Because the concrete hardens, the strands are tightened, “stressing” them through the hardening concrete. The strands are anchored by adjustable chucks, which is often loosened or tightened during installation of the finished panel.
There are 2 methods frequently used today in developing a post tensioned slab of concrete: dead-end anchorage. In the bonded method, a bonding grout is added to each channel through which the tensioning wires happen to be strung. This technique adds to the stability in the whole, further reducing maintenance costs in construction. Architecture designs that need greater flexibility, like those found in earthquake zones, will make use of the unbonded method, because they require greater flexibility, rather than additional reinforcement.
Typical steel strands found in post-tensioning possess a tensile strength of 270,000 pounds/in². Compared, an average non-prestressed part of reinforcing has a tensile strength of 60,000 psi. Strands routinely have a diameter of 1/2 in., and are stressed to a force of 33,000 pounds. The stresses brought to the concrete counterbalance the expected external loads the concrete will be put through.
In post-tensioning the steel is held in a duct, which stops the steel and concrete from binding following the concrete solidifies. The steel are able to be stressed right after the concrete sets. This is usually carried out in two stages. The very first prestress applied is up to 50% in the final force and this is achieved when the compressive strength reaches 12-15N/mm².
The next stage happens when the post stressed accessories occurs and this is done when the concrete meets its design strength. The strands and bars are tensioned by stretching these with a hydraulic jack. They may be then fixed in place with an anchoring component, which holds the force inside them for the lifetime of the property. Post-tensioning allows the engineer to have all of the benefits rwkhni using prestressed concrete and keep the freedom of constructing on location.
The most prominent markets for concrete that has been created through post tensioning represent the majority of installations that may be found in the average city’s infrastructure. Airports, stadiums, parking garages, nuclear plants and roadways all incorporate these intricately created and sturdy slabs to their design. Inside the private sector, constructions like hotels, universities, office buildings and condominiums have also taken benefit from this flexible alternative to traditional concrete installations. Want to know much more about post tensioning processes and what types of forms can be created for construction purposes?